Not sure if i am causing my own problems with my batteries

[nwredneck253]

i built 3 230 ah batteries for my RV.. 230 ah cells 150A Daly BMS i had 2 installed the coach and everything seemed fine..... now with the 3rd installed things have gone weird today one cell in the middle battery over charged to 4.7 volts and swelled really bad... the BMS was set to shut off at 3.7 but didnt shut off.. and not sure if its my fault...

The POS side of all 3 batteries are connected together and then run to the POS side of the coach..... the P- side of every bms ( black lead) are connected together than then run to the Neg side of the coach...

even after i disconnected the neg wire to the coach,,, the BMS app still says there is a load drawing on the batteries...

what am i missing

 

[NVS]

There has been discussions on this before. Daly bms aren't supposed to be connected in parallel together. And I think I've seen that on a Daly web site too. They don't say exactly why but maybe your finding out the hard way.

 

[BradCagle]

Are you 100% certain the sense wires are connected to the correct cells?

 

[nwredneck253]

There has been discussions on this before. Daly bms aren't supposed to be connected in parallel together. And I think I've seen that on a Daly web site too. They don't say exactly why but maybe your finding out the hard way.

yes it seems this was something i did not expect when i ordered them,,, i just researched it and they say theryte is a new one that works in parallel but of coarse thats not the one i have...... now have to monitor them close to make sure they dont over charge until such time as i can rplace the bms.... hopefully that one cell is not killed...it sure swelled up.....

 

[TacomaJoe]

I sure can't figure how a parallel connection can cause this. The BMSs don't communicate with each other, when the middle battery sees a cell going overvoltage what can keep it from shutting down? My inquiring mind wants to know.

 

[Lt.Dan]

If you have one cell run high and the BMS disconnects the 1 battery pack, but the other 2 don't disconnect, and then you discharge the 2 batteries to 50%, what do you think will happen when that 3rd battery comes back online?

There will be a HUGE current inrush going from the 2 batteries into the 1 with a bad cell. Which could damage 1 or all of the BMS's.

 

[TacomaJoe]

I understand the issue of one of the parallel BMS cutting out and the others picking up the slack, along with the back flush when the BMS reconnects. What I don't understand is the OPs issue where the BMS did not cut out when a cell overvoltage condition existed.

 

[Lt.Dan]

Daly BMS is known for failures. Plain and simple. I've had 2 that did not disconnect with once cell getting down to 1.7v, with the cutoff set to 2.5v. It SAID that it was disconnected, but power was still going through it, the MOSFETs failed in a manner that allowed current to continue flowing.