U.S. patent application number 09/275855 was filed with the patent office on 2001-07-19 for air manager control using cell load characteristics as auto-reference.
Invention is credited to GRAY, GARY E., KURLE, WAYNE, PEDICINI, CHRISTOPHER S.
Application Number | 20010008720 09/275855 |
Document ID | / |
Family ID | 25468322 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008720 |
Kind Code |
A1 |
PEDICINI, CHRISTOPHER S ; et
al. |
July 19, 2001 |
AIR MANAGER CONTROL USING CELL LOAD CHARACTERISTICS AS
AUTO-REFERENCE
Abstract
A metal-air battery with an air moving device controller to
determine when a load is present on the battery and the extent of
that load is described. The air moving device controller allows the
operation of the air moving device for the battery to be responsive
to the load. Advantageously, the controller allows the metal-air
battery to limit the intake of oxygen and other gases to that
amount needed to drive the load.
Inventors: |
PEDICINI, CHRISTOPHER S;
(ROSWELL, GA) ; GRAY, GARY E.; (MARIETTA, GA)
; KURLE, WAYNE; (WINSTON, GA) |
Correspondence
Address: |
JONES & ASKEW
191 PEACHTREE STREET NE 37TH FLOOR
ATLANTA
GA
303031769
|
Family ID: |
25468322 |
Appl. No.: |
09/275855 |
Filed: |
March 24, 1999 |
Current U.S.
Class: |
429/407 ;
429/83 |
Current CPC
Class: |
H01M 8/04552 20130101;
H01M 8/04611 20130101; H01M 8/04089 20130101; Y02E 60/10 20130101;
H01M 6/50 20130101; Y02E 60/50 20130101; H01M 8/04753 20130101;
H01M 10/44 20130101; H01M 12/06 20130101 |
Class at
Publication: |
429/23 ; 429/27;
429/13; 429/83 |
International
Class: |
H01M 012/06; H01M
008/04; H01M 002/12 |
Claims
We claim:
1. A metal-air battery, comprising: at least one metal-air cell
isolated from ambient air except through at least one passageway;
an air moving device operative to move air through said at least
one passageway to provide reactant air to said at least one
metal-air cell; said at least one passageway being operative, while
unsealed and while said air moving device is inactive, to restrict
air flow therethrough; and an air moving device controller; said
air moving device controller comprising means for determining
whether a load is on said metal-air battery and the extent of said
load such that the operation of said air moving device is
responsive to said air moving device controller.
2. The metal-air battery of claim 1, wherein said means for
determining whether a load is on said metal-air battery and the
extent of said load comprises a power sensor to monitor the current
supplied by said metal-air cell.
3. The metal-air batter of claim 2, wherein said air moving device
controller further comprises a fan controller to monitor the
voltage supplied by the metal-air cell.
4. The metal-air battery of claim 2, wherein said air moving device
controller turns said air moving device on when said voltage across
said metal-air cell, as measured by said fan controller, is less
than or equal to a first predetermined voltage.
5. The metal-air battery of claim 4, wherein said first
predetermined voltage is approximately 4.7 volts.
6. The metal-air battery of claim 4, wherein said air moving device
controller turns said air moving device on when the voltage across
said metal-air cell, as measured by said fan controller, is less
than or equal to the first predetermined voltage.
7. The metal-air battery of claim 4, wherein said air moving device
controller turns said air moving device off when the voltage across
said metal-air cell, as measured by said fan controller, is greater
than or equal to a second predetermined voltage.
8. The metal-air battery of claim 7, wherein said second
predetermined voltage is approximately 6.5 volts.
9. The metal-air battery of claim 7, wherein said second
predetermined voltage is approximately 7.0 volts.
10. The metal-air battery of claim 7, wherein said air moving
device controller turns said air moving device off when the voltage
across said metal-air cell, as measured by said power sensor, is
greater than or equal to the second predetermined voltage.
11. A method of operating a metal-air battery, said method
comprising the steps of: confining at least one metal-air cell
within a housing, said at least one metal-air cell comprising an
air electrode and said housing comprising an air movement device
and at least one air passageway; sensing the voltage across said
air electrode; activating said air movement device when a load is
present on said air electrode and the voltage across said air
electrode is less than or equal to a predetermined voltage so as to
move air through passageway; and deactivating said air movement
device when the voltage across said air electrode is greater than
or equal to a second predetermined voltage.
12. An apparatus for controlling the operation of a fan for a
metal-air battery, comprising; a power sensor operable for:
monitoring an input port for the presence of a load; connecting the
battery to the load in response to detecting the presence of the
load at the input port; and providing an output signal
representative of the voltage across the input port; and a fan
controller operable for: determining whether the output signal is
within a predetermined range; and activating the fan in response to
determining that the output signal is within the predetermined
range.
13. The apparatus of claim 12, further comprising a switch
driveable by the fan controller for connecting the battery to the
load.
14. The apparatus of claim 12, wherein the fan controller is
operable for blocking a reverse current from the load in response
to detecting a power source across the load.
15. The apparatus of claim 12, wherein the fan controller is
operative for dissipating an electrostatic charge across the
battery.
16. The apparatus of claim 15, wherein said electrostatic charge
protection device is operable for dissipating an electrostatic
charge across the load in response to detecting that the load has
an electrostatic charge build-up.
17. The apparatus of claim 14, wherein the voltage detector
comprises: a bridge circuit driveable by the load, the bridge
circuit operable for driving the switch for connecting the battery
to the load; and a hysteresis voltage driver driveable by the
bridge circuit, the hysteresis voltage driver operable for
preventing the battery from being disconnected from the load.
18. The apparatus of claim 12, wherein said predetermined range
comprises about 4.7 to about 6.5 Volts.
19. The apparatus of claim 12, wherein said predetermined range
comprises about 4.7 to about 7.0 Volts.
20. An apparatus for controlling the operation of a fan for a
metal-air battery, comprising; means for detecting current supplied
by said metal-air battery; said means for detecting current
comprising: means for monitoring an input port for the presence of
a load; means for connecting the battery to the load in response to
detecting the presence of the load at the input port; and means for
providing an output signal representative of the current the input
port; and means for monitoring the voltage of the metal-air
battery; said means for monitoring the voltage comprising: means
for determining whether the output signal is within a predetermined
range; and means for activating the fan in response to determining
that the output signal is within the predetermined range.
21. An apparatus for controlling the operation of a fan for a
metal-air battery, comprising; a power sensor operable for:
detecting a current and voltage associated with a load, determining
whether the current is greater than a first predetermined level,
connecting the battery to the load in response to determining that
the current is greater than the first predetermined level, and
providing output signals representative of the voltage across the
load and the current associated with the load; and a fan controller
operable for: receiving the output signals from the power sensor;
determining whether the current is greater than a second
predetermined current level; determining whether the voltage is
within a predetermined range; and activating the fan in response to
determining that the current is greater than the second
predetermined level and the voltage is within the predetermined
range.
22. The apparatus of claim 21, wherein the step of activating the
fan replenishes an oxygen level within the metal-air battery.
23. The apparatus of claim 21, wherein the first predetermined
level indicates whether the load is sufficient to activate the
operation of the fan controller when the metal-air battery is
connected to the load.
24. The apparatus of claim 21, wherein the first predetermined
level is approximately in the range of 350-500 millamperes.
25. The apparatus of claim 22, wherein the predetermined range
comprises: a first predetermined voltage for indicating that the
oxygen level within the metal-air battery is depleted; and a second
predetermined voltage for indicating that the oxygen level within
the metal-air battery is sufficient.
26. The apparatus of claim 21, wherein said predetermined range is
approximately 4.7-6.5 volts.
27. The apparatus of claim 21, wherein said predetermined range is
approximately 4.7-7.0 volts.
28. The metal-air battery of claim 21, wherein the second
predetermined level indicates whether the load is sufficient for
the fan controller to activate the fan when the metal-air battery
is connected to the load.
29. The metal-air battery of claim 21, wherein said second
predetermined voltage is approximately in the range 75-300
milliamperes.
30. The metal-air battery of claim 21, wherein the fan controller
turns the fan off when the voltage is greater than the
predetermined range or when said current is less than said second
predetermined current level.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation in part of
application Ser. No. 09/216,114, filed Dec. 18, 1998.
TECHNICAL FIELD
[0002] The present invention relates generally to a battery for
electrical power, and more particularly relates to an air-manager
system for a metal-air battery.
BACKGROUND OF THE INVENTION
[0003] Metal-air battery cells include an air permeable cathode and
an anode separated by an aqueous electrolyte. During discharge of a
metal-air battery, such as a zinc-air battery, oxygen from the
ambient air is converted at the cathode to hydroxide, zinc is
oxidized at the anode by the hydroxide, and water and electrons are
released to provide electrical energy. Metal-air batteries have a
relatively high energy density because the cathode utilizes oxygen
from the ambient air as a reactant in the electrochemical reaction,
rather than a heavier material such as a metal or a metallic
composition. Metal-air battery cells are often arranged in multiple
cell battery packs within a common housing to provide a sufficient
power output.
[0004] A steady supply of oxygen to the air cathodes is necessary
to operate the metal-air battery. Some prior systems sweep a
continuous flow of new ambient air across the air cathodes at a
flow rate sufficient to achieve the desired power output. Such an
arrangement is shown in U.S. Pat. No. 4,913,983 to Cheiky. Cheiky
uses a fan within the battery housing to supply a predetermined
flow of ambient air to a pack of metal-air battery cells. Before
the battery is turned on, a mechanical air inlet door and an air
outlet door are opened and the fan is activated to create the flow
of air into, through, and out of the housing. After operation of
the battery is complete, the air doors are sealed. The remaining
oxygen in the housing slowly discharges the anode until the
remaining oxygen is substantially depleted. The residual low power
remaining in the cells is disclosed as being sufficient to restart
the fan the next time the battery is used.
[0005] To ensure that a sufficient amount of oxygen is swept into
the housing during use, Cheiky discloses a fan control means with a
microprocessor to vary the speed of the fan according to
pre-determined power output requirements. The greater the power
requirement for the particular operation, the greater the fan speed
and the greater the airflow across the battery cells. Several
predetermined fan speeds are disclosed according to several
predetermined power levels of the load. The disclosed load is a
computer. The fan speed is therefore varied according to the power
requirements of the various functions of the computer. Conversely,
many other known air manager systems run the fan continuously when
a load is applied.
[0006] In addition to the need for a sufficient amount of oxygen,
another concern with metal-air batteries is the admission or loss
of too much oxygen or other gasses through the housing. For
example, one problem with a metal-air battery is that the ambient
humidity level can cause the battery to fail. Equilibrium vapor
pressure of the metal-air battery results in an equilibrium
relative humidity that is typically about 45 percent. If the
ambient humidity is greater than the equilibrium humidity within
the battery housing, the battery will absorb water from the air
through the cathode and fail due to a condition called flooding.
Flooding may cause the battery to leak. If the ambient humidity is
less than the equilibrium humidity within the battery housing, the
metal-air battery will release water vapor from the electrolyte
through the air cathode and fail due to drying out. The art,
therefore, has recognized that an ambient air humidity level
differing from the humidity level within the battery housing will
create a net transfer of water into or out of the battery. These
problems are particularly of concern when the battery is not in
use, because the humidity tends to either seep into or out of the
battery housing over an extended period of time.
[0007] Another problem associated with metal-air batteries is the
transfer of carbon dioxide or other contaminates from the ambient
air into the battery cell. Carbon dioxide tends to neutralize the
electrolyte, such as potassium hydroxide. In the past, carbon
dioxide absorbing layers have been placed against the exterior
cathode surface to trap carbon dioxide. An example of such a system
is shown in U.S. Pat. No. 4,054,725.
[0008] Maintaining a battery cell with proper levels of humidity
and excluding carbon dioxide has generally required a sealed
battery housing. As discussed above, prior art systems such as that
disclosed by Cheiky have used a fan of some sort to force ambient
air through large openings in the battery housing during use and a
sealed air door during non-use. If the air door is not present or
not shut during non-use, however, large amounts of ambient air will
seep into the housing. This flow of air would cause the humidity
and carbon dioxide problems within the housing as discussed
above.
[0009] The assignee of the present invention is also the owner of
U.S. Pat. No. 5,691,074, entitled "Diffusion Controlled Air Door,"
and application Ser. No. 08/556,613, entitled "Diffusion Controlled
Air Vent and Recirculation Air Manager for a Metal-Air Battery,"
filed Nov. 13, 1995, now U.S. Pat. No. ______. These references
disclose several preferred metal-air battery packs for use with the
present invention and are incorporated herein by reference. The air
inlet and outlet openings in the housing are sized with a length in
the direction through the thickness of the housing being greater
than a width in the direction perpendicular to the thickness of the
housing.
[0010] For example, the references disclose, in one embodiment, a
group of metal-air cells isolated from the ambient air except for
an inlet and an outlet passageway. These passageways may be, for
example, elongate tubes. An air-moving device positioned within the
housing forces air through the inlet and outlet passageways to
circulate the air across the oxygen electrodes and to refresh the
circulating air with ambient air. The passageways are sized to
allow sufficient airflow therethrough while the air mover is
operating but also to restrict the passage of water vapor
therethrough while the passageways are unsealed and the air mover
is not operating.
[0011] When the air mover is off and the humidity level within the
cell is relatively constant, only a very limited amount of air
diffuses through the passageways. The water vapor within the cell
protects the oxygen electrodes from exposure to oxygen. The oxygen
electrodes are sufficiently isolated from the ambient air by the
water vapor such that the cells have a long "shelf life" without
sealing the passageways with a mechanical air door. These
passageways may be referred to as "diffusion tubes", "isolating
passageways", or "diffusion limiting passageways" due to their
isolating capabilities. The isolating passageways also act to
minimize the detrimental impact of humidity on the metal-air cells,
especially while the air-moving device is off.
[0012] The efficiency of the isolating passageways in terms of the
transfer of air and water into and out of a metal-air cell can be
described in terms of an "isolation ratio." The "isolation ratio"
is the rate of the water loss or gain by the cell while its oxygen
electrodes are fully exposed to the ambient air as compared to the
rate of water loss or gain by a cell while its oxygen electrodes
are isolated from the ambient air except through one or more
limited openings. For example, given identical metal-air cells
having electrolyte solutions of approximately thirty-five percent
(35%) KOH in water, an internal relative humidity of approximately
fifty percent (50%), ambient air having a relative humidity of
approximately ten percent (10%), and no fan-forced circulation, the
water loss from a cell having an oxygen electrode fully exposed to
the ambient air should be more than 100 times greater than the
water loss from a cell having an oxygen electrode that is isolated
from the ambient air except through one or more isolating
passageways of the type described above. In this example, an
isolation ratio of more than 100 to 1 should be obtained.
[0013] In accordance with the above-referenced example from U.S.
Pat. No. 5,691,074, the isolating passageways function to limit the
amount of oxygen that can reach the oxygen electrodes when the fan
is off and the internal humidity level is relatively constant. This
isolation minimizes the self-discharge and leakage or drain current
of the metal-air cells. Self-discharge can be characterized as a
chemical reaction within a metal-air cell that does not provide a
usable electric current. Self-discharge diminishes the capacity of
the metal-air cell for providing a usable electric current.
Self-discharge occurs, for example, when a metal-air cell dries out
and the zinc anode of oxidized by the oxygen that seeps into the
cell during periods of non-use. Leakage current, which is
synonymous with drain current, can be characterized as the electric
current that can be supplied to a closed circuit by a metal-air
cell when air is not provided to the cell by an air moving device.
The isolating passageways as described above may limit the drain
current to an amount smaller than the output current by a factor of
at least fifty (50) times.
[0014] The use of the open air door battery housings described
herein therefore simplifies the design of the battery as a whole
and simplifies the use of the battery. In fact, these
battery-housing designs allow the metal-air battery to act more
like a conventional battery, i.e., the battery is available for the
given load without any additional activity such as opening the air
doors. The only requirement of these designs is that the fan or
other air movement device must be turned on to provide a sufficient
flow of oxygen for the cells.
[0015] In sum, the desired metal-air battery would be used in an
identical manner to a conventional battery in that all the user
needs to do is attach and activate the load. The battery itself
would need no separate activation. Further, such a battery would
have an energy efficient and quiet air manager system.
SUMMARY OF THE INVENTION
[0016] The present invention is directed towards a metal-air
battery with an air moving device controller to determine when a
load is present on the battery and the extent of that load. The air
moving device controller allows the operation of the air-moving
device for the battery to be responsive to the load.
Advantageously, the controller allows the metal-air battery to
limit the intake of oxygen and other gases to that amount needed to
drive the load.
[0017] One embodiment of the present invention includes a metal-air
battery with at least one metal-air cell isolated from ambient air
except through at least one passageway. The battery further
includes an air moving device operative to move air through the
passageway to provide reactant air to the metal-air cell. The
passageway is operative, while unsealed and while the air moving
device is inactive, to restrict airflow through the passageway. The
battery further includes an air moving device controller. The air
moving device controller includes means for determining whether a
load is on the metal-air battery and the extent of the load such
that the operation of the air-moving device is responsive to the
air moving device controller.
[0018] The means for determining whether a load is on the metal-air
battery and the extent of the load includes a power sensor to
monitor the voltage across the metal-air cell. The air moving
device controller turns the air-moving device on when the voltage
across the metal-air cell, as measured by said power sensor, is
less than or equal to a predetermined voltage. The air moving
device controller also turns the air moving device on when the
voltage across the metal-air cell, as measured by the power sensor,
is less than or equal to a first predetermined voltage. The
predetermined voltage may be approximately 4.7 volts. The air
moving device controller turns the air-moving device off when the
voltage across the metal-air cell, as measured by the power sensor,
is greater than or equal to a second predetermined voltage. The air
moving device controller also turns the air-moving device off when
the voltage across the metal-air cell, as measured by the power
sensor, is greater than or equal to a second predetermined voltage.
The predetermined voltage may be approximately 6.5-7.0 volts.
[0019] The method of the present invention provides for operating a
metal-air battery. The method includes the step of: confining at
least one metal-air cell within a housing. The metal-air cell
includes an air electrode and the housing includes an air movement
device and at least one air passageway. The method further includes
the steps of sensing the voltage across the air electrode;
activating the air movement device when a load is present on the
air electrode and the voltage across the air electrode is less than
or equal to a predetermined voltage so as to move air through
passageway; and deactivating the air movement device when the
voltage across the air electrode is greater than or equal to a
second predetermined voltage.
[0020] Another embodiment of the present invention provides an
apparatus for controlling the operation of a fan for a metal-air
battery. The apparatus includes a power sensor operable for
monitoring an input port for the presence of a load, connecting the
battery to the load in response to detecting the presence of the
load at the input port, and providing an output signal
representative of the voltage across the input port. The apparatus
further includes a fan controller operable for determining whether
the output signal is within a predetermined range and activating
the fan in response to determining that the output signal is within
the predetermined range. The predetermined range may be about 4.7
to about 7.0 Volts.
[0021] The apparatus also may include a switch driveable by the fan
controller for connecting the battery to the load. The apparatus
also may include an electrostatic charge protection device
driveable by the fan controller. The electrostatic charge
protection device is operable for dissipating an electrostatic
charge across the load in response to detecting that the load has
an electrostatic charge build-up. Further, the power sensor also
may include a bridge circuit driveable by the load. The bridge
circuit is operable for driving the switch for connecting the
battery to the load. The power sensor also may include a hysteresis
voltage driver driveable by the bridge circuit. The hysteresis
voltage driver is operable for preventing the battery from being
disconnected from the load.
[0022] A further embodiment of the present invention provides an
apparatus for controlling the operation of a fan for a metal-air
battery. The apparatus includes means for detecting voltage across
the metal-air battery. The means for detecting voltage includes
means for monitoring an input port for the presence of a load,
means for connecting the battery to the load in response to
detecting the presence of the load at the input port, and means for
providing an output signal representative of the voltage across the
input port. The apparatus further includes means for regulating the
voltage of the metal-air battery. The means for regulating the
voltage includes means for determining whether the output signal is
within a predetermined range and means for activating the fan in
response to determining that the output signal is within the
predetermined range.
[0023] A further embodiment of the invention provides means for
determining whether a load is on the metal-air battery and the
extent of the load includes a power sensor to monitor the load
current and the voltage across the metal-air cell. The air moving
device controller turns the air moving device on when both the
current through a current sensing element, such as a resistor, is
greater than a predetermined current value and the voltage across
the metal-air cell, as measured by said power sensor, is less than
or equal to a predetermined voltage. The air moving device
controller first determines whether the current passing through the
current sensing element is greater than a first predetermined
current value to activate the air-moving device. Typically, the
current is approximately between 350 and 500 milliamperes. Next,
the air moving device controller monitors the load to ensure that
the current it is above a second predetermined current level. The
current induced by the load must be greater than the second
predetermined level to sustain operation of the air moving device
controller. Typically, the second predetermined level is
approximately in the range of 75-300 milliamperes.
[0024] Once the air moving device controller determines that
sufficient current is present to sustain the operation of the air
moving device controller, the air moving device controller monitors
the voltage across the metal-air cell. When the voltage across the
metal-air cell, as measured by the power sensor, is less than or
equal to a first predetermined voltage, the air moving device
controller turns the air-moving device on. The predetermined
voltage may be approximately 4.7 volts. The air moving device
controller also turns the air-moving device off when the voltage
across the metal-air cell, as measured by the power sensor, is
greater than or equal to a second predetermined voltage. The
predetermined voltage may be approximately 7.0 volts.
[0025] Thus, it is an object of the present invention to provide an
improved air manager system for a metal-air battery.
[0026] It is another object of the present invention to provide a
self-regulating air manager system for a metal-air battery.
[0027] It is a further object of the present invention to provide
an air manager system for a metal-air battery without mechanical
air doors.
[0028] It is a still further object of the present invention to
provide an air manger system for a metal-air battery with an
automatic fan.
[0029] It is a still further object of the present invention to
provide for an efficient air manager system for a metal-air
battery.
[0030] It is a still further object of the present invention to
provide for an air manager system for a metal-air battery with a
long shelf life.
[0031] It is a still further object of the present invention to
provide a quiet air manager system for a metal-air battery.
[0032] It is a still further object of the present invention to
provide a charge prevention function to protect the camcorder
battery during charging operations.
[0033] Other objects, features, and advantages of the present
invention will become apparent upon reviewing the following
description of preferred embodiments of the invention, when taken
in conjunction with the drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a cut-away diagrammatic top view of the battery
housing embodying the present invention, showing the position of
the cells, the fan, and the air openings, in combination with the
direction of the flow of air with respect to the housing.
[0035] FIG. 2 is a vertical cross sectional view taken along line
2-2 of FIG. 1.
[0036] FIG. 3 is a diagrammatic pictorial view of a ventilation
opening.
[0037] FIG. 4 is a schematic view of the power sensor circuit.
[0038] FIG. 5 is a flow chart showing the operation of the fan
based upon the detected voltage.
[0039] FIG. 6 is a comparison chart showing the power consumption
of an air manager system in a six (6) volt battery with several fan
options.
[0040] FIG. 7 is a plan view of a camcorder battery of an
alternative embodiment of the present invention.
[0041] FIG. 8 is a side cross-sectional view of the camcorder
battery of the FIG. 7.
[0042] FIG. 9 is a schematic diagram showing the voltage control
circuit of the alternative embodiment.
[0043] FIG. 10 is a schematic view of the power sensor circuit of
the alternative embodiment.
[0044] FIG. 11 is a flow chart showing the operation of the fan
based on the detected current and detected voltage.
DETAILED DESCRIPTION
[0045] Referring now in more detail to the drawings, in which like
numerals refer to like parts throughout the several views, FIGS.
1-4 show a metal-air battery 10 embodying the present invention.
The metal-air battery 10 may be similar to that disclosed in
commonly owned U.S. Pat. No. 5,641,588 to Sieniinski, et al.,
commonly owned U.S. Pat. No. 5,356,729 to Pedicini, et al.,
commonly owned U.S. Pat. No. 5,691,074 to Pedicini, and commonly
owned application Ser. No. 08/556,613, which are incorporated
herein by reference, or other known metal-air battery
configurations.
[0046] The metal-air battery 10 includes a plurality of metal-air
cells 15 enclosed within a housing 20. The housing 20 isolates the
cells 15 from the outside air with the exception of a plurality of
diffusion tubes or ventilation openings 25. In the embodiment shown
in FIGS. 1 and 2, a single air inlet opening 30 and a single air
outlet opening 35 are utilized. The number of openings 25 is not as
important as the aggregate size of the openings 25 in connection
with the shape of each opening 25. Alternatively, a single opening
25 may be utilized to provide air to the cells 15. The openings 25
would function as both an inlet and an outlet with reciprocating
airflow therethrough. Further, multiple passageways or openings 25
can be utilized in the aggregate such that the openings 25 function
in unison as inlets, and thereafter function in unison as outlets,
in an alternating fashion.
[0047] The housing 20 itself may be any type of conventional,
substantially air-tight structure. The number of cells 15 within
the housing 20 depends upon the nature of the load intended for the
battery 10. The present invention is not dependent upon the
configuration of the cells 15 within the housing 20 or the number
of cells 15 within the housing 20. FIGS. 1 and 2 therefore show a
cutaway view of a metal-air battery housing 20 showing only the
essential elements of the present invention, i.e., a housing 20,
one or more cells 15, and the air openings 25. Although only two
cells 15 are shown in FIGS. 1 and 2, it is understood that the
number and configuration of the cells 15 depends upon the power
requirements for the battery 10.
[0048] A circulating fan 40 is provided for convective airflow both
in and out of the housing 20 and to circulate and mix the gasses
within the housing 20. The arrows shown in FIG. 1 represents a
typical circulation of gasses into, out of, and within the housing
20 to provide the reactant air to the cells 15. The capacity of the
fan 40 also depends upon the size of the housing 20 and the power
demands of the battery 10. The term "fan" 40 as used herein is
intended to mean any device to move air, including a pump.
[0049] The fan 40 may be positioned within the housing 20 or
adjacent to the housing 20 in communication with one of the
openings 25. If the fan 40 is located within the housing 20, the
ventilation openings 25 are positioned such that the inlet opening
30 and the outlet opening 35 are positioned on opposite sides of
the fan 40. The only requirement for the positioning within the
housing 20 of the fan 40 and the openings 25 is that they are in
sufficiently close proximity to each other to create a convective
air flow into, through, and out of the housing 20. The fan 40 may
be mounted within or adjacent to the housing 20 in any convenient
manner. The fan 40 is generally sealed into place by a gasket 41 or
other conventional means to ensure that the low pressure and high
pressure sides of the fan 40 are isolated from one another.
[0050] As is shown in FIG. 2, the plurality of cells 15 within
housing 20 are generally arranged such that a reactant air plenum
50 is positioned under or over the cells 15. The air plenum 50
defines an air plenum inlet 55, an air passageway 60, and an air
plenum outlet 65. The fan 40 is generally positioned between and
isolates the air plenum inlet 55 from the air plenum outlet 65 for
efficient airflow through the housing 20. Examples of air plenum
designs are shown in the commonly-owned references cited above. As
described above, the present invention is not dependent upon any
particular air plenum design.
[0051] As is shown in FIG. 3, the ventilation openings 25 are
preferably sized such that their length 26, i.e., the direction
through the thickness of the housing 20, is greater than their
width 27, i.e., the direction perpendicular to the thickness of the
housing 20. By using a large enough ratio between the length 26 and
the width 27 for the ventilation openings 25, it has been found
that diffusion of air through the openings 25, without the
assistance of the fan 40, is substantially eliminated. By
"substantially eliminated," it is meant that the rate of diffusion
of oxygen or contaminates through the openings 25 is so slow that
humidity transfer or drain current is sufficiently small and has
little appreciable impact on the efficiency or lifetime of the
battery 10. In sum, the openings 25 are sufficiently long and
narrow to provide a barrier to diffusion of gases therethrough when
the fan 40 is turned off.
[0052] This desired ratio between length 26 and width 27 is at
least about two to one. These ratios are sufficient to prevent
appreciable diffusion through the openings 25 when the fan 40 is
turned off while permitting convective airflow therethrough when
the fan 40 is turned on. The use of larger ratios between length 26
and width 27 is preferred. Depending upon the nature of the battery
10, the ratio can be more than 200 to 1. The preferred ratio is
about 10 to 1.
[0053] In use, ambient air is drawn into the air inlet 30 by pull
of the fan 40 when the fan 40 is turned on. As is shown by the
arrows 45 in FIG. 1, the air is then drawn through the fan 40 and
into the air plenum 50. The air enters the air plenum 50 through
air plenum inlet 55, travels though the pathway 60 to provide a
reactant airflow for the cells 15, and exits via the air plenum
outlet 65. The air is then again drawn into the fan 40 where it
either mixes when fresh incoming ambient air or is forced out of
the housing 20 via air outlet 35. When the fan 40 is turned off,
the rate of diffusion of air through the openings 25 is reduced to
acceptable levels such that a mechanical air door is not
required.
[0054] As is shown in FIGS. 1 and 4, the invention includes a
voltage monitor 100 to determine the voltage across the cell 15 or
other electrical characteristics and to control the operation of
the fan 40. The voltage monitor 100 can be positioned at any
convenient location within or adjacent to the housing 20. The
preferred voltage monitor 100 is a programmable voltage detection
or sensing device such as that sold by Maxim Integrated Products
under the mark MAX8211 and MAX8212. Depending upon the desired
operation of the fan, the voltage monitor 100 can be an analog
circuit for a simple "on/off" switch or can incorporate a
microprocessor (not shown) for a more complex algorithm. The
voltage monitor 100 of FIGS. 1 and 4 is an analog circuit.
[0055] The voltage monitor 100 determines the voltage across the
air electrode 150 of the cell 15. The air electrode 150 is shown in
phantom lines in FIG. 4. Because the zinc potential within the air
electrode 150 of each cell 15 is relatively stable, the air
electrode 150 is used to sense the residual oxygen in the cell 15.
As the oxygen within the housing 20 is depleted, the voltage across
each air electrode 150 diminishes. Likewise, as the flow of oxygen
into the housing 20 increases, the voltage across the air electrode
150 increases.
[0056] A preferred air electrode 150 is disclosed in commonly owned
U.S. Pat. No. 5,569,551 and commonly owned U.S.
[0057] Pat. No. 5,639,568, which are incorporated herein by
reference. U.S. Pat. No. 5,639,568 discloses a split anode for use
with a dual air electrode metal-air cell. Although the use of the
invention with a zinc-air battery is disclosed, this invention
should be understood as being applicable to other types of
metal-air battery cells.
[0058] As is shown in FIG. 4, the voltage monitor 100 is connected
to the cells 15 in a voltage monitor circuit 105 via a cathode tab
130 and an anode tab 140. The voltage monitor circuit 105 also
includes the fan 40. All of the cells 15 within the housing 20 are
connected in this circuit 105. The voltage across the cells 15 is
continually monitored to ensure that the voltage does not drop
below a predetermined voltage V.sub.p1. If the voltage does drop to
V.sub.p1, the fan 40 is turned on and then runs continuously until
the voltage is increased to a second predetermined voltage
V.sub.p2. The fan 40 is then turned off and remains off until the
voltage again drops to V.sub.p1. The predetermined voltages
V.sub.p1 and V.sub.p2 are programmable values in the voltage
monitor 100.
[0059] The operation of the fan 40 is shown in FIG. 5. The
algorithm is an "on/off" type with predetermined values. As is
shown in step 201, the voltage monitor 100 measures the voltage
across the air electrode 150. In step 202, the voltage monitor 100
determines if the voltage is less than or equal to V.sub.p1. If so,
the voltage monitor 100 turns on the fan 40 in step 203. If not,
the voltage monitor 100 determines if the voltage is greater than
or equal to V.sub.p2 in step 204. If so, the voltage monitor 100
turns off the fan 40 in step 205. If not, the voltage monitor 100
returns to step 201. This algorithm may be modified to add an
additional step of first checking if a load is present on the
battery 10. If so, the voltage monitor 100 proceeds to step 201 as
shown above. If not the fan 40 will remain in the off state.
[0060] Alternatively, the speed of the fan 40 maybe altered
depending upon the drain rate of the battery 10 as a whole or other
electrical parameters. In other words, the voltage monitor 100 can
be replaced with other types of conventional electrical sensors
known to those practicing in the art. For example, a conventional
power sensor, i.e., a sense resistor, could be used. This monitor
100 can set the speed of a variable speed fan 40 as a function of
current draw. Instead of the algorithm of FIG. 5, the circuit 105
would contain a conventional microprocessor with a look-up table to
compare the determined current draw with a voltage input value for
the fan 40. The input voltage and speed of the fan 40 varies with
the determined output current drain. The physical arrangement of
the components in this embodiment is the same as that described
above.
[0061] The operation of the invention is shown in an example using
a six (6) volt battery 10. Such a battery 10 has six (6) metal-air
cells 15, with each cell 15 having an output of about 1.0 volt or
slightly higher at about 1 to 4 amps. An up-converter (not shown)
also may be used. The housing 20 has openings 25 with a length 26
to width 27 ratio of about four (4) to one (1). The gas flow
through the housing when the fan 40 is on is about 15 to about 30
cubic inches per minute for an output current of about 1 amp. When
the fan 40 is turned off, the gas flow rate is reduced to about 0
to about 0.03 cubic inches per minute or less, with a leakage
current of less than 1 mA. The ratio of output current density with
the fan 40 turned on to drain current density with the fan 40
turned off is expected to be at least 100 to 1 in an efficient
battery 10. It is understood that the respective sizes, capacities,
densities, flow rates, and other parameters discussed above are
dependent upon the overall size and power requirements of the
battery 10.
[0062] The first predetermined voltage V.sub.p1 under which the
voltage should not fall may be about 1.0 volts per cell 15 or about
5.0 volts for the battery 10 as a whole. The fan 40 is turned on
when the voltage monitor 100 determines that the voltage of the
battery 10 has reached about 1.0 volts per cell 15 or about 5.0
volts for the battery 10 as a whole. The fan 40 then stays on until
the voltage of the battery 10 reaches about 1.1 volts per cell 15,
or about 5.5 volts for the battery 10 a whole. The fan 40 remains
off until the voltage again reached about 1.0 volts per cell 15 or
about 5.0 volts for the battery 10 as a whole.
[0063] Assuming the drain rates given above, it would take
approximately one month for the six (6) volt battery 10 of the
present example to fade from about 1.1 volts per cell 15 to about
1.0 volts per cell 15 to trigger the fan 40 during periods of
non-use. The shelf life of the battery 10 would be at least several
years. The battery 10 would be immediately ready for use without
the need for any independent activation of the battery 10 such as
by turning on the fan 40 or by opening a mechanical air door.
Rather, the battery 40 is ready for use. The activation of a load
on the battery 10 will cause the voltage across the cells 15 to
drop as the oxygen within the housing 20 is consumed. This voltage
drop will activate the fan 40 until the proper amount of oxygen is
introduced into the housing 20 and the proper voltage is
restored.
[0064] In addition to the present invention being self-regulating,
the present invention also provides an energy efficient air manager
system. The efficiency of the battery 10 as a whole is increased
because the running of the fan 40 is minimized. FIG. 6 compares the
energy to load ratio 300 of the present invention in terms of the
energy to load ratio 310 of a battery without a fan and with the
energy to load ratio 320 of a fan running constantly at various
drain rates. As described above, most air manager systems either
run the fan continuously or employ a variable speed fan as is
described in Cheiky. As is shown in FIG. 6, the present invention
provides efficiencies of essentially ninety percent (90%) of an air
manager system without a fan.
[0065] For example, the energy to load ratio 300 of the present
invention in a six (6) volts battery is about 235 Wh while the
energy to load ratio 310 of an air manager system without a fan is
about 250 Wh. The energy to load ratio 320 of an air manager system
with a fan running continuously is only about 135 Wh. The pulsing
fan operation of the present invention is therefore an improvement
of almost 100 Wh as compared to a constantly running fan. The
improvement is maintained until drain rates reach about 5 watts. At
that point, the fan 40 of the present invention is essentially
running continuously.
[0066] Although these efficiencies may be possible with the
variable speed fan of Cheiky, the present invention uses a simple
on/off switch rather than the complex, load specific algorithm
disclosed therein. In other words, Cheiky requires a specific
algorithm for each different type of load. The present invention,
however, is available to provide power to almost any type of
electrical device.
[0067] In sum, by pulsing the fan 40 as described herein, several
goals are achieved:
[0068] 1. The life of the battery 10 is maximized from the
standpoint of environmental exposure. In other words, only enough
oxygen is admitted into the housing 20 as is needed to maintain the
predetermined voltages.
[0069] 2. Power consumption of the fan 40 is minimized as a
percentage of the power consumed by the battery 10 as a whole. For
example, a fifty percent (50%) duty cycle may be all that is
required at low drain rates. This decreases the overhead energy
consumed by the battery 10 as a whole.
[0070] 3. Because the fan 40 runs in a duty cycle, the battery 10
as a whole is quieter than a battery 10 with a continuously running
fan 40.
[0071] The present invention therefore can provide a battery 10
with a relatively long shelf life without the need for a mechanical
air door or a fan switch. The present invention can function as,
for example, a power source of an emergency device than can be
automatically activated because there is no need for a separate
activation step. More importantly, the present invention provides
for an efficient air manager system that minimizes the running of
the fan 40 and the energy drain associated with the fan 40.
[0072] FIGS. 7 and 8 show a further embodiment of the present
invention. These figures show a metal-air battery 500. The
metal-air battery 500 is in the form of, for example, a camcorder
battery. The metal-air battery 500 includes six (6) metal-air cells
510. The metal-air cells 510 are of conventional design and may be
similar to the cells 15 described above. Likewise, each metal-air
cell 510 has one or more air electrodes 515. The air electrodes 515
are also of conventional design and may be similar to the air
electrodes 150 described above. In this embodiment, the metal-air
cells 510 are arranged in three (3) pairs 520 with each pair 520
sharing an air plenum 530. The air plenums 530 may be of
conventional design. The metal-air cell pairs 520 are each
separated by a separator layer 540. The separator layers 540 may be
made from a substantially rigid, non-air permeable material or
simply may be a plurality of protrusions on the outer casing of the
metal-air cells 510. The metal-air cells 510 each have dimensions
of approximately 4 by 7 by 0.6 cm. Likewise, the air plenums 530
may have a width of approximately 0.1 cm. Each cell 510 may have a
voltage of about one (1) Volt such that the battery 500 as a whole
will have a voltage of about six (6) Volts.
[0073] Positioned over the metal-air cells 510 is an air manager
unit 550. The air manager unit 550 includes a fan 560 and one or
more diffusion tubes or ventilation openings 570 extending through
the battery housing as described above. The fan 560 may be of any
conventional design and may be similar to the fan 40 described
above. The needed fan capacity should be varied based on the size
of the cells to which air is supplied and the amount of electrical
current being supported by the battery. In this embodiment, the fan
560 may have a capacity of about 1-10 liters per minute of standard
air, to support a current of up to about 6 amperes. The one or more
diffusion tubes 570 may be similar to the ventilation openings 25
described above, i.e., the diffusion of air through the diffusion
tubes 570, without the assistance of the fan 560, is substantially
eliminated such that the rate of diffusion of oxygen or
contaminates through the tubes 570 is sufficiently slow and has
little appreciable impact on the efficiency or lifetime of the
battery 500.
[0074] Also positioned within or adjacent to the air manager unit
550 is a fan control circuit 580. The fan control circuit 580
includes a voltage monitor 590 to determine the voltage across the
cells 510 or other electrical characteristics and to control the
operation of the fan 560. The voltage monitor 590 may be of
conventional design and may be similar to the voltage monitor 100
described above. In this embodiment, the voltage monitor 590
incorporates a camcorder battery circuit 600 as described below for
the execution of a more complex function than the "on/off" design
of the voltage monitor 100.
[0075] FIG. 9 shows an electrical schematic for the preferred
embodiment of the camcorder battery circuit 600. The camcorder
battery circuit 600 has two main functions: (1) to monitor the
voltage output of the battery 500 and (2) to monitor the voltage
output to the internal fan 560 which forces air into the air
plenums 530. The electrical circuit 600 is comprised of three
circuit components shown by the dashed lines in FIG. 9: a power
sensor 602; a switch 604; and a fan controller 606.
[0076] The camcorder battery circuit 600 contains a first
comparator 608, a second comparator 610, a third comparator 614 and
a fourth comparator 616. The combination of comparators 608, 610,
614, 616 is preferably implemented by a quad, ultra low power, and
low offset voltage comparator, such as the model LP339M
manufactured by Texas Instruments Corporation, of Dallas, Tex.
[0077] The power sensor 602 includes the first comparator 608 and
the second comparator 610. The resistors R.sub.5, R.sub.6, R.sub.8,
R.sub.10, R.sub.11, and R.sub.12 form a resistive bridge. The first
comparator 608 in combination with the resistive bridge formed by
the resistors R.sub.5, R.sub.6, R.sub.8, R.sub.10, R.sub.11, and
R.sub.12 form a bridge circuit 609. When there is no load applied
across battery output terminals E.sub.3 and E.sub.4, the output of
the comparator 608 is high. The voltages at the inverting terminal
and non-inverting terminal of first comparator 608 are unequal and
the output of first comparator 608 is high.
[0078] When a load is applied across the output battery terminals
E.sub.3 and E.sub.4, current flows through the resistor R.sub.12.
The voltage that appears at the inverting input of the first
comparator 608 will be greater than voltage at the non-inverting
input such that the output voltage of first comparator 608 will be
at ground. When the output of first comparator 608 is at ground, a
current path is established through the resistors R.sub.15 and
R.sub.16 and the first comparator 608 from the terminal E, to the
terminal E.sub.2. The resulting voltage drop across R.sub.16
provides a large forward bias voltage across the emitter-base
junction of transistor Q.sub.2, thereby allowing current to pass
therethrough. The combination of the transistor Q.sub.2 and the
resistors R.sub.15 and R.sub.16 form a voltage switch 612. The bias
voltage is chosen such that the transistor Q.sub.2 operates in
saturation mode whenever the output of the first comparator 608 is
at ground. This ensures that the voltage drop across the transistor
Q.sub.2 is minimal when the transistor Q.sub.2 is conducting.
Preferably, the transistor Q.sub.2 is a small signal pnp
transistor, such as the model MMBT3906 manufactured by the Motorola
Corporation, of Schaumburg, Ill.
[0079] Each function (e.g., record, rewind, play, view, etc,) of
the camcorder typically will have different operating current
levels. Each of these different operating currents produces a
corresponding voltage level across the current sensing resistor
R.sub.12. Some of these voltage levels may be below the initial
reference voltage at the non-inverting input of the first
comparator 608. To protect the circuit 600 from disconnecting the
load from the battery 500, the current-sensing circuit 602 lowers
the voltage at the non-inverting input of the first comparator 608
by establishing a hysteresis voltage driver. Second comparator 610
and resistor R.sub.9 form the hysteresis voltage driver. The output
of the first comparator 608 is connected to the non-inverting input
of the second comparator 610. When the output of the first
comparator 608 is high, the non-inverting input of the second
comparator 610 is also high. The inverting input of the second
comparator 610 is connected to the positive voltage across the
resistor R.sub.6. Because the voltage across the resistor R.sub.6
is less than an input voltage applied across input ports E.sub.1
and E.sub.2, the output of the second comparator 610 is high.
Therefore, when no load is applied to the output ports E.sub.3 and
E.sub.4, no current flows through the resistor R.sub.9.
[0080] When the output of the first comparator 608 is at ground,
the voltage level at the non-inverting input of the second
comparator 610 will be greater than the voltage level at the
inverting input of the second comparator 610. Therefore, the output
of the second comparator 610 is at ground, which causes current to
flow through the resistor R.sub.9. This places the resistor R.sub.9
in parallel with the resistors R.sub.8 and R.sub.10, which produces
a hysteresis effect. The resulting combination of the resistor
R.sub.9 in parallel with the resistors R.sub.8 and R.sub.10 reduces
the resistance of the bridge circuit, which causes a downward shift
in the voltage level at the non-inverting input of the first
comparator 608. The input voltage level at the non-inverting input
of the first comparator 608 is now at a level below the minimum
voltage, which corresponds to the minimum current required to
operate the camcorder in a given mode. Reducing the voltage at the
non-inverting input ensures that the load will not be disconnected
from the battery 500 due to changes in the voltage during the
operation of the camcorder.
[0081] The switch 604 comprises the component transistor Q.sub.1.
Typically, the transistor Q.sub.1 is a dual TMOS Power metal-oxide
semiconductor field effect transistor (MOSFET), such the model
MMDF3NO3HD manufactured by the Motorola Corporation, of Schaumburg,
Ill. The input signal of a gate of a transistor 620 is supplied by
the output of the transistor Q.sub.3, which in turn is driven, by
transistor Q.sub.2. Preferably, the transistor Q.sub.3 is a small
signal pnp transistor, such as the model MMBT3906 manufactured by
the Motorola Corporation, of Schaumburg, Ill.
[0082] When the transistor 620 is in the "OFF", or non-conducting
state, current flows through a body drain diode, which is inherent
to transistor 620. The output voltage at terminals E.sub.3 and
E.sub.4 is then approximately equal to a voltage drop across the
drain diode, V.sub.drain. When the transistor Q.sub.2 is
conducting, the emitter of Q.sub.3 will be at a voltage VCC, which
is essentially equal to the battery voltage V.sub.batt. Current
will flow through the base-emitter junction of Q.sub.3 due to the
base being tied to ground through R17. This allows Q.sub.3 to
conduct current to the collect node, which is connected to the gate
of the transistor 620. This allows the gate of transistor 620 to be
positively biased at nearly the battery voltage V.sub.batt (the
voltages V.sub.Q2 and V.sub.Q3 across the transistors Q.sub.2 and
Q.sub.3, respectively, are negligible). The positive bias at the
gate of the transistor 620 creates a channel so that current flows
from the drain to the source of the MOSFET transistor 620 and the
body drain diode is removed from the circuit. The entire load
current is conducted through the transistor 620 with negligible
losses. The source of the transistor 620 is connected to the output
terminal E.sub.3. Thus, when the transistor 620 is conducting, a
voltage nearly equal to the battery voltage appears across the
output terminals E.sub.3 and E.sub.4 of the battery 500.
[0083] The transistor 620 in combination with transistor Q.sub.3
and R.sub.18 acts as a charge prevention circuit. In the event that
a power source capable of causing current to flow in a direction
opposite to that of the load current, is attached to the output
battery terminals E.sub.3 and E.sub.4, the circuit keeps transistor
620 in the "OFF" state thereby preventing current from passing
through transistor 620. Resistor R.sub.18 provides a bleed path for
the gate charge on transistor 620 and the leakage current of
Q.sub.3 so that transistor 620 is not turned on when a power source
having a positive polarity is applied across terminal E.sub.3 and
E.sub.4.
[0084] Referring again to the transistor Q.sub.2, the output of the
transistor Q.sub.2 also is connected to the fan controller 606. The
output voltage VCC from the power sensor 602 powers the fan
controller 606. A voltage reference element, CR.sub.1 establishes a
constant voltage at a node 628. Preferably, CR.sub.1, is an
integrated circuit, micropower voltage reference element, such as
the model LM385BD-1.2 manufactured by the Motorola Corporation. In
the preferred embodiment, the voltage established by CR.sub.1 is
about 1.24 volts. Those skilled in the art will appreciate that
other voltage reference elements that have different voltage values
may be used as long as the specified voltage is less than the
voltage VCC established by the transistor Q.sub.2.
[0085] The Resistor R.sub.1 supplies enough bias current to meet
the requirements of CR.sub.1 and one input of each of the third and
fourth comparators 614 and 616. Therefore the resistor R.sub.1 and
CR.sub.1 establish a known, fixed voltage reference. The resistors
R.sub.2, R.sub.7, R.sub.3, and R.sub.4 form a voltage divider
circuit connected to the third and fourth comparators 614 and 616.
These comparators 614 and 616 are wired in a window comparator
configuration. In this configuration, if the output of either
comparator is negative, the output of both comparators is negative.
More specifically, if the voltage at the node 624, which is
connected to the non-inverting input of the third comparator 614 is
greater than the reference voltage established by CR.sub.1, the
output of the third comparator 614 will be positive, which
corresponds to an open circuit.
[0086] The output of the third and fourth comparators 614 and 616
are connected to the gate of the transistor 621 in the transistor
Q.sub.1. When either the output of the third comparator 614 or the
fourth comparator 616 is positive, the gate voltage of the
transistor 621 is positively biased which results in a low-channel
resistance being formed between the source to the drain. The drain
of the transistor 621 is connected to the negative terminal of the
fan 560. Therefore, whenever the gate of the transistor 621 is
positively biased, the transistor 621 will conduct. This causes a
voltage across the terminals E.sub.5 and E.sub.6 that activates the
fan 560.
[0087] Generally, when the output voltage VCC is within a
predetermined voltage range, the output of the comparators 614, 616
will be positive and voltage will be supplied to the fan 560
through the transistor 621. This range is set by the values chosen
for the resistors R.sub.2, R.sub.3, R.sub.4, and R.sub.7. In the
preferred embodiment, the predetermined voltage range is 4.7-6.5
volts, and the values of the resistors R.sub.2, R.sub.3, R.sub.4,
and R.sub.7 are 383 K.OMEGA., 51 K.OMEGA., 133 K.OMEGA., and 133
K.OMEGA., respectively. However, those skilled in the art will
appreciate that other predetermined voltage ranges that are within
the voltage limits of the battery 500 may be used by selecting
different values of the resistors R.sub.2, R.sub.3, R.sub.4, and
R.sub.7 without affecting the scope of the invention.
[0088] When the output voltage, VCC exceed 6.5 volts, the voltage
at the inverting input of fourth comparator 616 will exceed the
reference voltage established at the node 628. The output of fourth
comparator 616 will become negative, thereby cutting off the
voltage to the fan 560. Similarly, when VCC is less than the 4.7
volts, the voltage at the non-inverting input of the third
comparator 614 will be less than the reference voltage at the node
628. The output of the third comparator 614 will go negative
thereby cutting power off to the fan 560.
[0089] The resistor R.sub.13, is a step-down resistor that reduces
the voltage, which appears across terminals E.sub.5 and E.sub.6 to
match the voltage requirements of the fan 560. TP.sub.1 and
TP.sub.2 form a socket in which an additional resistor can be added
to output voltage across terminals E.sub.5 and E.sub.6.
[0090] Finally, diode CR.sub.2 is a Zener diode that protects the
transistor Q.sub.1 from large electrostatic discharge (ESD).
Preferably, CR.sub.2 is a Zener diode; such as the model number
BZX84C27 manufactured by Vishay/LiteOn Corporation.
[0091] As is shown in FIG. 10, the fan control circuit 580 includes
each of the elements described in shown in FIG. 4. Specifically,
the voltage monitor 590 is connected to the cells 510 via a cathode
tab 512 and an anode tab 514 and to the fan 560. All of the cells
510 within the battery 500 are connected in this circuit 580. The
voltage across the cells 510 is continually monitored to ensure
that the voltage does not drop below a predetermined voltage
V.sub.p1. If the voltage does drop to or below V.sub.p1, the
voltage monitor 590 first determines if a sufficient load is on,
the battery 500.
[0092] Specifically, the voltage monitor 590 determines if the
external current flow on the battery 500 is greater than the
minimum camcorder current. In this embodiment, the minimum
camcorder current is about 500 milliamperes to enable the operation
of the camcorder and at least 100 milliamperes to sustain the
operation of the camcorder. This first step is possible because
this minimum camcorder current is reduced as compared to other
known designs. If the voltage drops to or below V.sub.p1, the fan
560 is turned on and then runs continuously until the voltage is
increased to or above a second predetermined voltage V.sub.p2. The
fan 560 is then turned off and remains off until the voltage again
drops to or below V.sub.p1. As described above with respect to FIG.
9, the predetermined voltages V.sub.p1 and V.sub.p2 are
programmable values in the voltage monitor 590. In the present
embodiment, V.sub.p1 and V.sub.p2, V.sub.p1 may be about 4.7 Volts
and V.sub.p2 may be about 7.0 Volts.
[0093] The camcorder battery circuit 600 of the voltage monitor 590
also may use hysteresis to prevent erratic operation of the fan 560
as operating modes of the camcorder are changed. In other words, a
sudden but short increase in the electrical load on the battery 500
when, for example, the user presses the Play, Record, or Rewind
buttons, will not necessarily activate or deactivate the fan 560
immediately.
[0094] Other features of the camcorder battery circuit 600 include
the use of charge prevention. Charge prevention is accomplished by
having a minimal voltage drop at the battery tabs 512, 514 during
normal battery discharge. In other words, the battery voltage at
the tabs 512, 514 will be approximately 50-100 mV less than the
internal raw battery 500 voltage. The camcorder battery circuit 600
also incorporates electrostatic discharge protection on the battery
tabs 512, 514 to prevent damage to the circuitry within the battery
500.
[0095] The algorithm 700 in FIG. 11 shows an alternative embodiment
of the operation of the fan 40. The algorithm 700 is an "on/off"
type with predetermined values. As is shown in step 702, the
hysteresis is OFF, which corresponds to the output of the
hysteresis voltage driver 611 being open circuit. In step 704, the
power sensor 602 determines whether the current through the current
sensing resistor R.sub.12 is greater than an upper threshold
current I.sub.H. Typically, the threshold current I.sub.H is in the
range of approximately 350-500 milliamperes. If so, the hysteresis
is ON in step 706, which corresponds to the output of the
hysteresis voltage driver 611 being low. This prevents the load
from becoming disconnected during the operation of the
camcorder.
[0096] The power sensor 602 next determines whether the load
current through resistor R.sub.12 is less than a lower threshold
current, I.sub.L in step 708. Typically, the lower threshold
voltage I.sub.L is in the range of approximately 75-300
milliamperes. If the load current is greater than the lower
threshold current, the "NO" branch is followed to step 710 in which
the fan controller 606 determines whether the load voltage is
greater than V.sub.p1. If so, the fan controller 606 turns the fan
40 off in step 714. If not, the algorithm proceeds to 712, in which
the fan controller 606 determines if the load voltage is greater
than V.sub.p2. If the load voltage is greater than V.sub.p2, the
fan controller 606 turns off the fan 40 in step 714. Step 714 is
followed by step 718 in which the fan controller 606 determines
whether the hysteresis is ON. If so, the algorithm loops back to
step 708. If not, the algorithm loops back to step 704.
[0097] Returning to step 712, if the load voltage is less than
V.sub.p2, the voltage monitor 100 turns the fan on at step 716. The
algorithm branches back to step 708 to continue monitoring the load
current and voltage.
[0098] Returning to step 708, if the load current is less than the
lower threshold current, I.sub.L, then the "YES" branch is followed
to step 720, in which the hysteresis function is OFF. The fan
monitor 606 then turns the fan 40 off in step 714. The algorithm
proceeds to step 718, in which the determination is made whether
the hysteresis is ON. If the hysteresis function is ON, the
algorithm loops back to step 708. If not, the algorithm loops back
to step 704.
[0099] Returning to step 704, if the power sensor 602 determines
that the current through resistor R.sub.12 is less than the upper
threshold current I.sub.H, The algorithm proceeds to step 720, in
which the power sensor 602 switches the hysteresis OFF. In
response, the fan controller 606 turns the fan off at step 714.
[0100] It should be understood that the foregoing relates only to
preferred embodiments of the present invention, and that numerous
changes may be made therein without departing from the spirit and
scope of the invention as defined by the following claims.
* * * * *