# Cold weather charging



## dougingraham (Jul 26, 2011)

It isn't quite as cold as that where I live but it has felt like it this winter.

I built insulated battery boxes hoping that the self heating of the cells during usage would be enough. It isn't. No amount of hard driving warms the cells enough to be an issue even in the summer. This winter I have not driven the vehicle if the temp when I get home is going to be below freezing. My plan is to add a resistive heating element under the cells which will warm the battery boxes to around 40-50 degrees F. This will provide enough heat to make the pack usable even on very cold days. I am going to put around 1.5 watts per cell in the box and see what that does.


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## davidwillis (Feb 10, 2014)

Good to know. So I guess I will be fine with insulated boxes and electric heating during the winter, and I will just have to remove the insulation in the summer.


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## dougingraham (Jul 26, 2011)

davidwillis said:


> Good to know. So I guess I will be fine with insulated boxes and electric heating during the winter, and I will just have to remove the insulation in the summer.


The insulation does not seem to be a problem in the summer. I can't get it to overheat even on days where the ambient outside temp is over 100 F. If these were not LiFePO4 prismatics I would be more concerned.


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## TheSGC (Nov 15, 2007)

Where I live the winters spend most of their time below freezing. I have some insulation around my lithiums, but I have found that if you charge them right after you stop driving they will stay warm. My drive is usually 15-to 30 miles before I charge, and if the batteries are stone cold it takes about 10 miles for them to warm up. I do have a temperature gauge in the battery pack to monitor them.


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## Yabert (Feb 7, 2010)

davidwillis said:


> So I am trying to figure out a way to keep my batteries above freezing, but not cause any over heating.


Use a thermostat to control and monitor the temperature of your pack. 10-20$ can be found on ebay.
Heating your battery is really important bellow 0°C (32F). Performance and range is directly affected.


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## davidwillis (Feb 10, 2014)

Yabert said:


> Use a thermostat to control and monitor the temperature of your pack. 10-20$ can be found on ebay.
> Heating your battery is really important bellow 0°C (32F). Performance and range is directly affected.


Thanks. I was planning on useing a thermostat, but I was concerned with having them in an insulated box they may over heat even with the heating turned off, especially in the summer time.


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## davidwillis (Feb 10, 2014)

TheSGC said:


> Where I live the winters spend most of their time below freezing. I have some insulation around my lithiums, but I have found that if you charge them right after you stop driving they will stay warm. My drive is usually 15-to 30 miles before I charge, and if the batteries are stone cold it takes about 10 miles for them to warm up. I do have a temperature gauge in the battery pack to monitor them.



I plan on driving 30 miles to work, then the will sit there in the cold for 10 hours before I drive home. I am affraid without heating they will be very cold by that time, and may not get me home.

However my biggest concern is making sure it is up to 32 deg when I get home to charge, becuase charging when it is cold will damage the battery.


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## dtbaker (Jan 5, 2008)

the build I am just starting will be a vehicle that is stored outside overnights.... so I am planning on building a battery box with 'heatline' in the bottom of the box. This is a product that can run off either DC or AC, and is variable resistive according to temp with 1-8 watts per foot so it is basically self-regulating and won't OVER heat even without a thermostat/switch.

I am considering ways to make it powered by a second AC plug when charging so that the charger does not see the amps drawn from traction pack and mess up the end-of-charge. Then switch the plug to draw from traction back during the day when the car is out and about to keep the temp up.


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## davidwillis (Feb 10, 2014)

dtbaker said:


> the build I am just starting will be a vehicle that is stored outside overnights.... so I am planning on building a battery box with 'heatline' in the bottom of the box. This is a product that can run off either DC or AC, and is variable resistive according to temp with 1-8 watts per foot so it is basically self-regulating and won't OVER heat even without a thermostat/switch.
> 
> I am considering ways to make it powered by a second AC plug when charging so that the charger does not see the amps drawn from traction pack and mess up the end-of-charge. Then switch the plug to draw from traction back during the day when the car is out and about to keep the temp up.


Can you tell me more about this 'heatline'? And where I would get one?


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## dtbaker (Jan 5, 2008)

davidwillis said:


> Can you tell me more about this 'heatline'? And where I would get one?



you can buy it by the foot.... similar to romex wire; just add a plug.
http://heatline.com/length.htm


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## steelneck (Apr 19, 2013)

davidwillis said:


> So I Live in an area that gets cold (it is usually down to 0 deg F for most of the winter). I have read that you can't charge LIthium batteries at temperatures below 32 deg, without causing damage.


Depends a bit on the battery chemistry. Lithium-Yttrium-Ironphosphate (LYP) batteries can be charged down to -25C. But they will loose power when cold just as other lithium batteries will, so heating is still a good idea.

In this "flyer" Winston batteries even state that they can be charged down to -45C! (I do not buy that..):
http://kostov-motors.com/files/productattachments/4bb011961bc431591c5cfbd8c975d4b7_100Ah.pdf


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## tomofreno (Mar 3, 2009)

I've been using the Farnum heater pads for 4 years now, and they have worked well. Over those years there have been a number of nights at -5F to 5F, and the cells remained at set point temperature. I currently set them at 65F. That way they will remain above 50F if the car sits outside several hours with temps in mid 20's F. 

The heaters are 35W each, and something like 7" wide by 10" long. Made of 3 insulating sheets with thin nichrome wire wound around the center one. I don't think you want higher power density. You want a small thermal gradient through the cell so you aren't overheating the cell bottom to bring the top up to temperature. They heat up slowly, a few F/hr, which is good I think. It isn't usually an issue because they rarely get below 55 C. 

I have ten total connected in parallel and controlled with a Pakstat thermostat sold by kta-ev who also sells the pads. Works off 240 or 120 VAC. I think you could find cheaper controllers. One problem with the Pakstat is it uses an RTD sensor in a cylindrical probe which is not conducive to mounting on cells. I bolted it to one of the cell clamps. The leads are also only about 4 ft long, and replacement RTD's from someplace like Omega are pricey. I'd try and find something that uses a thermocouple.

I used aluminum tape to attach the heaters to the back of aluminum pans cut to fit snugly into the battery boxes. I covered the area around the wire connections on the heaters with two layers of Kapton tape to further insulate them from the aluminum. The aluminum pans have a half inch tall lip on them so they don't cut into the insulation around the sides.

This is a photo of the heaters taped on the aluminum:







and this one is the top side of the aluminum after installation in a battery box which holds 8 180Ah cells: 







The insulation is 1/2" thick polyurethane. Sounds like it is colder where you live, so I'd likely use 1" thick. With that, and the heating from driving to work they may stay above 30F for the 10 hours.

The battery boxes are steel and the tops are just 3/8" plywood with no insulation other than thin carpet. In your area I would insulate the tops too - and remove it in summer. If you use multiple battery boxes and they are exposed to different temperatures like under the hood and inside the cabin, I would use multiple controllers to maintain them at similar temperatures.

The cells have not overheated in summer, but have been up around 116 F in around 100F ambient. I have not driven them hard nor for a long time in that high of ambient. To me, keeping them cool if driven hard, like long highway driving, in that high of ambient is more problematic than keeping them warm in winter.

I also added themal switches on a cell in each box to avoid overheating the cells. I had one heater fail, and it was the cell group the sensor was on. That group didn't heat, so the heater controller remained on and drove the other cells to around 100F before I noticed it. The switches interrupt the power at 80F. That occurred before I taped the heaters to aluminum. The cells just sat on the heaters and scrubbed around on them, which broke the wire on one after a few years. Cells are now strapped down.

People have also used the heater film used for electric radiant floor heat. You should find quite a lot here on heating if you do a search.


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## evpower (Aug 9, 2013)

Check some ideas and know-how for the lithium battery technology in cold winter: 

*Some tips to operate the battery in cold climate*

a) Make proper insulation of the pack so that the pack does not lose temperature to outside cold environment

b) Arrange for the pack heating (during charge). Properly insulated pack may be preheated to quite high temperature (even to 30*C) to absorb the thermal energy. This way the properly insulated pack of large capacity may stay warm for several days.

c) Arrange for the pack “defrosting”. Properly insulated pack may use some part of its energy to warm itself before or at the beginning of the operation in cold climate. Usually about 5% to 8% od energy may be used to increase the temperature of the properly insulated battery pack.

Taken from http://gwl-power.tumblr.com/tagged/temperature


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## Zak650 (Sep 20, 2008)

These are nice, hard abs outside, internal thermostat 25 watts $35 ea.

K&H Heated Resting Mat for Small Animals, 9 By 12 Inches from Amazon.com

Use a router to cut a through hole in 1/2" plywood battery box bottom board. 
An 1/8" aluminum heat spreader plate under the batteries with a 1/4" gap to isolate it from the insulated sidewalls.


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## dtbaker (Jan 5, 2008)

Zak650 said:


> These are nice, hard abs outside, internal thermostat 25 watts $35 ea.
> 
> K&H Heated Resting Mat for Small Animals, 9 By 12 Inches from Amazon.com
> 
> ...



the problem with most of the heating mats is that the switches are rated only for AC, and don't last long switching DC on/off.... KTA and some of the other guys stock 'Farnum' heating mats which run on either Ac/DC, and you add you relay of choice to handle DC.

I have not used the heatline yet, but was excited about it because you don't need a thermostat OR a switch and it runs on either AC or DC just fine. It costs something like $3.50/ft (from memory), but looked like it was going to be more economical to do a whole battery box than any flat pads I found.


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## Zak650 (Sep 20, 2008)

That Heatline looks pretty good Dan


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## davidwillis (Feb 10, 2014)

Thanks for the comments, and all the great ideas.

The heatline looks good, but I actually think I like the idea of running a thermostat. That way I could heat it up more while it is at home charging, and maybe maintain the heat a little longer without using Battery power to heat it up. I would like something that I could control, so I could set the temperature high while at home (maybe 70 deg F), then when I am running on battery power I could let it cool down to 40 deg F before the heaters tun on.

Also I plan on having An inverter installed in the car to use as a power backup for my house, so if I needed to use ac power for the heating pads, that should not be a problem, and may actually be better because I could plug the heat into ac power at home while charging, then use the inverter to run the heaters while away from home (if needed).


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## davidwillis (Feb 10, 2014)

> The cells have not overheated in summer, but have been up around 116 F in around 100F ambient. I have not driven them hard nor for a long time in that high of ambient. To me, keeping them cool if driven hard, like long highway driving, in that high of ambient is more problematic than keeping them warm in winter.


I am also concerned with this, especially when the batteries are in a well insulated box. I am thinking about running a vent line to feed fresh air through the box during the summer.


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## dtbaker (Jan 5, 2008)

davidwillis said:


> I am also concerned with this, especially when the batteries are in a well insulated box. I am thinking about running a vent line to feed fresh air through the box during the summer.


I stuck a remote thermometer in battery box, which is fully enclosed 1/4 thick plastic with 1/2" foam insulation in bottom under batteries, with no venting.... and in the summer on a typical 'hot' day for santa fe which is maybe 85-90 deg F I saw just a few degrees temp rise over ambient during normal city driving. I saw 10-15 degrees over ambient on my longest highway pull I ever do, which is about 5 miles steady uphill grade where I am pulling around 200 amps to maintain 75mph.

If I were doing long grades uphill on the highway on a daily basis, I would consider something like vents I could open/close seasonally, but am not too worried about it. I'm much more concerned with being able to charge a car overnight outside below freezing, and maintain the pack above 50 deg during the day if left outside at work or whatever to reduce sag and preserve range.


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## davidwillis (Feb 10, 2014)

dtbaker said:


> I stuck a remote thermometer in battery box, which is fully enclosed 1/4 thick plastic with 1/2" foam insulation in bottom under batteries, with no venting.... and in the summer on a typical 'hot' day for santa fe which is maybe 85-90 deg F I saw just a few degrees temp rise over ambient during normal city driving. I saw 10-15 degrees over ambient on my longest highway pull I ever do, which is about 5 miles steady uphill grade where I am pulling around 200 amps to maintain 75mph.
> 
> If I were doing long grades uphill on the highway on a daily basis, I would consider something like vents I could open/close seasonally, but am not too worried about it. I'm much more concerned with being able to charge a car overnight outside below freezing, and maintain the pack above 50 deg during the day if left outside at work or whatever to reduce sag and preserve range.



I think I will want some venting, because I will be driving steady for about 45 min. at 55 mph. I am also using a 4000 lb vehicle, so this will be pulling about 100-150 amps for 45 min. I suspect this will start to heat up without some sort of venting.


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## davidwillis (Feb 10, 2014)

Thanks everyone for your ideas. I think in my situation the K&H Heated Resting Mat for Small Animals will work the best. However I want to set them up on a thermostat that I can adjust, and see the temperature in each battery compartment.

Does anyone know of a good cheap thermostat for this. I wold like to easily see the temperature in each battery box (I will have 3 or 4 boxes), and set the temperature for each (they can all be set to the same temperature, but need to be separately controlled because they will be in different location that may heat up more than other locations). I will just use 120v ac to run them, and plan to mostly just use my home ac to heat during charging, but will have an inverter to heat them when away from home if needed).


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## Caps18 (Jun 8, 2008)

Here is what the specs are for the LiFePO4 batteries I am getting:


Operation Thermal Ambient 


Charging 


0°C ~ 45°C 


Discharging 


-20°C ~ 55°C 




Storage Thermal 
Ambient 


Short-term (within 1 month) 


-20°C ~ 45°C 




My garage is at 3°C (37°F) right now with temperatures -5°C (23°F) outside. It has been colder outside below -20°C (-4°F) this year, but I would like to know if it was sitting outside for a few hours at -30°C (-22°F), would the batteries operate at all, or would they be dead until they warmed up some? I don't need to design this for the extreme cases though

I am planning on making an insulated box out of a Pelican case I have already mounted and 2" ridged blue foam insulation. I'm just wondering if it would be beneficial to add a heating pad (or a few?) that I could plug into 120V AC power into it. The only cabin heating I plan on having will be from a portable space heater that will be plugged into the garage AC power to pre-heat it. I can survive a few cold car trips back from places in the cabin without heat, most of my trips are under 15 minutes. Then again, maybe I will add a heating pad under the seats next winter...that shouldn't be a hard thing to do.

I will have a thermocouple or two inside the case to monitor the temperatures, but I also worry about the high side of the temperature range. I could add a fan to the case, but I don't see that as a necessary thing to do right now. We will see how hot the batteries will get in the Summer time. They will be in the garage and can be charged in the morning or night.


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## dougingraham (Jul 26, 2011)

Caps18 said:


> My garage is at 3°C (37°F) right now with temperatures -5°C (23°F) outside. It has been colder outside below -20°C (-4°F) this year, but I would like to know if it was sitting outside for a few hours at -30°C (-22°F), would the batteries operate at all, or would they be dead until they warmed up some? I don't need to design this for the extreme cases though


My guess is that it will move but you won't be enthused with the performance. I have never tried to drive mine when that cold and I have no desire to. I see pretty dreadful sag when no more than -5C.


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## dtbaker (Jan 5, 2008)

Caps18 said:


> ... if it was sitting outside for a few hours at -30°C (-22°F), would the batteries operate at all, or would they be dead until they warmed up some?



they will operate fine.... sag a little more than usual when cold, which reduces range a bit. They should not be CHARGED when below freezing, but run ok. 

I found about 20% reduction in range when left outside overnight ambient 25-35 degrees, and sag under full load considerably more than when above 50-60 degrees.


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## steelneck (Apr 19, 2013)

I do not think it is wise to go without cabin heating. The car cabin will get cold very quickly. Just think a couple of degrees below freezing and snow, or even worse close to raining. You go into some store for 15 min and come back to your cold car, wipe off the wind screen and start to drive away, one minute later in the traffic your windscreen start to ice up since you do not have a defroster, quickly find a spot to stop, scrape the windscreen and two minutes later you have the same situation all over again. Your car could even be considered unsafe to drive in traffic.

One of my thoughts about this was to make a conversion that will work in the cold, in many cases even be a better alternative than taking the ICE-car to work when it is cold. I live 100Km above the arctic circle in Sweden and we have loong winters (not that terrible cold though), so this has been a factor of importance to me.

Recently we had a cold period, was between -20C and -30C for over three weeks in a row, at work people started to wait for each other on the parking lot, just to see that everyone got their cars started. Then i thought, all that fear of my car not starting i do not have to think about when driving electric, just jump into my EV and drive away, instant cabin heat and so on. Those with diesel cars do not even get their engines up to normal temperature at those temperatures, some of them even have diesel burning cabin heaters. I will just turn on the heat and some seconds later i get hot air into the cabin for my 10min ride home, no engine that has to get hot first.

Range? Well yes, it will get shorter in the cold. But when looking in the mirror on my last ten years of driving, i have driven around 10K km a year and more than 9K has been all those 10min rides to work, the supermarket and such. I think that my EV will my obvious choice in the winter as long as i design it for it, and i have batteries of the LYP kind that can be charged way under the freezing point. When charging i will anyway have some floor heating in my battery boxes.


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