how to interpret this data? something is not working

[want to build]

Voltage means almost nothing.

If you want to futz with it, test using my #3 post to see whether or not you wasted your time.

Keep doing it to see if its health is declining.

Ideally you would do it for each cell before re-assembling your pack, and

more precisely with a proper CC dummy load.

is the third post you talk about Discharging to 0% will very quickly murder even a top quality pack, every LI chemistry with LTO as the sole exception.

Certainly if you define 0% as dead flat.

The **average** DoD% over the battery's life has a huge impact on cycle lifespan, a much stronger factor than the charge-termination voltage.

(Using at-rest isolated voltages here, those under load are meaningless. Also assuming other care factors well-coddled.)

If you are using the maker data sheet minimum voltage, say 2.5V as your 0%, just going up to 3.0V can double or triple lifetime.

And 3.4V or 3.6V double or triple again.

And just like avoiding the top voltage shoulder, the sacrifice of capacity utilisation is not significant.?

 

[ZeroEm]

If you are using the maker data sheet minimum voltage, say 2.5V as your 0%, just going up to 3.0V can double or triple lifetime.

You keep looking right over the information. Look up your cells and find what 0% SOC (State of Charge) is for your cells. most cells it is 3V or it could be 2.5V but when a cell is 0V it is no longer usable or safe to use.

There is a lot of threads on batteries here, they are worth reading.

 

[want to build]

If you are using the maker data sheet minimum voltage, say 2.5V as your 0%, just going up to 3.0V can double or triple lifetime.

You keep looking right over the information. Look up your cells and find what 0% SOC (State of Charge) is for your cells. most cells it is 3V or it could be 2.5V but when a cell is 0V it is no longer usable or safe to use.

There is a lot of threads on batteries here, they are worth reading.

sony vtc4 are 2.5 rated. the 4 cell at 0 will be discarted.
the battery never served. Are you saying that even though the 11 x2 cells are showing 3.5 volt they have to be tested? i feel if they were faulty the voltage would show 3.5 . i dont get why the 11x2 cells could be a problem can you tell me?

 

[john61ct]

I don't know why you are talking about 0%, not relevant to what I'm talking about here.

Use 3.5V as your definition of 0% if you like.

Also learn to quote properly, not mix up your words and those you are quoting.

 

[ZeroEm]

by want to build » Sep 01 2021 6:16pm

Greendog wrote: ↑Aug 31 2021 8:52pm
totally get wanting to build bike with minimum expenditure , but somethings are worth spending on,
a good battery is the heart of a nice ebike , 2p pack of different cells not great ,I'd put cost of repair towards a new pack with plus points not having do soldering and increased safety of new pack also more power and range = more fun

it is a test battery mostly to test my new motor and how it goes up the hills.
changing the 4 cells would be less than one hour. it know it would be a tiny capacity but it is a test to also tels test my setup on bike and wiring. ... so since i already have 4 spare cell do you think replacing them would allow me to have a tiny workable battery?

1. You battery pack is not big enough to test motors going up hill, you are just killing the battery.
2. You say you want to test, start with the battery cells.
3. If I remember you have been trying to charge this battery and the Cells are only at 3.5V. I would say they are all dead if they only charge to 30%.
4. So when you put in new cells in two groups only, what is going to happen when the battery does not charge. Test the motor on the hill because the motor turns now?

 

[docw009]

As I understand it, OP has a 13S-2P cell showing 39V max on his charger. When he checked the voltage, 11 groups are around 3.5V, and two are 0V. That would match what his pictures show.

Those two cell groups are killed. Yes, you could unsolder them and splice in 4 replacements. What people are warning you is that unless you know why those two groups discharged, the replacements could die too, The easiest explanation is that your BMS drained them, either because it uses those cells to power itself, or it developed a fault. Another possible explanation is your soldering started them off on the road to failure.

I'd pick a scientific approach. Replace the four cells. Bring the battery up to full charge. See what you have. If everything is 4.2V, that's good. If you have scattered readings, well it's a junk pack. Then let the battery sit, with the BMS balance cable disconnected, and see how it self discharges after two weeks. If it holds, that's good. Reconnect the balance cable and see what happens.

And if it wasn't made clear in the other threads, I don't think a 48V controller will power up on 39V worth of battery.

 

[want to build]

As I understand it, OP has a 13S-2P cell showing 39V max on his charger. When he checked the voltage, 11 groups are around 3.5V, and two are 0V. That would match what his pictures show.

Those two cell groups are killed. Yes, you could unsolder them and splice in 4 replacements. What people are warning you is that unless you know why those two groups discharged, the replacements could die too, The easiest explanation is that your BMS drained them, either because it uses those cells to power itself, or it developed a fault. Another possible explanation is your soldering started them off on the road to failure.

I'd pick a scientific approach. Replace the four cells. Bring the battery up to full charge. See what you have. If everything is 4.2V, that's good. If you have scattered readings, well it's a junk pack. Then let the battery sit, with the BMS balance cable disconnected, and see how it self discharges after two weeks. If it holds, that's good. Reconnect the balance cable and see what happens.

And if it wasn't made clear in the other threads, I don't think a 48V controller will power up on 39V worth of battery.

Hi ok i understand the situation better now. on top of replacing the cell i will change the link from them to the other neigboring cells. i appreciate that you confirme that this way of doing is possible and can still be tested because unsoldering all cells takes a while . ill check what my remaining cells look like . we keep in touch.

 

[want to build]

I gave you a link to my post in the old thread with specific suggestions.

Ask there if you are unclear on any details

Voltage by itself tells very little

hi
the link when i click it brings me back to how to interpret this data? something is not working is this what youre talking about?

The link should be going directly to my post #3 of that thread.

i see it now tx