Do NiMh cells ever have integrated protection circuits?

martinaee · Nov 5, 2017

Do NiMh cells ever have integrated battery protections? Like built in overcharging protection circuits like some 18650s say they do?

I use LaCrosse NiMh chargers for my Eneloop/Amazon NiMh AA/AAA cells, but have a really old 4 slot Rayovac charger that is cheap and I'm assuming doesn't really have fancy protections in the charger... I want to give that to someone with some Eneloop AAAs. Should I just tell them to not leave the cells in the charger beyond something like 12 hours or does it not really matter? Doesn't have much info on the charger, but it says input of 8W and output of 2-4 AA at 160mA or 2-4 AAA at 90Ma. Doesn't even have separate basic leds for each slot lol. Nothing I'd use as a semi-flashaholic myself, but will be great for someone who could use a few rechargeable NiMh cells.

fivemega · Nov 6, 2017

NiMh batteries don't have any protection circuit inside but must be charged on smart charger to prevent overcharging, overheating and detect short/open circuit.

iamlucky13 · Nov 6, 2017

NiMH are a bit more tolerant of abuse and less likely to experience thermal runaway than lithium ion batteries. Lack of cell protection is not a significant concern for NiMH. The main issue with overcharging or over-discharging is reduced cycle life.

All the info you've given on that Rayovac charger (charges 2-4 batteries at a time, very low charge rate, lack of individual charge status lights) hint at it being a dumb charger. Again, it's not a serious concern, and you can just tell them not to leave the batteries on the charger for more than 12 hours as a minor precaution, but personally, if you're already going to buy them a set of Eneloops, I'd just spend the extra $7-8 to buy them a set that comes with a Panasonic charger (BQ-CC17, BQ-CC55, or BQ-CC75 are all smart chargers).

I'd expect the Rayovac probably does still have a maximum voltage cutoff and/or charge time cutoff.

TinderBox (UK) · Nov 6, 2017

Dont some of the 15min charger NiMh come with a thermistor in the cell to stop the charging.

John.

martinaee · Nov 6, 2017

fivemega said:
NiMh batteries don't have any protection circuit inside but must be charged on smart charger to prevent overcharging, overheating and detect short/open circuit.

I'm wondering if there is something wrong with my XTAR VC4 charger then. Its supposed to be able to charge NiMh AA/AAA/D etc. as well as most lithium ion batteries. I usually use specific La Crosse for my Eneloop cells, but when I first got the XTAR I charged a set of NiMh in it and all are... dead. No voltage at all. I also have a set of 4 unlabeled red 18650's that seemingly don't have a charge anymore after I just left them in the VC4. It's supposed to be a "smart charger" but could it be overcharging cells? I have noticed when I put 18650s in it even when the indicator says it's at 4.2v it keeps charging beyond that. I don't know... I read some cells can charge to 4.25, but I'd rather go a bit lower and don't know why it's not cutting off the current sooner.

martinaee · Nov 6, 2017

iamlucky13 said:
NiMH are a bit more tolerant of abuse and less likely to experience thermal runaway than lithium ion batteries. Lack of cell protection is not a significant concern for NiMH. The main issue with overcharging or over-discharging is reduced cycle life.

All the info you've given on that Rayovac charger (charges 2-4 batteries at a time, very low charge rate, lack of individual charge status lights) hint at it being a dumb charger. Again, it's not a serious concern, and you can just tell them not to leave the batteries on the charger for more than 12 hours as a minor precaution, but personally, if you're already going to buy them a set of Eneloops, I'd just spend the extra $7-8 to buy them a set that comes with a Panasonic charger (BQ-CC17, BQ-CC55, or BQ-CC75 are all smart chargers).

I'd expect the Rayovac probably does still have a maximum voltage cutoff and/or charge time cutoff.

I was just going to give a few of the Eneloops I already have so I don't have to spend any money. I guess I'll just say be sure to take them off the charger after 10-12 hours or so.

Do NiMh cells ever have integrated protection circuits?

martinaee

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fivemega

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iamlucky13

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TinderBox (UK)

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martinaee

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martinaee

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