Voltage variation on agm 1

[frankz66]

Hi everyone, I know for sure that the references si soc are highly indicative but it is necessary to rely on the voltage detected on the regulator to get an idea of the charge in place. It would be appropriate to check its status by shunt and ammeter, but in any case the voltage read on the regulator or on the epever software gives me a approximate indication of the status.

My system is a test and pleasure plant, so at the moment I do tests to check the operation ....

I wanted to have your opinion on the tests carried out.

At the time of the cut out, I find myself reading on the regulator a voltage of 12.60 and a soc of 57 % (let's forget the soc) with a small load of just 30 watts + 10 watts of inverter. By turning on an example of a TV, I find a total load of about 81 watts, which I read in the LCD instrument of my ammeter. Starting from a residual charge of 48 % always of soc .... After about 2 hours I find myself a difference of only 6 % less with an accumulation of 330 amps at 12v.

As soon as I turn off the loads leaving only 38 watts, I see that the voltage of the batteries e.g. 12.20 begins to rise to 12.28, as if it resumed to have voltage.

I ask as a beginner if this variation is normal for it to come back once consumed? I would expect that once the power is consumed after 2 hours of almost 95 watts the voltage will not be able to rise. I know we are talking about poor 10 mv but this makes a difference in the perception of consumption.

Could it be that the load is almost at the limit for the characteristics of the batteries and therefore after dispensing current they return to tension?

The batteries in parallel are 3 from 110 amps 12v c100

 

[pollenface]

Yeah that's pretty normal. Loads pull voltage down, quite noticeable on lead acid batteries.

 

[frankz66]

Yeah that's pretty normal. Loads pull voltage down, quite noticeable on lead acid batteries.

Sorry I wanted to ask you, it's okay that the soc is approximate, but I wonder despite the voltage is at 12.60 which should mean battery almost charged at 80% because you read 54%? I think there is a lot of difference ....

 

[RCinFLA]

All batteries have an overpotential voltage (also called polarization voltage) which is battery internal energy necessary to drive the chemical/kinetic processes necessary to provide the battery current.

This causes a voltage slump with load and voltage rise with charging. It also has an exponential decay slump/rise versus time.

Lead-acid has a more complex chemical process then lithium-ion batteries, so it suffers greater voltage slump with load current compared to Li-Ion battery.

The exponential time to equilibrium on LFP is typically less than 3 minutes where flooded lead-acid is 15-30 minutes. AGM is less than flooded lead-acid battery.

When you remove load current, the battery recovers to equilibrium terminal voltage for zero current, based on its remaining SoC level.

AGM construction has lower overpotential voltage than flooded lead-acid battery but still much greater than LFP battery chemistry.

This is example of LFP battery, but the general principle applies to all battery chemistries just different amount of slump voltage and decay times.

 

[pollenface]

Sorry I wanted to ask you, it's okay that the soc is approximate, but I wonder despite the voltage is at 12.60 which should mean battery almost charged at 80% because you read 54%? I think there is a lot of difference ....

I don't really get what you're asking but the percentage on your charge controller is not a reliable SOC reference.

 

[frankz66]

All batteries have an overpotential voltage (also called polarization voltage) which is battery internal energy necessary to drive the chemical/kinetic processes necessary to provide the battery current.

This causes a voltage slump with load and voltage rise with charging. It also has an exponential decay slump/rise versus time.

Lead-acid has a more complex chemical process then lithium-ion batteries, so it suffers greater voltage slump with load current compared to Li-Ion battery.

The exponential time to equilibrium on LFP is typically less than 3 minutes where flooded lead-acid is 15-30 minutes. AGM is less than flooded lead-acid battery.

When you remove load current, the battery recovers to equilibrium terminal voltage for zero current, based on its remaining SoC level.

AGM construction has lower overpotential voltage than flooded lead-acid battery but still much greater than LFP battery chemistry.

This is example of LFP battery, but the general principle applies to all battery chemistries just different amount of slump voltage and decay times.
View attachment 131888

Thank you, your fairly technical answer clarified my question. Thank you

 

[frankz66]

I don't really get what you're asking but the percentage on your charge controller is not a reliable SOC reference.

Sorry, but what I wanted to say is that if the voltage at the cut off with constant load is 12.50 -12.60 even if as written many times the soc is approximate, they would do well to take it away that it does not server to anything. If the battery at 12.60 is at 80 % the soc even wrong that it is should not score 56 57 % and so on but then approach 80% not indicating I don't know type 68 % and so on. I know that the soc is the result of a calculated formula, but I think it is very poorly calculated.So for example this morning I found a 34 % residue with 12.00 volts which according to the tables does not correspond to 34 % but much more . The moral is to know: how much energy do I have effectively left to consume? How much power do my batteries have at the end of the day after charging? I know you need an ammeter shunt, but it becomes complicated to know in real time or rather cumbersome to see the charging and discharge conditions.I also wanted to add that the soc becomes a bit precise from the percentages ranging from 10% to a maximum of 35 37 %, because reading the voltage values well or badly they approach the agm tables that highlight the state of charge of the battery. But if you go above this percentage the value is highly inaccurate, in fact as previously written, it seems absurd to me that the voltage at 12.60 that indicates 80% is interpreted at 57 % by the regulator.

 

[pollenface]

Ignore the percentage on your SCC. Epevers SOC percentages correspond to the relationship between the current voltage and the LVD. If you change the LVD it will report a different SOC.

Disconnecting the battery from all loads and letting the voltage settle for a while will give you a rough indication (use a multimeter), but if you really want to be thorough I believe you should fit a shunt and coulomb meter to measure incoming and outgoing energy.

I personally do not use a shunt, I know how much usable capacity I have and what my loads draw in 24hrs, so as long as my batteries get a full charge most of the time, I'm still sitting in the happy zone.

I suggest measuring your outgoing energy at the inverter with a kill-a-watt or similar device, then add 10-15% to account for heat loss.

Eg. If you are using a healthy 110ah AGM @ 20-25c you have at most 660wh of available DC energy which would account for about 550wh AC

FWIW, if you are seeing 12.0v with no loads, it's definitely time to recharge.

Hope this helps

 

[frankz66]

Ignore the percentage on your SCC. Epevers SOC percentages correspond to the relationship between the current voltage and the LVD. If you change the LVD it will report a different SOC.

Disconnecting the battery from all loads and letting the voltage settle for a while will give you a rough indication (use a multimeter), but if you really want to be thorough I believe you should fit a shunt and coulomb meter to measure incoming and outgoing energy.

I personally do not use a shunt, I know how much usable capacity I have and what my loads draw in 24hrs, so as long as my batteries get a full charge most of the time, I'm still sitting in the happy zone.

I suggest measuring your outgoing energy at the inverter with a kill-a-watt or similar device, then add 10-15% to account for heat loss.

Eg. If you are using a healthy 110ah AGM @ 20-25c you have at most 660wh of available DC energy which would account for about 550wh AC

FWIW, if you are seeing 12.0v with no loads, it's definitely time to recharge.

Hope this helps

Thank you, I can say that in what you wrote, I have also adopted these evaluations in a similar way. The battery is 100c, so the values change, so I only have one doubt: If I turn off all the loads, leaving only a few watts of access I mean 10 watts of the reverse on 330 amps of batteries, I read 12.65 so is it correct to say that the batteries are almost all charged? You say to measure the voltage without load after a few minutes, if I try tonight after a sunny day and starting from a residue unfortunately of the soc of 34 % and I find a voltage at no loads of 12.65 is it reliable?

 

[RCinFLA]

Chart is no-load rested voltage vs SoC for most flooded lead-acid batteries. AGM's have slightly greater electrolyte acid concentration that results in a small increase in open circuit voltage for given state of charge.

A little quirk in lead-acid battery if left on float for some time. They will build up a thicker layer of lead-oxide on positive plate that increases impedance of battery. This results in an initial slumping of terminal voltage that will rise up a bit within a couple of minutes as excess lead-oxide is burned off, then progress with a normal discharge voltage drop.

Retail lead-acid batteries have often been sitting on shelf for several months. Avoid buying a 12v lead-acid battery that has an open circuit voltage less than 12.50v.

Acid concentration effects OCV. There is variation in a given battery electrolyte mix. True deep discharge batteries often use lower acid concentration. The higher the starting acid concentration the more 'jacked up' the battery, 'live fast, die young' result.

Electrolyte acid concentration is a compromise between what is good for discharging (greater) and what is good for charging (lower).

 

[frankz66]

Chart is no-load rested voltage vs SoC for most flooded lead-acid batteries. AGM's have slightly greater electrolyte acid concentration that results in a small increase in open circuit voltage for given state of charge.

A little quirk in lead-acid battery if left on float for some time. They will build up a thicker layer of lead-oxide on positive plate that increases impedance of battery. This results in an initial slumping of terminal voltage that will rise up a bit within a couple of minutes as excess lead-oxide is burned off, then progress with a normal discharge voltage drop.

Retail lead-acid batteries have often been sitting on shelf for several months. Avoid buying a 12v lead-acid battery that has an open circuit voltage less than 12.50v.

Acid concentration effects OCV. There is variation in a given battery electrolyte mix. True deep discharge batteries often use lower acid concentration. The higher the starting acid concentration the more 'jacked up' the battery, 'live fast, die young' result.

Electrolyte acid concentration is a compromise between what is good for discharging (greater) and what is good for charging (lower).
View attachment 132025
View attachment 132026

Thank you for your technical response which turns out to be very clear and exhaustive. Since the SOC is approximate and refers to LVD , what is a correct value to be set on LVD beyond the default value which is 11.10 ?In addition, by varying this parameter, can they affect the battery charge values or do they only give me the value of SOC?

 

[pollenface]

You really have to test and observe depending on your load and what your desired outcome is. More load = more voltage sag.

Eg. I run a small load from my Gel bank. I set the LVD to 12.4v, after disconnecting the Gels rest at 12.7v.

12.0-12.2v is what I would suggest as a generic figure, try to keep them resting above 12v for longer life.

 

[frankz66]

You really have to test and observe depending on your load and what your desired outcome is. More load = more voltage sag.

Eg. I run a small load from my Gel bank. I set the LVD to 12.4v, after disconnecting the Gels rest at 12.7v.

12.0-12.2v is what I would suggest as a generic figure, try to keep them resting above 12v for longer life.

Could you tell me which ones to change? Thanks a lot

 

[pollenface]

Not really without understanding your system or what you're wishing to achieve?

If it's a non-important load connected to load terminals of the SCC, and you want to keep some reserve capacity/protect battery then change the "Low Voltage Disconnect" that you have set to 11.08v

 

[frankz66]

Not really without understanding your system or what you're wishing to achieve?

If it's a non-important load connected to load terminals of the SCC, and you want to keep some reserve capacity/protect battery then change the "Low Voltage Disconnect" that you have set to 11.08v

Ok, however you were very kind to provide me with all the information. At the moment my technical comprehension skills are limited, so I stop here to reflect on what you wrote to me. I thank you and all the others who dedicate time to the people who approach this wonderful world of PV.