Odd Battery Utilization and Charging

[Iwojima]

Running 4x180ah AGM batteries with a 3kw system (2 banks of 24v).

Batteries are rated at 180ah @ 10hrs. They are not new by any means but before I tear down the setup and start load-testing each battery in turn I thought I'd see if anyone else agrees something looks off.

SOC drops to around 73% at the end of the session below, but jumps back up to 95% when AC kicks back in. Similarly voltage drops to around 24.7v, but springs back up to 27v (float) very quickly afterwards and currently is @ 27.2v and climbing (which i assume is part of the bulk charge routine)

3 hr load shedding session:

Load:


SOC:


Voltage/current:

 

[chrisc]

You don't mention how old these are
I've had inverters since 2013 and every single lead-acid battery I have used does not perform well after 3-4 years
The SOC values look impressive
How does this translate in real-life useage?

Even a lithium-ion battery must be run as close as possible to 100% SOC. My neighbour let his run down to 40% and was alarmed when the battery shut down after 2 hours

 

[Iwojima]

You don't mention how old these are
I've had inverters since 2013 and every single lead-acid battery I have used does not perform well after 3-4 years
The SOC values look impressive
How does this translate in real-life useage?

Even a lithium-ion battery must be run as close as possible to 100% SOC. My neighbour let his run down to 40% and was alarmed when the battery shut down after 2 hours

I honestly don't know unfortunately. Likely 2 to 4 years.

Buddy of mine had a few of these systems at various sites, changed them all to lithium recently at the same time and recovered all of the old batteries. He gave me 4 for mahala.

It is likely that the 4 did not all come from the same site so we can assume unequal levels of wear on each battery. So it may be a case of one battery bringing them all down, in which case I'm sure I can swap that out for one of his others.

 

[Messugga]

Bat

Running 4x180ah AGM batteries with a 3kw system (2 banks of 24v).

Batteries are rated at 180ah @ 10hrs. They are not new by any means but before I tear down the setup and start load-testing each battery in turn I thought I'd see if anyone else agrees something looks off.

SOC drops to around 73% at the end of the session below, but jumps back up to 95% when AC kicks back in. Similarly voltage drops to around 24.7v, but springs back up to 27v (float) very quickly afterwards and currently is @ 27.2v and climbing (which i assume is part of the bulk charge routine)

3 hr load shedding session:

Load:
View attachment 1335792

SOC:
View attachment 1335794

Voltage/current:
View attachment 1335796

Battery voltage drops when batteries are put under load. When AC kicks in, I'm going to guess they're no longer under load, hence why their voltage climbs.

 

[Iwojima]

Bat

Battery voltage drops when batteries are put under load. When AC kicks in, I'm going to guess they're no longer under load, hence why their voltage climbs.

Yup, I get that. It's easily seen multiple times during the 3 hour session. Load climbs, voltage dips. Load drops, voltage climbs.

My concern or confusion is how rapidly the voltage/SOC climbs back to 27v/95% (within 2min) after AC returns given that I've taken, according to lowest SOC indicated at the end of the session, 27% out of the battery and used approx 1.2kwh from battery (according solar-assistant) during the period.

 

[Iwojima]

Further possible indication of oddities:

It took only roughly 45min (@25A charge current) to get back up to 100% SOC

 

[wingnut771]

Yup, I get that. It's easily seen multiple times during the 3 hour session. Load climbs, voltage dips. Load drops, voltage climbs.

My concern or confusion is how rapidly the voltage/SOC climbs back to 27v/95% (within 2min) after AC returns given that I've taken, according to lowest SOC indicated at the end of the session, 27% out of the battery and used approx 1.2kwh from battery (according solar-assistant) during the period.

because voltage is higher when charging than when it's just resting. If you switched it off (no charge) after a load, you will see voltage climb slower to a lower number.

Seeing you have mismatched batteries, I would start with balancing them all to each other by parallelling all 4 together and charge with 12V charger just to ensure there is less chance for imbalance in the 2 series strings.

Are all the voltages for the 4 batteries equal?

 

[Iwojima]

Seeing you have mismatched batteries, I would start with balancing them all to each other by parallelling all 4 together and charge with 12V charger just to ensure there is less chance for imbalance in the 2 series strings.

Are all the voltages for the 4 batteries equal?

Sadly my multimeter has grown legs so I can't check, but I do have an 8amp smart car battery charger on one of the banks at the moment, letting it do its thing.

Do you think it would be 100% necessary to do all 4 in parallel at once?

 

[wingnut771]

Sadly my multimeter has grown legs so I can't check, but I do have an 8amp smart car battery charger on one of the banks at the moment, letting it do its thing.

Do you think it would be 100% necessary to do all 4 in parallel at once?

It would be preferable to get a good balance and to save time but I guess 1 by 1 is better than nothing.

Maybe when they're all done, do another round just to top them up again as that won't take too long.

 

[Iwojima]

It would be preferable to get a good balance and to save time but I guess 1 by 1 is better than nothing.

Maybe when they're all done, do another round just to top them up again as that won't take too long.

Only issue is I'd need to make up another short cable to do the second parallel vs the current setup...and me without a crimper

 

[wingnut771]

Only issue is I'd need to make up another short cable to do the second parallel vs the current setup...and me without a crimper

Got any jumper cables?

 

[chrisc]

Use some pliers. Or solder it

 

[Rickster]

Doesnt LA suffer from the memory effect thus needing to be calibrated?

Hence bringing them to minimum SOC then fully charge a few times?

 

[wingnut771]

Doesnt LA suffer from the memory effect thus needing to be calibrated?

Hence bringing them to minimum SOC then fully charge a few times?

No.

 

[wingnut771]

Running 4x180ah AGM batteries with a 3kw system (2 banks of 24v).

Batteries are rated at 180ah @ 10hrs. They are not new by any means but before I tear down the setup and start load-testing each battery in turn I thought I'd see if anyone else agrees something looks off.

SOC drops to around 73% at the end of the session below, but jumps back up to 95% when AC kicks back in. Similarly voltage drops to around 24.7v, but springs back up to 27v (float) very quickly afterwards and currently is @ 27.2v and climbing (which i assume is part of the bulk charge routine)

3 hr load shedding session:

Load:
View attachment 1335792

SOC:
View attachment 1335794

Voltage/current:
View attachment 1335796

What are your settings for BULK, FLOAT and CURRENT? Also, what are the specs on the side of the battery?

 

[Iwojima]

Got any jumper cables?

Now there's a plan...

 

[Iwojima]

What are your settings for BULK, FLOAT and CURRENT? Also, what are the specs on the side of the battery?

Battery specs attached.

All charge settings are as per the default settings for AGM on the inverter.
Bulk: 28.2v
Float: 27v
Current: 25A

 

[wingnut771]

Battery specs attached.

All charge settings are as per the default settings for AGM on the inverter.
Bulk: 28.2v
Float: 27v
Current: 25A

Looks good.

You can double your charge amps seeing you have 2P2S setup, especially when stage 8 loadshitting comes around.
Actually, 180Ax0.25C = 45amps max so you could go up to 90A in emergencies, but slower is always better, but a full charge is more important.

 

[wingnut771]

Battery specs attached.

All charge settings are as per the default settings for AGM on the inverter.
Bulk: 28.2v
Float: 27v
Current: 25A

I would change to USER and use same settings but also so you can change low voltage cut-off to 24V.

 

[Iwojima]

I would change to USER and use same settings but also so you can change low voltage cut-off to 24V.

Will do. 21v is far too low.