Yesterday Epever MPPT started overcharging 48 volt lifePo4 battery after 2 months of use???

[digitalsteve]

Lots of helpful info on this forum, so maybe someone has an answer for me.

My cargo trailer system has been running fine for about 2 months, but yesterday I noticed the inverter trips off for high voltage for a second, once the batteries reach 54.5 volts (.5v above my charging limit voltage setting). The inverter is 60v max, and I watched the voltage reading on it (and another voltmeter) spike above 60v just as the MPPT toggled back due to the battery voltage above 54.5v (my Over Voltage Disconnect Voltage). Previously, it was always lowering the output at exactly 54v.

The inverter comes right back on, but then goes through the same cycle about every 5 minutes. When I disconnect the MPPT, then the inverter will run for hours without interruption.

When I "read-in" the MPPT parameters, they had reverted to a 12v, which make no sense, So I reloaded the ones I saved for the 48 volt batteries. Did not fix problem.

I seems like the MPPT is skipping the charging limit voltage setting of 54v and but does shut off at 54.5v (overvoltage disconnect setting). The battery is in parallel with the MPPT at the Inverter, so the spike must come from the MPPT? My panels (6 parallel- 435 Watt Sunpower Solar Panels 128 Cell) output voltage is usually between 65v and 75v (VOC 86.6).

Bad MPPT?

 

[snoobler]

Do you have your SCC attached to our inverter input with alligator clips?

If so, that's horrible. They should be direct to the battery. It may not have anything to do with your issue, but it's just bad practice. It may be the cause.

To get a spike, the SCC would need to supply a fairly large surge of current.

Are you seeing this in conjunction with a large load cycling off?

 

[digitalsteve]

The alligator clips are a temporary hook up for a small 48v 5" cooling fan and have a small fuse in line.
No load was cycling on and off, there was about 10 amps charging the battery.

 

[Semoreo]

I had something very similar happen to me with a powerwall I built for myself. My inverter charger would discharge and charge just fine until the batteries got near full. Then did did exactly what your charger does. The voltage would spike triggering an over voltage protection circuit and shut the whole thing down. I could reset the inverter which would see fully charged batteries and got straight into float mode. This cycle would repeat everytime it would try to charge the batteries or top them off.

Turns out my battery bms's didn't like the near max voltage they were seeing before the charger switched to constant voltage mode. One or more of the bms's would internally disconnect the charging current to protect the battery cells. Since the charger was still supplying the full current when one bms tripped, it increased the supply to the other 3 battery banks. I actually saw my breakers protecting the batteries chain trip after that which tipped me off to the issue.

I had two flaws in my system that I had to correct. First was an active cell balancer so that one cell group within each battery bank didn't hit full voltage too early. Second was increasing the cells in series to better match my charger's charging profile. I went from 13s 48v to 14s 48v. I had to buy all new bmss but it solved it and matches my charger's sweet spot better.

Tldr: check your batteries cells to make sure they are balanced correctly, if you can. Dial your charging voltage profile back a notch so it doesn't trip the safeties in them. Might only be one battery causing the problem. You could charge each one individually to check them.

 

[digitalsteve]

Thanks for your reply. I will try backing off the charge voltage on the MPPT to eliminate or prove the high cell volt possibility. Note: My inverter only inverts, does not charge and the batteries voltage meter never dropped in voltage, (but it might have a slow response). The other thing, is the MPPT is currently set to stop charging at 54v and has been doing that until yesterday. Now it keeps charging until 54.5v, which is when the inverter trips off and on.

 

[digitalsteve]

It appears my problem was a programming error. In the battery advanced settings, I had programmed my desired settings into the MPPT via blu-tooth and saved to the controller. Then read them to verify they were correct. Then when to standard setting page and noticed that the battery type was not Lifeo4, so I changed it and saved to the controller. Then read them to verify they were correct. What I didn't know, is choosing the Lifepo4 in the standard screen over-wrote all of my custom settings in the advanced screen,. Much higher voltages for charging than recommended for my cells.