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building a solar powered barn
So my wife and I are building a new barn for our 3 horses, and we've been toying with different ideas on how to power it, the barns needs should be fairly modest, several lights, a small electric fence, some sort of well pump, and possibly a small amount of heat in the tack room to keep the water line from freezing. So we've decided to go with a small solar array and a battery pack made up of old laptop cells which I'm able to come across fairly easily though work.  So far I've just been stripping the laptop packs into individual cells, I've ordered a couple LitoKala Lii-500 chargers for testing as well as enough cell holders and nickel strips for 400 cells to get me started.

I also have an old UPS that I'm thinking I may be able to use as an inverter, the 24v sla batteries in it are shot but the rest of the unit works, I'll have to spend some time to research this to see if it will work for this or not.

pafreitasadv likes this post
A direct DC system would probably best suit your needs. The lights, well pump and electric fence could all be run off the battery directly in a 24v configuration fairly efficiently, just add some solar panels and 24V MPPT controller and you're in business.

There is no efficient way to generate heat from a battery pack with an electric heat element. You could use a diesel heater, the battery pack would then only be needed for the fan and fuel pump.

The little UPS is not built for efficiency and not big enough to be practical, it would struggle with most water pumps.

If you do want to go down the UPS route a 2200 or 3000VA unit would do what you're asking and can be had cheap with dead batteries, but you need to factory in ~100wh just for the UPS to be on without doing anything.
+1 to go all DC.
Maybe the water line could be arranged to be self draining, eg downhill, only full when pump is on?
Running off solar, DIY & electronics fan :-)
a lot of good advice fellas, thanks, I'll set the ups on the back burner for now.

I was able to get a hold of some more batteries today, new old stock hp laptop batteries! have another 100 or so left to unbox, then start breaking them down into cells.

ordered some single cell holders and tp4056 chargers, got them wired together to start charging some cells, so far I've cleaned about 600 cells with anther 900 or so to go still in packs.

Here i'm testing the chargers, now that I know they work I'll clean them up and secure everything down.

my LiitoKala chargers finally arrived, now begins the slow process of testing cells, so far most are in the high 2500 to mid 2600 mAh which is encouraging 

If you're going to use the UPS: they have basically no cooling system in place, since the small battery would run out of power before anything could overheat. Back in the day, I drilled holes to the sides and mounted a cooling fan to blow air across the electronics inside.
Also, I think the voltages are fixed for SLA use, so it may be better to buy a proper off-grid charger/inverter.
Modular PowerShelf using 3D printed packs.  60kWh and growing.
I too started with APC UPSs Smile    A 7s 18650 lithium-ion battery works great with them.   It will charge them up to aprox 27.5v (3.93v/cell) at max and cutt-off around 3.0v - e.g. within operating range and on the high end, well below 4.2v/cell for a good chance at long life.  

I use a standard 7s7p (15ah) battery pack with Chargery for my BMS.  You'll need a BMS.

Here's my 'lab' setup with 7s7p + Chargery 8T BMS - I use it to power my iCharger X8 for battery builds 

These consume around 40w of power in idle which is 960w each day.  So you need to size your PV array to provide the additional power.  I think the idle power consumption + 3.9v/cell max charge are among the reasons that they are not as widely used as one might imagine - but I've had APCs for 20+ years and in my experience they are excellent pieces of equipment.

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