Low amp hours

[Paul Thomas]

I have (8) 100 watt panels on my roof. I have a Renogy 3000 watt inverter with an imprint MPPT 60 amp charge controller. I also have (6) Weizmann 100 ah batteries wired in parallel. My problem is when the sun is out I can power all kinds of things at the same time, but at night after 15 minutes my batteries start dropping voltage quickly? I don’t think I’m getting the entire 600 amp hours?

 

[sunshine_eggo]

When you stop charging and start discharging batteries, the voltage drop is usually abrupt and significant. Your 3000w inverter also has an idle load where it's going to draw power even if you don't have any loads.

If you are using a voltage based % charge indicator, and you are alarmed by the % drop, ignore it. It's useless.

Since you didn't give any numbers, it's hard to give you any more than that.

 

[Paul Thomas]

When you stop charging and start discharging batteries, the voltage drop is usually abrupt and significant. Your 3000w inverter also has an idle load where it's going to draw power even if you don't have any loads.

If you are using a voltage based % charge indicator, and you are alarmed by the % drop, ignore it. It's useless.

Since you didn't give any numbers, it's hard to give you any more than that.

Thanks eggo

 

[Paul Thomas]

do you think better batteries like battle born would last longer?

 

[sunshine_eggo]

do you think better batteries like battle born would last longer?

Context? you mean total life, or are you referring to your perceived voltage issue?

I see no evidence that you have a problem. You only see a voltage drop, but you haven't given numbers.

If you could be more specific, we might be able to give better answers.

 

[MurphyGuy]

The technical term is "hysteresis"

When charging, the "charge hysteresis" will show a battery voltage higher than the battery voltage actually is. This is because you can't charge a 12 volt battery with 12 volts.. You need at least 12.1 volts.

Discharge hysteresis is the same thing in reverse. When pulling current out of the battery, the apparent voltage of the battery will be slightly lower than it actually is.

When you switch from charging to discharging, there can be a significant difference in apparent voltage.

You are always reading apparent voltage unless you disconnect everything from the battery and let it rest for an hour or two.

The more current that is moving in or out of a battery of a given size, the larger the hysteresis error.

 

[Paul Thomas]

do you think better batteries like battle born would last longer?

I just disconnected my batteries and they are only reading 12.47v? Got’em on the charger

 

[Paul Thomas]

Here’s a dumb question: what voltage can you run down a lifepo4 battery and still be safe and not harm them…

 

[sunshine_eggo]

I just disconnected my batteries and they are only reading 12.47v? Got’em on the charger

12.47V resting LFP is a very low SoC.

Are your batteries reaching 14.2-14.4V every day?

 

[HarryN]

It sounds like your batteries are not really getting charged hardly at all.

Take a look at your solar panel wiring and make sure that at least some of them are wired in series or the MPPT can't really do it's job right.

 

[sunshine_eggo]

My gut says we're dealing with consumption in excess of daily PV production.

 

[Paul Thomas]

12.47V resting LFP is a very low SoC.

Are your batteries reaching 14.2-14.4V every day?

No

 

[Paul Thomas]

No

 

[sunshine_eggo]

No

Then your batteries aren't getting fully charged, and you are likely using more energy than your PV can provide in a day, or your charger isn't working, or you have shading, or something else.

System compensates with battery capacity until they run dry. Then you're done.