Off grid system, 48V UPS, multiple charge controllers each connected to battery?

[Will-UK]

Hi I'm new and want to build an off grid system for fun / for power security and reducing fossil fuel consumption. I have a workshop area and a cabin. Currently sketching system diagrams and gathering parts.

I have an old 3000VA APC UPS which uses 48 volts of batteries.
I have purchased some reclaimed sealed lead acid batteries. They are 12V 38ah. I have.. 64 of them. Yes, sixty four. (I make that 29kw/h if I connect them all up)

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I was thinking 4 banks of 16 making the required 48V. I could even do them in 2 separate lots.

Doesn't seem to be many budget charge controllers that output 48V so I was considering having something like one charge controller per battery. (or battery string) So each battery will be charged by 3 or 4 PV panels, via its own charge controller, and the batteries will be in series so that the 48V UPS/inverter can run from them. Can anyone see a reason why this wouldn't work?

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I have some constant loads I would like to run via solar at least. A CCTV DVR system, PC and a couple of routers/ switches, plus some outdoor flood lighting. (80w mercury lamp, and some LED lamps)

There are some high wattage things here such as the air compressor but that will be staying on grid, along with stuff like the mig welder. I was even consideirng putting in two ring mains so I can swap appliances from grid to off-grid outlets according to state of battery / sunlight.

It is summer at the mo and I've not been using many power tools so in the last 2 or 3 days I have used about 6 to 10 units per 24h.

I have found a source of well priced 250W mono panels locally and have bought a couple to experiment with. I am planning to buy 12 or maybe 16 total. (3-4kwp)

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I'm considering building a tracking frame for them as well, as a nice little project.

[paulcheung]

Doesn't seem to be many charge controllers that output 48V so I was considering having something like one charge controller per battery. .

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Actually all the quality charge controllers which sell more than US$500 are capable charge battery banks from 12 volts to 48 volts. some are rates 96 amps like The Classic 150.

[Colt45]

The UPS will not survive life as an inverter unless it was an online UPS. You can (will need to) do some heavy mods to ones like the Smart UPS to make them even think about working as a stand alone inverter.

As mentioned one charge controller will work for 48v. I would be worried that the batteries you have will not all play well with each other. Depends on the conditions each is in but that is a lot of cells! Having less but larger batteries is what you want.

And good luck getting anything you mentioned past an inspector in the US.

[Mike90250]

Way too many batteries and interconnects to be able to manage. With that many used batteries, there is always going to be one dieing on you, and your job to find it will drive you nuts after 3 or 4 of them.
For the price of all the interconnects, buss bars, crimp terminals and crimp tools, you would come out ahead buying 4 new 12V 100ah deep cycle batteries from the closest big box store.

UPS batteries are generally GEL batteries, and have a limited number of deep cycles. GEL batteries also do not recharge very fast, and so are not used in solar, but generally just in Float service (UPS, emergency lights.....)

[Will-UK]

Thanks for replies. Actually I thought that having one charge controller per battery string might actually be an advantage in terms of them not going out of balance. I had a 24 volt vehicle before, and it was sometimes a pain.

These batteries are all 18 months old and all test good. I did also wonder about the life of them being discharged regularly but i figured having lots of them would go some way to compensate. They were way cheaper than anything else and if I get everything running, I can still buy deep cycle batteries in a couple of years . I have lots of wire and crimps, I'm also going to have a lot of fuses fitted.

Another thing is I was thinking of having some 24 or 12vdc lighting so with separate charge controller per 12v battery string, it should make it possible whereas i think it would really upset the balance having one 48v charge controller accross the lot.

Currently looking at different charge controllers on offer and liking the idea of the MPPT ones. (lots on Ebay etc) Is there a section on the forum where each model of charge controller out there is discussed / rated?

[SunEagle]

Thanks for replies. Actually I thought that having one charge controller per battery string might actually be an advantage in terms of them not going out of balance. I had a 24 volt vehicle before, and it was sometimes a pain.

These batteries are all 18 months old and all test good. I did also wonder about the life of them being discharged regularly but i figured having lots of them would go some way to compensate. They were way cheaper than anything else and if I get everything running, I can still buy deep cycle batteries in a couple of years . I have lots of wire and crimps, I'm also going to have a lot of fuses fitted.

Another thing is I was thinking of having some 24 or 12vdc lighting so with separate charge controller per 12v battery string, it should make it possible whereas i think it would really upset the balance having one 48v charge controller accross the lot.

Currently looking at different charge controllers on offer and liking the idea of the MPPT ones. (lots on Ebay etc) Is there a section on the forum where each model of charge controller out there is discussed / rated?

The biggest consensus is that most of those cheap MPPT charge controllers you find on eBay are garbage and really have PWM circuitry. The better MPPT type charges will cost more but are of a higher quality grade. Morningstar and Midnight solar are two that come to mind.

[Will-UK]

Thanks I did wonder. Be nice if ONE was useable.

The Outback ones look good too and some of these controllers seem to have long warranties.