20s battery pack reads very low voltage (20v)

[eikido]

A friend has a 20s battery pack with BMS which he connected to some LED lamps.
He forgot to turn off the lamps and ran the battery low, but not for a long time (like a few hours).

Now it reads 20v. Wouldn't you think the BMS would cut-off of the voltage before something like this happens?

I will have it in my hands soon to open it up and measure the cell groups but I'm more curious to know why the BMS didn't do anything about it.

 

[Chalo]

When the BMS has cut off the pack, there will be a residual leaked charge across the output leads. In my experience, the measured voltage will drop steadily for as long as you measure it.

To understand what total voltage the cells have, you'll need to measure between the positive terminal and the negative cell terminal, not the BMS output.

 

[eikido]

When the BMS has cut off the pack, there will be a residual leaked charge across the output leads. In my experience, the measured voltage will drop steadily for as long as you measure it.

To understand what total voltage the cells have, you'll need to measure between the positive terminal and the negative cell terminal, not the BMS output.

Ok. Got it.
It will also not take charge.

 

[Chalo]

When the BMS has cut off the pack, there will be a residual leaked charge across the output leads. In my experience, the measured voltage will drop steadily for as long as you measure it.

To understand what total voltage the cells have, you'll need to measure between the positive terminal and the negative cell terminal, not the BMS output.

Ok. Got it.
It will also not take charge.

You may need to charge the pack at the cell connections until the voltage rises enough to put the BMS back in play.

 

[eikido]

When the BMS has cut off the pack, there will be a residual leaked charge across the output leads. In my experience, the measured voltage will drop steadily for as long as you measure it.

To understand what total voltage the cells have, you'll need to measure between the positive terminal and the negative cell terminal, not the BMS output.

Ok. Got it.
It will also not take charge.

You may need to charge the pack at the cell connections until the voltage rises enough to put the BMS back in play.

Great, thanks, will check.
I could understand if the BMS itself drains the battery pack. But not when the load comes from before the BMS. Then you would think the BMS kicks in and cuts everything.

 

[999zip999]

When you open up check the state of charge of the battery. Like this

1. 3.54v
2. 2.98v
3. 3.05v


20. Xxx volt
Voltage of battery before bms
Voltage of charger
Write it down on a piece of paper it's the only way you'll keep track of it for the future on a piece of paper.. Report back with the info