Battery voltage

[Julian-Indaiatuba]

Hello, sorry in advance if this is a silly question.
i have made a very simple solar set up on which I run a 1000W inverter during the day, and use the full lead acid batteries at night to power 6 led 8W 24V lights for the veranda. These are powered directly by the charge controller’s DC outlet.
When the inverter is turned off at the end of the day, and the batteries are full, the idle voltage for my batteries is about 27,6V
As soon as I turn on the lights, the voltage drops to about 25,8V and after the 12 hours the lights are on, the voltage is about 24,1V in the morning. I thought this low voltage wouldn’t be good for battery life.
I was using two 105Ah batteries in series, but when I saw the low voltage in the morning, I added another two of the same batch.
This didn’t seem to change anything at all. The voltages remained anout the same in the evening and the morning.
I was wondering if this is normal, or if I maybe have made a silly mistake.
Any help would be really appreciated.

I have attached a picture of my batteries. Maybe I have made errors in my setup?
Thank you!

 

[gnubie]

For your initial 105Ah single string - you have a notional 2A load on the battery for 12 hours, ie 24Ah. That's close enough to 1/4 of the battery's capacity to call it that. Unloaded and idle for several hours you can expect the battery will be around 24.9V (depends on exact chemistry) at 75% charged. Since you are seeing 24.1V loaded, that seems fine to me.

If you revert to the single string, bring it up to charged, run the lights overnight as per normal, then disconnect the charger and load from the battery and let it sit for a couple of hours, then measure the voltage with a multimeter, what do you see?

 

[Julian-Indaiatuba]

For your initial 105Ah single string - you have a notional 2A load on the battery for 12 hours, ie 24Ah. That's close enough to 1/4 of the battery's capacity to call it that. Unloaded and idle for several hours you can expect the battery will be around 24.9V (depends on exact chemistry) at 75% charged. Since you are seeing 24.1V loaded, that seems fine to me.

If you revert to the single string, bring it up to charged, run the lights overnight as per normal, then disconnect the charger and load from the battery and let it sit for a couple of hours, then measure the voltage with a multimeter, what do you see?

Thank you so much for your quick reply. I’ll have to try and measure the voltage in the morning then.
But am I right to understand that the volatage of 24,1V in the morning is nothing to worry about, even though I have 4 batteries connected?

 

[gnubie]

For the 105Ah string it seems reasonable, for two of them in parallel it seems low but first steps first. Some observations will set you right.

 

[Julian-Indaiatuba]

For the 105Ah string it seems reasonable, for two of them in parallel it seems low but first steps first. Some observations will set you right.

OK, thank you. I’ll see if I can measure the voltage tomorrow morning then.

 

[Julian-Indaiatuba]

OK, thank you. I’ll see if I can measure the voltage tomorrow morning then.

Hi again,
I didn’t manage to measure the batteries before work this morning, but tomorrow I definitely will.
I did however disconnect everything at the end of the day, and left the batteries ‘rest’ for an hour.
The total of my 4 batteries was 26,3V
The top string in the picture was 26,4V and the bottom string 25,2V.
When I measured each battery separately, 3 of them were between 13,27V and 13,49V, except for the one right bottom in the picture which was 11,19V!
It’s a brand new battery, so I don’t know if it has issues, or something in my setup might be off.
Can you see anything wrong in the way I have connected everything?
Thank you!

 

[gnubie]

If you can, bring them up to fully charged separately with a 12V charger. Then once all of them are fully charged let them sit idle for a few hours and check their voltages. They should all be roughly the same. If so hook them back up in your 2s2p configuration or just as two separate 24V batteries and run your load then recheck their voltages etc.

The new battery may not be fully charged when you put it into the array so there would have been imbalances as they charged. That can sort itself out in time if the absorption stage charging is left to fully complete, but there are consequences to it as the higher charged battery will be overcharged while the lower comes up to fully charged. For a sealed battery, even more so AGM, you don't want to expose any battery to extended over charging.

The 26.4V string is fine and is coping with your load without a problem. What you posted in your opening post based on this is not anything to be worried about with that string.

*edit to rephrase*

 

[Julian-Indaiatuba]

T

Hi again,
I didn’t manage to measure the batteries before work this morning, but tomorrow I definitely will.
I did however disconnect everything at the end of the day, and left the batteries ‘rest’ for an hour.
The total of my 4 batteries was 26,3V
The top string in the picture was 26,4V and the bottom string 25,2V.
When I measured each battery separately, 3 of them were between 13,27V and 13,49V, except for the one right bottom in the picture which was 11,19V!
It’s a brand new battery, so I don’t know if it has issues, or something in my setup might be off.
Can you see anything wrong in the way I have connected everything?
Thank you!

Thank you so much again for your reply.
I will do what you said, and see what results I get.
The battery with the low voltage has been connected this way for about a week now. Shouldn’t it be charged by now?