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Old Apr 21, 2012, 11:26 AM
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Chargers for batteries with built-in thermistors

I'm wondering why JST-XH3 chargers for 3.7V batteries with a thermistor are so hard to find.

I just read about how recharging LiPo batteries should never be left unattended. So I figure another way to go is to use a thermistor controlled battery charger that will interrupt the recharge if the battery would get too hot and keep it within safe limits.
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Old Apr 21, 2012, 01:30 PM
PGR
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The biggest potential problem with this idea is LiPo cells can suffer from a phenomenon known as thermal runaway and once the process begins you typically can't stop it by interrupting the charge cycle.

In other words, it's usually not enough to simply stop the charge cycle when a LiPo pack begins to heat up.

Pete
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Old Apr 22, 2012, 09:52 AM
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Yes, the cell can be far outside the limits AND be cool as a cucumber. That's cool.
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Old Apr 22, 2012, 11:42 AM
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It's always been my understanding that there should never be any heat generated by a pack during a charge cycle, and that's been my personal observation since 2004 when I began using LiPos.

But I need to qualify that a little: I typically charge at 1 or 2C and I can only recall charging at 3C a couple of times when I had some friends waiting on me for a formation flight. Consequently, I don't really know from personal experience whether packs will warm up at the maximum charge rates some packs are rated for and I have no desire whatsoever to find out.

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Old Apr 22, 2012, 12:17 PM
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My experience is that they will not warm much even at max rates. Maybe 1-2 degrees , and if one charges after use then they'll even cool down some. The newer max rates of 5-12C don't even warm much over a couple degrees. When multiplying the max rates by 2-5 times heat is generated similar to the heat generated by discharging at those same rates. I have limited experience charging at the discharge rates and it seems that similar temp increases happen whether discharging OR charging. It does kinda make sense that that would hold true.

I think a good point is that cell temp is a terrible predictor of charge status without a bunch of other info.
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