[Amps] transformer talk

[Steve Thompson]

TexasRF at aol.com wrote:
> Steve is right on the money here.

Steve's had one too many crispy fried transformers :-) I've also been 
burned (both metaphorically and literally) by attractive looking big 
transformers which turn out to have been designed for use with choke 
input. Hook them onto a capacitor input PSU, and you get much less power 
than you were expecting, lousy regulation, and the smell of burning 
insulation.

> Many capacitor filters will cause peak 
> currents about 5 times average but the current only flows 1/5 of the 
> cycle. Since heating is related to current squared, the total heating in 
> this case would approximate 5 times 5 or 25 times dived by 5 for a total 
> of 5 times as much heat compared to a resistive load.

You can sometimes take liberties if you keep the average current down 
(low rf clipping), overs short, and the tx/rx ratio low.
>  
> The high peak current also causes 5 times the voltage drop at the peak 
> of the cycle. Since we are trying to charge the filter to the peak 
> voltage this means the voltage sag is also five times more than with a 
> resistive load. More copper is needed to compensate.

And the problems compound if you want to run from a generator set - most 
are rated for resistive or motor loads, hit them with peak current 
demands from a capacitor input PSU, and the voltage dies.

Steve