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Re: Battery pack heat pads installation

Posted: Thu Dec 27, 2018 6:06 pm
by Yvesm
Glad to see that the battery is fine. Cool setup, highly advanced.

Good work !


Re: Battery pack heat pads installation

Posted: Mon Jan 14, 2019 11:58 pm
by Oilpan4
I have found that when my leaf is parked out side that the pack temperature sensors read a few degrees above ambient by the time the sun comes up even after 2.9kw L2 charging throughout the night.
If I don't charge it that night then it's pretty much at ambient temperature in the morning.

I would like to use bigger stick on pads, get the the 240v ones and wire them in serries on 240v so I can get the heat over a wider area but not get as hot of a hot spot.

I would stick them on and spray A+B foam over them. I have an A+B foam gun kit with a little bit of foam left in it for a small job like this.

Because of the metal stamping on thr bottom of the pack could I go with a larger heater pad or should I stick with the small ones like you guys used?

I'm in the high desert of NM and in the winter it usually gets down to 0F but I have seen it get as cold as -16F and I have only lived here since 2010.

For control I would just use a simple mechanical switch set for 40F and relay.
I have found that with leaf spy showing pack temp much below 45F I lose a good portion of my brake regen.
Maybe include a 120v relay bypass since the 240v heaters in serries would barely put off any heat with 120v power but would be better than nothing.
This winter, my first leaf winter I have already seen days with 2 and 3 bars. I can only CHAdeMO at 5kw with 3 bars, brake regen is almost non existent. With 2 bars there is no regen and I have not had the pleasure of trying CHAdeMO at 2 bars (I haven't seen seen 2 or 3 batt temp bars since I got my leaf spy so I don't have a numeric value range for it).

Re: Battery pack heat pads installation

Posted: Tue Jan 15, 2019 2:03 pm
by hwfailure
Hi Oilpan4,

First, you can look at the first picture I included of the bottom of the battery pack and see how long are each of the thermal pads I used. You can find a variety of forms and lengths for thermal pads.
The ones I have used had a sticky bottom so I could stick them directly on the metal following even the shapes of some metal channels in the bottom plate of the battery pack (look at the first picture mentioned, you see the orange thermal pad following the shape of the channels). I have added red RTV high temperature gasket maker on the side of the thermal pads to make sure they would stick in place.
Just make sure you can locate them between the screws and the plastic clips (both types used) that retain the plastic protector sheets under the battery pack. With 2 battery warmers (12V lead acid battery warmer, 80W each, working on 120V), 4 thermal pads (90W each, working on 12V) and 5 thermistors to locate under the battery pack, I had to make sure I was not putting them under a fixing hole for the plastic protector sheets.

Second, pay attention to your series thermal pads arrangement.
As it has already been mentioned at the beginning of this post, if you power two 120V thermal pads in series with a single 120V supply, you are doubling the total resistance and dividing by 2 the total power of the thermal pads.
Each one is getting the quarter of the power it would had had if not put in series (P = V**2/R, if you divide by 2 the voltage for the same pad resistance then you get the quarter of the power).
If you plan to buy 240V thermal pads and supply them with 120V, don't put them in series because you already have half of their nominal voltage. With 120V on a 240V thermal pad it will give you a quarter of the heating power for each thermal pad. I doubt that it will become very hot with only a quarter of its power.
You will see however that it become costly to "lose" this available power as you must install more thermal pads (in parallel) to achieve a sufficient heating power (or the one you are choosing).

You are right about the hot spots. Temperature can go very high on thermal pads (even above boiling temperature, depending on your thermal pad). The good thermal pads manufacturers recommend a thermal control. The only thing keeping the temperature at an acceptable level is the huge thermal mass of the battery pack itself.
The thermal pads stuck to this huge mass dissipate the heat in the metal bottom plate of the battery pack and probably not on the battery cells directly (each battery cell is itself in a metal box).

To avoid hot spots, I have built an electronic thermostat to regulate the temperature at very low levels. The battery warmers start at around 28 degrees F and stop at about 32 degrees F. For now the 4 thermal pads I installed are still unused. They were planned to try to maintain the battery temperature while the car is unplugged for a long time at work. Still have to work on this with a big 12V battery and thinking of its recharge. My intention is just to avoid the battery to freeze.

Two days ago I had a case of my 2 battery warmers being started (160W of heating power) continuously. I make a led blink to know for how much time the battery warmers are/were started. After returning from work with battery temperature with no bar, I plugged my home made battery heater. I saw later in the evening that it was started for 640 "approximative" minutes (more than 10 hours) and later saw a strange blink (I have limited the display time to 999 approximative minutes). Outside temperature was between -2.2 degrees F to -9.4 degrees F (-19 degrees C to -23 degrees C). Had only 1 bar of temperature while heating the battery at this time. The lowest temperature sensors in the battery were about 15.8 degrees F (-9 degrees C). The led blinking went back to normal later after the battery warmers have been stopped by the microcontroller.

You certainly don't want to have the foil-faced bubble wrap to isolate your battery during the summer. It is not a problem for me in Canada.

About the very approximative temperature inside the battery, you can check :

Hope this help.

Re: Battery pack heat pads installation

Posted: Tue Jan 15, 2019 2:26 pm
by Oilpan4
For me and unlike the really hot places that damage the battery like AZ, southern TX, socal, it will get over 100F here during the day. But it cools off to around 70F at night.

When the car hits 8 temperature bars I don't charge it and if possible I don't drive it.
But when I'm at work and it's time to leave and I start the leaf and it's showing 8 bars I don't have much choice.
But when I get home I can chose not to plug it in at all and let it cool for a while and drive my gasoline powered car the next day if I don't charge it or if it's showing 8 bars in the morning.

Re: Battery pack heat pads installation

Posted: Tue Jan 15, 2019 2:33 pm
by LeftieBiker
For me and unlike the really hot places that damage the battery like AZ, southern TX, socal, it will get over 100F here during the day. But it cools off to around 70F at night.
I've found that it has to cool to the mid sixties or lower for the pack to really cool off a lot overnight.

Re: Battery pack heat pads installation

Posted: Tue Jan 15, 2019 2:48 pm
by Oilpan4
This summer I probably left the car parked about 8 to 10 days because the battery was too hot to charge or too hot after charging for my liking.
I work 13 hour shifts on a 2 on, 2 off, 3 on 3, off type of thing. So a lot of days the car was too hot to drive or charge I didn't have to work. If I was working straight 5 days in a row I probably would have had to leave it parked twice as much as I did.

I'm going to try and more actively cool the battery this coming summer, rather than just leave it parked. But that's a whole different post.

Re: Battery pack heat pads installation

Posted: Sat Jan 19, 2019 3:17 am
by Oilpan4
I think I found the heater pads I will use.
I got some new, big, 5,600w 480v, 3 phase, 3 wire industrial ammonia compressor oil separator heater pads.
Yes, 5.6kw.
Probably won't run them off 480v 3 phase, or any 3 phase.
Actually 1 will probably be enough.