Guillermo,
Rich is correct. The transformer can be de-rated some in most amateur
applications. The ratings are known as ICAS (Intermittent Commercial and
Amateur Service), and CCS (Continuous Commercial Service). Most amateur amps
fall under ICAS. Here the size can be cut back by derating the current carrying
capability of the wire in the transformer coil. You still have to have a
certain amount of iron in its core, but by reducing the wire size, a core
laminate with smaller windows can be used. This is because it takes a smaller
window in the core for the amount and size of wire in the coil. By using a
smaller lam, you gain in weight savings. The central core size in square inches
has to be the same so the transformer will not go into saturation. This can
also be dropped in size by using a laminate steel with a higher flux density.
The only problem is, when doing this, and raising it's efficiency, the cost
goes up a good bit. The most efficient core would use a laminate steel like M-6
(Hipersil) to M-2, but a cheaper, and almost as good core can be made with
M-19 steel, with not that much of a difference in losses. The price difference
between M-19 and M-6 is almost X 2. M-22 will also work with just a shade more
losses, again with a price savings, but the weight will go up slightly as the
flux density drops.
The major difference in ICAS to CCS is that CCS is designed for 100% usage, or
brick on key transmitting. A CCS amp is designed to be under load 24 hours a
day. ICAS has a time limit like 5 minutes on and 5 minutes off to allow the
transformer to cool off. ICAS is not for a continuous load. The main two
differences then between ICAS and CCS is using a wire size of around 700-800
cir. mils per ampere for ICAS and 1000-1100 cir mil per ampere for CCS. I think
if I recall that is about 2-3 wire sizes difference without looking at a chart.
Best,
Will
----- Original Message -----
From: R@contesting.com, Measures <r@somis.org>
To: GGLL <nagato@arnet.com.ar>
Subject: Re: [Amps] Transformer spec's for linear amplifier - added
Date: Thu, 7 Jul 2005 06:35:05 -0700
>
>
> On Jul 7, 2005, at 4:00 AM, GGLL wrote:
>
> > Having the need of a 2500VDC @ 350 mA maximum current power supply, and
> > planning to use a full wave voltage doubler, how can I establish the correct
> > current rating for the transformer?.
>
> A good clue is the R of the secondary winding. This is discussed on my
> Web site. Another consideration is whether the current will be
> continuous - as for FM broadcasting - or intermittent - as for
> voice-SSB, where the average current is c. 30% of the maximum current.
>
> > It should be nearly 930 VAC and exactly
> > 700 mA of current, or can I reduce somewhat its current rating
> > (taking in care
> > amateur, CW/SSB use, also AM at reduced carrier) so as not to expend more $$
> > than really needed?.
> >
> > My question is oriented to duty cycle, so , if possible and
> > advisable, how can
> > I lower current ratings to save costs. I've read in many articles (all for
> > amateur use, with transformers already salvaged from TV sets, and so) where
> > smaller current ratings where used instead of theoretical ones.
> >
> > Thanks in advance
> >
> > Best regards
> > Guillermo - LU8EYW.
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
>
>
>
> Rich Measures, 805.386.3734, AG6K, www.somis.org
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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