Cell Temperature during testing...

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Oran Maliphant

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Joined
Jan 2, 2018
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33
Do you guys keep an eye on cell Temps when testing?

Never noticed them getting hot when testing on the MiBoxer C4 (400ma) but the Opus 3100 I just got will do 1000ma draw and Im seeing 45-49C on the first batch of cells...

Is that temp too high for 18650s?
Whats the cost off point for temp where it is dangerous?
Would you bin batteries for being too hot under load?

Maybe I just do tests at 700ma?

Oh and I see what you guys mean about the Opus over estimating...

The C4 gave 2273mah & 2275mah on the 2 cells Im testing and they are 2455mah & 2463mah on the Opus...

Thats about an 8% over estimate...
 
I do depending on the charger my hobby charger has a temp probe for active monitor and you can also set a threshold value to terminate charge.

If I am using a parallel charging cradle with multiple cells or a 4 bay charger, I just use a non-contact IR thermometer. Often times I just touch them with my hand to see if anything is getting abnormally hot.

I don't keep anything that generates notable heat at 1A charge or discharge.
 
Do you have a definition of notable heat?

2 cells were at 36-38c and 2 were at 46c and 48c, all 1a discharge
 
For me that starts in the 40C range...

The default value on my hobby charger for temp cut-off was 50C, but I lowered that value to 40C.

I think its important to note, ambient temp matters. Mine is about 24C ambient

Per another members comments...Anything 10C above ambient I would considered bad at those charge rates.

I started a thread on this a while back... you can see some comments here:
https://secondlifestorage.com/t-Safe-18650-Temperatures
 
19.7c ambient, 48% humidity....

Worth noting this is on the OPUS BT-3100 V2.2 tester...

On the MiBoxer C4 at 400mah these cells dont get noticeably hotter than ambient, maybe a tiny warmth, say 25c VS 19.5-20c ambient...
 
All of those cells were way more than 10C over ambient... personally I would not use them.

I think its worth mentioning my cell holders are separated / away from my actual charger/discharge. I dont have any heat contamination coming from the tester so you might want to take that into consideration.
 
Temperature limit is .. 100C or 212F as i recall .. almost for every cell manufacturer.. of course this is critical temperature .. but i had some to heat up like to 60
Opus .. there is a problem with venting all the heat .. it kept cutting while discharging ... it took like 50% more time to test until i made this contraption :D stuck it on air filter :D

lalmry0.jpg
 
Just doing a 2nd cycle on the same 4 cells which are now at 30.4c, 31.0c, 40.8c and 40.9c this time round so Im wondering if as mentioned on the other linked thread they just need a few cycles as they are new old stock which has sat for a very long time. Most cells were in the 2v range but charging and leaving for 3 weeks has shown less than a 0.05v drop... (with the exception of a couple of cells which have crapped themselves at 0.5v-1.2v after 3 weeks sitting at 4.2v initial).
 
In the opus, and most other top load dischargers, the load resistors are underneath the pcb. So this means that heat rises and heats up the cells. The cells themselves are probably not heating up to those temps on their own.
There have been several discussions on this problem. A quick fix is to take off the base and replace the fan with a better one. There are others that 3D printed a new based with more air flow. Others have put a squirrel fan on the inlet to force more air into the base unit.

All these methods have one thing in common. It keeps the load resistors cool, and forces the heat out before it gets a chance to rise to the cells. This has the added benefit that the thermistor that is under the cells to actually read the cell temp, not the imposed temp that's coming from below.
 
thunderheart pid='28595' dateline='1523478819' said:
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Use Miboxer C2-6000 or C4-12. They have metal plates in all slots which are glued to thermoresistors. These guys show adequate temperature.

My Miboxer C4-12 review with disassembling (in Russian): https://mysku.ru/blog/usa-stores/59241.html
My Miboxer C2-6000 review with disassmbling (in Russian): https://mysku.ru/blog/aliexpress/55626.html
Click to expand...

Thanks :)

I have found a dell RAM fan and modified it to work as an underbody blown diffuser (Im a motorsport fan sorry!)

Now cells not exceedin 31c in 21c ambient....

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