It's a component that works like an electronic switch in the BMS. There's one for charging and a few in parallel for discharging. They're black flat three legged devices. The BMS monitors the individual cell voltages and the discharge current. The charge mosfet will switch off the charging when any cell reaches 4.2v or goes below 2.5v. The discharge ones switch off when any cell goes below 2.9v or when the current goes over the maximum. The discharge ones are on, so all the cells must be above 2.9v and with only about 34v total, it's very unlikely that one would be above 4.2v. I would therefore deduce that you have a faulty BMS.

 

One last check that you can do. Pull the multipin connector and with your black probe on the cell-pack negative (B-), measure the voltage on each pin of the connector and list them here.

One last check that you can do. Pull the multipin connector and with your black probe on the cell-pack negative (B-), measure the voltage on each pin of the connector and list them here.

 

Red 1: 33.2v

Red 2: 33.2v

Black 1: 33.7v

Black 2: 33.7v

I meant the balance leads one with 10 or 11 pins next to it, sorry. Check the voltage on the connector you pull out, not the BMS

There are 9 pins on the adjacent connector

 

Readings are as follows: -

4.0

8.3

12.5

16.7

16.7

21.0

25.2

29.4

29.4

That means that the cell voltages are:

4.0

4.3

4.2

4.2

0

4.3

4.2

4.2

0

4.0 (assuming total is still 34.4v)

 

That explains why the Charge Mosfet is switched off and your voltage is still low. If you're very lucky, the two balance wires are not connected to the cell pack. Assuming that you can't send it back, you need to follow those wires to where they're attached to the cells, You'll probably have to do a bit of unwrapping.

Thanks. I thought that might be the case

 

Hopefully it is just loose wires as you suggested. A job for tomorrow night.

 

Will keep you posted.

No loose wires.

 

Edited June 29, 201510 yr by Kramer

Is it possible to measure the voltage of the cell it's joined to by getting your probes directly on the metal ends of the cell?

It is. I'm getting 0v on all ten of the cells.

Something's not right with your measuring because 8 of the cell-strings were around 4.2v.

maybe I didn't put it right.

 

There are 50 cells altogether, in 10 strings. 2 dud strings = 10 cells.

That makes more sense them, but it's bad news. You need to take a few photos showing your measurements of zero volts, which you should show to the supplier along with the list of the 10 cell-string results. Tell them that the battery is totally bad and can't be used. Keep your statents simple, like:

 

Not possible to charge the battery.

Reason: BMS shut off charging

Problem:

Cell1 4.3v

Cell2 4.2v

etc.

 

Highlight the two at zero volts.

Can I have a replacement battery?

 

Time to name and shame the supplier and give us a link to the listing.