# 18650 cell cooling



## aeroscott (Jan 5, 2008)

I was thinking the same thing.


----------



## PZigouras (Jun 5, 2010)

avidsensei said:


> I am wondering if air cooling will be sufficient or if anyone has ever tried mineral oil cooling on 18650 cells?
> Bad idea, good idea? What do you think?


 I used to run mineral oil in my oil lamp... it definitely burns... so it may not be the best choice if something should short out for whatever reason. Keep in mind that most 18650 cells go into thermal runaway at only 300 F.


----------



## riba2233 (Apr 29, 2015)

avidsensei said:


> I am building a 18650 li-ion battery pack for my electric motorcycle. It has over 1000 cells and will hold over 9kWh of power. I am running the cells at a 1C discharge with peak discharge of 3C for no more than 30 sec.
> I am wondering if air cooling will be sufficient or if anyone has ever tried mineral oil cooling on 18650 cells?
> Bad idea, good idea? What do you think?


What cells are we talking about? There are 2A cells, and there are 30A cells, huge difference  

Also, it's 9 kWh of energy, not power


----------



## Moltenmetal (Mar 20, 2014)

Mineral oil is combustible but not flammable. It will burn off a wick or if you atomize it into a flame, but not otherwise. It'd be a safer coolant than anything water based. There are various grades with different viscosities like any oil.


----------



## Tomdb (Jan 28, 2013)

there was a thread on glycol cooling so that might be practical. And possibly easier, thinking about finding some ip64 enclosures and testing it.

http://www.diyelectriccar.com/forums/showthread.php/dc-motor-submerged-glycol-coolant-171738.html

some good science http://www.electronics-cooling.com/2015/12/tech-brief-low-electrical-conductivity-liquid-coolants-for-electronics-cooling/


----------



## riba2233 (Apr 29, 2015)

That's all very nice, but really needless if you chose proper cells and size your pack right. It's probably the cheaper option in the end


----------



## Tomdb (Jan 28, 2013)

Yes, But for extreme applications, for racing vehicles or sports hybrids. A fluid buffer might just be good to try out, but expensive battery cases.


----------



## avidsensei (Apr 25, 2016)

Thanks for all the information guys! 
For everyone saying fire risk, watch these idiots put lipo packs in mineral oil
https://youtu.be/1PdLzYufSqw

Now as for glycol, Its slightly conductive (about 1.5 to 5 Meg ohms) Which will be a parasitic drain on the pack for its whole life. Wouldn't that be bad? Where as mineral oil has a resistivity that is greater than 1000 Meg ohm (whats that a gigaohm?)

More info about my cells 2600mAh 8A max discharge rated. The pack will be 20S51P 72v nominal. I have a BMS and will be pulling 300A for no more than 30 sec at a time. Normal draw is 75A to 130A. I am doing tesla style cell level fuses and buss fuses. I am building a custom aluminium enclosure to protect the pack while it is installed on the motorcycle. 

The cooling is really only to make sure that I get the maximum cycles out of my investment please let me know if you think this is all not worth it.


----------



## Hollie Maea (Dec 9, 2009)

What model cell are you using? 8A rating doesn't really tell us much, the internal resistance is what will determine how hot they'll get.


----------



## avidsensei (Apr 25, 2016)

2600mAh 18650C is the label.
I did load testing on 5 cells and at a 1C load the temp rise was about 2 deg C. Even when I abused them with a 10A discharge on 1 cell it got warm but you could still hold it in your hand.

Here is the datasheet from the manufacturer.


----------



## Hollie Maea (Dec 9, 2009)

As is often the case, the datasheet doesn't list DC resistance, only AC impedance. But you can get somewhat of a relative idea, and this sets a lower bound for DC resistance. Fifty milliOhm is pretty high for impedance, and resistance is probably at least 55. That would correspond to about 3.5 Watts when running at 8A. That comes out to just about 1kW for your whole pack. So it definitely will get warm. You might want to do some better tests, running the cell at the expected load profile, and actually measuring the temperature rise--if you are relying on "too hot to touch" it is already way too warm for the health of the cell.

I suspect that you could benefit from liquid cooling. That's not to say that I endorse the idea of filling the box with mineral oil. But these types of cells benefit a lot from staying cool. If you can keep them below 40C at all times, that's really helpful for their life cycle.


----------



## avidsensei (Apr 25, 2016)

Also, could you break your numbers down and explain it. I can't make the math jive out for the numbers you cited. Trying to learn, batteries are a different sort of electrical work than I do for my day job.


----------



## kennybobby (Aug 10, 2012)

Jintion batteries (Great Power Battery Company)--curiously there is no specification listed for the weight of the cell? Seems like that would be somewhat important...

they seem to have a fairly low charge rate compared with other 18650's.

What are you building--a race bike or daily commuter?


----------



## avidsensei (Apr 25, 2016)

This is a commuter bike. Its been running on lead acids for about 2 years now. But I am tired of the voltage sag and running out of power all the time. Also my charger crapped out for the second time so I figured now was a good time to switch. 
Glad to hear you think highly of Jintion. They have been really awesome working with me and getting these batteries to me on time, and they are exactly what they promised so far. 
The cells weigh in at 55g if I am remembering correctly. 

The charge rate is pretty low but with the number of cells I will have in parallel I will only be charging at about a .1C rate per cell. 

Are most people using passive cooling or fans to cool their batteries?


----------



## riba2233 (Apr 29, 2015)

So, you bought chinese cells? Sorry to tell you, but that's epic fail, there are cheap brand 18650 cells like sampsung or panasonic that are miles better than any chinese cell. Your cells wont last long whether you cool them or not, so don't bother. I wouldn't even bother with assembling the pack with them, you will invest your time and hard work for nothing. 

Why didn't you ask for advice on cell model before buying? You can't simply trust some chinese datasheet on batteries. Most of it looks copied from samsung or LG...

And most people use absolutely nothing to cool their cells because there's no need to


----------



## avidsensei (Apr 25, 2016)

I know I bought cheap cells. That is what my budget was for the project. However, I do have access to some really good battery testing equipment and these cells test out about 10-20% better than what that datasheet says. Is it going to last as long as it could with name brand batteries? Probably not. But your attitude of "why even bother putting it together" is not in the DIY spirit. By your logic I should probably just buy a production electric motorcycle. I mean why bother building it myself? 
Their was a guy I talked to just like you that said my kelly controller would explode after 6 months of use because it is cheap chinese crap. That was really wrong! Kelly is an awesome company to work with and that controller has been working flawlessly for over two years now!
Anyways sorry for the rant.


----------



## kennybobby (Aug 10, 2012)

If you can build your pack such that you closely monitor every string and can readily access the cells to swap out any laggards, then it shouldn't matter. 

Maybe you can run some bench testing with the entire pack. There will likely be some defective cells that don't hold up, but if you can detect them early and change out before installation that would be easier. Or test each individual cell before installation.


----------



## avidsensei (Apr 25, 2016)

I am, at this point, not worried about the cell quality. I have tested over 100 of the 1020 cells and have had 0 defects so far. I will of course be doing some pack testing when it is all assembled.


----------



## GoElectric (Nov 15, 2015)

Hi - my 2 cents is to measure the internal resistance of the cells, then calculate how much heat you will generate while riding normally and during short bursts. Then use the heat capacity of a lithium ion cell (1350 J//kg/degree Celcius) to determine the rise in temperature of your batteries. 

You will have to find someone-else who can estimate cooling, or just try a fan and see. You have a BMS, so can monitor temps. 

Jim


----------



## avidsensei (Apr 25, 2016)

Jim, could you lay out an example of that math for me?


----------



## Hollie Maea (Dec 9, 2009)

avidsensei said:


> Jim, could you lay out an example of that math for me?


If you're having trouble with the math, I'd just do some real world tests of heating. Get some power resistors that you can rearrange in a few different configurations. Run it at 8 Amps for a while, try it at 5A, at 3A etc, and see what kind of heating you experience.

I'd probably get something like a few of these:

http://www.digikey.com/product-detail/en/te-connectivity-amp-connectors/HSA50R50J/A102448-ND/2366456


----------



## avidsensei (Apr 25, 2016)

I plan on doing the real world tests, but could you show your work on those equations so that I know how to do it in the future please?


----------



## Sunking (Aug 10, 2009)

First mineral oil is is used to cool large utility transformers and capacitors. Like any oil it will burn, and burn good. It can used in a diesel engine for fuel. In fact there is quite a lot of folks who use waste Transformer oil as diesel fuel. However that doe snot mean you cannot use it as a coolant.

Dc resistance measurement of a battery is super easy to measure and DIY. It takes minimal equipment to perform. As for test equipment all it takes is two good 4.5 digit DMM with a DV voltage accuracy of 1% or less. One DMM is used to measure voltage, and the other to read current simultaneously. 

The method is simple by using a Delta Voltage Current method. In other words you do two voltage and current measurements. You first measure the battery voltage and current at a low C-rate like .5C, and another at a high C-rate like 5C. Actual rates are not critical as it can be .1C and 1C or 1C and 10C. 

To calculate DC resistance the formula is *R = Dv / Di*. 

So here is how you do it. Start with a battery that is roughly 50% SOC at room temps. Connect a power resistor, current meter, and volt meter for low current test. Say a 3.3 Ohm 5 watt power Resistor. Record the battery voltage and current under load. Lets say you measure V1 = 3.300 and I1 = 1.000 amps.

Repeat test with a high current setup like using a .33 Ohm 50 watt resistor and record the voltage and current. Example V2 = 2.8500 and I2 = 9.955 amps. 

Now time for pencil and paper. 

First find Dv = V1 - V2. So 3.3000 - 2.8500 = .45 volts = Dv

Di = I2 - I1 = 9,9950 amps - 1.0000 amps = 8.9950 amps = Di

R = Dv / Di = .45 volts / 8.9950 amps = .05 Ohms.


----------



## avidsensei (Apr 25, 2016)

Awesome! Thank you so much for laying that out for me. Would you also show how to do the heating calculations off of the dc resistance?


----------



## Sunking (Aug 10, 2009)

avidsensei said:


> Awesome! Thank you so much for laying that out for me. Would you also show how to do the heating calculations off of the dc resistance?


You are welcome. I cannot help much on heat calculations and not sure it is a big issue. I am an EE, so heat calcs are not my area of expertise. 

I can tell you how many BTU's of heat will be generated. BTU = Current x Current X Resistance x 3.41 BTU/hour.

The problem is picking the current used, volume required thermal conductance, and ambient temps. 

Example lets say you are using a 40S50P 100AH battery pack assuming each cell is .05 Ohms with 1C current. 100 x 100 x .04 Ohms x 3.41 = 1364 BTU's per hour, Or 400 watt hours. Technically that is enough to bring about 1/2 gallon of room temp water to a boil in 1 hour.


----------



## riba2233 (Apr 29, 2015)

avidsensei said:


> I know I bought cheap cells. That is what my budget was for the project. However, I do have access to some really good battery testing equipment and these cells test out about 10-20% better than what that datasheet says. Is it going to last as long as it could with name brand batteries? Probably not. But your attitude of "why even bother putting it together" is not in the DIY spirit. By your logic I should probably just buy a production electric motorcycle. I mean why bother building it myself?
> Their was a guy I talked to just like you that said my kelly controller would explode after 6 months of use because it is cheap chinese crap. That was really wrong! Kelly is an awesome company to work with and that controller has been working flawlessly for over two years now!
> Anyways sorry for the rant.



You got me wrong, and you didn't read my whole post with understanding. 

You didn't buy cheap cells, you bought cells that are expensive comparing to brand name cells. Why? Because price difference is small, and your cells wont last long. Sure, they look good now, but they just wont hold their performance for long and in the end they will turn out more expensive. 

I mean did you look at the prices of brand cells like Panasonic PF or Samsung 29E? They go for 2.7€ in your quantity. I don't know how much you've paid for your cells, but I'm sure it's not a big difference, after shipping and all.

I'm not saying you should do your own pack, quite the opposite, I'm encouraging it (I've developed and sold JP spot welder, you can google it), but I'm just saying that you failed epic with your choice of cells. 

BTW I'm also using kelly controller and I'm very happy with it


----------



## avidsensei (Apr 25, 2016)

I did look at the cost of name brand cells and for the same capacity cells It would have been just under 3x more expensive.


----------



## riba2233 (Apr 29, 2015)

I don't believe that. What was the final cost per cell for your chinese cells?


----------



## avidsensei (Apr 25, 2016)

$1.50 per cell


----------



## Hollie Maea (Dec 9, 2009)

Anyway, that's about half the cost of name brand cells. They could last half as long. The cells are bought, let's see how they do.


----------



## riba2233 (Apr 29, 2015)

Was that with shipping included? Also, if you are from EU were they any custom charges?


----------



## avidsensei (Apr 25, 2016)

Performed some heating tests today. I will probably be ok on cooler days but I think some additional cooling will be needed on hot summer days. 

Room temp was 20C at test start,
I started the test with a 1C discharge (2.6A) the battery temp continued to climb for about 30 min and stabilized at 34C I then performed some high discharge tests. Two periods of 6.5A discharge for 1 min on the first and 1.5 min on the second. The first peaked at 38.6C the second peaked at 41C. 
I went back to a 1C discharge for 5 min and temps went back down to 34.5C. For the rest of the capacity of the battery I discharged at 3.5A and temps stayed at 39.5C 

So I think I might be able to get away with air cooling. Perhaps a ram air duct or maybe a fan. What do you think?


----------



## kennybobby (Aug 10, 2012)

Did you measure the open circuit voltage before starting your test, and did you monitor voltage during the test? If so then you could calculate the internal resistance of the cell to compare with the spec sheet.

Rint = Vocv - Vload/ I


----------



## Hollie Maea (Dec 9, 2009)

avidsensei said:


> Performed some heating tests today. I will probably be ok on cooler days but I think some additional cooling will be needed on hot summer days.
> 
> Room temp was 20C at test start,
> I started the test with a 1C discharge (2.6A) the battery temp continued to climb for about 30 min and stabilized at 34C I then performed some high discharge tests. Two periods of 6.5A discharge for 1 min on the first and 1.5 min on the second. The first peaked at 38.6C the second peaked at 41C.
> ...


I would sprinkle some temperature sensors in your pack. If it gets too hot (45C or something) you can derate your power. If it happens often enough to be obnoxious, beef up your cooling.


----------



## avidsensei (Apr 25, 2016)

Kennybobby, I did but it came out at 140 mil the first time and 100 the second so I am not sure if I am doing it right.


----------



## avidsensei (Apr 25, 2016)

hollie maea,
you said 40C was the safe area last time. Is 45C the safe zone or is 40?


----------



## Hollie Maea (Dec 9, 2009)

avidsensei said:


> hollie maea,
> you said 40C was the safe area last time. Is 45C the safe zone or is 40?


"Safe" isn't an exact point (The datasheet for most cells is 60C, and even higher than that before they go into thermal runaway, depending on the chemistry). But elevated temperature is hard on them. Once you get into the 40s, it's hard on them, and you want to limit the time at that point. You could certainly put your limit at 40C (or even lower!) but without liquid cooling that might be a bit ambitious. It's kind of a gray zone. But certainly if you approach that 60C from the spec sheet, you are actively and rapidly killing your cells. Especially if they are at a high SOC.


----------



## kennybobby (Aug 10, 2012)

avidsensei said:


> Kennybobby, I did but it came out at 140 mil the first time and 100 the second so I am not sure if I am doing it right.


That sounds like it could be right. The spec calls out =< 50 milliOhms, but that was for an AC impedance test at 1kHz frequency. The DC internal resistance is more important for your consideration since the heating power in the cell is proportional to this Rint x I^2 (current squared times resistance).

So at 140 milliOhms and 1C, you had about 1 Watt of heating in your cell, hence the temperature rise.

For comparison you could test a resistor and monitor it's temperature rise with various levels of current, e.g. a 1 W resistor at 0.1, .25, .5 and 1 Watt power levels and you will see how hot a Watt can get--it will blister your fingers if you hold or touch it.

But you probably won't be driving at 1C except for rapid accelerations, so you may not need cooling, but more testing is needed to know for sure.


----------



## Sunking (Aug 10, 2009)

avidsensei said:


> Kennybobby, I did but it came out at 140 mil the first time and 100 the second so I am not sure if I am doing it right.


If Impedance is listed at 50 Milli-ohms, then DC resistance should be around 60 milli-ohms. 

That is not to say you are measuring it incorrectly, but if it is 100 to 140 milli-ohms you have a poor performing cell.


----------



## Sunking (Aug 10, 2009)

kennybobby said:


> But you probably won't be driving at 1C except for rapid accelerations, so you may not need cooling, but more testing is needed to know for sure.


I have to disagree with that. Unless he has a enormous over sized battery, cruise will be at around 1C, with acceleration of 4 to 5C. Example with a range of 50 to 70 miles is 1C rate. Commercial EV's with ranges of 100+m plus miles cruise at less than 1C, but DIY cannot usually afford to do that with the lower operating voltages and lower energy density cells we can afford to use. Example 144 volts @ 100 AH DIY (14.4 Kwh) is a lot smaller than a Nissan Leaf 360 volts @ 66 AH (24 Kwh).


----------



## kennybobby (Aug 10, 2012)

Normally i would agree with your disagreement with me, but in this case he is building a motorsickle with a 20s50p pack, so 1C would be over 130 Amps--and that would be a hellacious constant current load for just puttin' around town and commuting, plus his pack won't last long at that rate, it's just not capable of sustained 1C discharge.


----------



## GoElectric (Nov 15, 2015)

GoElectric said:


> Hi - my 2 cents is to measure the internal resistance of the cells, then calculate how much heat you will generate while riding normally and during short bursts. Then use the heat capacity of a lithium ion cell (1350 J//kg/degree Celcius) to determine the rise in temperature of your batteries.
> 
> You will have to find someone-else who can estimate cooling, or just try a fan and see. You have a BMS, so can monitor temps.
> 
> Jim


Hi - sorry not to reply sooner. If you don't know how to do those calculations, it is better to stick with what you are doing I think: real-world testing. 

It does sound like they are getting hot alright, try running a fan over them and see how much difference it makes? Also, how are you measuring temperature? So many variables.

I'm not sure how warm it gets where you are, but I think you need to post somewhere-else to get feedback from guys who are building electric bikes. If the majority are using air cooling, then that should tell you a lot. 

If you really want to know how to do those calculations, I would be willing to talk you through it on the phone.

Jim


----------



## avidsensei (Apr 25, 2016)

Running a fan over the cells helps quite a bit (about 10 deg C), but that is one cell in free air. I am wondering how it will do when they are all inside of an aluminum box together. I think the cells in the middle will get much hotter than the edges. 

My testing is a calibrated thermocouple on a fluke 286. The thermocouple is in the vent of the cell because that is the hottest part I could test. I think I need a FLIR camera lol. 

I will try maybe some PC fans on the cells and see if that works well enough after I get the pack built.


----------



## Sunking (Aug 10, 2009)

kennybobby said:


> Normally i would agree with your disagreement with me, but in this case he is building a motorsickle with a 20s50p pack, so 1C would be over 130 Amps--and that would be a hellacious constant current load for just puttin' around town and commuting, plus his pack won't last long at that rate, it's just not capable of sustained 1C discharge.


OK my bad.


----------



## Jimbo69ny (Feb 13, 2018)

avidsensei said:


> Running a fan over the cells helps quite a bit (about 10 deg C), but that is one cell in free air. I am wondering how it will do when they are all inside of an aluminum box together. I think the cells in the middle will get much hotter than the edges.
> 
> My testing is a calibrated thermocouple on a fluke 286. The thermocouple is in the vent of the cell because that is the hottest part I could test. I think I need a FLIR camera lol.
> 
> I will try maybe some PC fans on the cells and see if that works well enough after I get the pack built.


I know this is an old thread but I am wondering how the project turned out. I am building an add on pack for my EV and I am wondering if I need to incorporate cooling for my 18650 cells. I had planned on it but the more I read the more I think I might not.


----------



## avidsensei (Apr 25, 2016)

The project went really well. The battery pack preforms super well. I have around 75 miles of range and a top speed of 74 MPH. 

The battery cooling was a bit of a problem but only on the hottest days in the summer. I added a radiator fan to the battery pack and it does a good job of getting rid of some of the heat. I only have to use it if the temperature is above 90f.


----------



## avidsensei (Apr 25, 2016)

Oh also, if I had to do it again. I would build multiple smaller packs instead of one giant super pack.

The giant pack makes it really hard to work on and I think the cooling would be lots better with smaller packs.


----------



## kennybobby (Aug 10, 2012)

Did you ever get a measured weight of the bike plus rider--it would be interesting to compare the 75 mile range to weight and pack capacity.


----------



## avidsensei (Apr 25, 2016)

I never ofically weighed it after the conversion but with the lead acids the bike weighed 740 lbs. The lead acids batteries were 180 lbs and my new pack is just over 200 but my mounting system for the new pack is way lighter so that probably saves 10 lbs. Best guess is that it weighs 750-775 now and I weigh 190lbs.

Total power of the pack is about 9.5 kwh.

I am in Afghanistan right now so I don't have my notes or the bike with me so all these numbers are from memory so take with a grain of salt.


----------



## avidsensei (Apr 25, 2016)

Here are a few pictures of the pack being built. Their are two layers this size sandwiched together.


----------



## Jimbo69ny (Feb 13, 2018)

Weird I didnt get a notification that you responded. I am subscribed. I wonder why I didnt get one.

Regardless, very cool! Thank you for the update! That is definitely a big module. Do you know how many amps you are doing per cell at peak draw?


----------



## avidsensei (Apr 25, 2016)

Peak draw is 300A which is about 6A per cell.
Cruise is about 1.5A per cell


----------



## Karter2 (Nov 17, 2011)

Maybe you should upgrade to these cells for better cooling..
https://youtu.be/hcPwdBcXsrg


----------



## avidsensei (Apr 25, 2016)

Har har har


----------



## GoElectric (Nov 15, 2015)

Glad I watched the whole thing - April Fools'


----------



## Mustang101 (Apr 17, 2008)

avidsensei,
Where did you buy your cells from? I'm about to build a pack for my car and google couldn't find 18650 Jintion batteries.

The best batteries I can find are Samsung INR 18650 2500mAh 3.6V for $3.60 a piece. 

https://www.batteryjunction.com/sam...icc3pMbv1KrPUpQs2FDqSKc4HsRUVrv4aAo-fEALw_wcB


----------



## Jimbo69ny (Feb 13, 2018)

Mustang101 said:


> avidsensei,
> Where did you buy your cells from? I'm about to build a pack for my car and google couldn't find 18650 Jintion batteries.
> 
> The best batteries I can find are Samsung INR 18650 2500mAh 3.6V for $3.60 a piece.
> ...


Wow thats a bad deal. Keep looking and emailing stores. I am looking at two options LG MJ1 3500 mah for $3.80 each or Samsung 2600 mah recycled for $1 each.


----------



## Mustang101 (Apr 17, 2008)

Jimbo69ny said:


> Wow thats a bad deal. Keep looking and emailing stores. I am looking at two options LG MJ1 3500 mah for $3.80 each or Samsung 2600 mah recycled for $1 each.


Jimbo: do you have website or store for those batteries? Also, what's a recycled battery? Same number of cycles?


----------



## Jimbo69ny (Feb 13, 2018)

Mustang101 said:


> Jimbo: do you have website or store for those batteries? Also, what's a recycled battery? Same number of cycles?


No. These are prices I received from reps of different companies after searching and searching. Both are reliable companies and are prices that I negotiated. No offense but my post wasn't an invite. I was just saying that you should keep searching and you will find better deals. One night I searched all over for companies that sold 18650 batteries. I tried to stay with US based businesses. Then I got email addresses from their website and emailed about 20 different places. Out of those I worked it down to the 2 best deals. I have many weeks into this.

I could possibly include you but I would have to mark the cells up because I have a lot of time into this. I'm not sure which way I am going to go yet though.

A recycled battery is a battery that was previously used in something else, like a laptop battery pack, a modem, or other battery back up devices. They are tested, retested and placed back into use.


----------

