[Boatanchors] 120 - 240vac and output

[Vic Rosenthal]

WA5CAB at cs.com wrote:

> You don't have twice the voltage drop in the primary 

God help me, I didn't SAY that!  I said the following (and if I don't get 
through this time, I'll give up):

1) Other things being equal, an amplifier will draw about twice as much current 
on 120V than on 240V.  Ignoring losses in the transformer, VA out must equal VA in.

2) The IR drop on the resistance of the WIRING to the transformer from the pole 
will therefore be twice as great.  NOTHING to do with how the transformer is 
wound, wired, etc.

3) Since the transformer is multiplying the voltage twice as much when using 
120V than 240V, any DROP is also multiplied twice as much.  Twice the drop times 
twice the multiplication = 4X greater drop in HV due to wiring resistance.  This 
drop is added to the normal drop in the power supply due to secondary 
resistance, etc.

Simplified example:  the resistance of the house circuit is 1 ohm.  Amplifier 
draws 10 amps at 240V, 20 amps at 120V (full load).  The IR drop in the wiring 
is 10V at 240V and 20V at 120V.  Suppose the power supply puts out 3000V no 
load.  Then it is multiplying the voltage 12.5 times when operating on 2400V. 
In this case the voltage drop of the power supply output due to the wiring 
resistance will be 10V * 12.5 = 125 volts.

Now suppose we use the same equipment on 120V.  The voltage multiplication is 25 
times, so the output voltage will drop 20V * 25 = 500 volts, before even 
considering the drop due to secondary resistance, etc.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco