[Collins] Transformers

[james.liles at comcast.net]

Hi Jerry:

The reactance of a 30uf capacitor will not be anywhere near the combined 
inductive reactance apparent in the primary unless the transformer is 
drawing 1 or better amps with no load.  Any load from the secondary imposed 
on the primary will be essentially resistive.   Remember, I use the 30uf to 
35uf cap in a radio that will draw approximately 100 watts depending on the 
voltage drop that I require.  Resonance is not an issue here.

This combination works fine and is not as sensitive to load as you might 
think.  Best I can do is say try it --- should take 20 minutes to test.  If 
you do, use Polypropylene --- usually called motor start/run caps.

Been a pleasure, got to pack, we're headed to the mountains.  A super day to 
you!

Kindest regards Jim K9AXN


-----Original Message----- 
From: Dr. Gerald N. Johnson
Sent: Thursday, August 29, 2013 7:51 PM
To: james.liles at comcast.net
Cc: collins at mailman.qth.net
Subject: Re: [Collins] Transformers

There are two inductances in the transformer equivalent circuit.
Magnetization which is loaded by the secondary loads and leakage which
is not coupled to the secondary. Leakage is responsible for much of the
transformer impedance I discussed earlier, as much as 4% for a
transformer wound on an E-I core. Resonating that with the series
capacitor can get some odd results.

With a low impedance source, it doesn't take high Q to get a voltage
rise. A Q of 2 (Xl = 2 R) is enough.

I have used the series capacitor to slow a fan and it worked for decades.

73, Jerry, Technical Adviser to the Collins Radio Association.

On 8/29/2013 7:18 PM, james.liles at comcast.net wrote:
> Hi Jerry:
>
> That would be true if there was almost no load at all because that would
> be the only time that the primary would display measureable inductive
> properties. If there is any load at all the capacitor would see
> resistive properties passed back from the secondary. The load that the
> filaments alone provide in a 100 watt radio with a 30uf series cap
> render the magnetizing inductive properties irrelevant. The first
> thought that comes to mind is the series resonance effect from the
> capacitor will cause catastrophic current in the primary. Not so. Try it
> it will be worth your time.
>
> Kindest regards Jim K9AXN
>
>