50 bat. Off-grid back-up system sizing, help needed.

[evancanada]

Hi,

I have 50x UPS12-400MR 12V 102Ah batteries

I would like to back up for 2 days: 5x 1 hp 120V 1 phase circulating pumps 5x1000W=5000W
1x 120V 5A 1 phase blower 600W
LED lights around 330W
Total 9000W


My first question, can I combine 50 (48) batteries in one bank to make 4x12 48V 1224Ah system or what is a better solution?


My calculation: 9000Wx 12h= 108000Wh

x2= 234,78 kWh
D.o.D /0.5= 469.56kWh
/48V= 9782.5Ah I guess I need to reduce my load or use a generator!

My first question, can I combine 50 (48) batteries in one bank to make 4x12 48V 1224Ah system for back up or what is a better solution?
What inverter and charge controller or hybrid inverter should I use?
Please advise, what charging current should be applied for a bank like this? 140A?

[SunEagle]

I see a few issues with that battery bank.

First off you have 12 parallel strings of 4 x 12V batteries. That provides a very high chance of not equally charging or discharging them all which will lead to failures.

Next with a 48 x 12V 102Ah battery bank you will need over 120 amps of changing which will require multiple CC's since the largest most common can delivery only 80amps.

IMO you would be better off with a generator to run that pump because batteries (especially used UPS type) will be quickly killed off requiring you to purchase new ones.

Another solution would be to get low voltage (2v, 4v or 6v) high Amp Hour rated batteries and wire them in series to eliminate multiple parallel wired strings.

[evancanada]

I see a few issues with that battery bank.

First off you have 12 parallel strings of 4 x 12V batteries. That provides a very high chance of not equally charging or discharging them all which will lead to failures.

Next with a 48 x 12V 102Ah battery bank you will need over 120 amps of changing which will require multiple CC's since the largest most common can delivery only 80amps.

IMO you would be better off with a generator to run that pump because batteries (especially used UPS type) will be quickly killed off requiring you to purchase new ones.

Another solution would be to get low voltage (2v, 4v or 6v) high Amp Hour rated batteries and wire them in series to eliminate multiple parallel wired strings.

Thank you so much for looking into this! I will consider the generator for sure.

I got the batteries almost for free and don't want to waste them.

Can I use them for back up just for the LED lights and the blower then? Where else I can use them?

[Mike90250]

There is a good reason used telecom batteries are so cheap - better to sell them for pennies to a sucker, than to have to pay disposal fees. When they refresh a plant, they have hundreds of the batteries that are considered industrial toxic waste.

[Ampster]

There is a good reason used telecom batteries are so cheap - better to sell them for pennies to a sucker, than to have to pay disposal fees. When they refresh a plant, they have hundreds of the batteries that are considered industrial toxic waste.

And the thing people don't realize is those batteries are designed to be maintained by trickle charge. They aren't designed for the deeper and more frequent discharge cycles that an off grid user would need them for.

[littleharbor]

There is a good reason used telecom batteries are so cheap - better to sell them for pennies to a sucker, than to have to pay disposal fees. When they refresh a plant, they have hundreds of the batteries that are considered industrial toxic waste.

Typical lead acid AGM batteries can be recycled at any battery recycler. The last set I took in for recycle really surprised me. They were 105 pounds each and the recycler paid me 38 cents per pound for scrap value. Needless to say I was pleasantly surprised, expecting to get about $15.00 per battery and getting over $38.00 each instead.

[evancanada]

Thank you for your replies!

You think it is not a good idea to even try to back up the LED lights for 2-3 days with them?

[Mike90250]

The batteries are old, used and were removed from service because they are unrelaible, They may be good enough for your use, so have a go at it, but don't be surprised if they don't last 5 years.

[SunEagle]

The batteries are old, used and were removed from service because they are unrelaible, They may be good enough for your use, so have a go at it, but don't be surprised if they don't last 5 years.

Or one year depending on how many are wired in parallel or can be charged anywhere close to 80% SOC.