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RE: MOT to NST "extra transformer"



Hi Will, all,

> Original Poster: "Payne, Will E" <will.e.payne-at-lmco-dot-com> 
> 
> The ARRL Handbook has a very practical section on re-winding transformers,
> once a popular practice among hams.  A quick review: 
> 
> 1) Get a transformer rated for the kVA you want, and test it.  
> 2) Disassemble the core. (detailed instructions included)
> 3) Unwind unwanted secondary winding, noting number of turns.
> 4) Divide # turns by the voltage of that secondary, get turns per volt.
> 5) Wind your own secondary using same ratio.
> 6) Reassemble.
> 
> Step 4 is where the "extra transformer" could run into trouble.  
> You can wind the correct turns ratio and still not get proper
> operation of the core.  Using the original primary avoids 
> this problem entirely, up to the maximum power handling 
> capability of the core.

The core doesn't have a power rating as such as the most it ever has 
to do is handle the magnetizing flux which always stays the same 
with the original primary regardless of loading. It is the copper 
mass which determines the power rating.

Malcolm

 > Of course you can rewind a MOT secondary for more 
turns. > The ARRL handbook gives good rules of thumb for wire gauge,
> core properties, insulation, etc,.  Most of their audience
> wants only a couple of kVA at a few kV, but its a very good
> reference anyway.
> 
> Will
> 
> 
>