Battery heating system

(54) Designation Device for heating the accumulator battery (56) Published publications: FR 2 120 417 (H01m 45/02), US 2 679 549 (136: 161) US 2 899 623 (320: 2) (57) Abstract. _HeatElectric accumulator batteries used at low ambient temperature are provided by alternating current supplied from a generator (12), which is powered by an internal combustion engine (53) j e.g. a vehicle engine. The power factor therein can be held high by coupled capacitors (18), but a current sensing transformer (228, Fig. 4) can also be used which controls the current flow through the generator's field windings.

The current is substantially unchanged regardless of variations in engine speed, and the output impedance of the generator tower is significantly greater than the internal resistance of the batteries, which means that the heating intensity is inversely proportional to the internal resistance of the batteries, ie. the heating becomes intense when the resistance is large, but is reduced as the electrolyte temperature rises and the resistance decreases.

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The present invention relates to a device for heating electric accumulator batteries at low ambient temperature.

When the batteries are used at low ambient temperatures, it may be necessary to heat the electrolyte. This can be done by supplying alternating current to the batteries, whereby their internal resistance causes heat to be released, which in turn raises the temperature of the electrolyte. It may be necessary to change the battery temperature in a wide range₅ and there is a risk of overheating if the internal resistance of the battery becomes too low. If the AC is supplied by a generator powered by a primary source, e.g. of a vehicle engine, the heating current can sometimes become too weak at low vehicle speeds, or too strong at high speeds.

The object of the present invention is to propose a device for the battery heating system where the above-mentioned inconveniences have been eliminated or in any case significantly reduced.

In accordance with the invention, it is arranged that the alternating current supplied to the battery, respectively, is maintained at a

7807789-8 substantially constant value, irrespective of speed variations at the primary motor.

A substantially constant alternating current can be obtained by arranging that the effective output impedance of the alternator is significantly higher than the maximum internal resistance of the battery. This can be achieved either by using a permanent magnet generator, or a field winding generator and provided with field control which is dependent on the output current from the generator.

The invention will be described below with reference to the accompanying drawing, in which Figures 1-4 show various arrangements for charging and heating accumulator batteries.

Fig. 1 shows a combined system 10 for charging and heating accumulator batteries, which includes a three-phase permanent magnet AC generator 12, which is connected to the star-coupled primary winding 14 in a transformer 16. Three output coupled capacitors 18 can also be connected to the output of generator 12 . The secondary winding 19 of the transformer 16 is connected to connections between three pairs of series-connected accumulator batteries 20, 22; 24, 26 and 28, 30. The pairs of batteries are connected between conductors 32 and 34.

The design of the generator 12 and of the transformer 16 is such that the effective output impedance at the generator is significantly higher than the maximum internal resistance of the batteries (attributed to the transformer primary circuit).

System 10 also includes a second alternating current generator 36, which is connected to a rectifier 38 comprising six diodes 40. The rectifier 38 feeds positive and negative conductors 42, respectively. 44, which in turn are associated with the leaders. 32 and 34 for charging the batteries. A voltage regulator 46 is connected between conductors 42 and 44, and is connected to generator 36 through conductors 48 and 5θ ·

Both alternators 12 and 36 are driven from a common shaft 52 connected to a variable speed primary motor, e.g. a vehicle internal combustion engine 53 ·

The high, efficient output impedance of generator 12 means that the heating current will not vary, to a significant degree with changes in the internal resistance of the batteries, everything

7807789-8 as the temperature in them changes. If conduit controllers 18 are used, their capacitance values ​​are selected to increase the power factor of generator 12 so that the alternating current supplied to batteries 20, 22; 24, 26; 28, 30 remain substantially constant regardless of changes in the engine speed 53.

If a system 10 is used to charge batteries when the electrolyte therein has a low output temperature and thus a large internal resistance, then generator 36 cannot deliver any significant charge current. Since generator 12 supplies alternating current for heating the batteries, the electrolyte will be rapidly heated, so that the batteries reach a state of low internal resistance, allowing the use of strong charging current. Since the capacitance values ​​of the capacitors 18 have been chosen so that the alternating current is kept substantially constant within the effective speed range of the internal combustion engine 53, there is no risk of the heating becoming insufficient at low speeds, or too high at high speeds. Although the internal resistance of the batteries decreases as the temperature of the electrolyte rises, the high inductance of the windings in the permanent magnet generator, together with the capacitors 18, will prevent the alternating current from being too strong.

Because the secondary windings. 19 are connected, with connections between the batteries of the different pairs, there is no risk that the charging DC current will pass through the secondary windings so that the core of the transformer 16 is saturated by direct current.

In Fig. 2 another combined heating and charging system 54 is shown, which comprises a single-phase permanent magnet generator 56 connected to the primary winding 5θ in ^one transformer 60. A capacitor 62 is connected between, the conductors connecting the generator 5θ to the primary winding. One end of the transformer secondary winding 63 is connected to a point between two series coupled capacitors 64 and 65, and the other end of the secondary winding is connected to a connection between two series connected batteries 66 and 68. The pair of capacitors and the pair of batteries are connected parallel between two conductors 7θ and 72.

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System 56 further comprises one. other alternators

74, which supplies a direct current via a rectifier 76 to two conductors 78 and 80 connected to conductors 7θ and 72 for the purpose of charging the batteries 66 and 68. A voltage regulator 82 is connected across conductors 78 and 80, and is connected through conductors 84 and 86 connected to the second alternator 74.

Both generators 56 and 74 are driven by a common shaft 88, from an internal combustion engine 89.

The capacitance of capacitor 62 is so selected as to increase the power factor of generator 56, thereby generating a substantially constant alternating current within the effective speed range of the internal combustion engine 89.

System 54 functions broadly in the same way as system 10 of Fig. 1, ie. generator 56 supplies alternating current to batteries 66 and 68 for heating the electrolyte therein at low ambient temperature, and generator 74 supplies charging current.

Capacitors 64 and 65 prevent the charging direct current from passing into secondary winding 63, thereby avoiding saturation of the core of transformer 60.

Fig. 3 shows a further embodiment of a combined heating and charging system 110, which contains a three-phase permanent magnet alternator current 112, which is connected to the star-coupled primary winding 14 in a three-phase transformer 116. To the output of generator 112, also three delta coupled capacitors 118 are connected. The secondary windings 120 at the transformer 116 are connected via batteries 122 to a conductor 124, and the star point 126 at the secondary windings 120 and. conductor 124 is connected to two DC connections, 128 and 12, respectively. 130th

System 110 contains a second three-phase generator 132 which is connected via positive and negative conductors 138 and 14O via a rectifier 134, which in turn is connected to DC terminals 128 and 130. A voltage regulator 142 is connected between conductors 138 and 140, and is connected to the field winding circuit at generator 132 through conductors 144 and 146 for the purpose of controlling current flow through the field winding so that a constant voltage is maintained between

7807789-8 conductors 13θ and ΐ4θ.

Both generators 112 and 132 are driven by a common shaft 148 from an internal combustion engine 149 ·

The capacitance values ​​of the capacitors are chosen so that the power factor of the generator 118 is increased, whereby the alternating current is kept substantially constant within the effective speed range of the internal combustion engine 149.

System 110 operates in much the same way as system 10 of Fig. 1, wherein generator 112 supplies alternating current for heating purposes, and generator 132 supplies direct current for charging the batteries.

Fig. 4 shows a combined heating and charging circuit 200 comprising a three-phase alternator 212 connected to the star-coupled primary windings 214 of a transformer 216. Its secondary windings 218 are connected via batteries 220 to a conductor 222 and the star iron point of the windings. 218 and conductor 222 are connected to two DC terminals 224 and 226.

A three-phase, current-sensing transformer 228 is connected to the output of generator 212 and is arranged to output an input to a current regulator 230. This is connected to the field winding of generator 212 through conductors 232 and 234, and controls the current flow in the field winding, so that the alternating current 212 is kept substantially constant, regardless of changes in the internal resistance of the batteries 220, or the speed of the internal combustion engine.

System 200 further comprises a second three-phase generator 236 which, via a rectifier 238 provided with diodes 240, supplies direct charging current to conductors 242, 244, which in turn are connected to terminals 224, 226. A voltage regulator 246 is also connected here over conductors 242 and 244, and controls the current flow in the field winding of generator 236 via conductors 248, 250, so that a constant voltage is maintained between conductors' 242 and 244.

Both generators 212 and 236 are driven at varying speeds by a common shaft 2j2 from an internal combustion engine 253 »

Generator 212 supplies current for heating the electrolyte in batteries 220, and generator 236 supplies charging current.

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When system 200 is used to heat batteries that have a low temperature in the initial position, the heating will proceed quickly while charging is slow, as the internal resistance of the batteries is high. As the temperature of the electrolyte rises, the heating will decrease while, the degree of charge will increase.

Since generator 212 delivers a constant alternating current independent of the speed of the internal combustion engine 253, there is no risk that the heating will be insufficient at low speeds or excessive at high speeds.

In system 110 of Fig. 3 and in system 200 of Fig. 4, secondary winding areas 120 and 1, respectively. 218 at transformers 116 and 216 wound on three-branched cores, and although the direct current will pass these windings, it does not cause any residual magnetization. 0m the currents in the three phases are balanced, the magnetic forces (components caused by the DC currents will also be balanced. Therefore, there is no risk that the core is saturated by the influence of the DC current. Also, there will be no noticeable AC voltage component at the DC terminals 28, 30, respectively. 124, 126.

Although both generators in all of the above described examples have been driven by a common primary motor, it is obvious that the generators can be driven by different motors. In each system, heating and charging have been interconnected, but the heating system can only be used, e.g. to heat electrolyte in already charged batteries, which will be used for power supply.

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