Home baked UPS

[gdi2k]

Greetings,

I have a small internet cafe in the Philippines, and the electricity supply is very unreliable. We have unscheduled blackouts at least a couple of times a week for a few hours and a scheduled 8 hour blackout every second Sunday. It's rubbish.

I'm trying to assess whether it would make financial sense to install a generator.

Ideally there would be no power interruption between the utility power going down and the generator kicking in, otherwise the computers all have to reboot and customers may lose their important game highscores, umm, I mean work. I know there are complete systems that do this, especially in the computer industry, but they're way out of my price range for.

From what I've been able to google, to achieve this I would need an auto-on generator, a small battery bank, an inverter, a charge controller and a good electrician. Am I on the right track here?

I already have a suitable generator in sight, but I have no idea about the other components, so any guidance would be welcome, especially with regard to estimated cost.

 

[boatnik1]

A UPS is basicly a battery charger and an inverter which is in circuit all the time. The computers run off the inverter output and the mains supply the battery charger which keeps the batteries charged. Hense when the mains die the batteries will keep the computers running long enough for a controlled shutdown. If you wanted to switch over to a generator then this would have to be through a contactor which locked out the mains.
To home build a system you would need an inverter of a size to suit the number of computers you have running,
A battery bank preferably 24v with min 200 AH, A very heavy duty battery charger, and a changeover contactor.
Example: a 24v input 3000w continuous inverter would need approx 130A power from a 24v battery and a battery charger with at least a similar output at 24v to keep everything running. The generator supplying the battery charger with 220v would need to be capable of a continuous 3500watts.
That lot should be able to run about ten PCs with a power requirement of 300w each.
The alternative to the large battery charger would be to get your customers to shut down on a power failure while the UPS is running and when all is shut down change over to a direct generator power bypassing the UPS.
Lots of grief but only you know the value of keeping the systems running.
With regard to prices, Expensive in this country but most of the stuff can be picked up used and a system could be cobbled together for very little, excluding the inverter and generator.

 

[gdi2k]

Thanks for your detailed response boatnik1, this is sounding a lot more complicated than I envisaged ;-)

I don't like the idea that the inverter is constantly in use, as it reduces efficiency and would increase my electricity costs 10-20%. I'm also starting to think that the cost of such a capable inverter and charger may be larger than just having a low-cost UPS for each computer that keeps them all running until the generator is fired up. Those only switch over when power is lost, so no inefficiencies, and they don't require the PC to be shut down when the generator comes online as far as I can tell.