BMS /w Fuel Gauge wiring

[Deere John]

I have problems with new battery pack. I think it might be the switch on the battery. There are a fuel gauge and two switches. One for power and one for rear light. The switch for rear light doesn't work anymore (stucked). And when pushing the power switch it doesn't switch the circuit on.

It worked for a few days, the power goes on and it indicates on the fuel gauge. And the output gets 36V. But it started working worse and worse and now it doesn't work at all. I wanted to remove the whole fuel gauge circuit, replace the switches with new ones.There are four wires, red, black, two whites. To this PCB. But what are those white wires for? I can't understand it really, have measured also voltages from 10V, 25V and 35V and the switches are most probable 2x DPDT so I don't dare just trying something here unless I know what I am doing.

As I can see it is wired like this:

Can anyone please explain how this gauge-PCB is wired so I can replace this with two standard switches?


(Here is also a photo of the full bike)
http://www.pedelecs.co.uk/forum/attachments/elcruiser-batterifix-jpg.11007/

 

[Deleted member 4366]

You only have to worry about the main PCB. You can chuck the rest. The photos don't show everything, but my interpretation is that it's a standard BMS with a manual override switch to switch on/off the output FETs. It must be the white wires that go to that switch. The FETs are activated by a line of about 12v, which will be active when all the cells are within the correct charge range. The swoswitch probably interrupts that line.

The thin red and black wires power the test LEDs and the rear light. You can re-wire them however you want as long as there's no danger of them shorting.

When the battery is fully charged, it should be nearly 42v. If it isn't, you've probably got defective cells, which will switch off the BMS.

 

[Deere John]

OK, so I isolate the black/red (for now when I don't ned light anyway) and then put a SPST switch on the white Wired. Ie the white wires shorted activates the output FET's? Sounds like the most logical choice yes.

 

[Deleted member 4366]

That's what I would do. I'm sorry that you've had a problem so soon after building your bike. Let us know if it works after modification.

 

[Deere John]

Ok, I tried with a switch now, like this:

It didn't work! (I have 36,5V in the pack now, can try charge it tomorrow)

 

[Deere John]

Anyway, thanks for answer! Yes it's really a shame that it didn't last longer than a week the pack was seriously clumsy soldered, just hope something hasn't broke.

 

[Deleted member 4366]

Check the voltages on the sense wires and list them here.

 

[Deere John]

I measured with Com-lead on the red wire and the Black lead on each of the two white wires.

OFF: 10V one side, 35V other
ON: 25V on both

 

[Deere John]

...aha, you mean on every cell. Hmm that will be good. I'll measure that later. Thanks

 

[Deere John]

I did some measuring and found that the balance (sensors) connector was not really in location. I had noticed that before and put melt glue there but now it has become bad again. So... I pushed it in a little and then the BMS works!! I actually noticed that when charging, it wouldn't charge either.

So there was many connection faults here.

(earlier: the Red in the output connector was loose! one of the balance sensor wires was almost broken in one place and in the battery end it was loose! shitty building!)

Glad I found this now, now it might work a few days more


Here is a photo of this gauge-PCB:

And a photo of the BMS-PCB with this glued connector to the left. Notice now when I have the PCB screws of it's a little to the right, when I screw this in place the sensor wires strain and the connector gets out.

(the blue thing to the right is a 5VDC-converter for a USB-charge port. It is connected to Red and Blue)

The voltages I measure now are:

1. 3,646
2. 7,290
3. 10,94
4. 14,58
5. 18,23
6. 21,87
7. 25,52
8. 29,16
9. 32,81
10. 36,46

 

[Deleted member 4366]

For the BMS to give power, each of the 10 points where it measures the cell voltages must be above 2.9v. For the BMS to allow charging, they must be in the range 2.9v to 4.2v, so any problem with the multi-pin connector will stop charging as well as discharging.

You don't need to screw down the BMS. It has very little mass and it's held by the wires. If you want a bit more security for ir, you could hold it still with gaffa tape.

The cell voltages all look good.

 

[Deere John]

It's screwed in a cooling plate so the FET's are attached to that plate. I'll have grind off one millimeter somewhere to fix this good I think

Yes the lowest one are 3,34V (cell2), cell 1 is 3,95V and the other ones are 3,64-3,65V so the first two out of balance a little but that might settle after a few charges I hope.

 

[Deleted member 4366]

Based on the voltages you gave above, they're all between 3.60 and 3.65. How did you get 3.95v?

 

[Deere John]

Based on the voltages you gave above, they're all between 3.60 and 3.65. How did you get 3.95v?

you're Right. I had put wrong number in my Excel-sheet. Now everyone is 3,64-3,65. Great.

 

[Deere John]

Yes!! Finally done with everything (had to fix a problem with the motor wheel also).

I managed to route the sensor wires behind the BMS so I gained a few mm so the sense connector actually went in full! Also some melt glue to secure.

The switch is positioned in the hole for the fuse holder (see right in photo). Perfect fit! (the fuse is not soldered anywhere anyway so I just removed it)

Went out for a test ride 20 km in various terrains. Works like a charm! Thanks for help d8veh. Now my commuting vehicle is in function again!

 

[Deere John]

Just noticed this thread also, have now made better schematics of the electric circuit in both main and battery pack. Thinking about building my own battery pack with good quality cells and maybe another BMS.

Thought it would be appropiate to post here also. There is also PDF in another thread:
http://www.pedelecs.co.uk/forum/threads/kunteng-electronics.20920/#post-277555