U.S. patent application number 13/278752 was filed with the patent office on 2012-02-16 for systems and methods for charging super capacitors.
This patent application is currently assigned to SmartSynch, Inc.. Invention is credited to Zafarullah Khan.
Application Number | 20120038328 13/278752 |
Document ID | / |
Family ID | 40095264 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120038328 |
Kind Code |
A1 |
Khan; Zafarullah |
February 16, 2012 |
Systems and Methods for Charging Super Capacitors
Abstract
Systems and methods are provided for charging a super capacitor
bank. One method provides for determining a charge voltage for the
super capacitor bank, providing a charging current, limiting the
charging current according to a corresponding worst case
temperature within the super capacitor bank operating temperature
range, limiting the charge voltage according to the worst case
temperature, and turning off the charging current once the super
capacitor bank is charged. One system provides a super capacitor
bank for storing energy providing specified power demand to a
circuit, a current charger providing charging current to the super
capacitor bank, the charging current limited in accordance with a
corresponding worst case temperature within the super capacitor
bank operating temperature range, a voltage sense circuit to detect
the super capacitor bank voltage, and a control to disconnect the
current charger from the super capacitor bank once the super
capacitor bank is charged.
Inventors: |
Khan; Zafarullah; (Kenner,
LA) |
Assignee: |
SmartSynch, Inc.
Jackson
MS
|
Family ID: |
40095264 |
Appl. No.: |
13/278752 |
Filed: |
October 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12122935 |
May 19, 2008 |
8049470 |
|
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13278752 |
|
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60943135 |
Jun 11, 2007 |
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Current U.S.
Class: |
320/167 |
Current CPC
Class: |
H02J 7/007194 20200101;
H02J 7/0088 20130101; H02J 7/007192 20200101; H02J 7/045 20130101;
H02J 7/345 20130101; H02J 7/007188 20200101; Y02E 60/13 20130101;
H01G 9/155 20130101; H02J 7/0071 20200101 |
Class at
Publication: |
320/167 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1. A method for charging a super capacitor bank, the method
comprising: determining a desired charge voltage for the super
capacitor bank; providing a charging current to the super capacitor
bank; limiting the charging current according to a corresponding
worst case temperature within the super capacitor bank operating
temperature range; limiting the charge voltage according to the
worst case temperature within the super capacitor bank operating
temperature range; and turning off the charging current upon a
determination that the super capacitor bank has been charged to the
desired charge voltage.
2. The method of claim 1, further comprising turning on the
charging current upon a determination that the super capacitor bank
charge voltage has dropped a specified percentage below the desired
charge voltage.
3. The method of claim 1, further comprising: maintaining the
charging current below a specified maximum charging current for the
super capacitor bank; and limiting a charge time below a
corresponding maximum allowable charge time for the super capacitor
bank.
4. The method of claim 1, further comprising maintaining the
charging current at a constant value.
5. The method of claim 1, wherein energy capacity and voltage
rating of the super capacitor bank are configured to store energy
sufficient for a specified application.
6. A method for charging a super capacitor bank, the method
comprising: determining a charging current limit for the super
capacitor bank, wherein the charging current limit is the maximum
charging current for the super capacitor bank at worst case
temperature within the super capacitor bank operating temperature
range; determining a charging voltage limit for the super capacitor
bank, wherein the charging voltage limit is the maximum voltage for
the super capacitor bank at worst case temperature within the super
capacitor bank operating temperature range; providing a charging
current to the super capacitor bank, wherein the charging current
is less than the charging current limit; maintaining the charging
voltage below the charging voltage limit; and turning off the
charging current upon determining that the super capacitor bank has
charged to a specified charge voltage.
7. The method of claim 6, further comprising turning on the
charging current upon a determination that the super capacitor bank
charge voltage has dropped a specified percentage below the
specified charge voltage.
8. The method of claim 6, further comprising limiting a charge time
for the charging current, wherein the limited charge time is below
a corresponding maximum allowable charge time for the super
capacitor bank.
9. The method of claim 6, further comprising maintaining the
charging current at a constant value.
10. The method of claim 6, wherein energy capacity and voltage
rating of the super capacitor bank are configured to store energy
sufficient for a specified application.
11. A method for charging a super capacitor bank, the method
comprising: providing a regulated voltage, wherein the regulated
voltage is the maximum voltage for the super capacitor bank at
worst case temperature within the super capacitor bank operating
temperature range; providing a charging current to the super
capacitor bank; and limiting the charging current below a specified
maximum charging current, wherein the maximum charging current is
specified for the super capacitor bank according to worst case
temperature within the super capacitor bank operating temperature
range.
12. The method of claim 11, further comprising limiting a charge
time for the charging current, wherein the limited charge time is
below a corresponding maximum allowable charge time for the super
capacitor bank.
13. The method of claim 11, further comprising maintaining the
charging current at a constant value.
14. The method of claim 11, wherein energy capacity and voltage
rating of the super capacitor bank are configured to store energy
sufficient for a specified application.
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Patent Application Ser. No.
60/943,135, entitled "Systems and Methods for Charging Super
Capacitors," filed Jun. 11, 2007, which is incorporated herein by
reference as if set forth herein in its entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to charging super
capacitors, and more particularly to charging super capacitor banks
irrespective of temperature effects on the voltage ratings of the
capacitors.
BACKGROUND
[0003] Super capacitors are typically used as a power reservoir to
supply temporary reserve power when available input power is unable
to handle a spike in power demand or when the input power supply is
no longer available due to a power failure. Super capacitors
provide reserve power, for example, for a telemetry device when
enabling a temporary boost in transmission power, or when enabling
a "last gasp" transmission opportunity in the event of power
failure.
[0004] The maximum charging voltage for super capacitors is a
function of the operating temperature. As the operating temperature
is increased, the maximum voltage rating of the super capacitor is
reduced. Since exceeding the maximum charging voltage reduces the
life of the super capacitor, temperature compensating circuits are
often used to limit the charging voltage at higher operating
temperatures.
SUMMARY
[0005] The present invention provides systems and methods for
charging a super capacitor bank. In one embodiment, a method for
charging a super capacitor bank comprises determining a desired
charge voltage for the super capacitor bank, providing a charging
current to the super capacitor bank, limiting the charging current
according to a corresponding worst case temperature within the
super capacitor bank operating temperature range, limiting the
charge voltage according to the worst case temperature within the
super capacitor bank operating temperature range, and turning off
the charging current upon a determination that the super capacitor
bank has been charged to the desired charge voltage.
[0006] Another method for charging a super capacitor bank comprises
determining a charging current limit for the super capacitor bank,
wherein the charging current limit is the maximum charging current
for the super capacitor bank at worst case temperature within the
super capacitor bank operating temperature range, determining a
charging voltage limit for the super capacitor bank, wherein the
charging voltage limit is the maximum voltage for the super
capacitor bank at worst case temperature within the super capacitor
bank operating temperature range, providing a charging current to
the super capacitor bank, wherein the charging current is less than
the charging current limit, maintaining the charging voltage below
the charging voltage limit, and turning off the charging current
upon determining that the super capacitor bank has charged to a
specified charge voltage.
[0007] In another embodiment, a method for charging a super
capacitor bank comprises providing a regulated voltage, where the
regulated voltage is the maximum voltage for the super capacitor
bank at worst case temperature within the super capacitor bank
operating temperature range, providing a charging current to the
super capacitor bank, and limiting the charging current below a
specified maximum charging current specified for the super
capacitor bank according to worst case temperature within the super
capacitor bank operating temperature range.
[0008] In another embodiment, a method for charging a super
capacitor bank comprises determining a charging current limit for
the super capacitor bank where the charging current limit is the
maximum charging current for the super capacitor bank at worst case
temperature within the super capacitor bank operating temperature
range, providing a regulated voltage where the regulated voltage is
the maximum voltage for the super capacitor bank at worst case
temperature within the super capacitor bank operating temperature
range, and providing a charging current to the super capacitor bank
where the charging current is less than the charging current
limit.
[0009] In yet another embodiment, a system for charging a super
capacitor bank comprises a super capacitor bank for storing energy
and to further provide a specified power demand to a circuit, a
current charger to provide a charging current to the super
capacitor bank, where the charging current is limited to a maximum
charging current corresponding to a worst case temperature within
the super capacitor bank operating temperature range, a voltage
sense circuit to detect the voltage of the super capacitor bank,
and a control configured to disconnect the current charger from the
super capacitor bank upon detecting a specified voltage at the
super capacitor bank.
[0010] Other systems, methods, features and advantages of the
present invention will be or become apparent to one with skill in
the art upon examination of the following drawings and detailed
description. It is intended that all such additional systems,
methods, features and advantages be included within this
description and be within the scope of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Many aspects of the invention can be better understood with
reference to the following drawings. The components in the drawings
are not necessarily to scale, emphasis instead being placed upon
clearly illustrating the principles of the present invention.
Moreover, in the drawings, like reference numerals designate
corresponding parts throughout the several views.
[0012] FIG. 1 is a block diagram illustrating a system for charging
a super capacitor bank irrespective of temperature effects on the
voltage ratings of the capacitors.
[0013] FIG. 2 is a block diagram illustrating an alternative system
for charging a super capacitor bank using a regulated voltage.
[0014] FIG. 3 is a flowchart illustrating a method for charging a
super capacitor bank according to the system of FIG. 1.
DETAILED DESCRIPTION
[0015] Reference is now made in detail to the description of the
embodiments of systems and methods for charging super capacitor
banks as illustrated in the accompanying drawings. The invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are intended to convey the scope of the invention
to those skilled in the art. Furthermore, all "examples" given
herein are intended to be non-limiting.
[0016] FIG. 1 is a block diagram illustrating an embodiment of a
system 100 for charging a super capacitor bank 140 irrespective of
temperature effects on the voltage ratings of the capacitors. A
charger 110 provides current from an unregulated voltage 120 for
charging the super capacitor bank 140. The charging current and
voltage are maintained at a level that is safe for the range of
operating conditions based on the super capacitor characteristics
as provided by the super capacitor manufacturer. A voltage sense
circuit 150 is provided for monitoring or detecting the voltage
level of the super capacitor bank. When the super capacitor bank
140 is charged to the desired voltage, the voltage sense circuit
150 provides an input that signals the on/off control 130 to
disconnect the charging current from the charger 110.
[0017] Additionally, when the super capacitor bank 140 voltage
drops below the desired voltage level, the voltage sense circuit
150 provides an input that signals the on/of control 130 to connect
the charging current from the charger 110. The super capacitor bank
140 begins charging again.
[0018] One skilled in the art will readily note that the charger
110 need not be limited to a constant current charge, so long as
the charging current does not exceed the maximum recommended
charging current for the super capacitors, and the charge time does
not exceed the maximum allowable charge time for the
application.
[0019] Super capacitors are typically used as a power reservoir to
supply temporary reserve power for circumstances when available
input power is unable to handle a spike in power demand, or other
relatively sudden increases in power demand, or when the input
power supply is no longer available due to a power failure. In one
non-limiting example, super capacitors provide reserve power for a
telemetry device when enabling a temporary boost in transmission
power. In another example, super capacitors provide reserve power
when enabling a "last gasp" transmission opportunity in the event
of power failure. Such "last gasp transmissions" allow for
notification to a server or other system devices that the
application or device may not be available, for example.
[0020] Super capacitors are charged to a temperature-dependent
maximum voltage. Exceeding the maximum charge voltage typically
reduces the life of a super capacitor. Super capacitors are
typically sized to supply adequate energy to, for example, a
communication module, under worst case conditions. Worst case
conditions typically occur near the high end of the operating
temperature range (typically 85 degrees Celsius).
[0021] Charging circuits typically protect components from
overheating by varying the charging voltage with temperature. The
charging voltage is allowed to track, but not to exceed, the
maximum working voltage at any given temperature. Necessarily then,
a circuit for adjusting the charging voltage according to
temperature increases cost as well as printed circuit board (PCB)
space requirements. It should be noted that embodiments of the
present invention simplify the circuitry for charging super
capacitor banks according to worst case voltage requirements while
also extending the life of the super capacitors. Even so,
functionality is not sacrificed.
[0022] The energy storage capacity of the super capacitor bank 140
is given by:
E = 1 2 CV 2 ##EQU00001##
E is the stored energy (joules), C is the capacitance (farads) of
the super capacitor bank 140, and V is the voltage (volts) across
the super capacitor bank 140. An increase in temperature reduces
the maximum voltage rating of the super capacitor. Thus, the energy
storage capacity of the super capacitor is lower at high
temperatures. The energy capacity and voltage rating of the super
capacitors are configured such that even with the reduced voltage
at high temperatures, e.g., 85 degrees Celsius, adequate energy is
stored and available for the particular application(s). The extra
energy that is available at lower temperatures is not used or
needed. The super capacitor bank 140 is charged for the worst case
voltage irrespective of temperature, and thus, temperature
compensated charging mechanisms are not necessary.
[0023] In one exemplary embodiment, a product is designed for a
circuit to operate in a temperature range from -40 degrees C. to
+85 degrees C., where the super capacitors have a maximum voltage
rating of 2 V at +85 degrees C. and a maximum voltage rating of 2.5
V at -40 degrees C. The super capacitors are charged to 2 V
throughout the temperature range, even though they have the
capacity for charging to 2.5 V at -40 degrees C. The functionality
of the circuit is not reduced because even with a temperature
compensated charging circuit, the load calculations would be based
on a worst case voltage of 2 V. Such load calculations would not
utilize the extra charge that would be available at higher
voltages.
[0024] In an exemplary embodiment, a worst case voltage rating for
the super capacitors of 2 V at 85 degrees Celsius, would
necessitate the charging voltage being maintained at or below 2 V
irrespective of the actual temperature. Similarly, a maximum safe
charging current of 1 A under worst case conditions would
necessitate maintaining the current at or below 1 A irrespective of
the actual temperature conditions.
[0025] Additional benefits provided by the system 100 of FIG. 1
include elimination of temperature compensated charging circuitry
and the associated costs. Further, the circuit is typically smaller
and therefore occupies less PCB space. The reduction of voltage
stress on the super capacitors results in increased life, since the
super capacitors are typically required to operate at maximum
charge voltage conditions only at 85 degrees C. At temperatures
below 85 degrees C., the super capacitors operate below their
maximum charge voltage conditions. It should also be noted that
reduced super capacitor voltage results in less heat dissipation in
downstream linear voltage regulators.
[0026] FIG. 2 is a block diagram illustrating an alternate
embodiment of a system 200 for charging a super capacitor bank 140
using a regulated voltage 210. Again, the super capacitor bank 140
is charged irrespective of temperature effects on the voltage
ratings of the capacitors. The regulated voltage 210 provides the
correct voltage as an input to the charger 110. A voltage regulator
(providing regulated voltage 210) implements the control
functionality, thus eliminating the need for an on/off control. The
regulated voltage 210 corresponds to the maximum voltage rating of
the super capacitors at the highest operating temperature. The
charger 110 suffices for charging the super capacitor bank 140, so
long as a regulated voltage 210 is supplied.
[0027] In one exemplary embodiment, the regulated voltage 210
provides the correct charging voltage, for the super capacitor bank
140, as the input voltage to the charger 110. The voltage regulator
effectively implements the voltage control function, thus
eliminating the need for an external voltage sensing circuit and an
on/off controller.
[0028] The embodiment of FIG. 2 is used, for example, in
intelligent devices that have a regulated switching power supply
feeding the charging circuit for the super capacitors.
[0029] FIG. 3 is a flowchart illustrating a method 300 for charging
a super capacitor bank 140. In step 310, a charging current limit
is set for the super capacitor bank 140. The charging current limit
is the maximum charging current for the super capacitor bank 140
under worst case temperature conditions within the operating
temperature range. In step 320, a charging voltage limit is set for
the super capacitor bank 140. The charging voltage limit is the
maximum voltage for the super capacitor bank 140 under worst case
temperature conditions within the operating temperature range. The
charging current is turned on and, limited by the charging current
limit, is provided to the super capacitor bank 140 at step 330. The
charging voltage is maintained below the charging voltage limit. In
step 340, if the super capacitor bank 140 has not yet been charged
to the desired voltage, the charging continues. Once the super
capacitor bank has been charged to the desired voltage, the
charging current is turned off at step 360.
[0030] Additionally, monitoring of the super capacitor bank 140
voltage continues after the super capacitors have achieved the
desired voltage. After the super capacitor bank 140 has been
charged to the desired voltage during step 340, a test is made to
determine whether the charging current is still turned on at step
350. If the charging current is on at this point, then it is turned
off at step 360 as above. If the charging current is off, then the
method loops back to check the super capacitor bank 140 voltage at
step 340. So long as the voltage remains at the desired level, this
loop continues. If the super capacitor bank 140 voltage drops below
the desired level due to usage or other leakage, then the
functionality of block 330 is activated to turn on the charging
current and charge the super capacitor bank 140. In addition to
charging the super capacitor bank 140, the voltage of the super
capacitor bank 140 is also monitored for loss or leakage so that
the super capacitor bank 140 is charged when the voltage drops
below a desired level.
[0031] The foregoing description of the exemplary embodiments of
the invention has been presented only for the purposes of
illustration and description and is not intended to be exhaustive
or to limit the invention to the precise forms disclosed. Many
modifications and variations are possible in light of the above
teaching.
[0032] The embodiments were chosen and described in order to
explain the principles of the invention and their practical
application so as to enable others skilled in the art to utilize
the invention and various embodiments and with various
modifications as are suited to the particular use contemplated.
Alternative embodiments will become apparent to those skilled in
the art to which the present invention pertains without departing
from its spirit and scope. Accordingly, the scope of the present
invention is defined by the appended claims rather than the
foregoing description and the exemplary embodiments described
therein.
* * * * *