[SOLVED] HEYO BMS gives 3.1 V on P-

[oskar]

So, I'm trying to connect the BMS to the battery pack I just assembled. Battery voltage is OK (cells and total) but BMS is showing low voltage when the balance leads are connected.

And the same low voltage when B- is connected

Also, resistance över B- and P- when only balance is connected is infinite.

Any ideas where to start troubleshooting this? Maybe I'm missing some step that's not documented

Battery pack
4x LifePo4 cells
3.27 - 3,28V per cell
13,1 V total

BMS: HEYO 4S 100A
Aliexpress

Balance leads are connected and I measure increased voltage for each lead - which is correct.

Connected the balance connector to BMS and expected zero resistance between B- and P- on BMS (according to manual) - Fail

Measurements from B+ to BMS which is only connected through balance leads:
B+ to B- on BMS: 13,1 V
B+ to P1 on BMS: 3,12 V

This is the first time I connected the BMS. I've got two of them showing the same behaviour. They could of course be faulty but I figured I'd try some troubleshooting before contacting support (if there is any).

 

[vk2emp]

Looks like a DALY clone. Edit: this one is backwards, seems they want you to connect balance leads first, then B-. Have you tried the multimeter in the opposite direction (swap probes between P- and B-)

 

[oskar]

With ONLY balance connector and plus from multimeter on B+
B- on BMS 13,1 V (same as B- on the cell which is connected through the negative balance lead.
B- on BMS and B- on cell pack are directly connected (tested with buzzer)

P- on BMS 3,12V

I tried the different connection order and short-circuit of B- and P- (10 seconds, both with B- connected and not) before you edited
And I'll add ring cable connectors.

 

[vk2emp]

well since you caught my initial post before I edited, did you try a charger? also if the BMS came with a temperature sensor, is it plugged into the NTC port on the BMS?

My identical, but DALY labelled one won't start without the temperature sensor connected, and it only starts if I supply it a charge. (I use 10A at 14.5V between B+ and P- once everything is connected - balance plug and B-)

 

[oskar]

THANKS!

The temp sensor was the culprit, when that was attached the BMS behaved like expected in the instructions. Zero resistance across B- and P- on the BMS and same output voltage on P- as across B- and B+ on the cell pack

I never thought that could have an impact, and wanted to start with a minimal system (without temp & BT) to reduce complexity.

Thanks again!

 

[vk2emp]

It took me 3 days to work out that the temp sensor was the culprit on mine too. I'm in australia, so don't need it... guess I do if I want the BMS to work