52V battery issues.......need ur help.

Hi all. Ive got a 52 volt battery (shark) that's Chinese and bought from ebay. The first week of usage it charged till 58 volts like it should and everything was fine. After a week it will only charge till 55 volt. I tried 2 different chargers and get the same result. Could a cell have died? BMS maybe?

Bad cell more likely, trying to charger higher than it can accept is dong no good

+1 on the bad cell. Can you get to the bms wiring to test the voltages of the cells groups?

e-beach said:

+1 on the bad cell. Can you get to the bms wiring to test the voltages of the cells groups?

Click to expand...

good idea.... I was wondering what was the best way of narrowing it down and yes I do have access to the BMS wiring.

ok, the proper sequence for testing the cell groups through the bms goes like this:

1: always take extra caution not to short anything out as it is possible to blow something if you do.

2: Make sure your pack is fully charged and balanced. (or as charged and balanced as possible.)

3: connect the negative probe of your meter to the black wire on the bms and then the red probe to the wire next to the black wire.

4: write down the voltage.

5: move the red probe and the black probe over one wire. The black probe is no longer metering the black wire. It is now metering the wire next to the black wire.

6: write down the voltage.

7. keep repeating the process of moving both probes over by one wire until you have finished all the wires and have written down all the voltages.

Let us know what you end up with.

Battery is a 14S4P config. I suspect each 14S should measure around 13 volts or so correct? If so then one of the 14S banks will read 3-3.5 volts less letting me know where the dead cell is correct? Thanks for ur info BTW.

What you are looking for is the parallel groups of 4 cells. So you are looking for a group of cells that are 4.2v fully charged. You should have 14 or these groups. Unless your bms balances lower then 4.2v. (I am also assuming you are running cell chemistry that charges to 4.2v.)

So, if you have a fully charged and balanced battery, you should have 14 numbers to report. They should all be the same. Somewhere around 4.2v. If one of the numbers is lower then the others, then you have found the group with a bad cell.

14S is 50-52V charged at rest, ~58V charging setpoint.

Subtract ~3.6V for 13S

But usually parallel fist at the lowest group level, if so that will mask, only show up in a capacity test of each group.

john61ct said:

14S is 50-52V charged at rest, ~58V charging setpoint.

Click to expand...

No, 14s is 58.8v charged, at rest. (assuming 4.2v per cell end of charge / balancing point)

The "52v" is the "average" voltage of the pack, at about half full. (or half empty, depending on your POV)

Charge to 4.1Vpc no CV absorb would be my normal-cycling Full.

Remove the surface charge, say half a % of capacity, and then sit 24hrs isolated, what will OCV read?

john61ct said:

Charge to 4.1Vpc no CV absorb would be my normal-cycling Full.

Remove the surface charge, say half a % of capacity, and then sit 24hrs isolated, what will OCV read?

Click to expand...

You'd have to check the spec sheet for your specific cell to see what half a percent of capacity equals, when starting at your chosen termination voltage. Then multiply whatever that remaining voltage is by the number of cells in series.

Separately, if your cells drop in voltage sitting there, there is something wrong with them, or they're connected to something that is draining them.

A good cell will remain at the voltage it is charged to; it shouldn't have any significant (or even noticeable) self-discharge.

In my experience with other chemistries settling at rest after charging is normal, as is bounceback after a load.

Some require more than 48hrs isolation between measures when building a V vs SoC correspondence chart for that model.

I guess the LI used here are different.

OP - you are thinking about this in the wrong way. You are not measuring four, 14S groups, you are measuring fourteen, 4P groups. Parallel adds amps, series adds volts.

The numbers will be additive, ie 4.2, 8.4, 12.6, etc. Important to write these down as there will be some minor fluctuation, and maybe a major one. That big one is the one you are looking for.

4.2, 8.3 (this measures a 4.1, second group), 12.5, then 16.2, instead of the expected 16.7. The fourth group shows a charge of only 3.7. That is a problem. Check all four cells and replace the bad one, or more. You may be able to obtain a matching cell from your vendor under warranty.

Or not.

You will likely see a much larger discrepancy than that listed, or perhaps more than one. Check ALL strings, post ALL numbers, as originally measured. Doing it twice and verifying all numbers, also a new battery in the voltmeter, is not a bad idea. While I have only shown one digit after the decimal, you should have two.

Thanks for the insight guys.