Battery overcharge

[howieb]

My renogy rover MPPT has been showing my 12v 100a has a maximum battery voltage of 24.8. This is an intermittent issue. Most of the time everything is fine but there are a moments when the rover blinks and the error code says battery overcharge. But moments later its back to normal. Sometimes the history on dc-home and renogy bt shows this as the maximum daily voltage. This seems to only happen when the battery is "full" and on the boost charge during low amperage, or would be if it was charging. Because it is so intermittent, I can't take a voltage at the battery.

The setup is a battery, a mppt, and panels with no load.

I've moved and am just setting up the system, and just got 2 new LI Time 12v 100a batteries. I was charging and testing my new batteries. At first I thought it was the battery, but it happened on all four batteries I have, 2 new litime and two older renogy.

I thought is was the brand new out of the box renogy rover 40a MPPT. I changed the MPPT to the old rover 30 I had from the old house. It still does it.

I checked the battery connections and the cables from the MPPT to the battery, even removing and re-attaching them.

I replaced some sticky connectors on the solar panel cables.

I switched from my Aqua Blu 325 solar panel to 4 renogy 100 watts in series and it still does it.

It does it at night, and seemingly when the panels are disconnected. Once again, this doesn't happen if the batteries are not full. Today I have a history of a 28 maximum watts and 24.8 volts, but I disconnected the panels last night. The battery voltage is 13.2

Any ideas what this is and how to fix it? This didn't happen in the old setup at the old house with the 30 amp MPPT, the 2 renogy batteries in parallel, and the 4 100 watt panels in series. I am assuming my battery BMS prevents any real damage.

Thanks in advance,

Howie

 

[mikefitz]

Any ideas what this is and how to fix it

What may be occurring, is the battery BMS entering protection due to cell overvolts, this opens the charge path. The solar controller cannot respond fast enough and a voltage surge occurs. Cell overvolts is most likely to occur when the battery is in a high state of charge.
It's probable that if there was a load on the system , some of the surge would be absorbed.

Suggest you lower the charge volts, boost volts, to a lower voltage. Try 13.8 volts as the boost volts.

What are your charge settings at the moment?

Additional comments.

4 Renogy panels in series may exceed the 100 volt Input limit of the controller. Voc is 24 volts and increases by 0.3%/deg C below 25 deg C.

 

[howieb]

 

[Frugal Devonian]

BMS reading a different voltage than the charge controller?

 

[Frugal Devonian]

I've got a renogy 60a and that reads voltage higher than everything else I've got connected.

 

[howieb]

4 Renogy panels in series may exceed the 100 volt Input limit of the controller. Voc is 24 volts and increases by 0.6%/deg C below 25 deg C.

I wondered about that when I first set this up. These older renogy solar panels have a VOC of 21.6 volts X 4 = total of 86.4 V. I figured this was ok. I lived in the Mojave Desert and I kept an eye on the voltage, it never got near that. Now I'm setting them up in the Oregon sunless winter and it's much colder but no real sun even when its sunny.

but 0.6 %/deg is a lot more than I thought.

 

[mikefitz]

0.6 %/deg is a lot more than I thought

My error, a mistype. It's around 0.3%/deg C. Now corrected. You should be OK with the older panels, it's the newer with the 24v Voc.

Reduce the charge volts, float is far too high. Try 14.2 boost and 13.5 float. Equilisation equal to boost volts.
Boost duration 60 minutes.
If the issue is not solved, reduce boost to a lower voltage and increase boost duration.

Verify with a voltmeter if possible, Renogy voltage calibration is poor and the actual volts can be higher.

 

[alcook62]

I've got a renogy 60a and that reads voltage higher than everything else I've got connected.

I've got the Midnite MNMPPT60DIY, a Renogy Rover 60 clone (SRNE made I believe), and can confirm you are not alone in that regard. My SCC constantly reads .2 volts over my DMM, my Midnite 200 classic, and my inverter. I wish I could calibrate/fine-tune this. The Midnite 200 has a sub-menu (Tweaks) that allows this, but the Midnite 60 DIY doesn't.

P.S. I like your Led Zep IV avatar!

 

[wpns]

I've got a renogy 60a and that reads voltage higher than everything else I've got connected.

Does it read higher than a decent DVM connected across its terminals? If not, you may have wiring issues, 60A is a lot...

 

[alcook62]

Does it read higher than a decent DVM connected across its terminals? If not, you may have wiring issues, 60A is a lot...

I believe Frugal Devonian is referring to the Renogy Rover 60, a 150-volt 60-amp solar charge controller. But yeah, if it does indeed display a difference of 60a, that is a lot!

 

[Frugal Devonian]

Yes i was referencing a rover 60a controller, lazy late night response.