Solar panel battery voltage fluctuations

[356DNA]

Hi all. I would appreciate your thoughts on the apparent variation I am seeing in battery voltage when my van is left for a few days with just solar charging. Specifically it seems to get up to 13.8+ volts after solar input but then drops down to 12.x overnight. There’s nothing left on in the van aside from the Victron MPPT charger to draw current. I have added a screen shot for the past few days when the van remained parked and locked. Is this normal or indicative of an issue I need to explore? Thanks.

 

[356DNA]

I should add that it’s a t5 California with the standard dual leisure battery install.

 

[babble]

How old are the batteries? If they are old, then maybe 12.5 - 12.6v is around normal?

 

[356DNA]

How old are the batteries? If they are old, then maybe 12.5 - 12.6v is around normal?

2 years old.

 

[Steve1]

Hi all. I would appreciate your thoughts on the apparent variation I am seeing in battery voltage when my van is left for a few days with just solar charging. Specifically it seems to get up to 13.8+ volts after solar input but then drops down to 12.x overnight. There’s nothing left on in the van aside from the Victron MPPT charger to draw current. I have added a screen shot for the past few days when the van remained parked andView attachment 107702 locked. Is this normal or indicative of an issue I need to explore? Thanks.

Fluctuation (max to min) is expected. The charge voltage (max) is 13.8V + as you mention, but at night when no charge is applied, then the battery will return to it's rest voltage which should indicate its state of charge like in the red, yellow, green table in the post above. However in your case your rest voltage seems quite low. Do you think you have seen enough total sunlight for them to be fully charged, because if they are not yet fully charged then the rest voltage will be lower than expected. I notice that in your picture the overnight rest voltage seems to be increasing each day so maybe they are not fully charged and are charging a little more every day ??? If thats the case the rest voltage (min) should eventually increase day by day until it stays at 12.7V to 12.8V overnight assuming they are the AGM type batteries fitted by VW.

 

[Steve1]

Fluctuation (max to min) is expected. The charge voltage (max) is 13.8V + as you mention, but at night when no charge is applied, then the battery will return to it's rest voltage which should indicate its state of charge like in the red, yellow, green table in the post above. However in your case your rest voltage seems quite low. Do you think you have seen enough total sunlight for them to be fully charged, because if they are not yet fully charged then the rest voltage will be lower than expected. I notice that in your picture the overnight rest voltage seems to be increasing each day so maybe they are not fully charged and are charging a little more every day ??? If thats the case the rest voltage (min) should eventually increase day by day until it stays at 12.7V to 12.8V overnight assuming they are the AGM type batteries fitted by VW.

@356DNA actually i just noticed that the picture is the other way round so your rest voltage is getting lower each day not higher which means what I suggested above is not correct. This means you either have something turned on which is slowly using your battery charge each day at a rate higher than the solar can put back in, or your batteries are faulty and not holding charge over night.
I would also add that I am not hugely familiar with solar charge voltages (more with powered battery charger ones), but 14.8V seems to be a particularly high charging voltage for the max. If it does that for any length of time I would expect it to cause damage, but perhaps it is only momentary.

 

[flying banana]

what does the control panel say in the van ? what happens on hook up ?

 

[Ch1pbutty]

Its fine, battery will drop to 12+ v when not being charged. higher reading 14v + is when its being charged by solar.

 

[356DNA]

Thanks everyone. As Steve points out though, the falling daily voltage does seem to suggest either poor batteries or another current draw?

Everything seems to work well on hookup.

I couldn’t get the OEM batteries or the Varta LA80 when I changed them and had to go for some Explorer spiral AGM replacements (same capacity). I wonder if these are not the best and failing early too.

 

[Kingfisher]

The three blocks in each bar on the graph show that the charger has gone through a full cycle each day, so the batteries have been charged to full every day. By touching each bar in the app, you can see how long it has been charging in the bulk, absorption and float phase.

I would not worry too much right now. Maybe your replacement batteries have a slightly lower resting voltage by design. Any night to night variation in the resting voltage could also be temperature related, I would assume. If the voltage keeps falling to, say, 12.3 or lower, then it’s time to worry. Same if the parking heater refuses to start.

 

[dspuk]

They are not live readings. They are the max the battery was through the day and the min the battery was through the day. The numbers shown are normal. There can be any number or reasons you have a sudden drop. If you check across the actual battery, you will get the live reading. My money is it is on or about 13v.