In a recent post concerning Genset problems someone suggested using a UPS. I have checked out the threads concerning UPS. There's not a lot of information, so here goes:

Some years ago I managed to pick up a returned-under-warranty UPS of the type sold in Indonesia for PCs. The battery apparently had died, and the cause was not known. I possessed an identical unit that was functioning normally. (Kenika 600W 220V 50 hertz)

The broken unit seemed fine – what good luck! But each unit provided only a trickle charge. That makes sense when you consider that such a unit is rarely called upon and most people save their work and shut down as soon as possible.

I wanted to use a UPS in an Indonesian school in the mountains that has a really unreliable power supply, and it might take a half hour to find someone game to start and hook up a genset....

My brilliant, “original” idea was to hook up a bigger 12V battery which would have to be charged independently according to demand. Well, the physics teacher could organize that…. Maybe. What worried me was that the simple trickle-charging circuit (I don’t understand these things too well) might be overloaded if I connected a bigger battery. But this did not prove the case. Experience on small yacht systems tell me that the minimal charge current required to just maintain charge is directly proportional to the size of the batteries. (One does not hook up a 1000 Amp hour battery system to a 20W solar panel!)

But I did not consider how the inverter section of the UPS could cope with continuous demand. The unit did not get used much. When power fails people here light candles and chat.

Last year I found a guy who had purchased a UPS with a big battery. It turned out that a shop in Surabaya was selling standard UPS units, with modifications that as far as I could see consisted of wires leading out to the external battery, and a computer fan fitted over a hole cut in the UPS case. Ah, I thought, it’s bloody hot in Surabaya – hence the fan! In Indonesia some years ago all continuously used PC’s ran with their cases open and big external fans….

I tested this particular unit and found that it got hot quickly under a moderate load. This could be explained by a fault – one that I could not identify. But then I discovered that the UPS case showed signs of much earlier meltings.

I decided – you might enlighten me – that these cheap units are horribly inefficient, generate excess heat with prolonged use, and of course are meant only to let one save a few files before shutting down a computer. I decided to discard the idea.

But what seemed to work well in these units is the switching device that cuts in when the mains voltage falls, switching on the inverter. An inverter I can buy, but how can I hook it up to turn on and off according to the mains fluctuation?

Good inverters seem cheap enough, but buying a reasonable UPS that will supply say 1 KW from a big battery (yes, minimum 80 amps) seems impossible. I just can’t find any information outside the industrial stream – people with big bucks and big power demands.

How I wish I could hook up my 600W inverter to just the switching circuit of one of those computer UPSs, running it off a big battery and giving me time to start up the genset!

Any ideas?

 

A grid-tie power inverter. The type used for solar and wind can do what you want.

You do not need a "UPS" per se. (Even though that is what this is)


You can set up a sub-panel that is to be used when the main-power fails. This can be some of the same circuits in your master box.

When the grid-tie senses the failure, it will switch to the inverter. The inverter powered by your batteries. Deep-cycle batteries. You can use an off the shelf battery bank charger to maintain the batteries during normal power on times.

You can use a solar design for a home or business, but replace the solar panels with a battery charger

 

Apart from the difficulties of getting a grid-tie power inverter in Indonesia, there is little chance of selling power to the electricity company; furthermore, I will only be using a genset when the power is down, ie I would not be able to feed power to the grid.

I note that specs on the net talk about hundreds of volts DC input, suggesting the need for big battery banks.

 

The grid tie was mentioned for a transfer switch for when the power went out. not for selling back power. As for needing big banks:

If you plan to install a system that will have a battery bank, and your loads will include more power sensitive computer and digital audio/video equipment, you will probably want to consider one or more Trace (Xantrex) or Outback sine wave inverters powered from a 24 or 48-volt DC battery bank.

This is just to show you can use a small bank of batteries to run an inverter. Even 1 car battery to a 12v inverter will give 600w. albeit for a limited time. I was trying to show how a grid-tie type system can be incorporated into your mains, to continue to power the school from the existing circuits. If you had a bunch ov inverters and batteries, you would have to plug in what you wanted to work during outages, instead of it being pre-set.

 

For instance:

If you look at the attached, This is connected to the mains. when the power goes out, the battery-powered inverter switches on to supply your power. When the power company restores power, your batteries are set to recharge and the school will be powered from the power company.

You do-not need the grid-tie. you can use a few batteries and an inverter. just plug it in and turn it on when the power is out.

For a grid-monitor, you could possibly use you UPS to automatically engage your batterybank/inverter automatically.

This link shows how you can make as large of a rechargeable power unit as you want:
http://www.dansdata.com/diyups.htm

 

There are two general classes of UPS, 'Offline' and 'Online'.

The Offline type (that you have) only run when the mains power fails.

The Online type have the capability to run continuously, they kick in any time the supply is out of limits and work as an active regulator.

These are designed for 100% duty cycle, so could run happily off external batteries. They also tend to have high current chargers as the 'charger' part supplies the full load when in regulation mode.

I got some APC 'Smart-UPS' 1500VA units off ebay very cheap, these are the online type and are working extremely well, though I had to fit new batteries to one after about a year.

Some models of that series (with XL in the type number) have built-in connectors for external battery packs to give very long run times - they quote 24 hours for some setups.