# What kind of battery warmer do you use?



## m38mike (Dec 27, 2008)

I know we're going into the warm season here in the mountains, but for about 8 months a year we've got frost in the mornings. I'm needing advice on what kind of battery warmer to consider.

I've thought about draping a 12v car blanket over the packs. I've also thought about using gutter heat tape from the hardware store. And a third idea was to use a small space heater blowing heated air into a cloth cover around the batteries. 

What have some of you done? Has it worked to keep the batteries warm?

I have a separate, unheated garage. The EV is out of the wind, but not out of the cold.


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## 86Honda (Apr 15, 2009)

I always wondered if a waterbed heater under the batteries would work. They are flat, waterproof and have a thermostat, but I'm not sure how they would take battery acid.


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## customcircuits (Dec 21, 2008)

We've used waterbed heaters with great success. We used two 120W heaters with a thin sheet of metal on top of them to help spread the heat and protect them. So far so good. We can bring our 12 batteries up to a nice 75F in about an hour.

We started out using a single 300W unit which turned out to be too hot for the batteries in the center of the pack but spreading out two 120W is just about perfect.


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## Peetaah (Oct 15, 2008)

I found some soil heating cable which cuts off at 74 degrees. I lined the interiors of my battery boxes with foam and then strung the heat cable through. I have had the system up and running for almost a month. Looks like the batteries maintain between 74-78 degrees continuously. Check out my blog for more info (lots of pics): 360.yahoo.com/peetaah. 

So far it has worked very well, with the garage around 35 degrees, I unplugged the system and after 24 hours it had only dropped 2 degrees-- so the insulation is key for efficiency. I should mention it took almost 8 hours to bring 8 batteries from 40 degrees up to 75. But how often is your pack going to get that cold anyway (especially with how slowly it looses heat).


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## m38mike (Dec 27, 2008)

Peetaah,

Where did you find the soil heating cable? That is a really flexible system, and I like that idea. How long is your cable? or is it two or more cables? Does it have a built in thermostat in the cable or is there one attached to the end of the cable? I appreciate you sharing what you're doing with your EV. 

I live in the mountains in Colorado. I have frost to deep cold 9 months a year, so finding a good heating system for my batteries is VERY important.

Mike


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## Peetaah (Oct 15, 2008)

m38mike said:


> Peetaah,
> 
> Where did you find the soil heating cable? That is a really flexible system, and I like that idea. How long is your cable? or is it two or more cables? Does it have a built in thermostat in the cable or is there one attached to the end of the cable? I appreciate you sharing what you're doing with your EV.
> 
> ...


I am in Utah so am in the same boat. The cable is "Gro Quick", I got the 48 foot cable for a box of 8 batteries (I intend to use the same length for the 13 battery box as well). The thermostat is actually built into the cable and preset for 74 degrees so I just buried it in the middle of the pack. If you check out the pictures on the blog you can see how I lined the box and there is a good pic of the thermometer as well.

Peter


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## m38mike (Dec 27, 2008)

Thanks Customcircuits for the waterbed heater idea. I'm gonna take a look at those.

Thanks Peter for the cable idea. I like the flexibility of that.


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## racunniff (Jan 14, 2009)

customcircuits said:


> We've used waterbed heaters with great success. We used two 120W heaters with a thin sheet of metal on top of them to help spread the heat and protect them. So far so good. We can bring our 12 batteries up to a nice 75F in about an hour.
> 
> We started out using a single 300W unit which turned out to be too hot for the batteries in the center of the pack but spreading out two 120W is just about perfect.


The waterbed heaters I've found have a wart on the "top" side - probably where the thermcouple is for the thermostat. It's about 1/2" deep, triangular. What do you do about this? I'm considering cutting a matching hole in the bottom of the battery box - but then, if that is where the thermocouple is, it won't be measuring the right temperature...


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## WSJ (Sep 18, 2008)

Battery heaters can be mounted on an albumin plate to disperse the heat over the battery case surface. Too much heat is one area can cause uneven heating and damage the battery case.

Battery temp sensor in center of battery.










Battery heater plate temp test for even heating.










Battery heater plates for several battery configurations.










Battery heater controller test data with 100° F set point.


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## Zemmo (Sep 13, 2007)

I have a battery heater system that I took off my car because the part of Texas I am in doesn't really require the heater system. If your interested in it, you can give me a PM. Here is the posting I have for it.

http://www.diyelectriccar.com/forum...y-warmer-controller-termostate-150-31177.html

Price is flexible.


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## m38mike (Dec 27, 2008)

Wayne, thanks for posting the heating graph. It's interesting to see how the heating panels work for you. I'm thinking that the cable I got will work in a similar fashion. I plan on embedding the cable into some 1/2 inch insulation under all of the batteries. That will allow me to make a larger space for the thermocouple in the middle of the cable, and still keep the batteries level and close together. 

Don't you think that 100 degrees F is too warm for batteries? I always heard that they worked best at somewhere in the 70's. So that's what I'm shooting for. That's what makes a soil warming cable so good. It's set for 74 degrees, right in the middle of the 70's.


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## electricmini (Oct 21, 2008)

On the electric mini, I used two 80 watt battery warmer blankets from Canadian Tire
(the units they have now seem to be made by Pyroil , but CanTire seem to be discontinuing them - I had to try several stores until I found some)

I wired two in series with some 35 degree C thermal switches attached to metal plates (all our outlets are 240V here in the UK). The metal plates were postioned between the warmers and the pack, so the thermal switches would sense the temperatures accurately. Worked well for keeping the pack of 10 Optimas warm, the pack also had 1 inch styrofoam insulation surrounding the battery box.


For the Supra's pack, I've just picked up another six warmers (I'm currently on vacation visiting friends here in Canada, and will be going home with a suitcase stuffed-to-the-gills with useful parts  ).

I'm sure other auto parts stores would have these, especially in areas that get cold in winter

HTH

Richard Bebbington


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## WSJ (Sep 18, 2008)

m38mike said:


> Wayne, thanks for posting the heating graph. It's interesting to see how the heating panels work for you. I'm thinking that the cable I got will work in a similar fashion. I plan on embedding the cable into some 1/2 inch insulation under all of the batteries. That will allow me to make a larger space for the thermocouple in the middle of the cable, and still keep the batteries level and close together.
> 
> Don't you think that 100 degrees F is too warm for batteries? I always heard that they worked best at somewhere in the 70's. So that's what I'm shooting for. That's what makes a soil warming cable so good. It's set for 74 degrees, right in the middle of the 70's.


Placement of the temperature sensor on the battery case is done to control the internal battery temperature and reach the desired set temperature in a reasonable amount of time. As seen in the graph it took over two hours to heat small AGM batteries, the time is about 12 hours for 6 or 8 volt flooded batteries. The 400 watt heaters were on 100% of the time during ramp up, after the set point was reached the set point was maintained with about 60 watts. The data was taken with a set point of 100° F and an ambient temp of 60° F in uninsulated plywood battery enclosures.

If the sensor is placed on the heating element, it may take weeks for the batteries to reach the set point. My waterbed takes two days to heat up from 60° F to 80° F with a 400 watt heater and the sensor is several feet from the heater.

Low thermal resistance between the heating element and heater plate allows the heat to be transfer to the plate and batteries. Insulation between the bottom of the plate and the battery mounting surface limits the heat loss, as does insulating the battery enclosure.

Battery capacity is specified at 77° F, however, additional capacity is useable above that level. The temperature set point was adjusted to 100° F for use in a racecar that lacked the capacity to finish the required number of laps. Battery test data indicates the temperature for best performance vs. life is 77° F.

I tested the performance of my design on the bench with a US 2200 battery. The present design represents many hours of testing, several revisions and a few melted spots on the battery case. It would be wise to evaluate your design on the bench before installation.


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## racunniff (Jan 14, 2009)

Peetaah said:


> Check out my blog for more info (lots of pics): 360.yahoo.com/peetaah.


Peetaah - thanks for the pointer on Gro-Quick - I've ordered some, will be installing them this week, since the volt914 is disassembled for a battery upgrade. For some reason, though, Yahoo is not pointing to your blog at this point.

Note that I think battery warming is a very underused technology. Even in more "temperate" areas of the United States, it is not uncommon for average temperatures to be in the 40s or 50s in the winter - which is enough to seriously undercharge your battery, especially since temperature-compensated charging technology is not common in bulk chargers. See the attached table for example - from the Concorde Charmain tech manual. Charging at 40 degrees should be done a full 0.6 volts higher than charging at 77 degrees.

It seems to me easier to warm the battery to "room temperature" than it is to compensate for cold temperatures. And you get the added benefit of extended range on top o fit.


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## MN Driver (Sep 29, 2009)

Keep in mind that charging batteries above standard temperatures, such as 100 degrees with a standard non-compensated charging method will overcharge the batteries for the same reason as above with the undercharging based on cold temperatures. Either the batteries need to have a maintained temperature or the charger needs to compensate for the temperature of the batteries.

HTH


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## racunniff (Jan 14, 2009)

MN Driver said:


> Keep in mind that charging batteries above standard temperatures, such as 100 degrees with a standard non-compensated charging method will overcharge the batteries for the same reason as above with the undercharging based on cold temperatures. Either the batteries need to have a maintained temperature or the charger needs to compensate for the temperature of the batteries.
> 
> HTH


True. If you are charging at 100 degrees, you should certainly reduce your charging voltage.

In my case, the average temperature in Fort Collins, Colorado varies between 27 degrees (winter) and 71 degrees (summer). So, I think a heater makes very good sense  The average min / max are lower / higher, of course, but the thermal mass of the batteries combined with an insulated box would tend to keep the batteries at a fairly constant temperature, I would think.


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## tomofreno (Mar 3, 2009)

Hi Peetah,

What type and how thick of foam insulation did you use, and where are you measuring temperature? 

Tom


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## fishguts (Dec 19, 2008)

My batteries will be in separate locations around the chassis, each with its own box, so I need individual heaters. Been trying to find a good source for these and prices vary widely from around $25 to $90. That sure adds to the cost of the battery. Any suggestions for a cheaper solution for individual batteries?


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## m38mike (Dec 27, 2008)

fishguts,
is there some good reason why you are not combining batteries in one or two locations? It sure seems inefficient to have them scattered all over. Otherwise you'll be stuck with the individual warmers. But on the bright side, a warmer should outlast your batteries, just like the boxes will.


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## Coley (Jul 26, 2007)

So far in the last 4 years, I haven't been bothered by the cold that much.

Might be different this winter with the GELs.

It is 30 F outside right now, so the run in the morning may show something.


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## fishguts (Dec 19, 2008)

m38mike said:


> fishguts,
> is there some good reason why you are not combining batteries in one or two locations? It sure seems inefficient to have them scattered all over. Otherwise you'll be stuck with the individual warmers. But on the bright side, a warmer should outlast your batteries, just like the boxes will.


I'm building a reverse trike with a narrowed VW body and custom chassis, so there's no space for putting all the batteries in one spot. There will be four up front, two where the gas tank used to be with the steering column going down between them and two on either side of the column mounted lower and behind the front beam (center steering). Two more will be on the floor on either side of the driver's seat.


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## gdirwin (Apr 7, 2009)

Found these very low power battery blankets: 
http://www.kimhotstart.com/zlcms/editor/uploads/files/battery_pads_wraps.pdf 

Thermostatically controlled battery heating blanket (on at 60F, off at 80F) - can be connected in sets or as singles.

Have not found pricing yet - hopefully reasonable... 

If anyone has used these or knows of a dealer, please let us know...


I am not sure about waterbed heaters - they seem to be very fussy about the water depth etc... so with no water (ie used under batteries) it may have hot-spots?


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## dexion (Aug 22, 2009)

A bit of googling.
http://www.kimhotstartheaters.com/search

Then in the search for bar (the first one) type

Battery wraps

Looks like 300ish for ones with thermo

and 56-120ish for the non-thermo ones.

Here are some that are interesting as well (self stickies)

http://www.kimhotstartheaters.com/category/564961


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## Zemmo (Sep 13, 2007)

My battery heater system (selfless mention of the one I am selling again) uses a battery pad something like this :

http://www.allelectronics.com/make-a-store/item/HLT-6/9-X-12-HEATER-PAD/1.html

It essentially is just a coil of wire between two panels.


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