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Re: [Amps] Limits of a Power transformer

To: amps@contesting.com
Subject: Re: [Amps] Limits of a Power transformer
From: Steve Thompson <g8gsq@eltac.co.uk>
Date: Wed, 02 Aug 2006 11:07:55 +0100
List-post: <mailto:amps@contesting.com>

Ian White GM3SEK wrote:

> Don't forget the effect of primary resistance. It may seem low (often so 
> low that it's difficult to measure accurately) but the value has to be 
> multiplied by (turns ratio)-squared, and then added to the secondary 
> resistance.
> 
> The total is the "effective Rs" value that you need to use in all 
> calculations of voltage regulation. Unless the primary winding has been 
> generously over-sized, the total effective Rs is often about 2x the 
> secondary resistance alone.
If you use the PSU simulater, don't forget to use the total 'effective 
Rs', not just the secondary resistance, with the secondary rms current 
to get the dissipation in the transformer. In this case, it's scary with 
cap input filter.

Steve
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