Do Li-ion protected cells need BMS?

Jack.Straw

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Jul 17, 2013
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Hi guys. I'm trying to come up with a battery & charging plan for a little amplifier that i'm making. I'm looking at a 12(ish) volt system, so i'm thinking i'll probably start with 3 of the Panosonic NCR18650B in series to start, but may add another 3 series pack in parallel if the battery life isn't good enough. (If there is a different battery that would be better for my application please suggest it.) I see that there are protected and unprotected versions of these batteries. I was under the impression that I would need to use a BMS board to monitor and protect the individual cells in the pack, but is that really necessary if I use the protected versions that i have a built-in protection circuit?

Also, when it comes to charging: I'm hoping to find a charging system that can be internal, and that is capable of supplying the load while charging so that the amp can be used while charging is in progress. Most of what i'm finding online are chargers that would require me to remove the batteries for charging, or wall-pack types that wouldn't allow for charging & usage at the same time. I know that I could build one using one of the Maxim IC chips, but i'm really hoping to avoid that this round. Any advice you guys can offer on a charging board that would suit my purposes would be appreciated!

Thanks for your time and advice!
 

hookemdevils22

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Nov 29, 2017
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A BMS would provide low-voltage cutoff (important) and balance charging with a 'dumb' charger. I have charged thousands of 18650 cells using an IMAX B6 charger (powerwall, electric scooters/go karts, lighting, etc.), and use that for balance charging with multiple cells in series. That said, I haven't actually attempted to charge while using the cells, so I'd be interested to see whether that would work, though I don't see why it wouldn't. It is, however, limited to 6 amps, so it may not charge if your amp pulls more, uhh, amps than that.

The NCR18650B does NOT have a PCB, so you run the risk of under-voltage without some form of monitoring.
 

HKJ

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Mar 26, 2008
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A protected battery has over voltage, under voltage and over current protection. A BMS may add balancing, but not all do.
If you use a hobby charger with balanced charging you do not need a BMS with balancing.
 

BurchSung

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Jun 5, 2018
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Hi...as per my knowledge Connecting two banks with different capacities in parallel is technically fine since the batteries will be operating at the same voltage. Charge and discharge current will be shared, based on capacity. It is best if the batteries are of the same type and age.
But different packs have different internal resistances. The Ohm's Law tells us that the stronger battery will discharge through the weaker battery -- you will always have current flowing
 
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