[Elecraft] [KPA500]KPA500 power cord question

[Ron D'Eau Claire]

The important point is whether the voltage to the finals at full output is
as different when the KPA500 is supplied by 240 or 120V mains. I believe the
answer is "no". AFAIK, the KPA500, and it's power supply, was designed and
tested to meet all of its performance specifications with either a 120V or
240V mains supply.

There's a reason why 240V is so popular as the standard mains voltage
throughout most of Europe for virtually everything in the home. It does make
things easier, especially when handling heavy loads. 

But that does not mean it justifies the expense of new wiring to operate the
KPA500.

Ron AC7AC



-----Original Message-----
From: Joe Subich, W4TV [mailto:lists at subich.com] 
Sent: Tuesday, May 03, 2011 2:19 PM
To: Ron D'Eau Claire
Cc: 'iain macdonnell - N6ML'; 'Clyde Washburn'; 'Elecraft - K3'
Subject: Re: [Elecraft] [KPA500]KPA500 power cord question


> No. The KPA500 peak demand is less from your 120 volt outlet than
> most household vacuum cleaners or window air conditioners. And,
> unless you are running a full-carrier mode, the average demand by
> your KPA500 is far  below the peak.

While the average current requirement may be less that the typical
vacuum cleaner or window air conditioner, the peak current demand
*will* be significantly higher if the KPA-500 has a capacitor input
filter in the (analog) power supply.

What Ron refers to as "peak" is a long term (multi-cycle) peak
current and that is much less than the true instantaneous peak
current in a "linear" capacitor input filter power supply.
Depending on the conduction angle of the rectifier/capacitor circuit,
instantaneous peak currents use can be many times the average current 
requirement - and significantly higher than the multi-cycle peak
current one would read on an amp meter in the supply line.  It is
the instantaneous peak current use that drives losses in the supply
wiring and thus the effective source voltage regulation while it is
the longer term currents (and duty cycle) that impact heating.

Even with a relatively low power (average current < 10A), the peak
currents can easily exceed 50A unless the power supply includes
"power factor correction".  While this will not trip breakers or
even cause heating in the wiring because of the very short duration,
with even 0.5 Ohms of resistance in the power lines, connectors, etc.
50 A peak currents can result in significant "short term" (partial
cycle) voltage drops.

Reducing the voltage drop in the supply by half is *always* a good
idea.  Using 240V instead of 120V - particularly if it is already
available - is never a bad idea and certainly worth sacrificing an
inexpensive IEC cable by cutting off the 115V plug and replacing it
with the proper 240V/15A plug (often known as an "air conditioner"
plug after the old window air conditioners that required 220V/15A).

73,

    ... Joe, W4TV