I’ve been doing a lot of reading but just want to double check some settings before I go changing from defaults. Application is off grid solar powering diesel heater with LifePO4 battery bank.
Equipment:
MPPT 75/15
4x Renogy 100w 12v panels (2 strings, 24v)
2x ERYY 12v 25ah batteries built in BMS (series)
Default settings I’m considering changing:
Battery spec sheet states 30 amp max, LifPO4 default charging is 15amp
I seem to remember seeing recommendation to set Absorption time to 1/2hr per 100ah - default is 2hr. Thats a big difference.
Operating mode default is BatterLife - the heater controller I’m using (Afterburner) has voltage monitoring and will shut down on low voltage so Constant On seems ideal.
Are you connecting your diesel heater to the load output of the MPPT. If you are make sure that the start up load of the fans and pumps will not exceed the 15A rating of the MPPT. Personally, I would connect the diesel heater to the batteries unless you really need one of the load output functions.
Your battery may be capable of accepting 30A charge, but the MPPT you have chosen is limited to 15A as the max output so you are not going to be able to change this. 15A charging on a 25Ah battery is perfectly acceptable. Absorption time I would set to 1 hour because I believe that this is the minimum you can set on the Victron MPPT. The absorption time with battery capacity is also related to the size of the charging source compared to the battery Ah rating.
ERYY battery with BMS up to 4 in series. I assumed battery BMS would handle balancing as long as charger kept providing sufficient voltage
Diesel heater is hooked to output of MPPT. From my observations, start up load is around 10 amp, running can be as low as 3amps. DOH! 15 amp charger. I was so focused on the manual and settings, forgot the obvious.
I was trying to find more info on capacity vs charging source, I’ve not found any calculators yet but I did find this thread Given the batteries have BMS on board and the cloudy day issue, would leaving it at 2 hours (or more) hurt?
The BMS in each battery will keep the cells in that battery balanced. However, with low cost batteries in series that do not share comms there is no guarantee that the batteries will remain balanced. Charge both batteries to 100% singly before connecting them in series. Keep an eye on the 2 batteries. It is possible to add a battery balancer to keep them in balance. I know it is after the fact, a single 24V battery is better than 2 12V in series.
Te absorption, see how you go, if the batteries get down to around 1A charge current consider they are full and see how long that takes once absorption voltage is reached.