Re: [Amps] Current draw at 110 volts for SB-200 and SB-1000

[Vic Rosenthal <vic@rakefet.com>]

Steve Thompson wrote:

> The high current 'gulps' I meant are the ones every line half cycle, not at
> syllabic rate. The line voltage your meter measures tends to reflect a cycle
> to cycle average, and doesn't indicate what happens during those few ms
> whereas the psu feels the full effect.
>
> An example (imprecise, so please don't shoot me down): If your amp is
> pulling an average of, say, 10A from the line for something approaching a kW
> input, the charge goes into the capacitors in a space of maybe 2ms during
> the half cycle of 8.33ms. The average current during those 2ms has to be
> 40A, with the peak being 50, 60 or even higher. That sets the voltage drop
> that the psu suffers whereas your voltmeter and lights don't react so much
> to the short term disturbance.

If you put a scope across the primary of the transformer, you might see a 
distorted waveform due to the large current drawn during part of the cycle.  But 
the output voltage of the supply is related to the voltage that appears across 
the filter capacitors.  This total charge is (I would guess) proportional to the 
area under the curve of the distorted waveform I mentioned.  So the resultant 
output voltage drop due to the resistance in the circuit feeding the PS is an 
average (of some kind) of the voltage drop across the primary over the period of 
the cycle multiplied by the square of the turns ratio.

Another way of putting this is that although the voltage drop due to the power 
line resistance varies greatly during the cycle, the capacitors even it out.

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

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