U.S. patent number 3,620,205 [Application Number 04/880,623] was granted by the patent office on 1971-11-16 for heating apparatus for caravans and the like.
This patent grant is currently assigned to Application de Gaz, Paris, FR. Invention is credited to Michel Vial.
United States Patent |
3,620,205 |
|
November 16, 1971 |
HEATING APPARATUS FOR CARAVANS AND THE LIKE
Abstract
A portable heater particularly for caravans forming a
thermogenerator comprises a casing containing a substantially flat
plate thermoelectric element heated by an inverted gas burner tube,
the air being circulated by a fan from the bottom of the casing
onto the underside of the base of the heating element, around the
element and over the outside of the burner tube which forms a heat
exchanger and is then distributed onto the room to be heated, means
being provided for regulating the heat passing to the room and for
charging a battery to supply electric current for lighting
room.
Inventors: |
Michel Vial (Rhone, FR) |
Assignee: |
Application de Gaz, Paris, FR
(N/A)
|
Family
ID: |
9695798 |
Appl.
No.: |
04/880,623 |
Filed: |
November 28, 1969 |
Foreign Application Priority Data
Current U.S.
Class: |
126/110E;
136/212; 126/116A |
Current CPC
Class: |
F24H
9/0052 (20130101); F24C 3/00 (20130101); F24H
3/065 (20130101); F24H 9/2085 (20130101); F24C
3/002 (20130101); F24C 3/004 (20130101); H01L
35/00 (20130101); F24C 3/122 (20130101); F24H
2240/08 (20130101) |
Current International
Class: |
F24H
9/20 (20060101); F24C 3/12 (20060101); F24C
3/00 (20060101); F24H 9/00 (20060101); H01L
35/00 (20060101); F24H 3/02 (20060101); F24H
3/06 (20060101); F24h 003/06 (); H01v 001/32 () |
Field of
Search: |
;126/110,110B,110E,116,116A,116B ;136/200,206,212,217,218 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Charles J. Myhre
Attorney, Agent or Firm: Alexander & Dowell
Claims
I claim:
1. An electric thermogenerator comprising: a flat thermoelectric
unit having a cold side and a hot side, said thermoelectric unit
being disposed substantially horizontally with its cold side facing
downwardly and with its hot side facing upwardly; heating means to
heat the upper hot side of said thermoelectric unit; and a fan to
supply cold air to the lower cold side of said thermoelectric unit
to cool same.
2. In an electric thermogenerator as claimed in claim 1, said
heating means being in the form of an inverted gas burner disposed
above said thermoelectric unit.
3. In an electric thermogenerator as claimed in claim 1, vanes
extending downwardly from the lower cold side of said
thermoelectric unit in heat-exchange relation with cold air
supplied by said fan.
4. In an electric thermogenerator as claimed in claim 3, said fan
having a vertical axis, and said vanes being disposed substantially
radially with respect to said axis.
5. In an electric thermogenerator as claimed in claim 2: a
substantially vertical burner casing surrounding said inverted gas
burner and extending downwardly to engage the upper hot side of
said thermoelectric unit in such manner as to define a hearth with
said hot side forming the lower wall of said hearth; means to
supply combustible gas and combustion air to said inverted burner;
and exhaust means for the combustion gases generated by said
inverted burner within said burner casing.
6. A combined heating and electricity-generating apparatus
comprising: a substantially vertical outer casing having a lower
air inlet and an upper air outlet; a flat thermoelectric unit
having a hot side, a cold side and an outer edge, said
thermoelectric unit being disposed substantially horizontally
within said outer casing above said lower air inlet and below said
upper air outlet with said hot side facing upwardly, with said cold
side facing downwardly and with said outer edge being spaced from
said outer casing so as to leave a first annular passage between
said edge and said casing; a fan disposed within said outer casing
below said thermoelectric unit to blow against said cold side
thereof an air stream drawn through said lower air inlet, said air
stream thereafter escaping upwardly through said first annular
passage; an inverted gas burner disposed within said casing above
said thermoelectric unit to heat the upper hot side thereof; a
burner casing surrounding said inverted gas burner within said
outer casing, said burner casing having substantially vertical
lateral walls and extending downwardly to engage the upper hot side
of said thermoelectric unit in such manner as to define a hearth
with said hot side forming the lower wall of said hearth, said
burner casing being spaced from said outer casing so as to leave a
second annular passage for the air stream flowing upwardly from
said first annular passage; means to supply combustible gas and
combustion air to said inverted gas burner; exhaust means to
discharge outside of said outer casing combustion gases generated
by said inverted burner within said burner casing; and vane means
in said hearth and in said second annular passage to transfer heat
from said burner casing to said air stream flowing through said
second annular passage before said air stream issues from said
outer casing through the upper air outlet thereof.
7. In an apparatus as claimed in claim 6, vanes extending
downwardly from the lower cold side of said thermoelectric unit in
heat-exchange relation with cold air supplied by said fan.
8. In an apparatus as claimed in claim 7, said fan being situated
below said vanes and having a substantially vertical axis, and said
vanes being disposed substantially radially with respect to said
axis.
9. In an apparatus as claimed in claim 6: a substantially
horizontal air conduit to supply air to said inverted gas burner
from the outside of said outer casing; a flat vertical air chamber
exterior to said outer casing and in which said air conduit opens,
said chamber being open laterally; and said exhaust means being in
the form of a substantially horizontal gas conduit disposed below
said air conduit and substantially parallel thereto, said gas
conduit passing through said air chamber to open beyond same.
10. A combined heating apparatus and electric thermogenerator
comprising: an outer casing having a lower air inlet and an upper
air outlet, with said outlet comprising first and second air
passage means; a thermoelectric unit disposed within said casing
with said unit having a hot side and a cold side; burner means
within said casing to heat the hot side of said thermoelectric
unit; means to discharge outside of said casing combustion gases
from said burner means; means to cause an air stream drawn from the
lower air inlet of said casing to cool the cold side of said
thermoelectric unit and to exhaust through the upper air outlet of
said casing; and two-way valve means within said casing to direct
said air stream towards said first air passage means or towards
said second air passage means.
11. In an apparatus as claimed in claim 10, heat transfer vane
means between the combustion gases of said burner means and said
air stream.
12. In an apparatus as claimed in claim 10, disposed in a room,
conduit means connecting said first air passage means with the
outside of said room, while said second air passage means open
directly into said room, whereby said air stream may be discharged
either into said room to heat same, or outside of said room when
same is not to be heated.
13. In an apparatus as claimed in claim 18: said casing having an
upper portion of rectangular inner cross section with an upper side
and four lateral sides; said burner means terminating short of said
upper portion; said first air passage means comprising at least one
perforation in a first one of said lateral sides of said upper
portion substantially above said burner means; said second air
passage means comprising at least one perforation in a second
lateral side of said upper portion substantially above said burner
means, with said second lateral side being opposed to said first
lateral side; and said two-way valve means comprising a
substantially rectangular rocking switch shutter having
substantially the same dimensions as the inner cross section of the
upper portion of said casing, and means to pivot said shutter about
an axis parallel to said first and second lateral sides.
Description
This invention relates to improvements in heating apparatus forming
an electric thermogenerator.
The apparatus is heated by gas and in particular butane or propane
gas liquified under pressure and stored in a transportable tank and
is particularly suitable to be used for camping; caravans and
similar applications.
It is known that the practice of camping by means of a motor
vehicle presents the double problem of heating and the supply of
electric energy. Numerous stoves have been thought of operating
with liquified gas and made in a form which is light and at the
same time taking up little space. Such systems resolve the problem
of heating in the practice of camping or in similar circumstances.
On the other hand the electric energy necessary for lighting only
can be provided at low voltage by connecting up to the accumulator
batteries of the motor vehicle connected to a camping caravan but
as this battery has only a limited capacity its regular recharging
is indispensable which normally makes it necessary to run the motor
of the vehicle idle if this latter is not used regularly. There has
also been the idea of combining with the heating apparatus
thermoelectric generator elements which supply the energy necessary
for this recharge and which even permits of providing for the
supply of energy to a battery separate from that of the
aforementioned vehicle.
The invention aims at permitting the making of such a combined
heating and electric energy-producing apparatus which has a high
output, of flexible use and which lends itself particularly well
suited to being installed aboard a camping caravan.
The invention also aims at realizing such an apparatus which
permits of recharging conventional 12-volt batteries by using for
this purpose only a single thermoelectric generator element of
known type giving a voltage of the order of 6 to 7 volts only.
The apparatus made in accordance with the invention is
characterized in that the base of its hearth is constituted by the
hot surface of a flat thermoelectric element heated by an inverted
gas burner and that the whole of this hearth is mounted inside a
casing into which air penetrates through the bottom by cooling
first of all the lower outer face of the base of the hearth, that
is to say the cold face of the thermoelement and to then ascend by
convection currents continuing to be heated by contact with the
lateral outer surface and possibly the upper surface of the hearth
before leaving this enclosure through the top from whence it may be
distributed into a room to be heated.
According to a preferred embodiment the upper part of the hearth is
made as a heat exchanger carrying on its inner and outer faces
vanes which extend in vertical planes.
The casing of the apparatus contains advantageously an axial fan
mounted under the hearth in the axis of the latter.
It is convenient to make in the upper part of the casing at least
two openings one communicating with a room to be heated and the
other communicating with the outside and to control them by a
shutter allowing for controlling one of these openings by more or
less closing the other.
In a preferred embodiment the lower part of the casing encloses a
thermostat for control of the burner as well as all the ignition
and regulating devices.
The invention will be described with reference to the accompanying
drawings:
FIG. 1 is a general vertical section of an apparatus according to
the invention;
FIG. 2 is a detail section enlarged on line II--II (FIG. 1) of the
head of the burner of this apparatus;
FIG. 3 is a schematic diagram of the various devices of the
apparatus;
FIG. 4 is a development of the starting control cam;
FIG. 5 shows a diagram of the electrical connections.
The apparatus shown in FIG. 1 comprises a casing 1, for example, of
aluminum the inside of which is divided in the vertical direction
into three parts or zones which have been given the references A, B
and C respectively. The lower zone A is defined in height by a
horizontal partition 2 perforated with a circular central opening
2a of large diameter surrounded by a cylindrical flange or skirting
2b directed downwards. The partition 2 is integral with arms 3
which support an electric motor 4 having a vertical axis. On the
upper end of the shaft of this motor is mounted a fan 5 which
rotates at a reduced speed inside the skirting 2b so as to blow
from the bottom upwards. In this zone A the wall of the casing 1 is
perforated by numerous openings 1a forming air inlets for the fan.
It will also be noted that the zone A encloses a regulator assembly
b, a thermostat 7 and a control unit 8 all as hereinafter
described.
The zone B of the inner space of the casing 1 encloses a
thermoelectric element or module 9 of flat shape and circular in
the example shown. Such elements being well known in practice a
detailed description will not be given. It will simply be noted
that the one shown comprises two plates 9a and 9b between which are
interposed cells 9c each of which constitutes a thermoelectric
couple these cells being mounted in series with their hot and cold
seams in thermal connection respectively with the upper and lower
plates 9a and 9b. The lower plate 9b is integral with radial vanes
10 disposed so as to form with the aforementioned plate a radiator
adapted to receive the air current blown by the fan 5 while the
upper plate 9a is fixed against the lower open end of the hearth
the lower part of which is constituted by an inverted cylindrical
box 11.
The upper part of the hearth constitutes a heat exchanger
comprising, affixed to the box 11, a hollow cylindrical body 12 the
upper end of which is closed, this body being integral with a
lateral discharge tube 13 which is engaged in a radial tube 1b
leaving the casing 1 laterally.
Axially through the hearth there extends an inverted gas burner
comprising a vertical biconical pipe 14 integral with the upper
face of the body 12 and adapted to form a venture discharge for
this pipe being connected to a central opening provided in the
upper base of the box 11. This base is in its turn integral with a
conical truncated chamber 15 wide mouthed at the bottom and the
large base of which is constituted by a perforated plate 16 while
its smaller upper end is connected to the pipe 14.
The body 12 of the heat exchanger carries radial vanes 17 and 18
respectively on its outer surface and on its inner surface. It will
also be noted that the base of the box 11 is perforated with
openings 11a in its annular part which surrounds the small base of
the conical truncated chamber 15.
The upper zone C of the inner space of the body 1 encloses an axial
head 19 the detail of which is as follows: This head 19 receives
the gas through a main piping 20 and distributes it to a tube 21
directed downwards into the throat of the venturi 14. The head 19
is in addition integral with a plate 19a which forms a cover of an
upper cylindrical part 14a connecting with the inlet of the venturi
14. The chamber defined by the cylindrical part 14a communicates
with the outside through an air inlet tube 22 which extends
radially beyond the wall of the body 1.
The upper zone C encloses a transverse spindle 23 on which is
mounted a rocking switch shutter 24. This latter of rectangular
shape has on its two sides parallel to the spindle 23 sealing pads
24a capable of bearing respectively against the upper horizontal
wall of the casing 1 or against a horizontal flange 25 located in
the plane of separation of the zones B and C. The operation of this
shutter 24 may be ensured by a button 26 hinged to one of the pads
24a and passing through a slot (not shown) provided in the wall of
the casing 1.
In the aforementioned zone C the vertical walls parallel to the
spindle 23, air outlet openings are made constituted by groups of
openings 1c and 1d respectively. The apparatus is normally intended
to be placed against the wall 27 of the area to be heated (for
example a caravan). This wall is perforated by an opening 27a
against which the wall of the casing 1 is applied which has the
openings 1d. Against the outer face of the wall 27 there is
disposed a plate 28 comprising a system of venetian blind slats 28a
to the right of the opening 27a. This plate 28 is connected by
crossmembers 29 to another plate 30 which defines with the
crossmember a hot air distribution space D into which opens the air
inlet tube 22. The tubing 1b aforementioned connects with the plate
30. The plate 30 is connected in its turn by the crossmembers 31 to
a third plate 32 disposed opposite the outlet of the tubing
aforementioned making an intermediate space E which constitutes the
smoke outlet chamber as will be better understood from the
following description. The general operation is as follows:
The gas which escapes downwards from the pipe 21 draws into the
venturi 14 air brought from outside through the chamber D and the
tube 22. The mixture thus arrives in the truncated conical chamber
15 and passes through the perforated wall 16 to burn inside the
casing 11 so that the flame licks the upper plate 9a of the
thermoelectric element 9 thus keeping it at a relatively high
temperature. The hot gases ascent again through the perforations 11
of the bottom of the casing 11 then into the body 12 and escape
outside through the tube 1b and the chamber E which forms a
screen.
At the same time the fan 5 provides an ascending current of cold
air which circulates in contact with the heat exchanger constituted
by the vanes 10 cooling these latter and therefore keeping the
lower plate 9b of the thermoelectric element 9 relatively cold. The
air which leaves the vanes 10 mounts into the zone B and passes in
contact with the vanes 17 absorbing the heat which these latter
receive from the body 12 and the inner vanes 18 of the latter.
It will be understood in fact that the assembly 18-12-17 of the
upper part of the hearth constitutes a heat exchanger between the
hot gases which ascend from the casing 11 and the air which, in its
turn, likewise rises in the annular space between the body and the
wall of the casing 1. The air thus-heated arrives into the upper
zone C of the casing and according to the position given to the
switch shutter 24 is delivered either inside the caravan through
the openings 1c or outside the latter through the openings 1d of
the chamber D which constitutes a protection against the influence
of any outside draught. It will be understood that in the first
case the apparatus ensures the heating of the caravan at the same
time as the production of electrical energy as hereinafter
described (cold weather conditions) while in the second case it
supplies only this energy without heating the room as is described
in hot weather. There is of course nothing to prevent placing the
shutter 24 in an intermediate position.
There remains to explain the lighting and regulating devices of the
apparatus as well as the diagram of electrical connections. It will
be convenient to describe first of all the detail of the head 19
hereinbefore mentioned. As FIG. 2 shows the head comprises a solid
body with a main entry 19b disposed laterally and which discharges
into a vertical channel 19c connected to the pipe 21. The body 19
also has an auxiliary inlet 19d which discharges into an annular
bore 19c surrounding the pipe 21. This bore is extended downwards
by a sleeve 33 which terminates a little above the end of the pipe
21. A connection 34 joins the auxiliary inlet 19d to piping 35
intended to supply gas to the sleeve 33 with a view to enriching
the mixture at the time of igniting the burner.
FIG. 3 shows the general operation of the apparatus.
The fan 5 brings air to the vanes that is to say, to the cooling
radiator of the thermoelectric element 9. The air leaving the vanes
10 arrives at the heat exchanger constituted by the assembly
18-12-17 and leaves in a heated state in the zone C to escape as
desired either to the inside through the openings 1c or outside
through the openings 1d. The outside air sucked through the tube 22
arrives at the burner 14 which supplies the heat to the
thermoelectric element 9 by discharging its burnt gases into the
exchanger 18-12-17 from which they pass through the chamber E to
the outside of the caravan. The combustible gas coming from a
cylinder, not shown, arrives at the regulating device 36. It passes
from there through a general tap 37, a safety valve 38 (of the type
held open by an electromagnet against a drawback spring) then an
electromagnetic valve 39 into the main inlet 19b of the head of the
burner. It will be noted that there is provided a bypass piping 40
in parallel with the valve 39 this piping having a calibrated
opening 41 shown in the diagram (FIG. 3) and provided so as to
permit a pilot operation of the burner when the valve 39 is
closed.
The piping 35 of FIG. 3 leaves the main piping before the valve 39
to supply the inlet 19d. It is controlled by a valve 42.
Connected to the burner 14 is a thermoelectric couple 43 which
feeds an electric holding magnet of the safety valve 38 to keep
this latter open when the flame has been ignited. The electric
diagram (which will be given in detail later) comprises the battery
F divided into two halves of 6 volts each. From the thermoelectric
generator 9 the current passes through a first working control
relay 44 (voltanetric relay) to which is connected a lamp 45. The
current arrives at a switch assembly 46, passes through a load
control relay 47 to which is connected a second lamp 48 then to a
general interruptor 49 and to the midpoint of the battery F. A
current shunt feeds the thermostat 7 which controls the valve 39.
Connected to the burner 14 is an ignition filament 50 (FIGS. 1 and
3) which can be controlled by means of a switch 51 (FIG. 4).
On the electric cable (FIG. 3) which connects the thermoelectric
couple 43 for the safety valve 38 is inserted a biplate switch 10a
intended to cut the circuit in the event of a premature stopping of
the fan causing the vanes 10 (and consequently also the lower plate
9b of the element 9) to become over heated.
The general control is effected by the unit 8 of FIG. 1 to which
are connected two cylindrical rotary knobs 52 and 53 respectively.
The central knob 52 operates the needle of the general tap 37. One
must therefore operate it to open the top before starting and close
it again when it is desired to stop the apparatus. The second knob
53 causes a cam to rotate the development of which has been
diagrammatically shown in FIG. 4. As can be seen an arm 54 has
three bosses 54a, 54b and 54c. The first controls the valve 42 for
enriching at the time of the ignition, the second leads to the
opening the safety valve 38 against the spring which brings it back
to closing finally and the third acts on the switch 51 to close it.
It will be understood that if the general tap is open when the cam
54 is operated the gas is brought to the apparatus at the same time
as the current is caused to pass through the filament 50. The gas
therefore arrives simultaneously at the pipe 21 and to the sleeve
33 thus determining the formation of a very rich mixture which
ignites on contact with the filament without causing any flame
return and which heats the thermocouple 43. At the end of some tens
of seconds this latter feeds into the electromagnet of the valve 38
a current sufficient to keep this latter in the open position. The
cam 54 may therefore be brought back towards its resting position
which puts out of action the ignition filament and couples the
additional admission of gas through the sleeve 33 bringing back the
full richness of the mixture in the burner to its normal value.
From this moment the burner operates at full working condition
assuming that the battery is fully charged and that the thermostat
7 is in the cold position for which the valve 39 is open. It will
be seen later on what happens with the electric circuits. When the
thermostat 7 comes to the hot position it closes the valve 39 so
the burner is only fed with gas through the calibrated opening 41
and operates due to this at slowed speed.
It will be understood that by placing the thermostat 7 in the
bottom of the casing 1, as shown in FIG. 1 it is caused to act as
an environment regulator since it detects the temperature of the
air drawn into the room. It therefore regulates the heating of the
latter in the manner desired if one is in the cold period and when
the battery is completely charged which will all be seen later.
In the case of stopping the fan 5 the vanes 10 become heated and
the biplate switch 10a cuts the circuit of the thermo couple thus
causing the closing of the safety valve 38.
FIG. 5 indicates the detail of the electric circuits diagram and
permits better understanding of the indications of FIG. 3. As
indicated above the battery F, assumed to be 12 volts is divided
into two halves F1, F2 of 6 volts each. A double switch 46a permits
of connecting alternatively one then the other of these two half
batteries to a line comprising two conductors 55 and 56. The
conductor 55 is connected to the positive pole of the
thermogenerator 9 by means of a diode 57 which prevents the battery
from discharging on the generator when this latter is at rest. In
its turn the conductor 56 is connected to the negative pole of the
generator by a movable charge control contact 47a controlled by the
winding of the relay 47 of FIG. 3. At the charge end (position of
the movable parts in broken lines) this contact connects the
negative pole aforementioned to a resistance 58 as will be
explained later.
The winding 47 is connected to a conductor 59 which is connected to
the negative pole of the battery F. Its other end is connected to
another conductor 60 adapted to be connected in its turn to the
positive pole of the battery F by the movable contact 44a of the
voltametric relay 44. At rest (position in broken lines) this
movable contact 44a connects the positive pole to the lamp 45 the
circuit of which is closed on the conductor 59. The conductor 60 is
connected by a movable contact 47b of the relay 47 to a circuit
comprising in series the thermostat 7 are the winding of the
electrovalve 39 connected to the conductor 59, the lamp 48 being
mounted in parallel across the assembly of this winding 39 and of
the thermostat 7. Between the two conductors 59 and 60 there is
mounted the switch device 46 which comprises a time base of
relatively long period and an electromagnet for control of the
switch 46a.
Between the positive pole and the negative pole of the battery are
mounted in series one with the other the ignition filament 50 and
its control switch 51.
There will be seen at 49 the general bipolar switch interposed
between the poles themselves of the battery and the circuits just
described.
Before explaining the operation of the electric circuits the object
assigned to them should be noted. It has been admitted that the
essential role imparted to the apparatus consists in keeping the
battery F charged even if that entails an excess of heating which
can be easily remedied by means of the valve 24. It is therefore
considered that the reduced working condition of the burner must
only occur once the battery is fully charged.
This being granted the operation is as follows:
At rest the contact 47a connects the generator 9 to the conductor
56. The contact 47b is opened thus insulating the electrovalve 39
which is arranged to be normally in the open position. The contact
44a is on the lamp 45. If the general switch 49 is closed the lamp
ignites the signal that the battery is in, circuit but is not on
charge. The lamp 48 remains on the contrary extinguished indicating
that the thermostat is out of action.
As soon as the generator 9 reaches a sufficient voltage (a little
more than 6 volts) the voltametric relay 44 comes into operation
displacing the contact 44e which connects the conductor 60 to the
positive pole of the battery. That has the effect of closing the
valve 45 and putting in circuit the winding of the charge control
relay 47. If it is assumed that the battery is not completely
charged, this relay 47 does not operate so that the thermostat 7
remains out of circuit and the valve 39 remains in the fully opened
position. The burner therefore continues to work at maximum working
conditions but the thermogenerator 9 may commence to act through
the diode 57 to charge that of the two half batteries F1 and F2
which are then in circuit. Simultaneously the switch device 46
comes into play to actuate periodically the switch 46a so that the
charge current coming from the generator 9 is sent alternatively to
the half-battery F1 then to the half-battery F2. There is thus
obtained a regular charge of a 12-volt battery with a single
thermogenerator of only 6 volts.
When the battery F is completely charged, that is to say, when both
of its two halves F1 and F2 have reached a voltage limited to the
order of 71/2 the relay 47 is put in operation displacing its two
movable contacts 47a and 47b. The displacement of the contact 47a
has the effect of stopping the charging of the battery while
maintaining the output of the generator 9 the current from which
circulates through the resistance 58. The contact 47b puts in
circuit the thermostat 7 and the winding of the electro valve 39
igniting simultaneously the lamp 48 which indicates the end of
charging.
As long as the battery is fully charged the thermostat 7 may
intervene to close the circuit of the winding of the electrovalve
39 and thus to cause the closing of this latter, the burner then
operating on a reduced supply as explained above (that is to say by
feeding through the calibrated opening 41 of the FIG. 3). This
reduced working reduces the consumption of combustible gas to the
minimum required to maintain at a sufficient temperature the hot
plate 9a (FIG. 1) of the thermogenerator element or module 9
consequently avoiding in the latter abrupt surges in temperature
liable to bring about its premature ageing.
It is easy to verify the above described circuits ensure the
complete safety of the automatic operation of the whole of the
apparatus and that they guarantee that the battery always remains
charged to a maximum.
* * * * *