Recently, I have managed to acquire a used, APC 3000 VA uninterruptible power supply – minus batteries. (APC branded battery packs cost almost as much as a new UPS. Generic sealed lead-acid batteries of the same capacity can be bought from the likes of
http://www.tayna.co.uk/ for a fraction of that.) The UPS is basically a self-contained battery pack, charger and inverter. It converts DC from a bank of batteries, which are ordinarily kept charged from the mains, to AC when the mains fails. I plan to use this, in conjunction with a bank of large batteries, to implement a solar energy storage system.
Now I have managed to pick up some batteries. Although they are not the right ones for this UPS, they are "just about" compatible – the right voltage, but the wrong capacity (there would normally be two series chains of four 12 V, 5.5 Ah batteries, in parallel for 48 V / 11 Ah; I have just one series chain of four 12 V, 7 Ah batteries, for 48 V / 7 Ah).
These batteries are rather used, and have a remaining usable capacity somewhat lower than advertised –
but they cost nothing, which is always a point in favour.
And of course, having some batteries, we can test out the UPS!
You can see clearly that these aren't the right batteries -- I have had to stand the battery tray on top of the UPS because these are too tall. The lamp was from an earlier test; look out for the black extension lead heading off the bottom left corner. The 4-way extension lead is fitted with a
"C20" plug for the UPS output (which can be up to 3000 VA, which is more than the usual "C14" / kettle-type can handle.) The other end goes to .....
This microwave oven! It's cooking just the burger from a microwave cheeseburger. I toasted the cob separately, and added my own special tomato and herb sauce.
I was worried that the microwave would pull down the battery voltage far enough to trip the undervoltage cut-out in the UPS –this was what happened with a 2 kW kettle. Fortunately, the slow-start action of the magnetron filament heating up was enough to allow the UPS batteries to recover.
This is a good sign. And the nice people at
http://www.tayna.co.uk/ are very helpful. They certainly know their batteries.
