Another battery problem

[mw1]

Hi all.
I have a battery that only shows 18.8v at the output wires, yet when I opened it up expecting to find low readings on some of the cells, all the readings seem fine.
So, if the readings are all good before going through the BMS, does that mean the BMS is the culprit, or am I missing something?
Thanks in advance for any help.
Regards, Mark

 

[Fordulike]

View attachment 19042 View attachment 19043 View attachment 19044 View attachment 19045 Hi all.
I have a battery that only shows 18.8v at the output wires, yet when I opened it up expecting to find low readings on some of the cells, all the readings seem fine.
So, if the readings are all good before going through the BMS, does that mean the BMS is the culprit, or am I missing something?
Thanks in advance for any help.
Regards, Mark

Have you tried changing the battery in the multimeter?

 

[mw1]

Have you tried changing the battery in the multimeter?

Hi, yeah it had a new one in it, but I changed it again & checked the original,lol, all good so it's not that.
Mark

 

[Deleted member 4366]

18.8v at the battery terminals means that the BMS is switched off. If you put the smallest load on it, you'll see it go down to zero volts. What you're seeing is just leakage charge. you have to find the reason for switching off, which is normally that you have less than 3.0v on one of the sense wires.

Measure the cell voltages where the sense wires connect to the BMS, not on the connector nor on the cells.

 

[mw1]

18.8v at the battery terminals means that the BMS is switched off. If you put the smallest load on it, you'll see it go down to zero volts. What you're seeing is just leakage charge. you have to find the reason for switching off, which is normally that you have less than 3.0v on one of the sense wires.

Measure the cell voltages where the sense wires connect to the BMS, not on the connector nor on the cells.

Thanks D8veh, will do.
Mark

 

[mw1]

Hi again,
The voltages I'm getting are 4.2,,8.4,,12.6,,16.7,,21.1,,25.3,,29.5,,33.7,,38,,42.2. So can't see where the problem lies....
Mark

 

[Deleted member 4366]

You're measuring on the BMS PCB?

Can you show a picture of the BMS?

 

[mw1]

You're measuring on the BMS PCB?

Can you show a picture of the BMS?

Here is where the measurements were taken from -

And a pic of the BMS. Hope they're clear enough.
Would I be able to put 36v from another battery into the BMS to switch it on?
Mark

 

[Deleted member 4366]

No, you can't try another battery. Instead, pull out the multi-pin connector, wait 10 seconds and plug it back in again to see of it re-sets.

 

[mw1]

No, you can't try another battery. Instead, pull out the multi-pin connector, wait 10 seconds and plug it back in again to see of it re-sets.

Hi D8veh,
Apologies for taking my time to get back to you, hardly had a chance to get on with it.
Unplugging it didn't have any effect, but in the process of doing so I was getting flashes of c 42v. It seemed to be when the BMS had some pressure on it or was being slightly flexed but couldn't get it to sustain the reading. To cut a long story short I swapped the BMS for another one, and all's good Did another battery with the same symptoms too. Thanks for your help, it certainly got me on the right track.
Kind regards, Mark

 

[Lister]

I hope I'm not hijacking this thread but can't see where else to post.
I have a Monsoon fat bike with two Samsung 48 volt 12 amp batteries.
Bought the bike new last November and then added a second battery a little while later, supplied by the person I bought the bike from.
The original one is not a problem, runs for a long while up hills etc., but the new one soon shows fully charged on the inbuilt lights and charger turns off,but when I put this battery on the bike ,it initially shows fully charged on bike display,it runs for a few seconds and turns off, then showing no charge.
I have two chargers,one for each battery but swapping them round does not seem to make any difference.
The bike has only done around 140 miles and is always kept in the garage with a battery on, and spare one in the house.
Any ideas please?

 

[Deleted member 4366]

Sounds like it has some duff cells in it, though could be just wildly out of balance from prolonged storage. When the charger goes green, unplu it and measure the voltage on the battery's terminals. when it cuts out on the bike, take it off and measure the voltage again. Those two results should indicate where the problem is.

 

[Lister]

Dave,
Thank you,
I have just checked the problem battery which is showing green on charger,and reading fully charged on the inbuilt indicator lights.
There are four terminals, I assume two positive and two negative.
The readings are all either positive or negative 54.6 volts.
I will try on the bike tomorrow, and check voltages before and when it fails.

 

[Lister]

Dave,
Just been out with the problem battery , it packed up after a few hundred yards ,voltage now 53.6.
What do you think?

 

[Deleted member 4366]

Hmmm!, That's a tricky one.

First, look closely at the terminals to make sure they're OK.

Next, you'll have to open the case to see what's going on inside. The solder joints on the back of the terminals is the first place I'd check, then any other solder joint on the power wire - where they join to the BMS and the cell-pack.

After that, check that the multi-pin connector is plugged into the BMS properly and that all solder joints on that connector are good.

Finally, measure the 13 voltages on the multi-pin connector, to see if they're all equal steps of 4.12 volts . If one is noticeably less than the others, that's where your problem is.

 

[Lister]

Thank you Dave, the battery is being replaced FOC and is now with the courier company.
The company have sold over 300 off road electric bikes but have had a similar problem with some of the last batch of batteries.
Thanks again for your thoughts.