🚀 go-pugleaf

In article <C0pFDq.I1n@watcgl.uwaterloo.ca> awpaeth@watpix.uwaterloo.ca (Alan Wm Paeth) writes:
>My brother received a "PowerStat" 12VDC - > 117VAC inverter over the holidays.
>It has been a real disappointment. The ad claimed it was good for 140W normal
>and 200W peak power. It barely manages 100W into a resistive load (lamp), and
>it simply cannot drive even the smallest drill (its intended use). My EE degree
>and scope can't help (I live half a continent away) hence this net posting.
>
>To anyone with experience or familiarity with this/such beasts:
>
>  (1) How can he test it a/o improve its output?
>  (2) How can he better cope with power factor/inductive loads?

(I'm fixing a UPS right now, and I've got my power electronics program
swapped into brain RAM.  Ever seen tantalum capacitors shoot red hot
flaming chunks two inches past your nose?  But I digress... )

Many power inverters are square wave output, and designed to drive loads
like computers that have diode bridges followed by capacitors.  Square
waves of uncertain frequency are peachy keen for this application.
Note that a square wave that is 170V peak is going to produce twice as
much RMS power than a sine wave that is 170V peak; hence the loading
problem with a light bulb.  You will probably get 200 watts out of a
100 watt bulb - for a while.

An induction motor such as that on your drill is going to want to see a sine
wave, which requires a more sophisticated power inverter, or something in
series to condition the signal, like a very big LC filter (I don't think 
they normally get that big).  I can think of some other things I would try
with a bench full of test equipment, but that won't help here.

You may want to hunt up a motor-generator set.  These take DC in one side
and produce AC out the other.  Mechanical, robust, very heavy.  Maybe cheap
if you can find one surplus.  Find a radio amateur on rec.ham-radio with
an M-G set and see if you can swap.

Good luck,
Keith


-- 
Keith Lofstrom         keithl@klic.rain.com       Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Power ICs