Cuts out under load, 52v battery shows 57v fully charged.

[Nealh]

A pic of any cell writing might be useful but if they are China cells they might not even be 10a capable ?

 

[Paulpmpmpm]

A pic of any cell writing might be useful but if they are China cells they might not even be 10a capable ?

That's all I can see on the cells.

 

[Paulpmpmpm]

IMHO, those cell voltages are quite acceptable and not anything to worry about. Yes, it is a little out of balance, but I'd expect that on a battery with unbranded cells, where you're taking 5.6 amps per cell. Also, there’s somthing wrong with your measuring. Those cell voltages add up to around 58v, but you were measuring as low as 52v on the output, and every time you measured the output voltage, you seemed to get a different value.

Before deciding anything, you should put a new battery in your meter and measure everything again carefully - cell voltage and voltage on the battery terminals.

Let's assume that your measurements were correct and your cell voltages add up to 58v, but you terminal voltage is only 52v. The reason for that would be what's causing your problem.

That's what I thought tbh i don't understand why I'm only getting 52.2v when all cells add up to.more individually.


What could be the reason for that? Faulty BMS?

I don't have another battery to test unfortunately.

 

[Paulpmpmpm]

To be safe you can only charge the low cell group singularly with a max 5v charger with a low 300- 500ma charge to be safe and then you have to very carefully monitor the live voltage rise for each cell group.

Oops I just finished charging the first one to 4.16 at 1ah, I'll turn it down to 0.5 for the rest.

 

[vfr400]

I don't have another battery to test unfortunately.

Your meter has a battery in it - normally a PP9 9v. That's what you should change, then do all your measurements again, not measure another battery.

First you have to determine the facts by measurement, then we can think about the cause.

 

[Paulpmpmpm]

Your meter has a battery in it - normally a PP9 9v. That's what you should change, then do all your measurements again, not measure another battery.

First you have to determine the facts by measurement, then we can think about the cause.

Oh sorry I misunderstood. I just try with a second multimeter and the readings are the same.

 

[Nealh]

That's all I can see on the cells.

They are 2600mah China cells, that's to that can be said, 9 x 2600 gives you the 23.4ah capacity.

 

[vfr400]

Oh sorry I misunderstood. I just try with a second multimeter and the readings are the same.

What’s the total voltage from the cells and what's the voltage on the output teminals? What's the same? The output voltage can't because you gave 3 or 4 different values before.

 

[Paulpmpmpm]

They are 2600mah China cells, that's to that can be said, 9 x 2600 gives you the 23.4ah capacity.

Hi sorry for late reply I have been away. I charged everything individually like you said then connected BMS back on and charged for a few hours and new readings are now :
1. 4.15
2. 4.15
3. 4.14
4. 4.15
5. 4.13
6. 4.13
7. 4.13
8. 4.13
9. 4.14
10. 4.15
11. 4.14
12. 4.15
13. 4.14
14. 4.15

And total output was 52.5v

 

[Paulpmpmpm]

What’s the total voltage from the cells and what's the voltage on the output teminals? What's the same? The output voltage can't because you gave 3 or 4 different values before.

Hi sorry for late reply I have been away.
1. 4.15
2. 4.15
3. 4.14
4. 4.15
5. 4.13
6. 4.13
7. 4.13
8. 4.13
9. 4.14
10. 4.15
11. 4.14
12. 4.15
13. 4.14
14. 4.15

And total output was 52.5v

 

[Nealh]

Voltage reading should about 57.98v so something is a miss with a reading of 52.5v.
If you take a voltage reading directly off the battery one should see an appropriate reading of 57.9v or so, if so the BMS must be faulty not to give a full reading on the discharge side.

 

[vfr400]

You're missing 5.5v!

You need to find out where it is. Measure the cell-pack voltage directly between where the thick red and thick black wires are attached, then from where the thick black attaches to the cell-pack to the positive output terminal, then keeping your red probe on the positive output terminal, move your black probe to where the thick black wire from the cell pack attaches to the BMS, then where it leaves the bms, then the output terminal. One of those five measurements will tell you where the voltgae has gone.

 

[Paulpmpmpm]

Voltage reading should about 57.98v so something is a miss with a reading of 52.5v.
If you take a voltage reading directly of the battery one should see an appropriate reading of 57.9v or so, if so the BMS must be faulty not to give a full reading on the discharge side.

You're missing 5.5v!

You need to find out where it is. Measure the cell-pack voltage directly between where the thick red and thick black wires are attached, then from where the thick black attaches to the cell-pack to the positive output terminal, then keeping your red probe on the positive output terminal, move your black probe to where the thick black wire from the cell pack attaches to the BMS, then where it leaves the bms, then the output terminal. One of those five measurements will tell you where the voltgae has gone.

Thanks so much guys it must be a faulty BMS. I'm getting 58.3 volts when bypassing the BMS. I'll order a new one and I appreciate all the help from you all.

 

[vfr400]

Thanks so much guys it must be a faulty BMS. I'm getting 58.3 volts when bypassing the BMS. I'll order a new one and I appreciate all the help from you all.

Don't buy anything until you find where the voltage drops. Do the tests I said.

There's no fault in a BMS that can cause a voltage drop. It's a bank of four switches that work in parallel, plus one for the charge control. The switches can only be on or off. Even if one was faulty, the volts would still go through the others. The only thing the complicated electronics does is turn the switches on or off, depending on the charge state of the cells and the amount of current flowing.

 

[Paulpmpmpm]

I have removed the BMS. Is there a specific BMS I need does it have to be 52v 26ah like my battery.

 

[Paulpmpmpm]

Don't buy anything until you find where the voltage drops. Do the tests I said.

Oops I already removed the BMS

 

[vfr400]

Oops I already removed the BMS

Read my post above again. I added to it.

 

[Paulpmpmpm]

Read my post above again. I added to it.

I see, do I need to solder BMS back on to carry out the tests? I had trouble following your instructions sorry.

EDIT: i keep reading your instructions and i think i get it now.

i dont have any thick black wires from the cell pack

i have 2 thick black wires that attach straight to the bms from my output connectors.

i have a thin black wire that comes from that white connecting block that also goes to the cell pack. Is that what im after? Thanks

 

[vfr400]

The wire that was attached to the pad marked B- is the negative wire that's attached to the cell-pack at the other end.

 

[vfr400]

7 tests to do. this shows the probe positions: