black label 5S balancing bms board 100A 21V
I recently bought this unbranded chinese balancing BMS board because it was the cheapest one that was spec'd for 30+ amps... I knew going in that I'd have to do some research to get some decent instructions for using it, but didn't expect it to be quite so difficult to get more info about.
"Wait!!!", you say, "...why the hell are you posting about cheapskate merchandise on github of all places? Wouldn't this make more sense to post on some kinda penny-pinchers forum for like-minded tech-savvy cheapskates?" Oh, that's because one idiot moderator at Slickdeals chose to delete this entire post which took hours of research and was created solely for the benefit of other members. Why? Because I listed "banggood" in the next section, in a list of places where this shady item is sold. (Which, apparently, is in an undocumented "filter" of blocked merchants.) That's all. The entire post was deleted. "Well, was that against the rules or something?" you might inquire... nope. Nothing in the rules forbids that at all.
This same board, or nearly-identical boards are sold.... everywhere that sells unbranded chinese stuff: aliexpress, banggood, ebay, amazon, etc (just search for "100a 21v bms" or "synopline"). But from my scouring around to find more info, I found... essentially zero more info. The retailers all copy each other's information, including wiring diagrams. (Actually only a fraction of the retailers even had that.) And these seemingly universally used wiring diagrams were awful and labeled uselessly with "contact diagram" and "synopline diagram". I'll include them here so you can see:
The "synopline" diagram is wired so the draining load uses the same contact/pin as the charging device. This is how older cordless tools worked (like my 18V dewalt and Ryobi "one+" tools). But, did you know synopline is not a word?! Yup! That's right. It sure sounds cool, like it SHOULD have a meaning... but google it and the only place you'll find it is on the specs for this BMS board. (!?!) I'm guessing it has to be a typo/translation error. In any case, I didn't want to fry my battery cells so kept looking for info.
Eventually I figured maybe someone had previously discussed this thing, potentially in more detail, on youtube. Here are 3 valuable links:
- english with a thick accent, verifying the unit's functionality, describing the operation of the unit and its LEDs https://www.youtube.com/watch?v=5yEXaKuphhc
- russian language with available auto-translated subtitles that are pretty bad but much of it is understandable and informative https://www.youtube.com/watch?v=w2ug81AgRVs
- techno music, screwdriver waving, no audio or subtitles... BUT spec-sheet!! (at 1m18s) https://www.youtube.com/watch?v=brw1dhDpqUY
The spec-sheet in that video suggests the board's controller is a BM3451 series chip. In retrospect I probably could have just scratched off the plasticy opaque coating on it and figured that out myself but... you live and learn. Googling for the terms in the screengrab of the spec-sheet from that video pointed me to a pdf that, of course, no longer existed. But after a half hour of trying old/dead/funky links, I found a spec sheet that looks even more original than that one, and I'm attaching it here. (I found it here as "BM3451 Datasheet PDF - BYD Microelectronics")
This spec-sheet is basically a detailed whitepaper and..... includes detailed wiring diagrams! Woot! (I'm also uploading them to imgur, here)
