[cricketo]

I dislike what most hobby (and some "professional") BMSes do for balancing. I like the idea of using BMS strictly for monitoring, and using the Chinese inductive balancing modules. I am trying that out on the small scale now, but would be interesting to read if anyone has looked into it on a larger scale like here.

casey, this is the one example of the thing I am talking about :

3S 4S 6S 10S ~12S Li-ion Lifepo4 LFP Battery Active Equalizer BMS 1.2A Balancer | eBay

Find many great new & used options and get the best deals for 3S 4S 6S 10S ~12S Li-ion Lifepo4 LFP Battery Active Equalizer BMS 1.2A Balancer at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I think the biggest unit I've seen was 17s, they're stackable though.

 

[cricketo]

^ anyone got a schematic for these? The docs that come with them on how they're applied?

They're quite straighforward. Here is a wiring diagram from a listing on Ali :

 

[cricketo]

That part I get, lol

What is your question then ? The thing is analog, has no voltage thresholds on anything like that - if the two adjacent cells have different voltages, it bleeds one into the other. Has a very small "standby" current.

 

[cricketo]

I don't see any transistors on it, but there is a tiny 8-pin IC (per cell pair). Here is a picture, but it is definitely difficult to make out any details even in person :

 

[cricketo]

If I paired those with the manzanita micro pfc20 I think I'd have a reasonably safe battery pack?

No, you're still playing with fire. You need to have a way to stop charging if any of the cell groups reaches max voltage, and without a BMS you wouldn't know.

 

[cricketo]

Ok gotcha. Would the manzanita regulator boards be the right move in that case? I don't love the idea that the safety of the pack is determined by software programs and an ethernet cable but it doesn't seem like there's an alternative.

That's probably what you'd want, but looking at the spec sheets they provide I can't quite tell the level of integration PFC20 has with their BMS. On the picture I see a connector labeled "reg bus", which I suspect is the hookup to the BMS, but it's not called out. I'd recommend reaching out to their support to clarify that question - overvoltage charger cutoff. And I mean this is to be totally safe. I don't believe there is never any room for shortcuts, but if you're planning to use that thing on a regular basis and want to leave it unattended doing its thing, you should build safeties into the design.

 

[cricketo]

That datasheet is a great find! Explains the mystery. Couple of pics of my 14s and 16s ones...

 

[cricketo]

Most Chinese sellers of these boards claim 1.2A, which isn't unreasonable, since we're talking very small voltages and very little resistance (hence little heat). I have used this so far to balance out some Nissan Leaf module packs, seemed to work well. I've wired both the BMS and the balancer with the same GX plug pinouts, and the plan was to make a Y harness so the two can be paralleled, but got busy and didn't get to that. Looking at the board it may be difficult to figure out which resister it is, so next time I'm playing with these I will just clamp a DC current meter around one of the wires, and just measure the current live.