Charging problem! Did I screw up?

[Mark44]

I do not see this particular problem in any thread so here goes!

I just received my bench top power supply. I put all of my cells in Parallel to start out, and things seemed to go fine. I was charging at 3.4v and about 10.4A

Charging was taking place as my starting voltages on the cells was 3.01, 3.08, 3.09, and 3.10. After about 5 hours, the cells look like this: Cell1 3.238, cell2 3.227, Cell3 3.234, and cell 4 3.236. All in all fairly close. I put the cells back together in series, and put the BMS on (bluetooth xiaoxiang software controlling).

I have set my power supply to ~14.3V (dead open, no load), then connected and turned on the BMS. That is where I got my reading shown earlier.?

Now the sticky part. as soon as I turn on charging Cell 2 jumps to over 4V! The amperage swings wildly between 0 and 10.5 and every time the BMS tries to restart the charging, it soars again (the voltage) amperage drops, and it appears to go into overvoltage protection (I think). The other cells remain and the amperage is appropriate to charging (10.5 or so)

Any ideas on what happened? How can I test to see if the one cell is a runner, or if I have an issue with my BMS? I am going back to Parallel charging for now since that doesn't seem to hurt the cells. Indeed the cells seem to have balanced quite well in the short time they have been charging in parallel. Although that may be an illusion at this point.

I really need the brain trust here to come through with some sage advice, as this is my first LIFEP04 pack, and I do not want to repeat any errors I might have made. Thank you in advance for your time.?

 

[Bob B]

Not sure why you didn't let the parallel top balance continue til the cells were balanced.

There are 2 settings in the BMS protection that determine the high voltage disconnect level and the level when it will return to charge. The are in the protection area and are they are the .... cell over voltage... trigger value and release value.
You might be able to get the the cells to balance in series if you change that return value to 3400 mv and change the setting that requires the pack to be charging in order to balance ....... return these setting to normal after the balance is complete.

Did you attempt to clean any oxidation off the bus bars and terminal tops? It is also good to wrap emery cloth or very fine sandpaper around a flat block to make sure things are perfectly flat. It sounds like you may have some bad connections right now.

You may have to put them back in parallel and finish the top balance that way.

 

[Mark44]

Not sure why you didn't let the parallel top balance continue til the cells were balanced.

There are 2 settings in the BMS protection that determine the high voltage disconnect level and the level when it will return to charge. The are in the protection area and are they are the .... cell over voltage... trigger value and release value.
You might be able to get the the cells to balance in series if you change that return value to 3400 mv and change the setting that requires the pack to be charging in order to balance ....... return these setting to normal after the balance is complete.

Did you attempt to clean any oxidation off the bus bars and terminal tops? It is also good to wrap emery cloth or very fine sandpaper around a flat block to make sure things are perfectly flat. It sounds like you may have some bad connections right now.

You may have to put them back in parallel and finish the top balance that way.

So, to answer your first question, I wanted to see if the "runner" condition was still present after balancing (to some degree) the individual cells.

I am now using the parallel method to continue balancing, since the one cell went overvoltage immediately, and kept interrupting the charging cycle.

I guess my best bet is to continue to balance this way, making sure that I can reach 3.6V and then recombine the cells in series.

I suppose it would also be good to reset all settings in the Android app to factory if that is possible. I do also have a desktop app that I will try and assemble when I get closer to the top balance.

My bus bars are clean and free of oxidation. I filed and sanded to be sure. The terminals are clean also, though I did not subject them to sanding yet. As I said when I disassembled the cells from parallel, they all showed fairly close voltages, and I think that is what is throwing me. Why would one cell react like that, going into overvoltage right away, while the others do not?

 

[Bob B]

I have the Iphone version of the App..... with it, it is possible to save various configurations and name them so you could load them back later if you want.
I saved all the original settings .... and a couple of others. 1 of them I set up for aggressive balancing.

Just be aware that any time you write a parameter change, it will reset the SOC to a guestimate based on pack voltage and won't work right til the pack is full charged.

I'd wait to worry about the runner cell til you have done a full top balance ....just make sure to always adjust the voltage before you connect the supply and then don't touch it again.

 

[Bob B]

Also ... once you get them to full charge, disconnect the power supply and let them sit for 24 hours before re-doing the pack in series.

One pretty knowledgeable user on here found a cat hair under one of his bus bars that was creating a big problem .... so, it doesn't take much to mess up the connection.

 

[Mark44]

Also ... once you get them to full charge, disconnect the power supply and let them sit for 24 hours before re-doing the pack in series.

Once pretty knowledgeable user on here found a cat hair under one of his bus bars that was creating a big problem .... so, it doesn't take much to mess up the connection.

That sounds about right....

A cat hair huh? Well I guess I'm lucky I only have a dog!

I have tried to make sure the posts are clean and the pads under them as well. It seems to be doing fine on a parallel basis, so I am going to leave them alone until 3.6v or so is reached.

Thanks for your tips. I will respond here once I get to 3.6 or so.

 

[Luthj]

If you are seeing a cell jump from 3.2 to 4V right when you start charging, that indicates that you have a high resistance connection on that cell. Check your bus bars and fasteners. If necessary use some 600 grit sandpaper and a flat surface to polish everything.

 

[Mark44]

Thanks for this. I have checked, but I will do so again, as it is quite possible I missed something!

 

[Luthj]

If you haven't also confirm the BMS readings with a volt meter directly. Poor connections at the BMS can cause odd behavior sometimes.

 

[Mark44]

Now that is something I did NOT consider. Going to check both that and cleaning the contacts this evening.

Thanks everyone!