State of charge discrepancies.

[TheMachMan]

I’m confused, which is isn’t difficult as electricity is like witchcraft to me!
The information on my Exide gel batteries handbook states one thing, but my indicator in the van shows a different set of figures. On top of that the Victron shows a current battery voltage of 13.45V. Which on paper suggests the leisure batteries are full. If they are full shouldn’t they be floating or absorption phase? I’m only getting 68W despite having 215W of solar and it’s bright sunshine here in Spain. What does all of this mean??

 

[Lenny HB]

The 13.45v is the solar charge voltage it should rise to around 14.2v when the batteries are charged then after a few hours of absorbtion drop to a float of 13.5 - 13.8v.

You will only see the true battery voltage with no charging and no load on the battery.

 

[CAB96]

It's October, the sun is at an angle, even though it seems bright there is far less solar energy getting to the panels.

Your eyes are very good at adjusting to the level of light.

 

[TheMachMan]

Cheers, but still don’t understand why there is a difference in the measuring scales between Exide and the Malibu panel. Which is correct?

 

[CAB96]

Cheers, but still don’t understand why there is a difference in the measuring scales between Exide and the Malibu panel. Which is correct?

What did/does the Malibu panel show? There doesn't appear to be anything on your picture.

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[TheMachMan]

What did/does the Malibu panel show? There doesn't appear to be anything on your picture.

At the time 75%. But my main query is that the voltage vs % levels differ between the van and Exides handbook. I.e 100% = 13.5v or 12.8v, 25% = 11.5v or 12.2v

 

[Russell's Dad]

My Carthago panel only shows the batteries as full when they are charging, either via solar or ehu or alternator. This, I believe, is normal.
Maybe they set the panels up in case the optional lithium battery is fitted? Or something.......

 

[autorouter]

The figures in the battery handbook will be correct. However that's only for a battery with no loads on it, that is not being charged. And after letting the voltage settle for several hours. That's called the 'resting voltage'. Unfortunately in a motorhome those conditions hardly ever apply, especially if there's a solar panel.

To charge a battery, you need to apply a voltage a bit more than the resting voltage, to force charge backwards through the battery and reverse the chemical reactions that produce the electric charge. Applying about 13.5V will just about push a small trickle charge into the battery. Most chargers apply about 14.5V, and push 10A to 20A into the battery to charge it. Once it's charged, the charger drops the voltage to about 13.5V to just keep the battery topped up.

The Malibu chart is a bodge to save explaining all that to the customer. If EHU is connected for a long time, the voltage will be at 13.5V continuously, so the customer would be worried if that said more than 100%.

As you can see, the battery voltage is usually not a very indication of the battery state of charge. For accurate measurement, a different type of battery monitor is required, which measures the amps going into and out of the battery, and times for each amount of amps. In that way it can measure the amp-hours flowing into and out of the battery.

So if it starts off full with 100Ah of charge, and you take out 2 amps for 10 hours, that's 2 x 10 = 20 amp-hours (Ah). Then the 100Ah will be reduced to 80Ah, ie down to 80%. A monitor like this usually has a 'shunt resistor' to measure the amps, and is called a shunt monitor.