Re: UPS powered coil?

["Jim Lux" <jimlux-at-xxxxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Some things to think about:
(I've run a lot of things off inverters and UPSs over the years)

The battery in a typical UPS is designed for very high discharge rates:
Typical UPS batteries are rated for 20 minute discharge (i.e. the load is 3
times the AmpHr rating).  Most off the shelf "gel cell" batteries (i.e. the
ubiquitous 12V 7Ah units) are designed for a 4 hour discharge. Car
batteries are designed for a 20 hour discharge. Internal heating of the
battery is the problem.  If you are going to add external batteries, do a
ball park calculation of the current draw!  400 Watts is 30+ amps at 12V.
That's a lot of current.... 

Thermal design of the UPS is pretty marginal (to save money).  If you try
and run them at load for longer than 20-30 minutes (say, by adding an
external battery), they'll probably overheat.  

Remember, these are consumer products, typically... If it fails, most
people won't collect under warranty (true of most devices), and the failure
is unlikely to damage the equipment (i.e. it fails "safe").  It is cheaper
for the mfr to have 1% failures under load (how many times has YOUR UPS run
to battery dead?...most never do.. they ride through a 1 minute outage, or
the person shuts down after the power fails (after all, you're working in
the dark...).


A better solution is to get an inverter.  Careful reading of the specs
(avoiding the "peak music power" type ratings) will find a rating that
corresponds to 100% duty cycle for extended periods (typically about half
what the package advertises...).  

You're still stuck with the odd waveform, though.  Some collection of L and
C on the power might work to fix that, though.


Tesla list wrote:
> 
> Original poster: "David Trimmell" <davidt-at-pond-dot-net>
> 
> I have played with modified UPS's, a 300VA with original batteries removed
> and a large capacity deep cycle in it's place. It was a "modified" sine
> wave output, looked pretty sloppy on the scope, and very triangular with
> any kind of inductive load. Tried a 9KV 60mA neon off of it, and it killed
> the wave form with any kind of short (like a Jacobs latter), with very poor
> output. I really have wanted to play more with inverter power SU's, but
> haven't the time. I suspect the circuitry (of these UPS types) would not
> lend it's self to any RF nasties. We have several thousand LBS of dead
> UPS's at work, some big >1KVA types, I have been thinking about how to
> liberate a few from the junk pile. Yup, lead acid batteries tend to be very
> heavy ;-)
> 
> Regards,
> 
> David Trimmell
> www.ChaoticUniverse-dot-com
> 
> At 08:05 PM 11/14/00, you wrote:
> >Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >
> >Hi Alan,
> >
> >Yes!  It is thermal circuit breakered at 10 amps and could probably run a
> >300 watt coil for 10+ running minutes easily.  When it is unplugged it is
> >just a little 120VAC power source till the internal sealed lead acid
> >battery runs down.  Probably not a big deal to run it off a bigger battery
> >if one wanted to.  It is very small (but heavy!!) so it could easily travel
> >with the coil.  Parties, picnics, boating, camping, stuck on the freeway...
> >  You get the idea... ;-))  They are super cool things and mass production
> >really has them down to a darn good price.
> >
> >Cheers,
> >
> >         Terry
> >
> >
> >
> >At 10:49 PM 11/14/2000 -0500, you wrote:
> > >Terry
> > >    are you talking about plugging the coil into it and using that that
> > as a
> > >"battery" for short bursts?
> > >-Alan
> > >
> > >
> > >In a message dated 11/14/00 7:44:52 PM Pacific Standard Time,
> > >tesla-at-pupman-dot-com writes:
> > >
> > ><< Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> > >
> > > Hi All,
> > >
> > >    As part of my home web server project and at the strong
> > recommendation of
> > > several people, I got one of those 500VA APC uninterruptable power supply
> > > boxes to run my server, DSL, and Eithernet hub boxes.  They all said it
> > > would stop a ton of odd problems with 24/7 systems...  But I thought
of an
> > > additional problem for it ;-)))
> > >
> > > Now, I really can't help being tempted to run a truly go anywhere
coil with
> > > the little UPS box (like my small LTR coil).  I guess it has
protection out
> > > the wazzu, but if anyone knows of a reason it may blowup with a coil
> > > connected to it I would like to know... ;-)))  It has step simulated AC
> > > output which should do OK with a variac and a "little line noise".  I
worry
> > > about PFC correction (over correction) caps and such.  At $130 buck a
pop,
> > > I would hate to fry it but the temptation is overwhelming to give it
a try
> > > and see what happens ;-)))
> > >
> > > Cheers
> > >
> > >    Terry - Always on the bleeding edge ;-)) >>
> > >