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BMS Troubleshooting

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dpdoug

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Oct 3, 2019
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I bought the Daly 80 A-200A BMS (new) for my system, to be sure it was compatible with the LifePo4 12V 200 aH battery I bought from the same manufacturer -- "BLS Battery Official Store". I built my system and tested it out and everything worked perfect. Since we weren't yet ready to take our trailer out on the road, it sat there for several months. This week I got in it and turned on the 12V fan for a few minutes and then suddenly it went off. I tried all the lights and other 12V items and they wouldn't go on either.

So I got my multi-meter out and started testing to try to find the issue. No blown fuses or loose wires. Through a process of elimination I discovered the issue was that the BLM was not permitting the system to function. I tested the battery and found that it had the same charge as it had months ago: 13V+.

Do I need to replace the BMS or is there something I don't understand about it that I need to address?
 
Have you tried to unplug the balance lead plug and plug back in ? Sort of a reset move.
 
What is the balance lead plug? (please excuse my ignorance -- still learning)
 
There is a plug on the side of the Daly with thin wires connected to it. These thin wires in turn go to each of your cells and provide voltage information to the BMS for proper operation and cell balancing. Whenever you work on your pack ( wiring changes etc ) it is advisable to disconnect the plug as it will turn the BMS off.
 
The bms draws current while connected. What level is set for low voltage shut off? The bms could have drained the battery until it shut off.
 
The battery still has a full charge, but nothing works because the BMS has disconnected the battery. How do I troubleshoot the BMS? It disconnected after only a few minutes of use, on a nice day, for no obvious reason. The only thing that was on was the overhead fan.
 
dpdoug said:
for no obvious reason
Click to expand...
Have you checked the voltages of the individual cells? Maybe one cell is below the limit. I will assume you have checked the battery voltage.
You can check cell voltages from the “balance leads”. Its also a good way to test that they are wired correctly.
From wire 1 to wire 2, you should get ~3.25v
From wire 1 to wire 3, ~6.50.
From wire 1 to wire 4, ~9.75
... 1 to 5, ~13v. (Your battery voltage)

If not similar, then the balance wires may be wired wrong.
 
Last edited:
yes. I've checked the voltage of each cell and they are all nearly exactly the same.
 
dpdoug said:
yes. I've checked the voltage of each cell and they are all nearly exactly the same.
Click to expand...
Have you checked the balance leads? Did you install it?
This is how the bms monitors the cells. If wired wrong, the bms will detect problem and shut down.
 
dpdoug said:
Excuse my ignorance, but what are balance leads?
Click to expand...
No worries, its not what i call them, i was just following what piere was calling them. Its a loom in my book.
With a dmm you can test the cell voltages. They are all negative leads except the red wire in position 1.
7F1A8DF4-659A-4D83-A791-454C259199C0.png
 
Well, my BMS manufacturer calls them balance leads and my BMS starts with the black lead as the negative of cell #1 and the next is the positive of cell#1 and the rest are positives to the end. Of course it depends on your BMS.
Either way the wiring works but the numbering is important if you are going to try to diagnose a bad cell reading.
 
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dpdoug said:
I've already tried a reset that didn't work.
Click to expand...
Can you take a pic that shows the wiring, maybe someone can see something that will help. Its hard to troubleshoot "that didn't work".

Did you get a chance to test the voltages of cells and the things that would cause a BMS to shut down?
 
Cell Voltages:
1 - 3.284
2 - 3.274
3 - 3.275
4 - 3.273

All 4 cells: 13.1
New battery, never used. I've never balanced the battery. Don't know how to do that.Could that be a problem?

Maybe the BMS is bad, is there a way to test it?
 
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