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From: "John Jardine"
Subject: Re: 2.5kW-3kW-SMPS-(cheap)-suggestions?
Date: Tue, 17 Dec 2002 00:14:55 -0000
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Gibbo wrote in message
> I wrote:
> >I have quite a lot of experience of this type of thing (but not this
> >- mainly battery chargers upto about 5KW designed to run from generators
> >the AC side is gonna be similar) and here is how I would tackle it.
> >Firstly, you're running from a generator so pfc OR a generator 4 times
> >than a simple power calculation would reveal is indicated (do the sums
> >after having scoped a genny feeding a high power bridge
> >just trust me on this one !)
> >I'll assume you'll be sensible and go for PFC (I'll post the link for the
> >unitrode chip tomorrow - certainly the best around at present - the data
> >gives a schematic that is merely scaled up for more power - even gives
> >core data).
> >As it's generator power you'll have to lower the bandwidth on the voltage
> >waveform fed to the PFC controller otherwise you'll get all sorts of
> >problems and end up with the PSU drawing huge power for a few cycles then
> >nothing for the next few (not mentioned in the data sheet !). Generators
> >horrible things to run from with active PFC.
> >The PFC would feed a bog standard full bridge rectifier/smoother (at
> >volts in the case of the usual 80 to 150 volt building site genny :) ).
> >your usual txfmr isolated converter (push pull current mode at this power
> >- perhaps full bridge current mode).
> >The rest really is no different to what you're used to.
> And of course, this NG being what it is, someone will now post a complete
> schematic for a 4KW PSU with no pfc and half wave rectification using a
> converter which is just what you require :)
> Have you considered a 110 to 50 volts transformer ?
If a super-being can post such a revelation then I think the whole industry
will benefit ;-).
110-50 transformer?. No thanks!. Extremely efficient but too heavy, too
expensive (toroidal or otherwise). Fixed voltage ratio gives consequent
problems with power factors at other than nominal i/p.
I'll willingly put up with heavy heat-sinks and more waste heat.
Anyway ... Nice stuff !. You've been there, got the T shirt. It's just the
guidance I need. Your site generator knowledge is critical in this instance
as these poxy items used to be the bain of my life when I designed
tranformer versions of this kit.
Just as I'd managed to design down to a new low in generator performance.
The cheap alternator manufacturers (esp Italian) seemed to make more use of
their new finite element electromagnetics softwares sufficient to trim the
steel and copper contained in 'em down to a level to generate! a theoretical
minimum performance, at a precisely defined 110.0Vac, at a precise frequency
(50.0Hz)!. Customers are not technically aware enough to know that the cheap
gennie they are buying is (even when new) barely capable of doing the work.
I mustn't complain too loudly about the generators as their vagaries took me
all over Europe and the far east ;-)
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