The "thermal management of LiPo" thread!

Batteries, Chargers, and Battery Management Systems.
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dogman dan
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Re: The "thermal management of LiPo" thread!

Post by dogman dan » Jan 19, 2017 7:00 am

So you are saying in the winter, the pack cools to ambient, which is too cool.

I had the same issue when I carried lipo in aluminum battery boxes. In winter, I had to put a jacket on the box. Freezing air cooled the box too good, and I had a lot of good contact with the cells inside. The box was icing my pack, and it would be sag city.

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Re: The "thermal management of LiPo" thread!

Post by Ianhill » Jan 21, 2017 4:19 pm

Exactly that, When using passive cooling it can be over active when air temp is low and the pack may struggle a little or a lot depending on how much discharge capacity been used.
My ride is using around 25% of what the manufacturer states the cell can handle 2.5kw per pack, I have four in series for a potential 10kw output but I've found anything over 50% of c rating or 5kw and it pulls the volts right down even at 20°c.
I'm going to be using plastic for winter and swap to alu for summer, its the cheapest way of maintaining a ruff temp state and not having complex cooling and heating circuits as I don't have the room in a small scooter.

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Re: The "thermal management of LiPo" thread!

Post by mechhead » May 18, 2017 5:44 am

I have a possible novel solution to the thermal management of lipo batteries. its easy and cheap to do to , requiring some corflute of the learge hole size, a small fan and thermostat controller and possibly a heater for really cold weather. the cold weather variety would need a controllable cooling flap to to limit in cursion of outside air for heating. for medium requirements just jacketing the seriesed packs with coreflute would probably be enough but for really high draw systems seperating the individual cells with coreflute spacers enables airflow between individual cells

Coroplast/corflute ,what ever you call it can be both a good insulator and a good conductor as the thermal path would be through the thin wall of the sheets to the air inside, by aranging airflow manifolds carefully and putting the passages perpendicular to the cell long axis air can be blown through the shortest dimension of the pack keeping fluid resistance down. In heating mode a small ideally peltier effect heater draws heat from outside and and adds its thermal losses and rejected heat to the pack internal air flow spaces where the air is circulated to maintain an even temperature through out all cell gap spaces. The packs can be clamped as the thick corflute is quite strong in compression. in cooling mode outside air can be circulated through the coreflute spaces to cool and maintain even pack temps.

what do you think people?

I will post photos of my finished battery pack when its done, im using 2 multistar 10c 20ah 6s bricks with a flat 30mm thick by 90 mm dia 48pole drone motor direct drive rear wheel with left side chain on brake disk mount with a vesc-x
currently im using a 6354 outrunner friction drive with one 20 ah 6s and the vesc-x but the 200kv motor is only good for about 35kmh at 6s so I have another multistar brick on the way I do a 60 km commute and it gets flat 5kms short of home on the way back but there is a huge hill all the way there that uses 4/5 of the juice and the tyre cant take much more than 800w with out the motor slipping badly the battery temps at the end of the big 20km 240m altitude hill climb gets the batteries up to about 35 degrees c in the cold winter so i suspect they will need cooling in the summer.

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Re: The "thermal management of LiPo" thread!

Post by Ianhill » May 18, 2017 11:01 am

Air is going to have more thermal rise during a heavy discharge compared to a liquid, some very good ideas and thoughts raised mind I think k the cells need to be in a thermos flask type environment so the fluid flowing around them is least effected by outside conditions and maybe even presurised to 1bar eat atmosphere and sealed to prevent atmospheric distrubtion in the cells.

Ideally the pack would have liquid cooling with a peltier devices attached to its appropriate cooling fins that have access to good air flow, some how connect the peltier device so water can be diverted to go either side of the device with a thermostat on the device and a coolant temp sensor all being monitors by a arduino etc.

I bet that if a pack can be kept at it optimum temp in ruff climates that the energy needed to run the circuit will be near enough gained back if the case does its job, on a cold day the flask environment and liquid will help keep the cells warmer and the heat displaced by the cell itself, on a warm day the liquid will help keep any peak discharge temp from rising to fast and a thermal path to the peltier can be obtained through the liquid, needs proper r+d like tesla have done to get a sweat spot, if dine on a modular level it could be a building block for any size pack just like the automotive giants do.

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Re: The "thermal management of LiPo" thread!

Post by jonescg » May 19, 2017 3:58 am

Thanks for reviving an old thread guys!

I am actually employed to work on this stuff now, so it's wonderful to be spending hours on the ES forum and getting paid for it :D

So we have a few ideas here, some proprietary some common knowledge. But I am very interested in perusing the phase change material (pcm) ideas. Parafin wax has a surprisingly high specific latent heat of fusion, and can be used to prevent the pack from experiencing rapid temperature rises, however that heat is still stored in the material and needs to be shed somehow. So a thermal path to the outside of the pack would be ideal. I'm going to do a few experiments with some 10s packs and see how this parafin PCM goes. AllCell have been doing it for a while and the attached paper is quite an interesting read.
2 phase change material in battery temp reg.pdf
(2.34 MiB) Downloaded 28 times
The sheets of aluminium between pouches will definitely work for air cooling, but they will also suffer with low temperatures. Thus the only way to maintain a battery's happy space is with an active heat/cool feature like a recirculating coolant loop.

Since everyone is mad about 18650 cells here, I will include them in the discussion, however LiPo pouches are perfect for racing and other performance applications, so I reckon some ideas are worth sharing.

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Re: The "thermal management of LiPo" thread!

Post by bobc » May 19, 2017 4:43 am

I'll be interested to see how the thing progresses using a paraffin wax PCM. I'd never seen that reported anywhere else when I suggested it further up this thread, & assumed the idea had been discarded, maybe for safety concerns (?). But the numbers did look surprisingly effective (why I made the suggestion) & I wonder has anybody else tried it? (I couldn't see the material specified in the linked paper, except to suggest some graphite mixture..)
Incidentally, beeswax might be even better (get right away from those petroleum derivatives.....)
http://www.arpnjournals.org/jeas/resear ... 6_3404.pdf

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Re: The "thermal management of LiPo" thread!

Post by Punx0r » May 19, 2017 7:54 am

I think an important benchmark for any active or passive cooling system is how it compares to simply adding more/better battery instead, considering overall system weight, cost, complexity and reliability.

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Re: The "thermal management of LiPo" thread!

Post by jonescg » May 19, 2017 8:20 am

Punx0r wrote:I think an important benchmark for any active or passive cooling system is how it compares to simply adding more/better battery instead, considering overall system weight, cost, complexity and reliability.
Agree completely. Every application will have its constraints, and in the case of race bikes, it's volume followed by weight. Adding more battery can be done, but there is a trade-off with weight and how the shape of the battery impacts on the centre of gravity. On a race bike, cycle life it almost irrelevant - 100 cycles a year.

But the other element is battery longevity, and this will be achieved through either 1. not hitting the battery too hard or 2. adding some kind of cooling feature. Given racing is all about contravening point 1. there is some merit in exploring cooling.

I am a huge advocate for spec the battery right so that you don't generate as much heat, and therefore negate the need for cooling.

One thing I am not familiar with living in a hot part of the world is how low temperatures impact battery health. And given most of the EV-driving market lives above the 40th parallel, I guess some kind of temperature management is a good idea.

SO I will be adjusting for mass and volume in my experiments, for sure.

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Re: The "thermal management of LiPo" thread!

Post by Matador » May 19, 2017 8:18 pm

How about spinklers... spaying this : liquid difluoroethane in a controlled manner ... like this :


Words of caution :
1) Dust remover is NOT compressed air. It's difluoroethane. There has been a few case that documented people recreatively inhaling the stuff to get high. Some have died of sudden death after volontarly inhaling it. So please try not to breath this stuff on purpose too much (they've added a bittering agent in so you will know it's time to have a breath of fresh air...).
2) Like many organic substance, it's flammable (when in liquid state), but the flame will not self sustain (https://www.youtube.com/watch?v=nZGBbUgL5Vs ), and ...
3) Critical to get bottle upside down so it is LIQUID difluoroethane that gets out rather than the GAS layer. As it evaporates to gas state, the liquid difluoroethane pull all the heat off of the cells it hits....

You know that cold feeling you get on your skin when rubbing isopropyl alcool on it... it's because of rapid evaporation. Difluoroethane does it much more intensly... Liquid nitrogen seems impractical to handle (usually kept in an unsealed Dewar) and way too cold...

A small can of this Duster stuff would not take so much space and would be enough for a few races..

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Last edited by Matador on May 20, 2017 7:46 am, edited 2 times in total.

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Re: The "thermal management of LiPo" thread!

Post by Matador » May 19, 2017 9:38 pm

Seems it would be just cold enough from a good distance between nozzles and cells

Temperature ? ... :

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Re: The "thermal management of LiPo" thread!

Post by jonescg » May 20, 2017 4:58 am

Outside the box. Love it :D

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Re: The "thermal management of LiPo" thread!

Post by Toorbough ULL-Zeveigh » May 20, 2017 1:59 pm

bobc wrote:I'll be interested to see how the thing progresses using a paraffin wax PCM. I'd never seen that reported anywhere else when I suggested it further up this thread, & assumed the idea had been discarded, maybe for safety concerns (?). But the numbers did look surprisingly effective (why I made the suggestion) & I wonder has anybody else tried it? (I couldn't see the material specified in the linked paper, except to suggest some graphite mixture..)
Incidentally, beeswax might be even better (get right away from those petroleum derivatives.....)
http://www.arpnjournals.org/jeas/resear ... 6_3404.pdf
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Re: The "thermal management of LiPo" thread!

Post by jonescg » May 21, 2017 12:16 am

Nice! Although I suspect the wax in this instance was less about thermal management and more about solidifying the battery into a single block, which certainly appears to have worked.

I wonder about setting it in the wax in the first instance - pre-heat your battery (at 40% SOC or less) to 50'C, then pour 65'C molden wax into the unit to capacity. Let it set.

If the melting point of the wax was set to 55'C through the right mixture of C25 to C34 parafins it should be doing its thing at the right temperature.

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Re: The "thermal management of LiPo" thread!

Post by bobc » May 21, 2017 11:24 am

Toorbough ULL-Zeveigh wrote:
here's yet another E•S 10 anniversary wayback trip.
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If an idea isn't fatally flawed, there's every chance it has come up before... all good stuff
I'd expect paraffin wax to be stable in an electric field but maybe not beeswax. The links generally note beeswax superior latent heat, it probably costs a bit more as well.
How much weight of wax would you need to get the performance you need Chris? How hard to make your battery boxes leakproof?

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Re: The "thermal management of LiPo" thread!

Post by jonescg » May 21, 2017 8:14 pm

If I was to use parafin or bees wax as a PCM I would build aluminium enclosures. Once the material absorbs the heat it has to shed it somehow, and a polycarb enclosure wouldn't do that as well as aluminium.
Beeswax has a higher specific heat of fusion, but also has a higher melting point. You'd want the melting point to be as close as possible to the maximum 'normal' operating temperature of the cells. So probably 50'C to 55'C?

Luckily the density of wax is quite low - about 0.9 g/cm3 so it would only need to fill in the vacant space.

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Re: The "thermal management of LiPo" thread!

Post by jonescg » May 21, 2017 10:00 pm

A couple more papers on PCMs:
4 Therm prop of parafin with TiO2.pdf
(1.4 MiB) Downloaded 14 times
And an interesting comparison paper:
1 Comparison of ccoling methods in batteries.pdf
(2.24 MiB) Downloaded 28 times

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Re: The "thermal management of LiPo" thread!

Post by LockH » May 21, 2017 10:26 pm

Hehe... Fun convo folks! I tend to fall on the "K.I.S.S." Principle side of things... One "problem" (?) some may have is that ambient temps can get warmer/cooler, so my vote is for *active* cooling/warming (versus passive) AND to use AIR/a gas circulated (less mess when leaking). And one "best" method for air circulation is the forward motion of the vehicle (think air scoops on a gas/diseasal engine). My first car (Peoples Car aka "Volkswagon") had air scoops that opened/closed at passenger feet level to cool hot feet on sunny/warm days. Where the "active" part required passengers to reach down to open/close.
:wink:

... just my 2 cents Cdn.
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Liquid cooling

Post by llile » Nov 20, 2017 4:41 pm

Ppl are yakking about 3m Novek over on r/ebikes as an immersion liquid cooling medium.

https://www.reddit.com/r/ebikes/comment ... batteries/

My Smart Car Electric Drive uses liquid cooling for the batteries, same loop cools the motor, and is automatically temperature controlled so it doesn't get too hot during discharge, doesn't get too cold when charging int he winter. Don't know what fluid they use. It's a pretty damned slick electric vehicle, laugh if you want I'll laugh back.

It would be interesting to use a nonconductive and not too flammable liquid around 18650's, but at $395 aq gallon, Novek is probably out of my budget. https://www.safariland.com/products/for ... sdv71e563t

I had proposed the idea of using a silicone brake fluid - high flash point, cheap and available at any auto parts store for about $60 a gallon.

If this was arranged to be pumped past an aluminum heat sink, and the pump could turn off at low temperatures, this would accomplish battery cooling, still be an insulating fluid, and if the video is any indication, might mitigate the runaway effects of a Lipo fire (or not). Battery heating might not be all that necessary. Or would thermal convection be enough, if properly arranged? Pop the insulated cover on the heat sink in bitter cold weather.

What do folks think - is liquid cooling a DIY battery pack a thing?
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Re: The "thermal management of LiPo" thread!

Post by jonescg » Nov 23, 2017 12:34 am

I think liquid cooling on battery projects is needed when the investment is big enough to justify the effort. For e-bikes and e-motorcycles, it's probably not worth it, but for a 30-50 kWh car battery, you'd be mad not to.

I'm looking into it because the electric race bike needs 8-12 kWh worth of battery, but I'm reluctant to compromise too much on power. High energy density cells are out there, but the C-rate is usually 1 to 3 C - nothing like the 30 C I have currently. These cells are less efficient too - they convert more of their stored electrical energy into heat thanks to I2R losses. This heat shortens the life and capacity of the cells, so some kind of cooling isn't a bad idea.

Liquid immersion is certainly an option, but it does add weight and volume where a more passive air-cooled option would be lighter. Then it's a matter of creating a decent thermal path to the outside using an aluminium enclosure.

18650 cells get hot under normal use, so cooling is essential for longevity. Perhaps not critical on an e-bike, but at the very least passive heat-wicking to the outside is a good move.

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