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Re: [Amps] Need help understanding an old Transformer

To: W5CUL <w5cul@sbcglobal.net>
Subject: Re: [Amps] Need help understanding an old Transformer
From: Vic K2VCO <vic@rakefet.com>
Date: Mon, 26 May 2008 09:55:43 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
W5CUL wrote:

> So what I am thinking, and please correct me if I am wrong, I would see 3440
> Vac between either secondary leg and CT, or if across both 3440 secondary
> legs, I would see 6880Vac.  The "3000" D.C Volts shown in the catalog is
> only for one leg to CT and is rated low due to an older method of
> rectifying; basically using a smoothing choke with one or two diodes. 

It is what you would get from a choke-input filter and a full-wave 
rectifier with the ct grounded.

> The
> .5mA at 3000Vdc rating is across only one of the 3440 secondary legs to CT,
> with the other 3440 secondary leg to CT capable of the same amperage
> simultaneously. Or, if across both 3440 secondary legs with no center tap,
> the transformer could supply .5mA CCS at 6000Vdc, given a smoothing choke.

No! The spec is saying that you could draw 500 mA from the 
abovementioned full-wave center-tap circuit. The windings on each side 
of the ct are each supplying one-half cycle of the rectified output, so 
really each  winding is delivering power half of the time.

If you were to use a full-wave bridge rectifier with a choke-input 
filter you would get about 6000 volts at 250 mA, since then both 
windings would be delivering power on both halves of the cycle and the 
heating effect would be twice as great.

Other considerations to keep in mind are that 1) the current capacity 
would be reduced if you used a capacitor-input filter, although you 
could get a higher output voltage, and 2) the transformer is probably 
designed to be used in a full-wave center-tapped configuration and the 
insulation of the ct may not be adequate for operation with a bridge 
circuit in which it would be about 3000v above ground.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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