I just bought SmartSolar MPPT 150/45, 3 x 700w solar panels (in series @138V) and Redodo 24v 100ah LifoPO4 battery.
I am doing top balancing aka charging each battery on their own before connecting in series.
I charged first battery just fine. Today I tried to charge the second one. Everything seemed find until the second battery entered Absorption phase.
I have screenshots of the app:
Bulk: 28.54V @ 24.50A
Absorption: 30.34V @ 0A → 49.45V @ 0A
This is all happening within one minute.
There only components in the system: panel, mppt and battery. Nothing else, no consumers, no fuses.
The app also reports error: Battery voltage too high.
I measured the battery on second try with KEW 2000 and saw the same results: voltage spikes to 30 - 50V.
I tightened all the screws on the MPPT and battery, it was still happening.
I connected the first battery, it is happening with that one too.
NB! I also have two month old system using SmartSolar MPPT 150/35 and that is working just fine with the same 3 series solar panels and 48V battery (Redodo 12v 100ah x 4 in series).
The voltage you quote of 138V is very close to the 150V limit, which is a hard limit, transgressing this can damage the MPPT. Can you check if the panels have delivered a high voltage, were the panels cold as voltage increases when cold and max Voc should always be calculated at low temp when you are close.
Does not seem to be the issue. Maximum solar voltage for the day was 141.8V for the new MPPT (that is acting up) and the old one 142.2V (which is working fine). It is close (will remove one panel from series when it gets colder), but should not be the reason why the new one is acting up.
I think the battery is cutting off the charge current and that causes a voltage spike.
Dose the battery have Bluetooth and an app?
If yes, look if there are warnings about cell over voltage.
Unfortunately the battery BMS does not have bluetooth (now I am regretting buying without one).
Order of events:
I did charge the first battery yesterday, it did not start absorption charging.
This morning I charged the second battery which finished with 2h of absorption and 17min float.
Then I reconnected the first battery and tried to top it up.
Looking at the trends, successful second battery charging went like this today:
Charging was stable at 28.63V 0.5A for 1.5h
Then the voltage slowly went up (5 minute intervals):
28.63V 0.5A
29.75V 0.4A
30.35V 0.4A
30.87V 0.3A
31.09V 0.3A
31.33V 0.2A
31.62V 0.2A
31.76V 0.2A
28.28V 0A
It does seem like the charging stopped normally (history shows 2h absorption charging and 17min of float), but why did the MPPT voltage go so high?
I am using the Victron Smart Lithium (LiFePo4) battery preset and mppt should not go over 28.4V during absorption, right?
I disconnected the MPPT from solar and battery and let it sit for couple of minutes and then reconnected to the first battery (the one needed topping off). It started with 28.13V 12A for 40 minutes gradually reducing amps to 2.6A (@ 28.42V) and then went up 33.12V at 1.4A.
33.42V 1.3A
34.86V 0.6A
and then it seems reasonable to assume that battery disconnected (voltage is all over the place 32-40V and current is 0A).
According to the battery manual:
Charge/Bulk voltage: 28.8/29.2V (should actually mean 28.2V - 29.2V)
Absorption Voltage: 28.8/29.2V
Over Voltage disconnect: 30V
Over Voltage reconnect: 28.4V
I let the batteries rest for an hour and they were 27.2V and 27.4V, after 6h of connected parallel, they are both 27.2V (after connecting in series at 54.2V).
I was thinking that I will try again with two batteries in series (starting at 54.2V) and see if that causes the same issue.