[Boatanchors] 120 - 240vac and output

[Ron]

Vic,
No one will disagree with your example but the point here is that the 4X 
you calculate is simply due to the fact that 2 Squared is 4.  The 
specific answer to your specific example is  4. 
My fear is that your specific example will give everyone the impression 
that 4X is the general answer when it is not!   The general answer is 
the square of the current .

The only other example that I can think of is one 10 year old telling a 
5 year old that green beans come from can in a grocery store.  Well Yes 
,,,they do .....but not really.
I mean no dispespect with the above example but it was the only example 
I could think of where the answer is both right and wrong depending on 
how much detail you want. 
You are correct for your specific example but you example becomes really 
complicated when you start to go further and add the fact that the 
loading on the secondary is non- linear and then you value of 4 floats 
all over the place as the voltages and currents settle to the load line 
of the amplifier current voltage curve. That is specifically why you 
would work losses using currents and not voltages.
None of this really matters on the signal strength that an amp will 
provide to a communications but if you want a real answer , that is what 
you must do .  Other than that , your answer could simply be that the 
amp makes less power on 120 volts because of the voltage drop in the 
house wiring and green beans come in cans.
---
Ron



Vic Rosenthal wrote:

> 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.
>