Dead battery - diagnosis help puurrleeease !

[KirstinS]

Battery died on way home

Showed 75% so I charged it up which seemed to work just fine. Then showed 100% on the LEDs

I have tested the power lead, the battery terminal - both dead.

Then took base off and tested fuses and the power leads before the enter the fuses. Fuses fine but no power.

Next I took top off battery where BMS is. There are two negative / black and two positive red (on photo the red are at bottom and black are top right and top lef just by the plastic

If I test the top right black with either of the reds I get 41.4v. If I test the other black wire against either red I get zero v

Any ideas here ?

If the battery charged then the bms must be working , right?

 

[KirstinS]

 

[Deleted member 4366]

The thick black goes from the cells to the BMS MOSFETs, which switch off the power if anything is wrong, so with the BMS switched off either automatically (fault detection) or manually (switch on side of battery) you'll get what you found and the thick black coming out is not connected to the battery ground, so no power. The thick red normally passes straight through and is also connected directly to the charger red. The charger black is connected directly to the thick black to the cells.

The first thing to check is the battery on/off switch if you have one. It should have 36v going to it and, when switched on, returning. Check the return 36v directly on the pcb - not the connector.

Next, check the balance wire voltages. There should be a ground and 10 balance wires. If you can't find 11 wires, use the battery ground. Write down the 10 cell voltages and post them here.

 

[KirstinS]

Ah , well this battery manual on/off switch never worked. Always permantley on

This switch is connected via two thin yellow wires which end in a plug to the pcb. Here - looks a bit bashed up

 

[KirstinS]

I have unplugged the switch and tested the 2 contact points for manual switch directly on the pcb

Strangely I am only getting 28v here although still getting 41.4v on main cell wires

 

[Deleted member 4366]

Interesting. Check the voltage on each at the position where it connects to the PC. They should both be the same when switched on. Check between the cells' thick black and the yellows. The black probe can go anywhere connected to that black, but check the yellows on the pcb if you can.

 

[Deleted member 4366]

If in the end you can't fix it, you can bypass the BMS by splicing the output black wire to the incoming one. The BMS will still look after charging and balancing, and your controller will look after low voltage and high current control, so you're still covered, although you can damage your battery if you leave it connected to the controller for a long time because the controller still draws a small current when output is switched off. Tthis will drain the battery below its safe limit after a long time. Not a problem if you disconnect from the controller when not in use.

 

[KirstinS]

Ok , bit more info - and thanks so much once again d8veh - without you I'm stuffed !

So the two yellows tested against ground give 0 and 41.8v respectfully

The balance wires - only seems to be 9 which go into a single white plug

All tested vs ground an on the PCb

Black - 0.4
Brown - 0.9
Red- 1.5
Orange 2.3
Yellow 6.8
Green 11.5
Blue 20.2
Purple 22.6
Grey 30.5

The did jump about at bit on last 3 so rough middle reading is given

 

[saneagle]

Those balance wires have strange values. They should go up in steps of 4.2v. The missing ones will probably be on another small connector. Don't worry about them for now because you need 41.8v on both yellows for the BMS to give power. Check again now whether the switch is working. Maybe it works now, or it's changed to permanently off.
this me D8veh now on Saneagle's PC.

 

[KirstinS]

Thanks - still just got 41v on one of two yellow pins plugs but if I test the reverse side of PCb then both pins give 41v

Does this indicate a dodgy connection between female plug and PCb ?

 

[KirstinS]

Double checked balance wires and get same values. I did rechecked using 20 setting for lower values and 200v setting for higher.....same results

 

[KirstinS]

Right, the two yellow wired to the switch have an extension and heat shrink half way down . Here



I've been fiddling with the plug and now I get 41.8v on both yellow wires

But still nothing out of output at PCb

It seems unlikely to me that a cell is messing with the LVC as I get 41.8v readings ?

Just splice the ground and forget about it ?

 

[saneagle]

Thanks - still just got 41v on one of two yellow pins plugs but if I test the reverse side of PCb then both pins give 41v

Does this indicate a dodgy connection between female plug and PCb ?

The 41.8v is supposed to go up one yellow wire to the switch, and when the switch is on, it should come back down the wire to the PCB to switch on the main power MOSFETs. As long as the pad, where the return wire's soldered gets 41.8v, the BMS should be switched on.

Your battery is 41.8v for 10 strings of 4 cells, so each string should be 4.18v if balanced properly. They don't really go above 4.2v, so it's unlikely you've got any low ones. If you had 40.18v, one string could be down to 2.2v, which would switch off the BMS, but you haven't.

Starting from ground, you should have 4.18v, 8.36v, 12.54v, etc. Did you check with the connector disconnected?

 

[KirstinS]

To clarify I get 41.8v half way down one yellow and I now get 41.8v on the other when the switch is on. Or 0 when off

When on, and I test the underside of the PCB where the two yellows plug into I now also get 41.8v on both . I I switch off then one goes to 0

In short I think this is functioning normally from your descriptions (but may have had a dodgy connection previously)

And yes I tested balance wrong then ie with plugs out

I will try again now

 

[KirstinS]

Ah that's better - still only got the 9 leads but I get sensible answers

4.2
8.4
12.5
16.7
20.9
25.1
29.2
33.4
37.6

 

[KirstinS]

May as well give what else I have left !

Aside from 9pin balance and 2 pin switch I have

4pin connection at pcb made of 2red/2black

2 pin red plug - both read 41.8

2 pin black plug - one reads 39.2 and one 41.8

 

[saneagle]

The voltages are all correct. The last cell will be beween the last balance lead and the thick red, or the thick black and the first balance lead. Try to see if you can find it just to check because it's the one most likely to be wrong, although your total voltage id 41.8v, so it must be 41.8-37.6 = 4.2v.

Did you check that the output voltage is still zero after you confirmed that the switch is working?

 

[KirstinS]

Output voltage zero regardless of switch position I'm afraid

The first and last balance leads appear to go directly off and down the side if cell packs for about 6 inches and 1 inch respectively each side

I think the shorter goes to first cell and it reads 4.2v

 

[KirstinS]

I think I need to go for the splice trick you mention at this stage unless any other ideas ?

If so, and I read your post correctly , I can simply sun a short wire from the ground from cell to ground from PCb ,

These are right next to each other so I'd solder a jumper wire joining them. Here

Sound correct ?

 

[Deleted member 4366]

Cut the thick black wire that comes out of the BMS and solder it to the one going in, but leave the one going in connected to the BMS.