A very basic 12v BMS question. How to hook up a cheap Amazon BMS?

[Bobby June]

Just wondering what 0V stands for and why there is a plus and minus on this BMS is that a P- and a P +

I drew what I think is close. If you could close the loop, I’d Appreciate it!

 

[beemac]

0V means zero volts - or ground - so that looks ok.

12v is usually 4s so the + might connect to the positive of the 4th cell... and then the charge/discharge point would be the +/- points on the pcb. But that's just a guess so don't connect things up based on my guesswork - you definitely need to confirm what the pcb does.

 

[Bobby June]

I am a graphic designer I should’ve knew that was a zero it’s got a distinct shape OK thanks man appreciate all that you know Amazon makes it so hard to contact anybody that you buy from ...sucks. About the 3S for S would you think that the 3S is the wimpy safe territory 12 V and the 4S is the I got nuts where is the machine glowing red 12 V.?
It seems that the only difference between the two aside from all the power specs is if the device you’re hooking them to to power has a brain enough to deny the 3-4V of extra voltage

 

[DaLanMan]

Uhm, this might help, it is I think the one yuou are showing.. either way, the diagram is the same for any bms pretty much.

Here

 

[Bobby June]

Well thank you for that!

 

[DaLanMan]

Oh, and for the record, if you go down the links to do a return, eventually you get spit out into the specific info for the vendor. These pages are unique to each vendor and from what I can tell, don't have the same name/address over time. I have linked one, clicked the link a while later... 404. With others, address still works.

I don't know if is intentional, or just something that happens. Amazon pretty much does all the things they are supposed to... just not in a way that is easy to track or find and therefore making it nearly impossible to prove they did anything wrong. It is like the head of design engineering was a lawyer.

 

[beemac]

I am a graphic designer I should’ve knew that was a zero it’s got a distinct shape OK thanks man appreciate all that you know Amazon makes it so hard to contact anybody that you buy from ...sucks. About the 3S for S would you think that the 3S is the wimpy safe territory 12 V and the 4S is the I got nuts where is the machine glowing red 12 V.?
It seems that the only difference between the two aside from all the power specs is if the device you’re hooking them to to power has a brain enough to deny the 3-4V of extra voltage

It depends on the thing you're powering - all batteries have a usable voltage range. Lead acid '12v' Car batteries are full at 12.8V and empty at 10.8v or so but a car alternator puts out more like 14-15v - so a '12v' device in a car should operate with and tolerate 10-16v at least.

3s lipo is 3x3.7v nominal (11.1v) 3x4.2v full or charging (12.6v) but will go down to 7.5v if you run each cell down to 2.5v. So you can see that's a different range.

Similarly 4s will be 14.8 nominal - 16.8v full or charging - and 10v discharged... assuming 4.2-2.5v/cell.

Lifepo4 will give slightly different voltages (3.2v/cell nominal) - and is much closer at 4s to a lead acid 12v voltage range.

But that board is 3s only - based on the link DaLanMan posted. But if you want to get 20A continuous then you'll either need beefy cells or more parallel cells in each 's'...

e.g. 3s4p - 3 parallel groups of 4 cells, connected in series - so you get 4x the current and 3x the voltage of a single cell.