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Battery voltage raises too fast, causing inverter to cycle from solar to grid and back

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Need help with issue of battery voltage raising too fast during charging.
Setup - 24v 3000w inverter, Epever 30A MPPT, ATS switch, voltage relay.
How system operates ( or supposed to) :
1. Voltage relay is connected to battery.
2 When battery voltage is above 26v ( recommended threshold for AGM battery), voltage relay connects inverter to ATS. Utility power is connected to the second side of ATS
3.ATS senses inverter power and switches to solar. Battery starts discharging, MPPT controller still charging the battery ( actually partially powering the load, taking some load off the battery)
4. If load current is more then MPPT can supply, battery is discharging.
5. When battery battery voltage falls below 26v, voltage relay disables inverter.
6. ATS senses no power from inverter and switches to utility. MPPT continues to charge battery (can also add an external charger to help MPPT and to charge at night if needed)
7. Battery voltage raises to 28.4v ( full charge voltage) and voltage relay switches back to inverter.
Simple system, right? Problem is that after switching to utility, battery voltage rises too fast, in about 2-3 minutes and system switches back to battery power. I'm testing the system with a good load, about 60amps ( pool pump). Initially when battery is fully charged, it runs for 10-15 minutes on battery ( battery is only 80AH), switches to utility, voltage goes up to 28.4 in 3 min, system switches to solar, voltage goes down to 26. System switches back to utility and keeps cycling every 2-3 minutes. NO good. There is no way that in 3 min of charging at 20amp from MPPT controller, it can recharge what was spent in 3 min at 60amp. Which means battery will be completely discharged and permanently damaged.
Question 1 - why voltage is raising so fast. I tested batteries with battery tester, it says they are good.
Question 2 - could this be an issue with all-in-one inverter like Growatt? I'd like to buy this all-in-one box. But I'm reading that Growatt turns off charging immediately after reaching threshold value set in parameter 13 "Setting voltage point back to battery mode". Which means Growatt inverter will be switching back and forth from solar to utility every 3 minutes?
 
AGM don't take charging power like LifePo4 does so the voltage rises.

Switch to a bigger LifePo4 battery....Lithuim stays within a 4 volts from discharged to charged.
 
I'm going to get bigger batteries - probably 150 Ah. But AGM or gel type - too concern about Li fires. But does what you said mean that lead-acid batteries will not work well with Growatt and similar Chinese inverters? They all turn off charging immediately upon reaching set threshold value- leaving battery undercharged?
 
There is no way that in 3 min of charging at 20amp from MPPT controller, it can recharge what was spent in 3 min at 60amp.
Increasing the PV input to be above the usage will prevent cycling.
Changing batteries will only decrease the cycling rather than prevent.
 
I do not mind cycling the battery charging. This is how it all works anyway. Problem and question - why is it cycling too often. I expected the system to run low loads on solar power (which is does just fine with PV input above the usage) and run high loads on battery until battery drops below set point, then run load on utility power while battery is charging. I thought that after running say 60amp load for 15 min ( total 15 Ah), the battery would be charging for 60-90 min at 10amps from MPPT, while system is running on utility and then switches back to battery again. Problem and question - battery voltage rises to 28.4 in only few minutes, charging stops, system goes to battery power and starts cycling every 3 minutes. I do not mind cycling every 1 to 2 hours and fully charging battery in between - but not every 3 min, draining battery to ground. Battery, according to battery tester, is good. I cannot figure out what is going on. Any ideas?
 
Need help with issue of battery voltage raising too fast during charging.
Setup - 24v 3000w inverter, Epever 30A MPPT, ATS switch, voltage relay.
How system operates ( or supposed to) :
1. Voltage relay is connected to battery.
2 When battery voltage is above 26v ( recommended threshold for AGM battery), voltage relay connects inverter to ATS. Utility power is connected to the second side of ATS
3.ATS senses inverter power and switches to solar. Battery starts discharging, MPPT controller still charging the battery ( actually partially powering the load, taking some load off the battery)
4. If load current is more then MPPT can supply, battery is discharging.
5. When battery battery voltage falls below 26v, voltage relay disables inverter.
6. ATS senses no power from inverter and switches to utility. MPPT continues to charge battery (can also add an external charger to help MPPT and to charge at night if needed)
7. Battery voltage raises to 28.4v ( full charge voltage) and voltage relay switches back to inverter.
Simple system, right? Problem is that after switching to utility, battery voltage rises too fast, in about 2-3 minutes and system switches back to battery power. I'm testing the system with a good load, about 60amps ( pool pump). Initially when battery is fully charged, it runs for 10-15 minutes on battery ( battery is only 80AH), switches to utility, voltage goes up to 28.4 in 3 min, system switches to solar, voltage goes down to 26. System switches back to utility and keeps cycling every 2-3 minutes. NO good. There is no way that in 3 min of charging at 20amp from MPPT controller, it can recharge what was spent in 3 min at 60amp. Which means battery will be completely discharged and permanently damaged.
Question 1 - why voltage is raising so fast. I tested batteries with battery tester, it says they are good.
Question 2 - could this be an issue with all-in-one inverter like Growatt? I'd like to buy this all-in-one box. But I'm reading that Growatt turns off charging immediately after reaching threshold value set in parameter 13 "Setting voltage point back to battery mode". Which means Growatt inverter will be switching back and forth from solar to utility every 3 minutes?
You’re not getting a full charge. The voltage will rise fast because of the relatively small battery.

My personal opinion is the battery is to small for what your wanting to do.

I could be way off base here but there it is.

You could set you CC to hold that voltage for a longer time before switching back allowing for better absorption possibly also.

Does Growatt not have a Absorption, float setting?
 
I agree that battery is too small for real application, I'm using what I had for testing ( and made sure that these small batteries are good - at least battery tester says they are). But regardless of the size - I thought, that if I take 10 Ah from the battery, it will take 10 Ah to recharge it back to full. Which takes 1 hour at 10 amp from solar controller. I just do not understand why battery voltage goes up to full charge voltage so quick? And yes, I was thinking about setting a timer for an hour or two before system switches back to solar. But since battery voltage goes to 28.4, indicating full charge, solar controller stops charging!! So giving it another hours for charging will not help.
As to Growatt, it may have same problem with cycling. Well discussed here https://diysolarforum.com/threads/growatt-odd-behavior.22696/
Looks like it turns off charging immediately after reaching threshold value set in parameter 13 "Setting voltage point back to battery mode".
And at this time internal MPPT shuts off, system goes to battery power ( cycling the battery) and available solar energy is not used ( wasted)- instead of using solar to power the load, while battery remains full.
Charging resumes after reaching another set point - Parameter 12, voltage point back to utility source.
Which means in my case Growatt would be cycling in and out of solar as well.
 
But regardless of the size - I thought, that if I take 10 Ah from the battery, it will take 10 Ah to recharge it back to full. Which takes 1 hour at 10 amp from solar controller.
Yes it does, ignoring losses.
There is a difference between battery charging voltage and battery charged voltage. Most likely the system is not differentiating and is made worse by the relatively larger charging current going into the smaller batteries.
Edit- I get around Ohm's Law on my much smaller system by using a few voltage detectors with time delays to let the voltage stabilise. This will give you another area to look at for a fix.
 
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Read up on charging AGM batteries.

You need a differential between the charged voltage level and the recharge voltage level for your system to work.
Battery at around 24 volts would be my suggested point to start charging and 28.8 volts for a time duration to indicate end of charge. Without adding a timer to the 'charged voltage level' the battery would only be charging to around 80% SOC. Without a timer to allow the battery to fully absorb the system would still function but battery life will be reduced.
. I just do not understand why battery voltage goes up to full charge voltage so quick?
The internal resistance of the battery rises very quickly and thus the voltage of a battery under charge is not an indication of state of charge.
Once the battery gets to absorption voltage, ( that will be between 28.8 and 29.6 volts) it will be at part charge, say 75%. The voltage will hold steady for the remainder of the charge cycle that will take some time, ( in excess of 2 hours). The battery is not fully charged until the current drops to less than 1% of capacity, 1 amp per 100Ah battery. A 50% discharged battery will take a minimum of 4 to 5 hours to fully charge regardless of charge current.

Mike
 
Mike, thank you for a very good explanation. As I mentioned in the opening statement, my system voltage relay does switches to utility power when battery voltage drop to 23.8 or so. After that I expected solar controller to charge battery during sun hours and then turn on a external charger if needed until battery is fully charged. I thought battery voltage would be an indication of charge state. Turns out it is not - thanks to your reply. If this is true- battery voltage rises quickly- then good charger after reaching bulk voltage is actually looking at the current and only when current drops to say 1amp, calls it done, right? Then is there anything wrong with my solar MPPT controller ( I have Epever 30a MPPT)? Because it stops charging as soon as battery voltage reaches 28.8 ( this is the settings controller has for acid battery). Controller shows battery current going from 10amp to 1-2 amps as soon as battery voltage hits 28.8- no absorption. Even if I set a timer, it won't help, controller will be idling and not charging. Same thing I read about Growatt inverters- they stop charging after reaching set point voltage, no absorption. Does it mean all these Chinese controllers leave battery undercharged?
 
I'm going to get bigger batteries - probably 150 Ah. But AGM or gel type - too concern about Li fires. But does what you said mean that lead-acid batteries will not work well with Growatt and similar Chinese inverters? They all turn off charging immediately upon reaching set threshold value- leaving battery undercharged?
I promise you LIPO4 are not going to catch fire ,they have a pressure release. LI batterys do catch fire not LIPO4
 
I have the same issue with my all in one system. I think it's because the charger on the mains artificially (and incorrectly) shows the battery voltage to be that of the bulk charge voltage, so immediately thinks it's reached 100% charged.

I think the trick is to make sure the switch back to utility parameter should be greater than the bulk charge parameter...but I'm not sure.
 
After reading about and watching my Epever SCC, I think I know what the problem is. System switches from grid to solar, runs until battery is down to a set limit ( say 25 or 24 v), and then switches back to grid. While grid power is running the pump, SCC starts to charge the battery and enters boost mode quickly. Recommended boost voltage for AGM is around 29.4v. So switching pump back to solar immediately after reaching this voltage was incorrect, resulting in battery not recharged completely. Correct way is to either give it some time ( 1hr?) before switching back to solar or better wait until SCC drops voltage to floating ( about 27.6v). In this case battery is fully charged and system can be switched back to solar. That's what I did and now system is working fine, without frequently cycling the battery. The goal anyway is to run on solar only when there is enough sun - without draining the battery. And that is what I read here about some all in one inverters - they switch to battery mode after reaching boost voltage without giving the battery time to soak on boost mode. If I had one, it would be constantly cycling. That is why system built with separate components is better - I think. Now I'm looking for a device ( reasonably priced) to use as a solar radiation meter. I'd like to switch system to solar only when there is enough sun power to run the pump, without draining the battery. For now I'm using a tiny panel from garden solar light. It does generates voltage from 1.5 ( cloudy) to 2.8 ( full sun). But does not looks stable. One day shows 2.75, next day 2.65 at visually same sun conditions. Does anybody know such a device- in $20-$50 range, getting an industrial grade pyrometer is not an option.
 
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