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From: "Bevan Weiss"
References: <0001HW.B9DF7C5F00256614162B2870@news.covad.net> <email@example.com>
Subject: Re: Boosting output from 120V inverter
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X-Original-Trace: 27 Oct 2002 15:05:46 +1300, news.orcon.net.nz
Date: Sun, 27 Oct 2002 15:05:52 +1300
NNTP-Posting-Date: Sun, 27 Oct 2002 15:05:47 NZDT
"N. Thornton" wrote in message
> "Bevan Weiss" wrote in message
> > It's not that simple unfortuneately...
> > The transformer itself probably wont be rated that much above what the
> > entire inverter is rated at. So just replacing the MOSFET's wouldn't do
> > trick, you'd have to replace the transformer as well, and the
> > almost the entire cost of an inverter, apart from design.
> > "DaveC" wrote in message
> > news:0001HW.B9DF7C5F00256614162B2870@news.covad.net...
> > > 200W inverter needs to run a bit more power. I know how cheap these
> > > are, but I get my kicks from using and/or modifying what I have and
> > getting
> > > the experience of electronics theory/application.
> > >
> > > How should I go about matching up a higher-amperage MOSFET to replace
> > > ones there? Same g-d and g-s voltages? Higher d current? Pin
> > configuration,
> > > of course. What are the critical specs I should focus on when looking
> > an
> > > upgrade?
> > >
> > > The MOSFETS that switch the output are not heatsinked very well, and
> > is
> > > room for a small cooling fan.
> > > --
> > > Note that my return address is corrupted in an attempt to reduce spam.
> > you
> > > choose to e-mail me, please correct my address as described below.
> > >
> > > Thanks,
> > > Dave
> I think it could work actually, with a fan. Transformers will handle
> much more power when fan cooled. So I'd put as powerful a fan in there
> as you can squeeze, uprate your fets, and watch the TF temp to see
> what it'll manage continuous. Hopefully you'll get a significant
> Since youre running off battery, you'll want to power the fan
> If you're real determined, theres always the outer edge option of
> putting the TF in a well heatsunk tin full of oil - no fan power then.
> Regards, NT
Transformers generally aren't the best items to heatsink...
That's not the only problem that they have...
You have to consider that each winding in the transformer is an inductor
(easily thought of)... Now each of these seperate inductors will be
designed such that they have a maximum saturation current equal to the
maximum current the device is rated at. Any current higher than the
saturation current will begin to cause a much faster rate of heating, you
will begin to lose serious wattage through the iron and copper losses of the
transformer. Couple this with the normally very tight windings of small (as
these kind of transformers are designed) transformers and you have a serious
heating problem. It's just not worth the extra effort...
Work out how they design inverters (the principles aren't hard at all), then
spend a little time thinking of better ways to go about certain aspects (ie
the dc->ac conversion, and then the transformation of the voltage), then
begin to breadboard a new inverter (designed by yourself). Start with a low
current design (ie low wattage), then check to see which parts are the
limiting factors, and expand from there.
I'm sure that it'll be worth your time if you really want to pursue the
extra wattage yourself as opposed to just buying a higher wattage inverter.
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