Help troubleshoot battery overvoltage Renogy SCC

[metalheaddoc]

I just put together a renogy 400W premium kit that has a Rover 40a MPPT controller. It is hooked up to a Wiese 12v 100ah LiFePO4 battery. Within 30 seconds of hooking up the panels, I get a battery overvoltage error and the voltage reading on the SCC goes up to 17-18V. I confirmed that voltage at the battery terminals. The SCC is set for 12v and Li battery type. I have the panels in a 2s2p setup, but the error also happens with a single panel. I checked the stats on the 2s2p and I get 44V and about 8-9a before the shutdown occurs. I have put in a support ticket with Renogy, but I wanted to know if you guys had any ideas. This is my first build.

Jason

 

[sunshine_eggo]

A LFP battery BMS engaging over-voltage protection cuts off the charge. Imaging if you're climbing a steep hill in a car, and and axle breaks. Before you can react, the engine will rev very high. The SCC is unable to react quickly enough to prevent over-voltage due to sudden removal of load.

Recommend you try lower boost voltages starting at 13.8V and incrementing by 0.1V until you can replicate the problem. If the MPPT functions at lower boost voltages but not higher ones, that's indicating an issue with imbalance within the battery, not an issue with the MPPT.

 

[12VoltInstalls]

^^^that’s pretty smart testing right there.

The other thing that can do that symptom is a poor connection. I’ve seen it a few times from boat alternators to Jeeps with winches, to my solar system (with failing MC4s).
With my solar I would have basically no production for long periods and then a huge spike and the SCC would fault.

So if it ain’t electronics related I’d look at the connectors and terminals, etc.

 

[sunshine_eggo]

^^^that’s pretty smart testing right there.

The other thing that can do that symptom is a poor connection. I’ve seen it a few times from boat alternators to Jeeps with winches, to my solar system (with failing MC4s).
With my solar I would have basically no production for long periods and then a huge spike and the SCC would fault.

So if it ain’t electronics related I’d look at the connectors and terminals, etc.

Yep. I'm getting senile. The first step in chasing any "weird" voltage or current issue is, "check all connections."

 

[12VoltInstalls]

Yep. I'm getting senile. The first step in chasing any "weird" voltage or current issue is, "check all connections."

Are you?

I was just remembering the few weeks I chased my tail with voltage spikes and almost no charging only to find it was corrosion in the MC4s which I’d never imagined could happen. At first I thought it was my walmartha battery bank but it wasn’t (I’m still running them).

 

[metalheaddoc]

I did some additional testing. I connected my PV panels and battery directly to the SCC without circuit breakers or bus bars. The connections were solid. I still got the overvoltage error with both a single panel and a 2S2P setup.

Next I will try cutting the boost voltage down to 13.8V as suggested above.

I will report back.

 

[metalheaddoc]

Clouds rolled in so I can't test today. I will report back.

 

[mikefitz]

I suspect you have one a number of issues.
Firstly there is a good chance your low cost battery has unbalanced cells and at the Renogy default charge volts of 14.4 is causing cell overvolts and disable of the charge path. This would normally occur after charging for some time.
Secondly the BMS will shut down on over current, with a battery maximum of 50 amps and 400 watts of solar thats unlikely.
Thirdly the Renogy controller is malfunctioning. There have been numerous reports of issues with Renogy solar controllers.

Cell overvolts seems the most likely and often occurs when the charge voltage is in excess of 13.8 volts.
Do you have any idea of battery volts just before the error message occurs?

Mike

 

[metalheaddoc]

It looks like changing my Boost voltage down to 13.8V has solved the problem. I will continue testing and report back if there are additional problems. Thanks to all who gave advice.

 

[sunshine_eggo]

This likely confirms the BMS being the culprit.

 

[metalheaddoc]

I don't really understand the settings. If I leave it at stock setting which I think was 14.4, does that mean the SCC was trying to feed the battery at 14.4V and the BMS freaked out and shut down? But the BMS is happy at 13.8V? What does that mean for me in the real world? Does the battery take longer to charge at the lower Boost voltage or something like that?

 

[12VoltInstalls]

Does the battery take longer to charge at the lower Boost voltage or something like that?

14.4 / 13.8 = 4.3.% different so guessing 4% longer

 

[sunshine_eggo]

I don't really understand the settings. If I leave it at stock setting which I think was 14.4, does that mean the SCC was trying to feed the battery at 14.4V and the BMS freaked out and shut down?

"Freaked out" = sensed a single cell over-volt issue and engaged over voltage protection.

But the BMS is happy at 13.8V?

It would seem so.

What does that mean for me in the real world? Does the battery take longer to charge at the lower Boost voltage or something like that?

Charges will take longer and be at lower SoC.

Also recommend setting float at 13.8V (or 13.7V if it has to be lower).

Hopefully over the course of several days/weeks, the BMS will balance the cells to the point that they will charge to 14.4V without incident.

In a week or so, increase by 0.1V until you observe the over-voltage issue again. Back down to the highest voltage it will tolerate and check again in several days.

If you have a charger or power supply that can provide 13.8V constant voltage, that would help expedite things vs. relying on solar to get you there.