From: "John Jardine"
Subject: Re: 2.5kW-3kW-SMPS-(cheap)-suggestions?
Date: Wed, 18 Dec 2002 00:23:07 -0000
NNTP-Posting-Date: 18 Dec 2002 00:10:18 GMT
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wrote in message
> John Jardine wrote:
> > wrote in message
> > news:email@example.com...
> >> John Jardine wrote:
> >> > Help!
> > [clip]
> >> Take a few uf of motor run capacitors (well, low ESR anyway), attatch
> > across
> >> the plug.
> >> Now attatch a bridge to give you DC.
> >> Now put a biggish FET between that DC and the load, and PWM it so that
> >> the overall power factor comes back to a resistive load.
> >> Yes, the waveform across the resistive load isn't DC, but do you care?
> >> No magnetics or stability problems, ...
> > Yes!, I actually looked at this as a way of doing it about 10 years
> > The physical volume, weight and cost of the caps needed (at 50Hz),
> > further progress stone dead, after about an hours head scratching and
> > if' calcs.
> > Thanks though, a neat idea!.
> The cap is not in series with the line, to act as a dropper, but in
> parallel, to lower the impedance of the generator at the frequency of
> the PWM.
> For example, 50A load current RMS at 40V, and a peak voltage of 211V,
> you need to PWM the load at about 6.2%, with a peak current of ~200A.
> Assuming 1us on-time, to keep a 10V ripple on the cap, that's 20uF.
> You will of course need a choke between this and the generator output.
> Oh. EMC.
> http://inquisitor.i.am/ | mailto:firstname.lastname@example.org | Ian
> Two parrots sitting on a perch. One asks the other, "Can you smell fish?"
I'm thick!. What's the parrot/fish angle?.
Yes. I was thinking of a series connection :-(. This arrangement though
seems to have no electrial isolation. Which is a need. The idea's
interesting though and It's worth spicing the setup to get a handle on the
The cheap alternators I've come across in the past can have a lot of non
linear series inductance. Over one alternator revolution I've seen it range
from 10mH to 60mH. This may be of fortuitous benefit but I've got a feeling
that higher peak currents may cause a problem here, as the alternator AVR
setup may somehow notice the change in power 'take' and combined with the
loss reactance the average o/p voltage may drop off substantially.
Anyway, (After I've figured a frequency variable inductance), let the spice
show me the true path :-).
Ian ... it's a blast from the past, mantra ... "50Amp, 40V, 150Vac" ... I'm
quizzical here, mmmm!. That's the old Bgas ECE spec'. Have you had
involvement with the boxes? ;-)