Solar and batteries ?

[Wizz]

I have solar and lithium hab battery.

I don't profess to know much about anything technical, but my logical thinking has got me baffled.

The thing I don't understand is when it's a baking hot and bright sunshine, as its been today, with my motorhome and solar panel basking in a clear and unobstructed sun trap for pretty much all of it.

Why does my vehicle battery appear to lose some charge in the afternoon, even when it's still in full sun. It moves from 13.0 to 12.7 ?

Am I missing something, is this to be expected, even though there is nothing other than the alarm in the van switched on, is there a fault, battery/charger/solar ?

I have attached some images, taken morning, and at 3pm today to show examples of the readings for today.

Any observations, advice would be much appreciated.
Thanks.

 

[Richard n Ann]

It must be in the controllers profile to let the battery rest after a full charge.
Our optimate maintainer does it

 

[Raul]

What is charging your vehicle battery?

 

[Wizz]

The van has a battery master, so both batteries charging from solar.

 

[Jev88]

Battery full, charge turns off, battery returns to normal fully charged state of 12.7 or 12.8 volts?

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[Raul]

Yes battery master passes charge from leisure when on absorb, then when it goes in float, maybe it’s not enough over voltage to still pass current to starter. But the starter is full at 12,7v anyways.

 

[autorouter]

Deleted

 

[Kannon Fodda]

it’s worth checking the charger settings needed for your lithium. Your voltages may be low applicable for lead acid. My Sterling lithium float charge is something like 13.6v. Bulk charge over 14v.

 

[Wizz]

The install of solar panel, battery master and lithium battery were all done at the same time just FYI

 

[Wizz]

So, checked again this morning. Habitation battery showing full. Vehicle battery showing full. What I expect to follow if the same happens as has happened the past days. The habitation battery later today will still show full, and the vehicle battery will show a slight reduction, from 13.00 to 12.7.
This is the bit I don't understand, being that the van solar is stood under the baking sun all day, with nothing depleting it. I would have thought it would be constantly topped up all the time the sun is on the solar panel, and that the vehicle battery would remain topped up at 13.00.
Is this not the case ?

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[Revolvor]

Wizz
The Battery Master starts to charge the Vehicle battery when the Hab battery is approx 0.6 - 0.7 volts higher than the vehicle battery. When battery voltages are approx equal, it switches off.

The noted 13.0 volts on your Vehicle battery is approaching float voltage. Once the BM switches off, the vehicle battery will slowly drop to fully charged - 12.7 volts. If it drops significantly lower due to loads (alarm etc) the BM will cut back in and repeat the process.

 

[Wizz]

Many thanks for explaining that.
Much appreciated.

 

[Brains]

Hi Wizz

As your van is exactly the same as mine, I find a noticeable difference if the solar panel is given a wash.

I can just squeeze through the roof vent at the back.
Chuck a wet sponge up there and take the awning winding handle with you to move it up and down.
You can then wipe down the solar panel.

Voila! Double the solar power!

(We are heading down to Cornwall next week, where are you ?)

 

[Wizz]

Hi Brains,
Good to hear from you.
Thanks for that
we have just returned from a really enjoyable 15 days in Devon & Cornwall, absolutely beautiful!
Next trip slightly closer to home , Kent & Sussex. Hopefully followed by further afield later in the year .