MPPSolar Inverter Charger (PWM) AGM batteries low voltage setting?

[jtsi73]

Hi again!

I have tried to find info on my batteries online (Sznajder Explorer Plus AGM), specifically on the voltages and recomended lowest discharge voltage, can't find it. I have found a few info-sites, all with different info, but all seem to agree upon that you should not let your batteries go below 50%. The first inverter charger (a Chinese brand that the solarsystem seller here in Finland sold me) had the cut of level at 42% fixed, I used it for about a month (it had other issues so I returned it). The model I have now from MPPSolar has different settings and they are voltage settings, the default is 46V (48V system). This is the battery voltage when the inverter flips over to the grid, bypassing the batteries for the load. The PV:s then charge the batteries. Is this OK? Have my batteries allready been damaged from the Chinese inverter? I tried to set the low level voltage at 49V but, that seems to make the inverter flip into grid mode for even a small load increase. I have 8pcs of 70Ah AGM batteries connected to 48V (2 paralell-4 series). The inverter charger is a 4000W model with a max of 50 A charging (PWM) ( I have a 25 A 59V PV array). What should the setting for the voltage be? The maximum load I have is about 2,2KVA (dishwasher, when heating water + other loads, about 10 mins), average othervise is about 300VA.

[jtsi73]

Hello

I meassured the batteries this morning after disconnecting them last night and they where all 12,3V. The inverter showed 11,8 when I switched it off so I guess thats OK?

[MJLorton]

Hi,

Good question, as you noted and I always say, try not to use more than 50% of the rated capacity or go lower than 12v. A few times just below 12 volts is not going to add significantly more damage or deterioration to the batteries. However, even going to 50% of rated capacity or 12v will reduce the number life cycles. If you look at graphs for battery life the number of cycles increases a fair bit once you stay above 60-70% state of charge. Also, the rate at which you draw current will have an impact. More batteries in parallel will reduce the impact on each cell / battery.

Hope that helps.

Cheers,
Martin.

[jtsi73]

Thanks!

I'm concidering switching my system to a similar one you made a series on Youtube about. So that I'd have a grid tie inverter and a separate charger. These battery systems just eat up too much energy. Thanks for really good advise on the videos!

[MJLorton]

My pleasure. I have an interesting device on the way for testing and cycling batteries of various technologies. It has two independent channels so two batteries can be tested at the same time with different load and charge cycles. It logs all the data too.

I hope to expand the information, data and my knowledge in this area as I find it very interesting....will share the details soon.

Cheers,
Martin.