Weird readings on solar setup

[solaar]

Hey all, I noticed in the last few days I've been getting higher than normal voltage readings. My setup is designed to absorb at 14.7V, but it's been gradually reaching higher and today it was showing 15V in absorb mode. I plugged in to my Victron CC to have a look and noticed something else weird. The panel seemed to be putting out pretty low wattage (30W - cloudy day), but every time my fridge turned on, it would spike up to 60W plus and then dip and rise a few times, before dropping back down to around 30W when the fridge turned off. This was all during the absorb phase of charging.

Anyone have any idea what's going on? It's been working flawlessly for about 3 years until now.

It's a 12V system
Victron mppt 75/15
105 ah AGM
120W panel
Basic setup running 12V Engel fridge and few other things.

[littleharbor]

Not sure of your location but with a temp sensor connected to your charge controller , the absorb voltage will be higher when the batteries are cold.

[solaar]

I’ve been through Tassie and the mountains and it’s gotten into negative temps and never seen it get up to 15V. It’s pretty mild here at the moment.

[ewarnerusa]

The rise in absorption voltage readings seems normal for temperature correction. It sounds like you don't think your unit uses that though? My charge controller default settings will linearly raise all of the voltage setpoints as ambient temp (battery temp sensor) drops below the reference (I think 70F?), as well as reduce the voltage setpoints when ambient temps are above the reference. There are min/max voltage setpoints as well so it can't correct past a certain point. I can't remember how much voltage it corrects per degree, but in freezing temps the setpoint will be above 15V for my 2x6V GC deep cycle batteries. This is a good thing, you need the higher voltage setpoints to get the best charging done in the cold temps.

The panel wattage also sounds normal if it is tracking your fridge operation. When the fridge is actively cooling, it will put a 12V load on the system. Your batteries provide the current which acts to pull down their voltage. The solar controller sees the load pulling down the voltage, so it "allows" more current from the panels to pass to the batteries in an effort to maintain the battery voltage at the charging setpoint.

[solaar]

Ewarnusa, thanks for the info. No, the unit definitely has temp compensation switched on as I can see in the settings. Just never seen it go over 14.8 even in much colder places.

Good to know about the panel output. Yeah I thought in absorb mode it would still be pulling everything it could out of the panel, but I was wrong.

[chrisski]

I consider 30 watt output for a cloudy day good. The graph function on my Victron is not somethign I can make sense of, because it forgets the data when I change screens, but looking at my numbers as my solar panels provide amps for a load starting, I would expect it to be the same as your graph.

I would recommend checking the settings for the temp compensation. When I turned my charge controller from Celsius to Fahrenheit, it totally changed what I had in temp compensation. I noticed it when my charging voltage got to 15 on a cold day. Well, maybe it wasn't me changing it from Celsius to Fahrenheit that caused the problem, but the fact that I entered a positive coefficient instead of a negative coefficient. That caused my voltage to rise with the temp instead of entering a negative number so charging voltage drops with the temp.

What puzzles me about yours, is the weather is warming up, and your voltage is going up, so if the voltage should be less when now than when its colder.

[Bala]

Your battery is 3 years old. What sort of depth of discharge has it had in its life? and how long has it been left in low state of charge?

Your one panel is not a lot for the battery if there is not full sun. Do you have it charging from other sources.?