How hot is safe to run a lipo?

[AdrianH78]

Hi All,


I'm trying to stay safe with my kit, and sometimes the boost monster takes over....



I notice last night my cells (ultra shorty Absima 3800) were reaching around 45 degrees which felt quite warm to me..


Racing seems to be just this horrible trade off between motor performance and battery & motor temperature for me anyway :-s



I'm happy with the motor temp, but not with the battery temps, but should I worry?



Just as a bit of back ground, I run on carpet, high traction (load).




Thanks in advanced,


Adrian

[AdrianH78]

Any thoughts, its all good info

[chris24jt]

not sure on the offcial response but mine are always warm when i come off, not measured temperature for a while but you can easily hold them in your hand, they are warm rather than hot. i wait for them to cool down before charging though.

[Yorkiebar]

Similar to above, when I raced using NiCds back when dinosaurs still roamed the earth the measure was "comfortable" warm - easily gripped tight in the hand without feeling unpleasant. We used this for charging too.

I do the same test with my lipos now, if they are too hot to hold tight then something's not right somewhere - poor (high resistance) connection somewhere, poorly motor, poorly battery, poorly ESC or simply a lipo that doesn't have a high enough C rating for what you're asking from it - or way past it's best.

Never found an official figure but heat is the worst enemy of most electrical devices.

[mattr]

I looked for this a while ago, and unfortunately there are no hard and fast rules, as every model of battery is different, so the point you are measuring the temperature has little relationship to the actual temperature in the cell. (Unless you've got an internal thermocouple!)

Best i could find was "about" 40 degrees (that was for a ~6000mAh orion stick pack, which subsequently swelled and went in the bin.)

[AdrianH78]

Thanks for all the info honestly really appreciate it


Tough one, all three sets of my cells were hitting around 45 degrees last Friday and all have signs of slight swelling - whether this is direct cause and effect I am not sure.


For me I want to go fast, but not at the expense of my equipment - gets too expensive burning stuff out...


I've gone old skool and dropped it down a pinion, will see if they run cooler next Friday.


Thank you

[AdrianH78]

Originally Posted by Yorkiebar

Similar to above, when I raced using NiCds back when dinosaurs still roamed the earth the measure was "comfortable" warm - easily gripped tight in the hand without feeling unpleasant. We used this for charging too.

Least the blooming things didn't swell!!!! Scary how it has all advanced - my first cells probably had approximately 1200 mah, loaded in a Tamiya Thunderhot


With modern cells, it seems impossible to get them to dump inside 5 minutes, but you can certainly swell them up badly running too much advanced and boost I believe within 5 minutes

[mark christopher]

Legality there is no temp limit in brca rules, how ever lipo warmers are banned.
also in stock classes you will hear of people discharging at high rates of 40 to 60 amps, then charging at max allowed amps, this is to warm the cells, a warm lipo will have a lower internal resistance, which will give more punch.

It is possible your cells can not deliver the current your pulling, what c rating are they, good ones will be 60c upwards, as a discharge rate, with the top cells around 100c
This simply means a 3800 with 30c rate will delivers 114amps, where as a 3800 60c will deliver 228 amps

[mattr]

And there is no standard way to measure C ratings either. So my theoretically more powerful 5800/90C batteries are a lot less pokey than my 5300/50C batteries.
(FWIW, i measured my battery temp last night after a run. 38 degrees. Thats after 20 minutes in an 8th with moderately high traction and probably a fair bit too much boost........

[mark christopher]

Originally Posted by mattr

And there is no standard way to measure C ratings either. So my theoretically more powerful 5800/90C batteries are a lot less pokey than my 5300/50C batteries.
(FWIW, i measured my battery temp last night after a run. 38 degrees. Thats after 20 minutes in an 8th with moderately high traction and probably a fair bit too much boost........

Correct we have to rely on the manufactures, and the fact later lipos have watt hour on them and is now q requirement

[AdrianH78]

Originally Posted by mark christopher

It is possible your cells can not deliver the current your pulling, what c rating are they, good ones will be 60c upwards, as a discharge rate, with the top cells around 100c

They are Abisma 3800 ultra shorties rated at 110c :-s

Really interesting the bits on what the stock class do to get maximum performance - thanks for that.

[mattr]

Bugger, my run on tuesday was sufficiently boosted that i've blown both front tyres off the rims
Wondered why it was getting hard to turn in under power..........

[mattr]

Originally Posted by AdrianH78

They are Abisma 3800 ultra shorties rated at 110c :-s

You need to work out the maximum current deliverable, and the maximum current draw. First should be higher than the second. In theory.

Doing the calculations is made unnecessarily complicated by everyone using different methods for measuring (both ESC and battery), or just lying to sell kit.