Exploring A CHEAP 3-cell BMS Board!

Oh no - what was I thinking - "430" on a resistor is 43 and ZERO (no) Zeros, so 43 ohms - I'm going to let it ride. Thanks @Marsha Jackson !

I bought a similar charging board to this last year, but for 2 18650's. I could'nt get it to work, there were no instructions in the ebay listing or for the board number when I googled it. The beginning of this video is priceless. It turns out I had wired it up wrong, so thank you for this information. It's working a treat now. :)

Those 18650 holders have a ton of resistance. I did a little video on the difference in resistance between some of the cell holders I have and the Keystone SMD style cell holders have the lowest resistance of any cell holders out there. Not a big deal if you’re doing low current stuff but if you’re going over 5A (Like Jehu Garcia discovered) you’ll find out that the leaf springs on the cell holders become the hot point on the PCB.

Bro this is the testing I need to get my brain to learn I’ve been learning about BMS’ and balance charging and this right here gives me a lot of reference for why my cheap BMS heats up sometimes on discharge but not really, but generally on charge it warms a little, so that would explain why!

Great job on the PCB's, loved the video. I'm such a LiPO battery nerd. Can't get enough of this content! Keep up the great work.

For using machine screws in 3D printed cases, I like to use those brass inserts that you can get, just make the hole a bit bigger and you melt the insert into the hole with a soldering iron, then you have a nice fitting and demountable fixing.

Sorry to keep comment spamming but they are old cells. 4.13 is its resting voltage. It triggered over voltage protection at 4.25V and the cell rested at 4.13 because it’s an old cell. It didn’t Balance all the way because the balance current is so low and you were charging at 5A so cell 3 was only balancing from 4.10’ish until it hit 4.20-4.25 which didn’t take long. If you charge at a lower current it gives more time for the other cells to catch up

20:00 mark, the middle battery is off by 1/100 of a volt only and you talk about the cell "not well matched". That's very small and acceptable.

I may be wrong here but as far as I knowi SMD resistor coding works like this: first 2 digits are the value and the last digit shows how many zeroes will be added to it. So, 430 means 43 + "zero" zeroes = 43 ohms, 431 means 43 + one zero = 430 ohms and so on... Later edit: Yeah, the #1 rule of commenting is; read previous comments first. :-)

Awesome video, loved the level of detailed explanation of the design. Have you heard of "Battery hook up", it looks like a seller of used battery packs for us tinker's to salvage. Is a revision 2.0 possible for this board with, indicator LEDs , easy connector to add parallel batteries, potentiometer to adjust charging current... I figure I should stop before I feature creep too much. Will definitely be using the provided info in the building of my 3s7p pack for a mobile pi station. Would love to see a clip of you Shorting the pack or at least a cell, maybe demonstrate high current/ voltage on old/dead components you have laying around. I say a suggestion on another channels video of have the multimeters screen record on a separate camera then placed in a small overlay in the video that way we can easily read the display with out you struggling to fit everything in one frame, although e would up the editing time.

Lovely work. Board ordered! 👍😀

I had the same experience with the red rounded one, same thing, once a battery got to 4.2 it stopped and the rest were at 3.7. To be fair mine wasnt advertised as a balancer, so i manually balanced it, took a 2.8ohm 20w reistors and put it across the 4.2v cell. It took 5-10 minutes and it got smelly hot to get it back down to 3.7-8. This was with the rest not being charged. It would take way longer and youd need to dissipate more heat if you were trying to balance this cell while everthing else was charging id imagine, so no wonder these dont do any balancing. They'd need some heavy duty resistors to keep a discharge while everything else is charging. 20w worked fine in my case but only when everything was off and it took awhile. Anyhow this doesnt seem like a good way to balance, youre basically draining the life cycles of all your best cells to wait for the weakest one. You should just stop charging the 4.2, and charge the rest, but it seems a series connection doesnt allow this to happen, easily. Maybe you could just disconnect everyhting charge them individually and connect them again, that seems to me it would be the best way to balance without wasting lifecycles to do it, but i wonder why no balancer does it like this.

The current rating on the BMS boards is usually peak current to allow motor starting. Also only salvages power tool batteries are good for over 3-5 amps max. Different construction/chemistry.

I’m very surprised the BMS activated the balancing circuit so early. Usually they don’t turn on until 4.18V

i bet i will learn a thing or two in this video lol

You should top balance the batteries first, it's the Bms job to cut off the current if any cell is fully charged

not sure but i got like 4 of them and so far they have been working ok but not sure if its even doing anything or not but im using them lol

I have the same problem with this bms I try 3 psc all do the same thing voltage drop . This olso happens wen you charge the pack . Not a good bms

60A * 60A * 0.006 Ohm / 10 mosfets = 2.16W ....you would not want too much more than about 4W continuous for that board, BUT, I assume the mosfets are "chinese" rated, (usually nominally about 2x Rds i.e. 10-12 mOhm - test one and you will get a surprise :) ) making the power loss likely to be around that 4W mark. It may look over kill, but it's likely not. BTW I always design for "chinese" mosfets operation, because they are SO MUCH CHEAPER (even in spite of the higher no. of devices) so if you design for it, it works better than using full spec mosfets.

43 ohms is correct the 3rd number is the multiplier example, a 430 ohms would have a marking of 431.