Re: 1 second UPS
- From: "petrus bitbyter" <pieterkraltlaatditweg@xxxxxxxxxxxxxxxxx>
- Date: Tue, 6 Dec 2005 23:17:38 +0100
"stefanv" <stefan@xxxxxxxxxxxx> schreef in bericht
news:TZGdnYWjG5qZDQjeRVn_vA@xxxxxxxxxxxxxxx
> 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
>
>
>
>
Stefan,
Guess you have to refresh your basics on electricity. The energy stored in a
capacitor is CV/2 in J(oules) or W(att)s(econds). The energy required to
power the PC for half a second is 250 * 0.5 = 125Ws, which is much, much
more then your capacitor can hold.
petrus bitbyter
.
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