I've just been given two 105Ah leisure batteries. They seem to have charged up OK, although one did appear to leak a little around the top seal.
Anyway, would it be possible to use one of them as the basis of a UPS? If so, are they difficult to build from components, or would I be better getting one SH from ebay etc.?
You can get relatively inexpensive inverters from Amazon, eBay etc One of those combined with a suitable charger would do what you want. You will need to decide how much output power you need and then add some margin for start-up surges. Other choices are between "pure sine wave" and the cheaper ones that approximate it very crudely with a square wave that has zero voltage gaps between the positive and negative polarities. Pure sine wave is less likely to cause problems if you are driving pumps or central heating systems (which may need the neutral to be earthed for the flame sensor to work). Computer equipment is unlikely to care about the waveform. There is a whole ecosystem of caravan owners and off-grid enthusiasts who take a lot of interest in such things. Some of them are around here!
John
I forgot to add - there is no point in trying to build from components. The commercial inverters are so competitively priced you would struggle to get the parts for the price of a ready made one.
John
You don't want to build from components (those no-brand Chinese MOSFETs bought by the thousand are a fraction of the price you can buy branded ones for), but it is possible to build one from sub-assemblies - eg there's a collection of DIN rail parts: battery chargers, contactors, inverters, etc.
I would only do that if you can't find a commercial device to do what you want, though.
Theo
That depends exactly what you want to power from them. Back in the last nastiness of the miner strike, I used a small lawnmower battery with some series regulators to power all manner of portable gear from cassette tdecks, car amps radios and lots of other things. The hardest part was finding out the voltages and currents demanded by the various items and finding the right plugs for their sockets. Brian
First things first.
Put a plastic cover over one or both of the battery terminals to avoid an accidental and potentially disastrous short circuit. And put an automotive low voltage fuse in series with the supply lead.
A mains inverter would give you more output power for a lower price if you don't need reliable switchover when the mains fails. They are a fair bit cheaper than a UPS and capable of being used in the wilds.
Fairly high power large mains voltage storage capacitors and step up transformers can be potentially lethal if you make a mistake.
The cost of building one from parts would be several times what a mass produced one would cost fully built and tested with 1 year warrantee.
Noted, thanks.
I had an AA short circuit recently and it wasn't pretty - dread to think what one of these beasts would do.
Thinking about it, UPS isn't that important. The ability to power low current (<3A) devices is more what I'm after.
I was thinking in terms of using a S/H UPS as a donor for the batteries though.
Thanks - and to the others. I'll think in terms of an inverter of S/H APC UPS
Add a suitably large output 13.8v power supply to meet your current needs, plus a 12v to mains inverter - then you could run permanently on your homemade UPS.
For some things, you can also get a DC input power supply and do away with the inverter completely. You can certainly get 12V dc input ATX PSUs.
Something to look out for though is that some need a well regulated 12V input whereas others will cope with the wider voltage range that can come from a lead-acid battery either being charged or discharged. These are usually described as "automotive". The ones that need a well regulated
12v input simply pass on the input to the motherboard, whereas the automotive ones regulate the 12V supply as well as all the other outputs.John
I've certainly seen the unregulated ones, but they have been single boards, rather than a full ATX unit. I've not looked very far, so others may be as you say.
You can get "picopsu"s which are little larger than teh mother board plug. These come in two variants, as noted above.
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