I didn't top balance my packs before installing

[Andy]

I installed my eve280ks without top balancing thinking my JK BMS would bring it into line reasonably fast. It's been 6 months and I'm not there yet. It is advertised at 2A which I thought would be plenty. When I checked what the JK is doing, it was loading its capacitors (or similar) at 2A for 45 seconds and discharging at 2A for 15 seconds. ie in reality it is only moving 0.5A and the rest is lost. So to try and speed it up I've ordered some new toys. The crocodile clips should let me easily transfer between each bank to balance in turn.

I've ordered a pack of these toothless crocodile clips and a 5 amp balancer. I'm running flexible busbars which are made up of 100s of copper strands. These should grab on nicely.

I've also programmed my victron to float when the tail current is reached. When it drops the current to allow more balancing time, it is always charging at slightly higher than the relevant tail current at that voltage. That way I know I'm not overcooking the batteries. It's amazing how quickly they raise the voltage at the end. I thought if the voltage was set at 3.45V there would be a gradual reduction in current as it approached the set voltage. Instead it keeps 120A until the last few seconds and then drop-off a cliff. I'm not sure if that is a victron thing? The JK BMS has a rudimentary time based absorb period before floating. I found that it would hold the voltage far too long hence my protection. When it starts floating,I let the balancer do its thing and keep boosting the voltage back to the float voltage when the voltage is too low for it to do its thing.




I've also been a bit confused. Generally the cells are well matched in normal use. But around 60% one cell splits off from the others and then rejoins. What could be causing this? It does the same on the charge cycle which I've attached below.

[Tinbum]

What setting do you have ? eg balance start voltage, charge voltage?

Which firmware version are you running?

[Andy]

What setting do you have ? eg balance start voltage.

Which firmware version are you running?

I haven't updated to the latest .35 number which came out last week. I think I'm still running 17. With all the bugs, I left it at 17 which has been working fine for me.

I have the balance start voltage at 3.30V. It won't start balancing until a delta of .01V. So you can see the lowest dotted line in the chart. For most of It only starts balancing near the very end even though I have 3.30 set. It will be balancing during that weird split I have at 60% SOC as well.

The purple line at the bottom is the delta between max and min cell.

[Tinbum]

What is the charge voltage you have set (RCV) ?

[Andy]

I recently changed the balance start to 3.30. This is out of date now. It has been balancing as I have my current meter round the wires. its just not very effective.

[Andy]

Deleted link

You can see here. It bleeds off the highest voltage cell and loads the capacitor. Eventually it discharges to the lowest voltage cell.

[Tinbum]

I set my balance voltage at 3.36v which is what pylontech start at. Too low and it takes them out of balance.

It will take some time to balance them and you need to leave them floating for a good long time- maybe even a full day. I had my RCV initally set at 3.45v and left them their until the voltage difference came down. I then raised it to 3.5v did the same and then to 3.55v. I had to change the AH capacity setting a few times to reduce the SOC to get the inverter to keep on charging.

[Andy]

I set my balance voltage at 3.36v which is what pylontech start at. Too low and it takes them out of balance.

It will take some time to balance them and you need to leave them floating for a good long time- maybe even a full day. I had my RCV initally set at 3.45v and left them their until the voltage difference came down. I then raised it to 3.5v did the same and then to 3.55v. I had to change the AH capacity setting a few times to reduce the SOC to get the inverter to keep on charging.

Ok thanks, So more time required then. They don't actually balance most of the time because they are well balanced during most of the curve. I'll have a go when I'm not paying a fortune for the electricity. ie, the sun is higher than 20 degrees above the horizon.

[Tinbum]

They will only balance at the higher voltages due to the charge voltage curve of the batteries. At normal voltages you just can't see the imbalance, which will be there.

Remember to lower the voltage back down again after you have balanced them.

[Andy]

https://share.icloud.com/photos/0e3bWjk ... q3vnXm34Yw

You can see here. It bleeds off the highest voltage cell and loads the capacitor. Eventually it discharges to the lowest voltage cell.

It is unbalanced at low voltages here because clipping my charger on to the cell bumped the terminal and loosened the nut. It took me a few hours to work out why I was getting random voltage spreads when I didn't normally have any Luckily I don't have a huge charge or discharge current at this time of year.