Battery charging too quickly

[Simon95]

Hi,

I have a new diy solar system in my caravan. This consists of a 130w solar panel, 12V 160ah gel battery, mppt solar controller, and a 1200w-2400w inverter. Everything is working well - however I am concerned the battery is not charging properly - because:

1. When I received the new battery straight out of the box the solar charger said it was 99% full (13.4V) - which seems weird. It had probably been in a box for 3- 6 months, so surely should have been down to 80% or so.
2. The battery seems to drain down to 60-70% fairly quickly.
3. This is the werid part. It seems to fully charge in about half an hour of full sun. From everything I have read this battery should take hours to charge with a 130w solar panel.

So I am concerned that its not charging properly, or that the solar controller is not working properly.

In the caravan I am only running a small 240v fridge (which runs at about 73 watts or 550w on startup) and some lights and some phone laptop chargers. Nothing else. Runs fine during the day, seems to stay at 99% all day, even when cloudy. At night the fridge and inverter drains the battery down to about 70%.

It seems like 70% is actually quite weak (12.8V). I would expect this system to easily handle the fridge, and it does seem to handle it. But I just don't understand why its charging so quickly. I would have expected the fridge to drain the battery more over night and take a lot longer to charge.

So maybe the battery is actually still quite full and the solar controller is showing a lower reading or maybe the solar charger is not functioning properly.

Any thoughts?

Thanks

 

[brb58]

Using a solar charger to determine the SOC is fruitless. When you measured 13.4V was the solar panel connected and in direct sun? If so, it was charging the battery. You need to leave the battery with no load or charge and then measure with a multimeter.

 

[chrisski]

IMLE, you can only tell a battery is full on a SCC when its sunny and the panel should be putting out full power, you’ve seen it switch from constant current to constant voltage, and the SCC is putting out the bulk/absorption voltage, you’ve arched the amperage taper to next to nothing, and then the SCC switches to float.

At that point, with near certainty, the battery is charged.

Every other point Is simply guesswork.

 

[timselectric]

Being a gel battery. Resting voltage is a good reference for SOC.

 

[Simon95]

Yes I measured the voltage with a multimeter with no load attached. I disconnected the SCC and the inverter.
So I guess my questions are:

1. 1s 13.4V a good voltage for a fully charged gel battery? (I have ready that this can be as high as 14.4V).

2. Why is the battery fully charging in half an hour when I have also read that it should take 5-8 hours to fully charge a battery like this with 130W Solar.

 

[Simon95]

Using a solar charger to determine the SOC is fruitless. When you measured 13.4V was the solar panel connected and in direct sun? If so, it was charging the battery. You need to leave the battery with no load or charge and then measure with a multimeter.

Yes I measured with a multimeter with no load attached. And I have also measured in full sun with the scc attached and this shows 14.4v.

 

[brb58]

Typically, Gel batteries aren't much higher than 12.9V fully charged. It's possible your battery still had a surface charge after being on a charger. Let it sit an hour and measure again or put a small load on it, remove load and then measure

It's very possible your battery is fully charged.