Battery problem

[Scouseindehouse]

Hi,I'm 57 from lreland and have built an ebike about a year ago now. I have a problem with the original battery a 48v 1500 w.it charges to 51v but cuts out at 47v and still seems to have lots of power. I plug it out and back in and it runs for a short time and cuts out again and again. I'm wondering if it a bms problem ..can anyone shed any light on the problem, thanks

 

[tomjasz]

Is the cutout voltage consistent? If inconsistent look for connection issue.
Do you have a controller that you can check on it’s programming?

More details regarding bike, and motor would be helpful.

Who built the battery? Case model?

Those are kinda odd BMS symptoms...

 

[Scouseindehouse]

I have another 48v battery on the bike which runs fine. The old battery will run for about half the duration it was when new. I replaced 16 cells in it which I thought were damaged. The battery doesn't seem to lose power like a battery that's empty,it just cuts out suddenly. It's a 48 v 1500 w motor brushless

 

[tomjasz]

OK I get it. We can assume you’ve tested the cells? All matching cells or a salvage pack?

 

[Scouseindehouse]

Matching cells3.7v 2.6a cells brand new

 

[Scouseindehouse]

The battery had some water damage and some burst cells . It's a triangle battery. May have had some frost damage as I didnt realise frost would be a problem and left it outside

 

[Scouseindehouse]

Actually some of the removed cells are still ok I think as they're testing at 3.5volts uncharged

 

[tomjasz]

The battery had some water damage and some burst cells . It's a triangle battery. May have had some frost damage as I didnt realise frost would be a problem and left it outside

A couple of my batteries are in a garage all winter. I’m in Minnesota and do they’ve been in -17C and colder. No ill effects.

 

[Scouseindehouse]

Ok. That's not my problem so

 

[Scouseindehouse]

Am I right in saying that the battery shouldn't cut it until it reaches about 40v?

 

[tomjasz]

Am I right in saying that the battery shouldn't cut it until it reaches about 40v?

That depends on your settings. My controllers are configurable.

 

[Scouseindehouse]

Ok. It was my understanding that the bms controlled the battery cutoff

 

[Gionnirocket]

Ok. It was my understanding that the bms controlled the battery cutoff

True.. But the controller can also have a low V cutoff
But if you have another battery working well with the motor then it's the battery.
With a Frankenstein battery as you describe... It's most likely bad cells or Damaged BMS
You should be reaching 54.6V on a full charge

 

[Scouseindehouse]

When the charger is plugged in it reads 54v but when I plug out the charger and test it, it reads 51v

 

[Gionnirocket]

When the charger is plugged in it reads 54v but when I plug out the charger and test it, it reads 51v

I'm a little unsure what you mean. What reads 54? charger or battery?
Measure the output voltage of the charger... If 54.6v then measure the voltage of the battery after a full charge.
If that is 51v then you probably have bad cells. But it could possibly be the bms not allowing the full charge

 

[Scouseindehouse]

The battery reads 54 with the charger plugged in and 51 with it plugged out

 

[Gionnirocket]

The battery reads 54 with the charger plugged in and 51 with it plugged out

Ok. Then the 54v you are reading is probably the output of the charger
Best to measure the charger when plugged in but not into the battery so you know it's output. Do you use this charger for other batteries without this issue? If so then you can eliminate the charger as the issue.
If so.. You'll need to troubleshoot the battery cells and bms. See if the BMS is outputting to all cell groups during a charge.

 

[Scouseindehouse]

Charger works perfectly on other batteries . So if I disconnect the bms plug can I test each group of cells through the plug terminals?

 

[Scouseindehouse]

Or do I need to strip down the battery to test them?

 

[Scouseindehouse]

Its 13 groupsin series so each group should be4.2v when charged?