State of Charge

Boswell Bear

Boswell Bear

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Westfalia Amundsen
I charged my 2 110AH leisure batteries using the hookup this was the state of charge when I disconnected at 22:00

IMG_5972.webp



With everything turned off except for the Truma control panel by 11:00 the next morning this was the display:

IMG_5979.webp


I take it I either have something draining the batteries or the batteries are past their best?
 
Your resting voltage of over 13v is probably from the charge from the solar. What is the resting voltage with no solar charging?
 
You should only be considering voltages after about 30 minutes at rest after disconnection from chargers or discharge as the chemical reactions can still be taking place. So your 10pm reading is misleading and battery voltage was probably less than that.

But you don't tell us what type of batteries you have, only the capacity. Different types will have different max voltages i.e. lead acid typically 12.7V, lithium 13.6V

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As the solar output of late has been so appalling, the battery maintainer hasn't! I've had the hab battery on charge from time to time, yet the resting voltage drops to around 12.3V within about 36 hours of being taken off charge. The battery is less than two years old and has never seemed to have a high resting voltage even when driving long distances and solar is going great guns.
 
That solar controller has absolutely no way of knowing the state of charge of your batteries. If it's using the measured voltage, then that is a poor indication of state of charge, especially when something like the solar is charging it. It can't use the amps as a measure of state of charge because it can't measure all the amps going into and out of the battery.

If you don't have a shunt battery monitor, an alternative is to measure the battery voltage when the battery is 'resting', ie no charge going in, and no amps going out. Then use a chart for the exact type of battery you have (Gel, AGM, flooded etc). There are small variations between the different types, but for all of them, if it's over 13.0V something is charging it, so it's not a resting voltage.
 
We cannot conclude anything from the information presented.

The first image shows a retained (surface charge) voltage immediately after charge disconnection.

The second image shows a lower voltage, albeit still a (solar charging) voltage. It also shoes a graphic suggesting that some discharge (level unknown) appears to have taken place. However, it is possibly/probably just recognising that 13.3V (solar charging voltage) is lower than 13.8V (surface charge following EHU charge).

It’s impossible to tell from those images whether all, is good with your battery or all is not well with your battery.🤷‍♂️

Ian
 
Kannon Fodda said:
You should only be considering voltages after about 30 minutes at rest after disconnection from chargers or discharge as the chemical reactions can still be taking place. So your 10pm reading is misleading and battery voltage was probably less than that.

But you don't tell us what type of batteries you have, only the capacity. Different types will have different max voltages i.e. lead acid typically 12.7V, lithium 13.6V
Click to expand...
They are the dreaded AGM
 
autorouter said:
That solar controller has absolutely no way of knowing the state of charge of your batteries. If it's using the measured voltage, then that is a poor indication of state of charge, especially when something like the solar is charging it. It can't use the amps as a measure of state of charge because it can't measure all the amps going into and out of the battery.

If you don't have a shunt battery monitor, an alternative is to measure the battery voltage when the battery is 'resting', ie no charge going in, and no amps going out. Then use a chart for the exact type of battery you have (Gel, AGM, flooded etc). There are small variations between the different types, but for all of them, if it's over 13.0V something is charging it, so it's not a resting voltage.
Click to expand...
They are currently sat at 13V with no solar or other charger on.
 
The 13v will be a surface charge, and will go pretty quickly even with a small load - AGM resting voltage 12.7-128v (IIRC).

As a battery Sulphates or dries out over time (which can be surprisingly quick with AGM if not kept fully charged after each cycle) it can appear to be working perfectly normally, showing all the correct voltages. What is happening though is the capacity is dropping.

We had a large AGM bank once which after 18months was down to a small fraction of their spec and had to be replaced. When we were out and about it rarely got fully charged and relied on the alternator, or generator and charger. The alternator was 14v so not enough to fully charge an AGM which needs 14.7v. The generator was only run for a couple of hours since it was quite audible inside (although not outside). So only when on shorepower was a full charge possible.

The batts passed all of the usual voltage checks and the clip on type testers, but a capacity check revealed the issue. Although not good for the battery an old fashioned type drop tester was used to see what would happen, and it showed a very slow recovery time after the discharge but these are rarely used now, perhaps they do too much damage to the battery? The batteries were tested individually, but they were all knackered, so unlikely they were all bad batteries, just my charging regime wasn't good enough, although I suspect Flooded or Gels would have been fine, as would lithium....

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Boswell Bear said:
I ran two 2.3W Spot lights for an hour and it dropped from 13.1V to 12.8V.
Click to expand...
Assuming you have no charger/solar running, and that 4.6w was the only load ie 0.4ah, I think you have just removed the surface charge. If you have a multimeter ideally with a known good battery in it, it would be good to measure the voltage at the battery terminals (disconnected from each other) so you know the panel is correct. Putting a known load on would ideally be at around 5a for each your batteries separately, so you can see the effect on each battery, and judge it against the capacity specification, that is likely to be quoted based on a load close to 5amps (ie a discharge of C20 meaning the capacity / 20).

LA batteries will give greater capacity the smaller the load, and less capacity at bigger loads, so most are quoted at C20, although some makers will also quote for other loads in the spec sheet.

Somebody will explain this better I'm sure!
 
Boswell Bear said:
I charged my 2 110AH leisure batteries using the hookup this was the state of charge when I disconnected at 22:00

View attachment 989727


With everything turned off except for the Truma control panel by 11:00 the next morning this was the display:

View attachment 989728

I take it I either have something draining the batteries or the batteries are past their best?
Click to expand...
13.3v is the voltage when it's being propped up by that trickle of solar. Even if it's fully charged, a lead acid battery will be less than 13v.

I don't know how it's estimating your charge. Unless it knows it's significantly lower when there's more demand on the battery?
 

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