1 second UPS

Hi, I?m new to this forum, impressed to see there are still a lot of
people out there who love to play with electronics and do not mind sharing
some good ideas. So here?s my situation;

Dealing with a cabin with a lot of power outages. I have a trace inverter
system providing DC from 12 volts batteries. I also have a desktop
computer. When the grid power falls (or comes back) the inverter switches.
Most often not fast enough and the computer reboots :( I tried a simple UPS
(after the inverter) but it doesn?t recognized the modified sine wave from
the Trace as ?clean? power, so it just runs its battery dead after about
20 minutes without consider the Trace is there take over.

My search is to find an ?UPS? that that will bridge the half a second I
need for the Trace inverter to kick in. Time being so short, I figure I
don?t need clean power, both voltage and frequency don?t need to be
stable, just something half a second to fool my computer?s power supply AC
is still on.

I was thinking along following lines:
- feed power to computer using a NO contacts on a DPDT relay 110v AC that
goes on when AC (Trace) is present.
- charge (before this relay)through a rectifier a 680uf 200v cap up.
- create a 20ma 12v power using a rc bridge and a zenner over the cap to
run a 555 at about 60hz
- feed this frequency straight to an n-mosfet 200v 15amps switching the
capacitors charge to the NC contacts of the relay .
- put a resistor in series with the relay to run it at about 80V (so it
still goes on at regular 110 supply, but falls faster when the power
starts going down.)
- so when the power falls, the relay switches the line AC off and feeds a
straight square wave at 60 hz for as long as the cap will discharge.

Again this is ugly power, but I only need it for half a second or less.
When the Trace inverter kicks in the relay will switch back on and regular
power restored.

Figuring charge in a cap is CV2/2 in watts/sec, a 680 uf cap should hold 4
watts/sec. A computer power supply being approx 250 watts/hr, this is 0.07
watts/sec. No I?m not expecting my cap to give me a full minute, that
would likely make something explode :)

Comments? Better ideas? I like the challenge of doing this without a
transformer!

Sorry for the long post.

StefanV




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