Help identifying circuit... Battery balancer

Thread Starter

bigjoncoop

Joined Feb 1, 2019
123
Hey guys me again LOL,

I just came across this interesting solderless 18650 parallel battery pack solution that comes with balancing unit which seems like to me is just a couple of mosfets, big Power resistor, and some type of IC. I think it is a comparator Maybe. Basically it just senses the battery voltage and if it gets above 4.2 volts is switches on the mosfet to drain power through the resistor. Straightforward enough. I would like to build a bunch of my own and I was hoping somebody could look at the picture and determine exactly what it is and maybe the circuit itself. I know there's also an LED that lights up when the mosfet is putting power through the resistor but next to the IC there is this round component that I'm not exactly sure what it is. the picture below

Thanks again for all your guys's help I really appreciate it!!!

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Irving

Joined Jan 30, 2016
942
Hard to tell from those pics, but my guess is its an inductor and that's some form of SMPS. You don't balance a single 18650, you need at least 2. Is there more than one cell in the pack and how are they wired? Is this the only board? Does the IC have a part # on it and is there anything written on the 'round thing'.

Why do you want to build some of your own? There are many balancing solutions but not all are created equal... many are rubbish, but there are some good cheap ones - its rarely vfm to roll your own unless there's a specific need.

Can you do some clear, in focus, pictures of both sides of the PCB?
 

Irving

Joined Jan 30, 2016
942
Yes, I was thinking it might be an active balancer but then there won't normally be any power resistors. Without more info/better pictures it's hard to say. From what we can see it doesn't seem to have enough components to be an active balancer.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
123
Hard to tell from those pics, but my guess is its an inductor and that's some form of SMPS. You don't balance a single 18650, you need at least 2. Is there more than one cell in the pack and how are they wired? Is this the only board? Does the IC have a part # on it and is there anything written on the 'round thing'.

Why do you want to build some of your own? There are many balancing solutions but not all are created equal... many are rubbish, but there are some good cheap ones - its rarely vfm to roll your own unless there's a specific need.

Can you do some clear, in focus, pictures of both sides of the PCB?
The reason why I want to build one like that is because it can balance cells a hundred times faster then almost every other BMS or balancer on the market. Because of the big power resistor. Most decently priced BMS boards on the market can only balance at a very very slow rate through its small resistors. And when you have a 5kwh 7s battery using unmatched cells sometimes they're balance current is so slow it will never balance properly.

So with that said I don't particularly have to build a circuit the same as the one in the photo but I would like to build something similar. What type of IC would I need to use to turn on a mosfet when the voltage gets above 4.2 volts?
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
123
I've been building lithium ion battery packs for quite some time and I understand how they work and what's safe what's not safe. I'm just looking to find a circuit similar to the one in the photos that will turn on a mosfet to put current through a power resistor when the voltage goes above 4.2 volts I will cut off at 4.2 volts. I'm not sure what type of IC to use
 

Irving

Joined Jan 30, 2016
942
I too build big packs, but LiFePO4 for wheelchairs. I'm currently sitting on a 5kW (24v, 210Ah) pack, which is the 3rd generation of these, having built several for myself & others over the last 7 years.

At the moment I charge it @ 40A with an offboard charger (Revolectrix PL8) but I want to develop a fast onboard charger. To be viable it needs to be small, efficient and balance quickly. Resistive balancers just don't cut it, too slow, too wasteful of energy. The PL8 balances at 1A, better than most 3rd party BMS, but still too slow. I don't use a BMS anyway for good reasons.

I've been playing with the design of an active balancer for an 8S pack using a controller chip for EV.


What you have there may be an active balancer, but the power resistors make no sense. There are no power resistors in a true active balancer. Without more detail I can't tell you what you have there.
 
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