Re: [Amps] Transformer in GLA 1000 B : OK for 2xGI 7 ?

[craxd <craxd1@ezwv.com>]

Ken,
The Dahl transformer will provide 2.1 amperes continuous. However, if it 
were to be re-rated to ICAS, the current could be multiplied by 30%-50%. 
Keep in mind that the wire size must be correct and the correct amount 
of iron for 2.1 amperes and the wattage. The winding wire size if 
usually determined by circular mils. Most are wound between 500 and 1000 
circular mils per ampere. I always used 750 cir mils for ICAS and 1000 
cir mils for CCS. The best thing to determine how to derate that one is 
to see what the core size is, and the wire size.

C-cores are a whole horse of a different color as compared to EI cores. 
For their size, they produce the same watt rating as one larger. 
However, a C-core will not run as cool as an EI core will. There's a 
different formula for determining the size of the C-core as compared to 
an EI core. But, when I figure a C-core, I figure the core size the same 
as an EI due to heat. That way they run about the same as an EI does. 
Another difference is the flux density of the steel used in each. Plain 
EI lams are about 12,500 gausses per sq. cm. or 80,625 gausses per sq 
inch. If I recall, the C-cores steel runs about 18,000 at 60 Hz, or 
116,100 gausses per sq inch. The higher the flux density, the smaller 
the core can be. There is some EI lams like M-2 to M-6 with a high flux 
density similar to C-cores. The problem is that with a smaller core, and 
the same wattage, heat builds up quicker. A larger core will take heat 
away from the windings like a heatsink somewhat. If it runs hotter, it 
will transmit extra heat into the windings. This is what causes a 
transformer to fail, and generally short due to the insulation melting 
deep in the inner winding. For no more weight savings there is (about 
20%), I stick with EI cores. The physical size of a shell type C-core is 
about the same as an EI with the corners rounded off. That's where the 
weight savings comes in plus a smaller core over the flux density. EI 
cores are also less expensive, so is another reason to stick with them. 
Sometimes you can buy two fifty pound boxes of EI lams for the price of 
one C-core.

Will Matney

kenw2dtc wrote:

> Will,
>
> I have a Peter Dahl 2.1 amp CCS hypersil plate transformer.  I make 
> old buzzard transmissions on AM but never beyond 10 minutes, then the 
> transmitter gets a rest of at least 10 minutes.  I was wondering what 
> current over 2.1 amps I could draw.  Are you suggesting that perhaps I 
> could run in the neighorhood of 30% more current the way I operate?
>
> 73,
> Ken W2DTC
>
>
>
> _________________________________________
> Ken Barber  Middletown, NJ
> Webpage: http://kenw2dtc.home.comcast.net
> _________________________________________
>
> ----- Original Message ----- From: "craxd" <craxd1@ezwv.com>
> To: "kenw2dtc" <kenw2dtc@comcast.net>
> Sent: Tuesday, October 05, 2004 1:11 PM
> Subject: Re: [Amps] Transformer in GLA 1000 B : OK for 2xGI 7 ?
>
>
> > Ken,
> > That's a good question. Some transformer companies I've seen use a 
> > figure of 30% derating for ICAS and some 50%. In the RCA transmitting 
> > tube book, and others, they give the derating as 50%. This means that 
> > if you have a 50% duty cycle, you talk two minutes and let it rest 
> > for 2 minutes to cool off. CCS is rated for 100% duty cycle or hammer 
> > down all the time. CCS is (Continuous Commercial Service) and, ICAS 
> > is (Intermittent Commercial and Amateur Service). So with this, you 
> > could at least run it 30% more and maybe 50%. The best way to see 
> > what you have is by the core size of the transformer and the wires 
> > size it's wound with.
> >
> > Will Matney
> >
> > kenw2dtc wrote:
> >
> > > Will Matney wrote:  "The transformer in mention, I think is rated at 
> > > ICAS which would be
> > > about 1/2 the needed current for 100% duty cycle"
> > >
> > > I don't want to take this out of context but does this mean that if 
> > > I have a transformer with CCS ratings, I could use it at twice the 
> > > current rating in ICAS?
> > >
> > > 73,
> > > Ken W2DTC
> > >
> > >
> > >
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>
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