Battery low voltage switch over setting

[Jacque]

 

Good day

 

I need some advise with regards to my low battery  switch over voltage.

 

I have 4x110ah mombate battery supplying only dedicated circuits in my house. Currently I am only using the system as a backup due to verious problem. I do switch over every Sunday for a few hours just to cycle the batteries. Is that a good practice?

 

I am thinking of installing 6x 315w panels to basically run on the system 24/7. On an average the power consumption is about 590w during the day and 367w during the night.

I am not planning to add another 4xbatteries. The supplier/installer adviced me to set the low voltage cut setting to 49V to extent the batteries life to 10 years. If I leave the setting at 46V the batteries will only last 2 years.

Currently the low alarm (code 04) initiate at 48V and total cut off at 46V.

 

Could you please advice in this regards.

 

Thank you.

 

[Chris Hobson]

Hi Jaque 

Welcome 

You don't mention what inverter you are using but from you post I surmise an Axpert.

2 hours ago, Jacque said:

I do switch over every Sunday for a few hours just to cycle the batteries. Is that a good practice?

If you had flooded batteries I would say good idea. There is a school of thought that moderate cycling is good for the batteries and prevents stratification of the electrolyte. Since your 110Ah Monbat batteries are in all likelihood standby AGM batteries there is no advantage in cycling them lightly. I would go as far as to say that they have been designed to stay fully charged and occasionally (once or twice a quarter) have a discharge cycle and that you may be shortening their lifespan with your weekly discharge. Your batteries may give you 250 - 300 cycles if you are lucky. I'm guessing (as I am not sure what model they are) but I am not expecting the 1200-1600 cycles (or more) of true deep cycle batteries.

2 hours ago, Jacque said:

The supplier/installer adviced me to set the low voltage cut setting to 49V to extent the batteries life to 10 years.

You cannot set the low cut-off that high so if you set your back to grid  voltage to 49V (program 12) and back to solar (program 13) to FUL you would go some way to protecting your batteries. I would set your battery low cut off to 47V. I would like to set it higher but you have a very small bank and any higher you would probably find frustrating due to battery voltage sag even under moderate loads. At 48V your battery bank is roughly 50% discharged and the recommendation is that one does not discharge below this level for prolonged battery life.

2 hours ago, Jacque said:

On an average the power consumption is about 590w during the day and 367w during the night.

Working with your figures 

1. Your batteries are going to last roughly 6 hours into the night and then you enter the stage where you considerably shorten your batteries lifespan due to over discharge.
2. Your energy budget for the day is roughly 12kW and that in my book translates to about 3kW of panels if you wanted to run 24/7 on an Axpert.