# Battery Heater Pads



## TheSGC (Nov 15, 2007)

Does anyone have experience with Farnam Battery Heater pads from KTA-EV or a similar pad heater?

I am looking to get battery heaters to get my range back up so it can be an all weather EV for my 17 mile commute. The cold weather is limiting the range to 12 miles. I am very close to installing the cabin heat, but right now my insulation on the batteries can only retain heat, not actually warm them up.


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## tomofreno (Mar 3, 2009)

See the "SwiftE" thread under Builds for some info on performance of Farnam heaters.


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## jockepocke (Nov 24, 2009)

You should add more insulation to your batteries. If you have lead acid they will get warm as you drive (anda charge), and with enough insulation they will keep warm. I have done this solution in my volvo. I used (glass) mineral wool, about 10 cm thick layer everywhere, and my batteries are still warm and cosy, just from driving/charging (they were room temperature a week ago when I got it out of the garage).


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## TheSGC (Nov 15, 2007)

jockepocke said:


> You should add more insulation to your batteries. If you have lead acid they will get warm as you drive (anda charge), and with enough insulation they will keep warm. I have done this solution in my volvo. I used (glass) mineral wool, about 10 cm thick layer everywhere, and my batteries are still warm and cosy, just from driving/charging (they were room temperature a week ago when I got it out of the garage).


I do have insulation, however it will only keep the batteries about 20F above ambient temperature, which is usually below 30F, and the floodies work best at 80F. The batteries do get warm during charging, but the temperature drops quickly right after the charger shut down and the EV gets covered with snow again.

I'll try adding more insulation, but ideally I would like something that keeps them warm at night after charging completes.


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## jockepocke (Nov 24, 2009)

TheSGC said:


> I do have insulation, however it will only keep the batteries about 20F above ambient temperature, which is usually below 30F, and the floodies work best at 80F. The batteries do get warm during charging, but the temperature drops quickly right after the charger shut down and the EV gets covered with snow again.
> 
> I'll try adding more insulation, but ideally I would like something that keeps them warm at night after charging completes.



I see your point, though for me enough insulation really did the job. Also here in Sweden the weather is currently much lower than -1°C (30F), about -10°C, which is about 14F. Last time i checked, the batteries were probably between +10 and +20°C (50 to 70 F), although I have not driven for a while, so I imagine they are now cooler. 

I can really tell the difference in performance compared to when I was test-driving without the insulation. The car is much more responsive. 

I have heard about people using the kind of heat-cables you have beneath your bathroom floor with success. That way you will also have a thermostat.


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## Voltswagen (Nov 13, 2008)

SGC
I haven't tried this myself but I will and I see no reason why it shouldn't work.
Use an Electric Blanket. Wire it directly from your pack through a 20 amp 150v DC breaker.....not a toggle switch .

http://stores.mavericksolar.com/-strse-403/MidNite-Solar-MNEPV20-dsh-150-20A/Detail.bok

$11.44 plus shipping.


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## TheSGC (Nov 15, 2007)

Voltswagen said:


> SGC
> I haven't tried this myself but I will and I see no reason why it shouldn't work.
> Use an Electric Blanket. Wire it directly from your pack through a 20 amp 150v DC breaker.....not a toggle switch .
> 
> ...


I didn't even think about an electric blanket! I'll check out the local KMart and see what they have. I don't plan to run it off the battery, just off the wall because during the day the EV is charging away and sitting in the sunlight.


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## MN Driver (Sep 29, 2009)

I've read on another forum about the electric blankets that you can rip apart the blanket and arrange the heat wires appropriately amongst the space that you need to use them. I'm not sure how easy this is to do or if it is the same for all heated blankets but with their low cost it might not be a bad idea. I'm not sure how much heat a single heated blanket can produce though, I think they only use 200 watts or so, which would require very good insulation or multiple blankets along with probably never allowing the batteries to cool down in the first place.


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## TheSGC (Nov 15, 2007)

MN Driver said:


> I've read on another forum about the electric blankets that you can rip apart the blanket and arrange the heat wires appropriately amongst the space that you need to use them. I'm not sure how easy this is to do or if it is the same for all heated blankets but with their low cost it might not be a bad idea. I'm not sure how much heat a single heated blanket can produce though, I think they only use 200 watts or so, which would require very good insulation or multiple blankets along with probably never allowing the batteries to cool down in the first place.


I don't need to BBQ my batteries, just get them about 30F warmer than they are now. I found some blankets online that I am going to check out tomorrow in store, but 200 watts should suffice. I only have 8 batteries in a very contained area and with the battery heater on a timer should be great. The Farman battery pads also look good, being 35 watts a piece, is another option I am really considering, but a blanket would be the quickest and cheapest solution.


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## dtbaker (Jan 5, 2008)

I just ordered two different things to try.... 'Soil warming cable' from ebay which put out a constant 4 watts per foot and have a pre-set thermostat set for 74 degrees. The major cost seems to be the thermostat since various lengths are just about the same price! These are designed for 110vAC, so I dunno if the thermostat/switch would handle DC.

Second option I am going to try is 'cuto-to-length' auto-regulating cable from heatline.com . It puts out a max of 5 watts per ft, minimum of .5 watts over about 50 deg f. Good news is that it can handle DC and would just require a simple switch/circuit breaker. Its more expensive at $3.50/ft but that is still probably less than the number of Farnum pads plus thermostat for same output....

Since my car is usually not sitting outside during the day at work, because I work from home, I can probably get by with just plugging in heaters at night off house AC if I have to.... but I would LIKE to find a solution to wire direct to the main DC so that the car COULD sit outside and stay toasty. I dunno if the small total draw would mess up the charge cycle though because the charge would see that amp load if the heater comes on and perhaps think the batteries were still charging.... Might have to have a switch to select from pack/house heating.


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## TheSGC (Nov 15, 2007)

I couldn't find any electric blankets locally that I would trust to heat up my batteries, so I will probably insulate the crap out of my batteries and save up for the Farnam Battery Pads. I can easily build my own temperature control for them, which will probably be the same system I build for my interior heat.

I did find a few holes in my insulation that I am about to fix up with more foam and duct tape and see what the temps looks like after my charging has finished.


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## TheSGC (Nov 15, 2007)

I did get the Farnam heating pads and built a temperature control circuit to keep the pack at 75-80F, and they are GREAT! I also completely redid my insulation to help keep the heat in.

My winter performance has improved drastically, and I am going to say it's now the same as in the summer. I haven't driven my EV in this current setup in decent weather yet, so yesterday I was making use of the heated batteries to tear around town with my Zilla for the first time with the ability to draw more than 150 AMPs due to cold batteries. 

I am having a problem with my heater temperature circuit shutting down when it gets too cold(!!) and I thinks it's due to a voltage regulator not being what I thought it was.


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## gdirwin (Apr 7, 2009)

dtbaker said:


> ... I dunno if the small total draw would mess up the charge cycle though because the charge would see that amp load if the heater comes on and perhaps think the batteries were still charging....


I may have a similar problem with the interior heating system - when the car is plugged in I want the interior ceramic heaters on, which will draw DC power from the pack at the same time it is being charged (or after it is fully charged). If you have any further thoughts on how this impacts the charging cycle (I am using a Manzanita PFC40M, Elithion BMS and TS200AH cells), let me know... Maybe a new thread?


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## jorhyne (Aug 20, 2008)

gdirwin said:


> I may have a similar problem with the interior heating system - when the car is plugged in I want the interior ceramic heaters on, which will draw DC power from the pack at the same time it is being charged (or after it is fully charged). If you have any further thoughts on how this impacts the charging cycle (I am using a Manzanita PFC40M, Elithion BMS and TS200AH cells), let me know... Maybe a new thread?


Why not integrate a separate DC power supply that is used exclusively to power your heaters when plugged in? You could even wire it up to use the same plug as your charger does. I don't see why you would need to use pack power to generate heat when you could just as easily use electricity from the grid. Of course this wouldn't work when you were actually driving the car...


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## dtbaker (Jan 5, 2008)

gdirwin said:


> I may have a similar problem with the interior heating system - when the car is plugged in I want the interior ceramic heaters on, which will draw DC power from the pack at the same time it is being charged (or after it is fully charged). If you have any further thoughts on how this impacts the charging cycle (I am using a Manzanita PFC40M, Elithion BMS and TS200AH cells), let me know... Maybe a new thread?


I think a full-on 1500 watt heater running while charging is probably overkill for heat, and would at least double the time for your charging if you are on 120v (using around 10 amps) as well as mess up the BMS thinking the batteries were still absorbing 10+ amps. WHY do you want the heat running all the time?


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## dtbaker (Jan 5, 2008)

TheSGC said:


> I did get the Farnam heating pads and built a temperature control circuit to keep the pack at 75-80F, and they are GREAT! I also completely redid my insulation to help keep the heat in.


what are you going to do in the summer? do you have a removable panel for a little airflow so batts don't OVER heat?


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## TheSGC (Nov 15, 2007)

dtbaker said:


> what are you going to do in the summer? do you have a removable panel for a little airflow so batts don't OVER heat?


My insulation is nothing more than 1 inch foam board duct taped together, so I will be removing it in the summer and while it's out I will build a better box.


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## gdirwin (Apr 7, 2009)

dtbaker said:


> I think a full-on 1500 watt heater running while charging is probably overkill for heat, and would at least double the time for your charging if you are on 120v (using around 10 amps) as well as mess up the BMS thinking the batteries were still absorbing 10+ amps. WHY do you want the heat running all the time?


Actually it is 3000 watts (2 ceramic heaters)! The interior heat will turn on when plugged into AC through a timer (say 1 hour before leaving for work). I also use a digital temperature controller in the dash (instead of a manual hi/med/lo switch) which auto-regulates the temperature to a set-point, and generates a PWM signal to SSR relays - when the desired temperature is reached (which may never happen at -40) then less power is consumed... You are right though - this may mess up the BMS etc... Maybe I could use 2 SSRs in parallel - one AC and one DC - when plugged into AC it would then draw power directly from the AC grid, not through the charger and main pack - will have to think a bit...


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