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Discussion Starter #1
Has anyone ever used an electric heating blanket to heat their Li batteries?


I have Tesla modules, and am considering heating them (to aid charging when cold), but would like to avoid the perils of plumbing the coolant loop. Particularly within the battery boxes where I won't easily be able to see a leak. Thus I thought one could wrap them in electric blankets.



My concern with blankets would be that I don't think it would be a very effective way of heating the batteries, as I don't believe the contact between the batteries and the blanket would be very good.


Or perhaps one could use warm air?
 

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Hey Moonunit, you are using the model s modules, right? I have not watched any of the tear-down videos on youtube, but they might give you some insight into how Tesla routed the coolant lines originally. That might give you more confidence to tackle a liquid cooling system. If the pack I have is any indicator, they probably put some thought into how to protect the batteries in case of a coolant leak. On my Tesla branded mercedes pack, they ran all the coolant lines inside a water-proof trough at one end of the battery box, and put a little float switch at the bottom of it, which presumably shut off the coolant pump and flashed some serious warning lights. How are you planning on mounting the modules? Could you fit some sort of water-proof bulkhead on the end with the plumbing?



It seems to me that trying to heat the batteries from the outside in is going to be pretty slow - and it gives you no way to cool them. Granted, you are almost certainly not going to be asking as much from them in terms of peak demand or fast charging, so air cooling might be enough. Hopefully someone who has used these modules will weigh in. I will be watching with interest.
 

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First off, put in good temp sensing

then insulate the pack well.

Thin custom silicon heating pads with built-in thermostats can be ordered cheap from china, when things get back to normal.

eBay would be first stop
 

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Thin custom silicon heating pads with built-in thermostats can be ordered cheap from china, when things get back to normal. eBay would be first stop
Interesting - I shall investigate those. Many thanks for the tip.
 

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You can heat lithium batteries by applying 60hz+ AC current

AC current does not form dendrites

If you know the resistance of your pack you can use this to approximate their temperature (along with a temp sensor) as the pack temperature increases you can start biasing toward DC, once thawed you can charge as normal and the act of charging will warm them.

BEWARE - I do not know what affects this will have on their longevity but it does warm them.
 

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Except for lightly used stationary applications, you probably, for safety and useful life reasons, should use the OEM cooling features. The modules have thermistors near the inlet and outlet of the cooling loop. Presumably, this measures the in/out difference in coolant temperature. Along with the cell group voltages, the OEM BMS must use this, possible with other factors, to assess the health of the module and its cells. I think most aftermarket BMS systems have similar features. And please, don't even think about not using a BMS!

Similar to what OR-Carl says, maybe you could tip the battery box(es) so any leak could drain away from the cells and other parts. Tesla has put huge amounts of time and expense into designing these modules and their cooling system. You should really take advantage of that work and put in a liquid cooling system. It also would make it a lot easier to heat and cool the modules.

Also, you should design your battery box so that if a module goes into a thermal runaway, it can vent outside as safely as possible and not spread to the other modules in your system. You still will have a fire, it just won't be as catastrophic.
 

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Obviously, **if** through normal usage the internally generated heat gets them warm enough so normal charging rate is not dangerous, fine and good take advantage of that.

But any explicit intentional warming done for that purpose, should be applied from ambient warming from outside the battery casing.

Do **not** apply or draw current for that purpose, generating heat that way **will** reduce lifespan.

I agree if there are sound fluid circulating channels built into your packs it would make sense to re-use them if practical.
 

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Discussion Starter #11
Thanks for the input. The Tesla modules do have liquid cooling channels, which I may yet use. A warming blanket would be easier to use but I think much less effective and may mean the thermistors in the modules are not accurately reporting the battery temps.


The AC heating is an interesting idea, but, for me, is not something I understand well enough to want to use. If it is effective as a method, I'm surprised Tesla don't use it already.
 

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I use a good-size Tesla battery-set, and (like the ones from the Mercedes) they have the water-cooling jackets built in.

I have mine plumbed in so that when driving the car the batteries are cooled as part of the water-cooling setup, but when charging the car and if ambient is below 50F the water-valves "flip" so I re-circulate the water only around the cells and then through an in-line water heater powered from the charging voltage.

The temp control is nothing fancy (Arduino w thermistors) for reading ambient and regulating the heater-power, but I can maintain 65F pretty easily (but this is Texas).

The heater-pads etc do work, but they typically run off of relatively high voltages. When they start to go bad they develop a "spot" heats up more than the rest, and it gets worse and worse until eventually that spot burns through (if there is enough power to be had). I would recommend some kind of monitoring circuit for off-normal currents.
 

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custom heater pads can be made whatever voltage you like

the included thermostat should be for high-temp cutoff IMO, use your own regulation for normal ops.

Space between the pad and cells, warm the air inside an insulated box.

but using built-in liquid jackets is ideal if you can
 

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If you use the existing Tesla liquid circulating system, The heater could be as simple as a DIY glow plug based heater: http://www.peachparts.com/shopforum/attachments/alternative-fuels/29420d1131506671-austin-heres-pic-ot-my-glow-plug-wvo-heater-p1010474.jpg
Or, a glow plug unit based on the OEM coolant heaters used in warming-up VW, Audi, Peugeot, and other diesels.https://www.google.com/search?q=tdi+coolant+heater+glow+plug&client=firefox-b-1-d&sxsrf=ALeKk01WGnCW64VffhQBseGLY3Jq0ExNKQ:1583465226653&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiJ5-TS84ToAhXPHzQIHXRpAX4Q_AUoAnoECAwQBA&biw=1621&bih=841 . Your 12V battery and DC to DC converter need to be large enough to handle the power required.
Also, line voltage(100-240VAC) engine block heater(s) could be built into the system, when a 12V based system wouldn't work.
There must be OEM mechanical based thermostats to control the heaters as well as electronic based ones.
 
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