Integrated battery protection circuits for 18650s - typical quiescent current? - Page 1
Forum section: electronics / beginners

author: mortrek
author_rank: Contributor
timestamp: June 30, 2020, 03:17:01 pm
content: I have some Panasonic NCR18650B 18650 batteries that I ordered from IMR batteries, which have an integrated protection circuit/BMS. Since the circuit is considered aftermarket, it's not in the official datasheets. Does anyone know what typical specs are for these sorts of tiny battery-cap style protection circuits? Are they significantly less efficient and/or have higher quiescent current than a more typical BMS?I have the batteries in a 2S6P configuration with no extra protection.I was hoping they would not have any quiescent current while the batteries are not connected, since the battery pack's power output is controlled by a relay. I need them to last a long time (minimum 1 year) without "significant" (excessive for my project) self-discharge.I'll know for sure in a month or so what the rough discharge rate is, but I'd like to know ahead of time if I'll be running into any problems.Also, if there are relatively inexpensive primary batteries with higher current handling (probably 2-3A peaks with a 500-1000mA typical) and very low self-discharge, I'd be interested. I decided against alkalines because of how higher current draw kills their capacity, and lithium thionyls can only handle tiny currents and are nasty batteries anyway.Thank you for your insights once again.

author: mikerj
author_rank: Super Contributor
timestamp: June 30, 2020, 03:46:25 pm
content: The 18650 protection circuits draw some quiescent current all the time, I took one apart a couple of years back and measured a quiescent draw of around 30uA.For long life, high current primary cells you could look at lithium iron disulfide, e.g. Energiser "Lithium".

author: mortrek
author_rank: Contributor
timestamp: June 30, 2020, 04:46:54 pm
content: Good point, the Energizer Lithiums are pretty good. Looking at a paper on them (https://data.energizer.com/PDFs/lithiuml91l92_appman.pdf) shows that they are very resistant to temperature changes and can handle high loads without harming total capacity. It says they are just over 3000mAh per AA cell.I'd need a massive array to replace a 2S6P 3400mAh/cell 18650 array, but I wonder if it would work out better. I'd also be able to use a lower total capacity if their self-discharge is much lower, due to chemistry and lack of a BMS... interesting.I'd probably still want about 8-9V nominal w/6V or so dropout, so 6 AA cells to get 9V nominal, but that's 9V at 3000mAh, so to get, say, 12000mAh, I'd need 4 parallel banks, or 24 batteries total... but I may be able to get away with 3 banks/18 batteries. $1.25 or so per battery makes a full year run about $25-30. Not bad.Now I wish I had asked first or thought of this myself without spending money on the 18650s. Guess I'll have to find some other use for them. Thank you.

author: Peabody
author_rank: Super Contributor
timestamp: June 30, 2020, 06:43:52 pm
content: The DW01 chip is pretty much the standard protection chip for lithium batteries. Its datasheet says its current draw is 3µA. But that's all the time. It's never off.