SLA "Battery Warmers"?

[safe]

SLA "Battery Warmers"?

As we head into winter we quickly realize that our SLA batteries don't do very well in the cold. There is a direct relationship between the heat of the battery and it's ability to hold and release it's energy. On the negative side the constant maintenance of a high temperature would adversely effect the lifespan of the battery, so some deeper thought ought to be applied.

So here's the idea...

Wrap your SLA batteries in an insulating material. (lightweight) Then place into that material some sort of electric warming pad. An hour before you want to ride your bike you can plug in your charger and also plug in the heating pad and this will increase the nominal capacity of your battery. (you will be "topping off" the battery doing this)

You then disconnect your charger and heat pad and begin your ride. Since the batteries are insulated they will hold the heat long enough for your ride. (assuming it's only an hour)

When the ride is over you plug in the charger, but NOT the heat pad because you want to let the battery sit in storage at a cooler temperature to lengthen it's lifespan.

In the end you would get as much as a 30% boost in performance from your batteries.... (depending on outside temperature)

I'd guess that 120 degrees fahrenheit would be your maximum heating temperature beyond which you would probably be causing more harm than good. But I suppose you could experiment with that.

40 degree Fahrenheit = 4.4 degree Celsius (83% rating)
80 degree Fahrenheit = 26.6 degree Celsius (100% rating)
120 degree Fahrenheit = 48.8 degree Celsius (117% rating)

The chart is in Celsius:

 

[Eric G]

I've thought of doing the same type of thing in the past with a heating pad Safe.I find keeping the batteries indoors at around ~72 deg.F and putting them onto a float charge for around an hour or so before heading out works for around 30 minutes when you're outside in the cold.By then I'm ready to go inside. In the winter I don't go cruising around,I get on the bike and go to where I have to,then go home again ... Winter Sucks!

I drove home last night with the temp at 3deg.Celcius and noticed the umph gone. (I didn't have time to float the batts.)

Eric

 

[knightmb]

Good thing my NiMH packs produce their own heat :lol:

It is funny that you mention that, in the winter time when I go on rides the e-bike sits in the garage where it's about 60 F in the winter time. When I go for those polar rides, the batteries generate enough heat, plus being insulated in the back to stay warm. I get better mileage because the motor and controller are running very cold then. I can see the good point about SLA though, they don't get hot on their own (normally anyway), so the cold weather would really take a bite out of them.

 

[safe]

I find keeping the batteries indoors at around ~72 deg.F

Judging by the chart you could still get an additional 15% - 20% extra capacity if you could quickly force the batteries all the way up to 120 degrees for a top off charge. People try to squeeze extra performance out of a lot of areas and this one is pretty easy to do... I think.

I wonder if there is any record of this being done?

An extra 20% capacity might make the SLA's more competitive with other chemistries...

 

[safe]

Good thing my NiMH packs produce their own heat :lol:

I think SLA is the ONLY chemistry that prefers being warm... can you think of any others?

Wait... don't the LiFePO4's work better warm?

 

[safe]

Battery temperature increasing device and method

Document Type and Number:United States Patent 6078163

Link to this page:http://www.freepatentsonline.com/6078163.html

Abstract:An inductor (L), capacitor (C) and alternator (OSC) are connected in series to the positive and negative poles of a battery (15). The temperature of the battery (15) is increased by causing the alternator (OSC) to generate an alternating current having the resonance frequency of the inductor (L) and capacitor (C). The alternating current is consumed by the internal resistance of the battery (15) due to the resonance of the inductor (L) and capacitor (C), and the temperature of the battery therefore rises due to the heat thereby generated in the battery. In this way, the temperature of the battery (15) can be effectively increased with minimum power consumption.

Basically you could achieve the heating with the battery alone. So you have the "charger" and then the "heater and topper" that you use just before you go out on the ride.

Now what does this circuit look like?

 

[TylerDurden]

For years, EV owners have been warming batts before driving and insulating the containers to retain warmth in cold seasons.

It's basic chemistry: reactions accelerate with the addition of heat.

 

[vanilla ice]

Coleman battery box? Well thats pretty big, but those soft sided lunch boxes would do.

I liked the ice cube box idea for car a/c. You could do similarly here and use lunch heat packs to jam in to the insulated bat containers.

 

[Doctorbass]

Just about heating batter, the Killacycle guys heat up their A123 pack b puling 80C current burst to an heater to "warm-up" the batter before the race!!

 

[Drunkskunk]

thanks for the chart Safe. Score one more point for the 6 pack beer cooler as a battery bag

 

[TylerDurden]

Chart came from this resource:

http://homepages.which.net/~paul.hills/Batteries/Batteries.html

Lotsa good information there.

Thanks for putting credit where credit is due, Safe.

You can always tell when charts are not from Safe... they have clear labels.

 

[Eric G]

True you could warm the batteries to 120deg. to increase the performance but by doing this your also decreasing the life of the SLA batts. Seems there's allways a tradeoff. You lose a percentage of sla life with every 7deg (I think) increase from ambient temps. For racing and tweeking things out to get max.speed this is fine.For me,an every day commuter,getting the max.life out of the batteries is more important than squeezing out every last mph. It all depends on how you look at it,I don't mind the lack of umph in the colder months come next summer it'll return.

Edit: nice link Tyler

Eric

 

[fechter]

It's been done before. I remember on the old V forum, there were a few people that were doing that with Ego2 bikes. It makes a big difference in the winter. I don't think the increase in temperature would really shorten the lifespan of the batteries much as long as you don't heat them when you don't need them warm.

With cold batteries, they will run out of juice much faster and you run the risk of cell reversal.

In really cold weather, you might double the range by heating the batteries. A timer switch could be used to start the heater several hours before you need to ride. There might be some advantage to heating the batteries during charging as well. SLA batteries hate cold (except for storage).

They were using some kind of rubber mat heater wrapped around the batteries, with insulation over that. I wouldn't recommend putting any heater under the batteries because the weight of the batteries could damage the heater when you ride over bumps.

 

[safe]

Everyone Missed It

My question (the one that's the most interesting) is about that patent application concerning ELECTRIC methods of heating the battery using it's OWN resistance as the heating method.

http://www.freepatentsonline.com/6078163.html

To attempt to produce and sell a circuit that specifically heated the battery INTERNALLY would run up against his patent (so that's a problem) but to do it for yourself is legal.

How might a circuit (that probably resembles a desulphation circuit) be designed so as to perform the internal battery heating and "topping off" of the battery at the same time?

Does every get the idea?

You don't need an external heating pad.... you use the battery itself to provide heat for itself by exploiting the natural resistance of the battery. This entire process can be achieved with a specialized charger that has "heat adding and power topping" as an added feature.

So this "ideal" charger would have five modes:

1. Desulphation.

2. Full Charging.

3. Declining Voltage as Capacity is achieved.

4. Float charge to maintain low temperature charge.

5. Temperature increase and final capacity topping. (only do this just before you go for the ride)

 

[Eric G]

I have no idea on how to design such a circuit into a battery charger but if one were available on the market I would definately consider buying one.

Thanks on the heads up on cell reversal during the winter months Fechter I'll be paying closer attention this winter.

Eric

 

[fechter]

Seems to me that anything you do to the battery that causes it to get hot is usually pretty bad for it.

I'd go for the external rubber mat heater. The good ones are thermostatically controlled.

 

[safe]

I have no idea on how to design such a circuit into a battery charger but if one were available on the market I would definately consider buying one.

Fechter?

My guess is that the circuit would (as the patent describes) vibrate the natural resistance of the battery much like desulphation does. In fact, the heating process and the desulphation process might be performed at the same time. (eliminating that step in the beginning of charging)

If it's possible to quickly desulphate, warm up, and also top off the battery just before you go out on your ride (adding a little extra insulation surrounding your battery could help hold the temperature at peak levels longer) then it's a great idea.

On a cold 40 degree day you could expect to gain something on the order of a 34% maximum performance gain over a battery that is at outside temperature. (4 degrees Celsius to 48 degrees Celsius)

 

[safe]

Seems to me that anything you do to the battery that causes it to get hot is usually pretty bad for it.

I'd go for the external rubber mat heater. The good ones are thermostatically controlled.

Oh, you're there...

But the idea is to only heat the battery for the period of the ride and then let it cool off during storage. The duration of time at high heat would be small.

What is a heater after all?

It's simply a current running through a resistance.... the battery is a big resistor... the more you heat the resistor (battery) the LESS it resists current. It's like heating up syrup... the hotter it gets the more liquid it becomes... but if you heat it too far then it boils and burns. (so careful control would be important)

So pass the pancakes... :wink:

 

[Drunkskunk]

I'm no expert on batteries or battery chemestry, but it seems to me that anything you do by running current through a battery to get it hot will shorten its life. Its Not Just a giant resistor, anything you do to it is altering its internal chemistry. The chemestry is altered to charge a battery, then altered again to discharge it.

You could use a faster charging cycle to heat the batteries on rechaerge before a ride, but since SLA should be charged at the end of every ride, and not left discharged, that solution has limited use.

It seems to me the best solution is to recharge it while it's still warm after a ride, then keep it from getting cold during storage. Then if it needs it, heat it with a heating pad or electric blanket before the ride.


desulphation is great and all, but what you're doing is to break down the chemicle bonds of the sulfer compounds on the electrodes, and have the sulfor drop off into the electrolyte. A little of this is ok, but too much is a bad thing.

 

[fechter]

Possibly if you ran AC into the battery, it would not really charge or discharge on net, but the internal resistance could be used to heat the battery. It might work better at a higher frequency.

You wouldn't want to heat the battery by overcharging or discharging. I think that would harm it.

You'd need some way to monitor and control the battery temperature, since the AC impedance of batteries could vary quite a bit.

I didn't read the patent claim, but I don't always trust patents to be valid.

 

[safe]

Battery temperature increasing device and method

Document Type and Number:United States Patent 6078163

Link to this page: http://www.freepatentsonline.com/6078163.html

Abstract: An inductor (L), capacitor (C) and alternator (OSC) are connected in series to the positive and negative poles of a battery. The temperature of the battery is increased by causing the alternator (OSC) to generate an alternating current having the resonance frequency of the inductor (L) and capacitor (C). The alternating current is consumed by the internal resistance of the battery due to the resonance of the inductor (L) and capacitor (C), and the temperature of the battery therefore rises due to the heat thereby generated in the battery. In this way, the temperature of the battery can be effectively increased with minimum power consumption.

 

[fechter]

OK, good guess.

Then to design a circuit, you need to figure out a good frequency, and how much power it's going to take to heat up a giant brick of lead.

If you generate any heat at all in the battery, the temperature will go up. Depending on the insulation, it might not take much power. 5 watts might do it. You could also power the circuit from the batteries themselves if you wanted to ride in ridiculously cold temperatures.

You would still want to have a temperature sensor or thermostat stuck to the batteries to measure the temp. and cut the power when the desired temperature was reached.

 

[safe]

If you generate any heat at all in the battery, the temperature will go up. Depending on the insulation, it might not take much power. 5 watts might do it. You could also power the circuit from the batteries themselves if you wanted to ride in ridiculously cold temperatures. You would still want to have a temperature sensor or thermostat stuck to the batteries to measure the temp. and cut the power when the desired temperature was reached.

Yeah, it is suggested by the patent that heating is a low power thing to do. My automotive charger has desulphation that only lasts for about a minute at the beginning. I wonder it that alone could charge it? There's no manual override on my charger, but it's possible for me to restart again and again and again and if there was an accurate way to measure the battery temperature I might be able to know if that can do it.

I wouldn't necessarily want to waste energy keeping the batteries warm by using it's own energy, the whole idea is to increase performance and that would drain off some of the energy.

A temperature sensor would be a nice backup, but I suspect that there is a direct electrical resistance relationship with temperature. In other words, you should be able to have reasonable confidence that if the resistance is a certain amount that the battery is at a certain temperature. As the battery is heated the resistance goes down. You therefore need to know the correct cut off resistance value so that when the battery reaches 120 degrees it shuts down. The temperature outside the battery might only be 100 degrees because it takes time for the heat to radiate outward.

If you knew the "resistance to temperature" relationship AND you knew the proper resonance frequency to do heating properly then it's really simple. All you need is an AC current and a way to sense the resistance so as to know when to turn it off.

Then after all this work you realize that someone else beat you to it and holds a patent on the idea.

Maybe the preferred approach would be to seek out the patent holder (who would know those two parameters exactly) and find out if he's doing anything with the patent. If so, then maybe he has a product to buy.

 

[safe]

http://www.freepatentsonline.com/6078163.html

Inventors:
Horie, Hideaki (Yokosuka, JP)
Nakagawa, Toyoaki (Chigasaki, JP)
Kawai, Mikio (Yokosuka, JP)
Tanjo, Yuji (Yokohama, JP)
Abe, Takaaki (Yokosuka, JP)
Iwai, Ken (Yokosuka, JP)

Application Number:311882 Filing Date:05/14/1999 Publication Date:06/20/2000 View Patent Images:Images are available in PDF form when logged in. To view PDFs, Login or Create Account (Free!) Referenced by:View patents that cite this patent Export Citation:Click for automatic bibliography generation

Assignee:Nissan Motor Co., Ltd. (Yokohama, JP)

Primary Class:320/104 Other Classes:320/134, 320/150 International Classes:H01M 010/44, H01M 010/46 Field of Search:320/104, 134, 136, 142, 144, 150, FOR 134, FOR 142 323/355, 364, 371 US Patent References:3764926 Oct, 1973 Rypinsk, Jr.
4220906 Sep, 1980 Drummond.
Primary Examiner:Tso, Edward H. Attorney, Agent or Firm:Foley & Lardner Claims:What is claimed:

1. A temperature increasing device for increasing the temperature of a battery comprising a positive and negative pole, and plural cells connected in series, said device comprising:

a circuit comprising an inductor, capacitor and alternating current power supply connected in series between said two poles, and

a microprocessor programmed to control said alternating current power supply so that an alternating current having a resonance frequency of said inductor and capacitor is generated by said power supply.

2. A temperature increasing device as defined in claim 1, wherein said microprocessor is further programmed to control the amplitude of said alternating current so that a voltage of each of said cells is equal to or less than a preset upper limiting voltage.

3. A temperature increasing device as defined in claim 1, wherein said microprocessor is further programmed to control said battery to supply power to an external load connected to said poles so as to coercively discharge said battery when the charge amount of said battery is greater than a predetermined value, and to control said power supply to generate said alternating current when said charge amount is equal to or less than said predetermined value.

4. A temperature increasing device as described in claim 3, wherein said battery comprises a battery for driving an electric vehicle, and said external load comprises a heater which heats a vehicle compartment of said electric vehicle.

5. A temperature increasing device for increasing the temperature of a battery comprising a positive and negative pole, and plural cells connected in series, said device comprising:

a circuit comprising an inductor, capacitor and alternating current power supply connected in series between said two poles, and

means for controlling said alternating current power supply so that an alternating current having a resonance frequency of said inductor and capacitor is generated by said power supply.

6. A temperature increasing method for increasing the temperature of a battery comprising a positive and negative pole, and plural cells connected in series, said method comprising:

connecting a circuit comprising an inductor, capacitor and alternating current power supply in series between said two poles, and controlling said power supply to generate an alternating current having a resonance frequency of said inductor and capacitor.
--------------------------------------------------------------------------------
Description:FIELD OF THE INVENTION

This invention relates to temperature increasing of a battery.

BACKGROUND OF THE INVENTION

When the temperature of a battery is low, the internal resistance of the battery is large and the output is low.

In order to obtain a predetermined output in a low temperature environment, the temperature of the battery must be increased.

In this context, it is known that coercively causing the battery to discharge increases the battery temperature by electrical discharge energy.

SUMMARY OF THE INVENTION

However, such a coercive electric discharge causes mass consumption of battery power.

It is therefore an object of this invention to increase the temperature of a battery efficiently with low power consumption.

In order to achieve the above objects, this invention provides a temperature increasing device for increasing the temperature of a battery comprising a positive and negative pole, and plural cells connected in series. The device comprises a circuit comprising an inductor, capacitor and alternating current power supply connected in series between the two poles, and a microprocessor programmed to control the alternating current power supply so that an alternating current having a resonance frequency of the inductor and capacitor is generated by the power supply.

This invention also provides a temperature increasing method for increasing the temperature of a battery comprising a positive and negative pole, and plural cells connected in series. The method comprises connecting a circuit comprising an inductor, capacitor and alternating current power supply in series between the two poles, and controlling the power supply to generate an alternating current having a resonance frequency of the inductor and capacitor.

The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an schematic diagram of a hybrid vehicle according to this invention.

FIG. 2 is a circuit diagram of a battery temperature increasing device according to this invention.

FIG. 3 is a diagram describing the relation of electric discharge depth DOD and cell voltage Vc of a manganese-spinel system lithium ion battery applied to this invention.

FIG. 4 is a flowchart describing a temperature increase control process performed by the battery temperature increasing device according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a hybrid vehicle to which this invention is applied drives drive wheels 8 using the power of an engine 2 and motor 4.

The motor 4 is connected to an input shaft of a continuously variable transmission (CVT) 5.

The output shaft of the engine 2 is joined to a rotating shaft of the motor 4 via a clutch 3.

The output of the continuously variable transmission 5 is transmitted to the drive wheels 8 via a reduction gear 6 and a differential gear 7.

When the clutch 3 is engaged, therefore, the drive wheels 8 rotate due to a rotation torque of the engine 2 and motor 4, and when the clutch 3 is disengaged, the drive wheels 8 rotate due only to the rotation torque of the motor 4.

The continuously variable transmission 5 varies a speed ratio according to an oil pressure supplied from an oil pump 9 driven by a motor 10.

A motor/generator 1 is joined to the engine 2.

Due to a supply current from a battery 15, the motor/generator 1 functions as a starter motor for starting the engine 2, and functions as a generator to charge the battery 15 when the engine 2 is running.

The motor/generator 1 and motor 4, 10 are AC devices such as a triphase synchronous motor or triphase induction motor.

If a motor/generator is applied to the motor 4, electricity is generated by the rotation torque of the drive wheels 8 when the vehicle is slowing down, and a regenerative braking force based on the rotation resistance at this time may also be arranged to apply to the drive wheels 8.

The clutch 3 is an electromagnetic powder clutch which can regulate the transmission torque, but a dry type sheet clutch or wet type multiple disc clutch can also be used.

The motor/generator 1 and motor 4, 10 are respectively controlled by inverters 11, 12 and 13.

DC current motors may also be used for the motor/generator 1 and motor 44,10. In this case, DC/DC converters may be used instead of the inverters 11, 12 and 13.

The inverters 11, 12 and 13 are connected to the battery 15 via a common DC link 14.

The inverters 11, 12 and 13 convert DC power stored in the battery 15 to AC power, and supply this to the motor/generator 1 and motor 4,10.

The inverter 11 also converts AC power generated by the motor/generator 1 and charges the battery 15.

If the motor 4 performs regenerative braking as described above, the power generated by the motor 4 during regenerative braking may be used directly as a drive force for the DC motor 10 or motor/generator 1 via the DC link 14.

The rotation speed of the engine 2, transmission torque of the clutch 3, rotation speed of the motor/generator 1 and motor 4, 10, speed ratio of the continuously variable transmission 5 and charging/discharging of the battery 15 are respectively controlled by output signals from a controller 16.

The controller 16 comprises a microcomputer comprising a central processing unit (CPU), read only memory (ROM), random access memory (RAM) and input/output (I/O) interface.

Referring to FIG. 2 of the drawings, detection signals are input into the controller 16 from a vehicle key switch 17, temperature sensor 18 which detects a temperature TB of a battery 15, voltage sensor 19 which detects a terminal voltage VB of the battery 15, SOC detector 20 which detects the charge amount or state of charge SOC of the battery 15, and a vehicle compartment heater switch 21. The battery 15 comprises n cells Ce.sub.1 -Ce.sub.n connected in series.

Each cell Ce.sub.n has an internal-resistance r.sub.1 -r.sub.n (where n is a positive integer), and their combined R is expressed by the following formula. ##EQU1##

An inductor L, capacitor C and alternator OSC are connected between terminals Ta, Tb of the battery 15, and form part of a temperature increasing circuit of the battery 15 together with the internal resistances r.sub.1 -r.sub.n of the cells C.sub.1 -C.sub.n. The inductance of the inductor L will be referred to as L [H] for convenience, and the capacitance of the capacitor will be referred to as C [F] for convenience.

The alternator OSC generates alternating current of angular frequency .omega. [rad/sec] according to the output of the controller 16. The composite internal resistance R of the battery 15, inductor L and capacitor C of the temperature increase circuit form a series resonance circuit, and its resonance angular frequency .omega..sub.0 is expressed by the following equation. ##EQU2##

If the angular frequency .omega. of the alternator OSC is set to the resonance angular frequency .omega..sub.0 of the temperature increase circuit, a series resonance will occur in the temperature increase circuit, and an alternating current i will flow. Consequently, the internal resistance r.sub.n of each cell C.sub.n generates heat W.sub.n expressed by the following equation.

W.sub.n =i.sup.2 .multidot.r.sub.n

The heat W generated by the whole battery is expressed by the following equation.

W=i.sup.2 .multidot.R

A temperature TB of the battery 15 rises due to this heat W, and the electric discharge capacity increases.

When the temperature TB of the battery 15 is low, the internal resistance R is large, and the impedance of the inductor L and capacitor C when resonance occurs is low compared to the internal resistance R.

Therefore, most of the power consumption of the temperature increase circuit during resonance occurs in the internal resistance R (=.SIGMA.r.sub.n), and appears as heat.

That is, when resonance occurs, almost all power consumption occurs inside the battery 15, and the battery temperature TB rises due to generation of heat.

On the other hand, if power is supplied to an external resistance load, etc., to perform coercive electric discharge and raise the temperature of the battery, the power consumed by the external load is larger than the power consumed due to internal resistance, the heat generated by the battery 15 itself is small, and the temperature increase effect is small relative to the amount of power consumption.

Now, when resonance is made to occur in the temperature increase circuit, an AC voltage V is applied to both terminals of each of the cells C.sub.n of the battery 15.

Usually, an upper limiting voltage VH of the cell voltage Vc is set to prevent early deterioration of the cell, as shown in FIG. 3. Therefore, the peak value of the AC voltage V due to resonance must not exceed this maximum value VH. For this purpose, the controller 16 increases or decreases the amplitude of the alternating current output from the alternator OSC increases and decreases according to the terminal voltage VB of the battery 15, that is, the amplitude is decreased the higher the terminal voltage VB. The upper limiting voltage VH is for example set to be 4.1V.

In this way, the voltage Vc applied to the battery 15 during resonance is limited to below the maximum value VH, and the life of the battery 15 is increased.

Next, referring to FIG. 4, the battery temperature increasing process performed by the controller 16 will be described.

The controller 16 performs this process when the vehicle key switch 17 is turned on.

In a step S1, it is determined whether or not the temperature TB of the battery 15 detected by the temperature sensor 1 is equal to or less than a predetermined value K1.

When the battery temperature TB is higher than the predetermined value K1, it is determined that a temperature increasing operation does not need to be performed, and the process is terminated. The predetermined value K1 is for example set to be 0.degree. C.

When the battery temperature TB is equal to or less than the predetermined value K1, in a step S2, it is determined whether or not the heating switch 21 in the vehicle compartment is ON.

If the heating switch 21 is ON, the routine proceeds to a step S3, power is applied to a heater, not illustrated, from the battery 15, and the vehicle compartment is heated.

Due to the current flowing from the battery 15 to the heater, the battery 15 generates heat due to its internal resistance r.sub.n, and the temperature of the battery 15 rises. In this case, in a step S4, it is determined whether or not the battery temperature TB exceeded the predetermined value K1, and if it did exceed the predetermined value K1, the routine is terminated.

When it is determined that the battery temperature TB is equal to or less than the predetermined value K1, the routine proceeds to a step S5, and it is determined whether or not the charge amount SOC of the battery 15 detected by an SOC detecting device 20 is less than a predetermined value K2.

As mentioned above, the temperature increase effect of the battery due to coercive discharge to an external load is not very high, so when the SOC has fallen to or below the predetermined value K2, it is necessary to promptly raise the temperature TB of the battery 15 to increase its discharge capacity.

Therefore, when the SOC is equal to or less than the predetermined value K2, an alternating current of resonance frequency .omega..sub.0 is output from the alternator OSC in a step S6, and series resonance is generated in the temperature increase circuit as described above. At that time, the alternating current i which flows to the temperature increase circuit is controlled according to the terminal voltage VB of the battery 15 detected by the voltage sensor 19 so that the cell voltage Vc is equal to or less than the upper limiting value VH. After operating the temperature increasing circuit in this manner, the routine repeats the processing from the step S1.

On the other hand, if it is determined that SOC is larger than the predetermined value K2 in the step S5, the routine returns to the step S3, and the power supply to the heater is continued. The predetermined value K2 is for example set to be 70%.

The contents of Tokugan Hei 10-132182, with a filing date of May 14, 1998 in Japan, are hereby incorporated by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings.

For example, according to the above embodiment, the battery temperature increasing device is applied to a hybrid vehicle, but this invention may be applied to various kinds of electric vehicle including hybrid vehicles having a different drive system from that of this embodiment. It may also be applied to batteries other than those in electric vehicles.

Moreover, according to the above embodiment, a heating device was set as an external load, but the external load which performs coercive electric discharge is not limited to a heater.

 

[safe]

So apparently you WILL get heat in the battery during discharge because that's just normal. Having to force the current through the "syrup" wastes a lot of energy. Preheating the battery means that the energy can pass out of the battery more easily. It's actually "cheaper" in electrical terms to preheat the battery than to try to force a cold battery to perform.

And this idea applies to other batteries too... seems that even the lithium batteries need preheating in order to get maximum performance...