Battery at 12.3v under load. When load removed its 12.6v this isnt discharged?

[73powerstroke]

I hope I'm explaining this correctly. I have 3 deep cycle flooded lead acid batteries I'm pulling 50 amps out of them Under load to run my inverter when it reaches 12.3 V I shut off the inverter, the battery's bounce back to 12.6 V or so.
What is the proper way to determine the state of your battery?? Under load or at rest?
I don't want to damage brand new batteries. I've never really dealt with deep cycle batteries before and was always under the impression that people used them until they were completely dead for things like trolling motors on boats and what not. I've always figured that you could fully discharge them without causing any damage but most people say that 50% discharge is all that you want to do.
When I am shutting my load off at 12.3v am I truly 50% discharged regardless of battery resting voltage?

 

[Don B. Cilly]

SOC is usually measured under no load.

 

[73powerstroke]

SOC is usually measured under no load.

View attachment 100994

I've seen that chart. It claims 12.06 but most say 12.3 is 50%.
The real question is how far can I run my deep cycle batteries under load.

 

[mikefitz]

When I am shutting my load off at 12.3v am I truly 50% discharged regardless of battery resting voltage?

No its the resting voltage that determines the approximate state of charge. There are many types of deep cycle, its easy to put a label on a battery that says deep cycle. A true deep cycle battery will tolerate heavy use. Do you have a link to the battery?
Depending on the current drain and the battery capacity there will be a voltage sag.

When measuring voltage, it will differ depending where in the circuit you measure, at 50 amps its possible there will be volt drops in cables, connections and fuses . The voltage direct on the battery terminals will be higher than the voltage on the inverter terminals when its taking 50 amps.

The chart below indicates typical voltage and time from full to empty. C is the total battery capacity in Ah.

for example if we have a 100Ah battery with a 0.1C. (10 amp) current drain, full to completely empty will take around 10 hours. At around 4 hours the voltage is just over 12 volts and the battery is half charged.
The chart also shows that as the current increases, the effective battery capacity decreases. Increasing the current to 0.2C, 20 amps, you may expect full to empty would take half the time that a 10 amp discharge produced, in fact its less at 4 hours , not the 5 hours you would expect.



Battery cycle life depends on depth of discharge, for a very high quality deep cycle battery the manufacturer produced this graph.


Of course this test is under ideal conditions, in practice natural ageing and less than ideal treatment will reduce the number of cycles. However its a useful illustration of how depth of discharge effects cycle life.

Mike

 

[73powerstroke]

No its the resting voltage that determines, the approximate of charge. There are many types of deep cycle, its easy to put a label on a battery that says deep cycle. A true deep cycle battery will tolerate heavy use. Do you have a link to the battery?
Depending on the current drain and the battery capacity there will be a voltage sag.

When measuring voltage, it will differ depending where in the circuit you measure, at 50 amps its possible there will be volt drops in cables, connections and fuses . The voltage direct on the battery terminals will be higher than the voltage on the inverter terminals when its taking 50 amps.

The chart below indicates typical voltage and time from full to empty. C is the total battery capacity in Ah

View attachment 101104
Battery cycle life depends on depth of discharge, for a very high quality deep cycle battery the manufacturer produces this graph.

View attachment 101105
Of course this test is under ideal conditions, in practice natural ageing and less than ideal treatment will reduce the number of cycles considerably. However its a useful illustration of how depth of discharge effects cycle life.

Mike

So I would have to shut off everything and see where the battery rests at. Ok.
The batteries are walmart group 24 deep cycle marine. Not their starting ones.
I have a group 31 from a place I used to work. The guy was a battery importer.

I used to run the deal until the inverter shut off at 10.5v but don't recall what the battery voltage was afterwards. I decided to over panel so that more or less I would just be using the batteries like a smoothing capacitor. I have 8 x 240w panels. Just a 5000btu ac unit running off it.
So tonight when sun fades ill run it all the way down to 12.3 resting. That is the proper voltage for fla deep cycle batteries?
FYI there's 2 walmart group 24s and one performance plus group 31 in parallel

 

[mikefitz]

Being in Europe I have no experience of Walmart batteries, but similar distributer branded dep cycle batteries from Korea available here, are not what I would class as true deep cycle. Others based in the US may be able to comment on Walmart batteries.
I think a group 24 is about 80Ah and a 31 about 110 Ah, so a total of 270 Ah.
A typical charge current for this capacity would be 40amps, I cannot see how do you engineer this with1.9kW of solar.

If the batteries are fully charged, a 50 amp load to 50% capacity should take around 2.5 hours.

Mike

 

[73powerstroke]

Being in Europe I have no experience of Walmart batteries, but similar distributer branded dep cycle batteries from Korea available here, are not what I would class as true deep cycle. Others based in the US may be able to comment on Walmart batteries.
I think a group 24 is about 80Ah and a 31 about 110 Ah, so a total of 270 Ah.
A typical charge current for this capacity would be 40amps, I cannot see how do you engineer this with1.9kW of solar.

If the batteries are fully charged, a 50 amp load to 50% capacity should take around 2.5 hours.

Mike

I started with 2 100w panels. So that's why I have just 3. I don't want to invest alot in fla batteries .
Then I found out about santan solar 240w panels for $44
Batteries are probably made by Johnson controls or similar. That's what Walmart uses alot. They are pretty cheap $79 and they aren't picky about what core you give them. I turned in 2 ups sla batteries ?.
Any suggestions on how many batteries and best route? I'm not sure what is next at this point. I still need more charge controllers.

 

[brb58]

In the marine world, we call those Neverstart. If I was not using lithium batteries, I would go with 6V golf cart batteries which are true deep discharge batteries...these are not.

 

[73powerstroke]

In the marine world, we call those Neverstart. If I was not using lithium batteries, I would go with 6V golf cart batteries which are true deep discharge batteries...these are not.

I haven't seen golf cart batteries for a reasonable price in Northern arizona

 

[camelCase]

The 12v marine "deep cycle" batteries are only modestly more able to withstand deep discharges than regular starting batteries. Disconnecting the heavy loads when then voltage hits 12.3v will definitely help them last longer, but they won't actually be discharged to 50%, which is good, as those will die quickly if cycled that low.

Peukert’s Law Peukert’s Law and Lead Acid Batteries | EcoSoch Solar

Peukert's Law: when you discharge lead acid batteries at higher rates / you use larger loads, the efficiency of that battery drops. Know more

www.ecosoch.com

 

[73powerstroke]

The 12v marine "deep cycle" batteries are only modestly more able to withstand deep discharges than regular starting batteries. Disconnecting the heavy loads when then voltage hits 12.3v will definitely help them last longer, but they won't actually be discharged to 50%, which is good, as those will die quickly if cycled that low.

Peukert’s Law Peukert’s Law and Lead Acid Batteries | EcoSoch Solar

Peukert's Law: when you discharge lead acid batteries at higher rates / you use larger loads, the efficiency of that battery drops. Know more

www.ecosoch.com

Lovely. I guess what's the cheapest alternative?

 

[brb58]

I haven't seen golf cart batteries for a reasonable price in Northern arizona

Do you have Costcos there?

 

[73powerstroke]

Do you have Costcos there?

Yes

 

[BradCagle]

I've never really dealt with deep cycle batteries before and was always under the impression that people used them until they were completely dead for things like trolling motors on boats and what not.

I think most people with a recreational fishing boat don't know any better either, they buy new batteries each year like people buy a new lawn mower every season because it wont startup from improper maintenance/storage.

Now people that their livelihood depend on it such as fishing guides, etc.. I bet have figured it out.

 

[camelCase]

GC2 is the golf cart size battery they sell at Costco. Since you already have 3 12v batteries, personally, I would use them up before buying new ones and save up for some lithium batteries instead.

 

[73powerstroke]

GC2 is the golf cart size battery they sell at Costco. Since you already have 3 12v batteries, personally, I would use them up before buying new ones and save up for some lithium batteries instead.

How much are they usually?
How long should I expect from the 2 walmart batteries? The other one might be better but I doubt much

 

[OzSolar]

I hope I'm explaining this correctly. I have 3 deep cycle flooded lead acid batteries I'm pulling 50 amps out of them Under load to run my inverter when it reaches 12.3 V I shut off the inverter, the battery's bounce back to 12.6 V or so.
What is the proper way to determine the state of your battery?? Under load or at rest?
I don't want to damage brand new batteries. I've never really dealt with deep cycle batteries before and was always under the impression that people used them until they were completely dead for things like trolling motors on boats and what not. I've always figured that you could fully discharge them without causing any damage but most people say that 50% discharge is all that you want to do.
When I am shutting my load off at 12.3v am I truly 50% discharged regardless of battery resting voltage?

Voltage by itself is a bad way to determine battery SOC (state of charge).

For flooded lead acid specific gravity is pretty the only way to do it with a trustworthy level of accuracy and reliability but it looks like you have sealed lead acid so you can't use that.

Your next choice would be an amp hour meter like the Victron Smart shunt or the Trimetric . They are normally pretty good but they rely on being setting up correctly will drift out of accuracy over time.

 

[camelCase]

OzSolar is right. Voltage is only a good indicator of SOC when there is no load on the system. This is because the higher the load, the more the voltage sags. You've noticed this when you turned off the AC and the voltage slowly came back up.

How much are they usually?
How long should I expect from the 2 walmart batteries? The other one might be better but I doubt much

Their life span will be highly correlated with how much they get discharged. If you never draw them below 12.3v (resting), which is 70% SOC at 77f, they will probably last for years. If you draw them down to
11v regularly, then they'll last only months.

 

[73powerstroke]

Voltage by itself is a bad way to determine battery SOC (state of charge).

For flooded lead acid specific gravity is pretty the only way to do it with a trustworthy level of accuracy and reliability but it looks like you have sealed lead acid so you can't use that.

Your next choice would be an amp hour meter like the Victron Smart shunt or the Trimetric . They are normally pretty good but they rely on being setting up correctly will drift out of accuracy over time.

I have a shunt meter. Santan solar sells the ones that Amazon carries.
Currently our power is out. I'm running the fridge and TV for the kids lol. Coincidence. I think somebody drove into a telephone Pole again because my other neighbors have power on the other side of the street at any rate we got to do some testing And this is my meter running right now with the refrigerator and a big screen TV in the living room for the kids

 

[camelCase]

I notice you've got multiple wires coming in to the negative posts on your batteries. To get an accurate measurement of current going in and out, you want all the negatives connected at the shunt. You should also move the positive lead to the opposite battery in the string.