How do I know BMS is working?

So I’ve wired up my BMS to the battery pack and my PSU is an off the shelf one that feeds into a DC-DC converter that outputs the correct voltage that I want to charge my 18650 cells at which is about 4.05 volts each cell as I want to get a good cycle life out of them.

How can I tell the BMS is working? so far when I plug it all in and I check with a volt meter I can’t see that the cells are charging at all (they are at 3.58/3.6 volts so should increase as they charge).

How can I tell the BMS is working? during charge or discharge?

Show us a pic of your setup and your wire diagrams if you have it, if you can measure the amps going from the DC source to the BMS

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Thanks, I don’t have that here but checking the amps is a good test. Does the PSU have to be anything special or can it just be a constant voltage source?

Do you have your bms set for bypass or discharge?

Either way you should have a constant DC source going into the charge port of the BMS at a constant voltage equal to 4.2V times the series count (6, 7, 10, or 12)

I used one of those little BMS boards which doesn’t seem configurable, yes I have a constant voltage equal to 4.05v X the number of cells.

Maybe I should discharge a bit down to 3.4 volts per cell and then see if it charges up again

Whats your series count?

Its 4S for this part

4s? What kinda tiny pocket board is this?

Anyways give the BMS constant 16.8V and let it charge up, the cells wont balance unless they are full charge. Next time you charge you can pull the plug once a cell gets to 4.05V, make sure it gets balanced every few cycles

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Hey, I have a problem with my battery pack… I just went for a long ride and drained my battery to 30.6V. Now, when I plug in the charger nothing happens. When i opened the board the battery pack was a a bit warm in ONE place (the middle on the right row) now its not charging… what should I do? I checked the charging port connectors and everything goes smoothly into BMS but nothing is charging, the charger light doesn’t change to red when plugged in 1557337143640279613301608802735 15573371806923218806124129208418

Can you use a volt meter and measure each cell? you should find the warm cells are higher voltages than the cold cells. Which probably means the BMS has problems.

From what I can gather a lot of these cheap chinese direct BMS PCB are really junk quality…

I have charged the pack a couple of times and now this happened, I can’t check the batteries with multimeter cause then it would ruin the shrink whap and it was pain in the ass to put together…

Can’t you read the cell voltages through the white BMS connector on the BMS? no need to open the pack

those are chilly joints and you didnt tin the wires…, a little bit of vibration and they will pop off

i recommend getting some flux and a better iron

Hi All,

I thought I’d write back with the solution to this. I figured out what was wrong.

I tried multiple boards with the same result which was frustrating. I then swapped power supplies, I had been using a stock 24volt supply and I hooked it up to a DC-DC board to dial it back to the 16.8v for the 4S BMS.

Well instead I tried a benchtop supply and just set it to 16.8v with a current limit of 1 amp.

When i plugged it in, the voltage dropped to match the battery and it slowly went up as the battery charged. As the voltage reached the setpoint the current load dropped.

So it seems it was a PSU problem. Now I need to figure out what kind of PSU I need for this thing, I don’t want to have to charge with my benchtop supply. Any ideas?

I count 40 cells. You are running a 4s10p battery?!

Yep indeed I am