Posted by
Don Wilhelm on
Aug 30, 2017; 11:42am
URL: http://elecraft.85.s1.nabble.com/Wattage-Draw-K3S-100-vs-KPA500-KAT500-for-UPS-tp7633842p7633843.html
Bret,
The power rating of a transmitter is the output power, not the input draw.
If the overall efficiency is something like 33% (quite likely), then the
input draw will 3 times the output power.
The efficiency of an RF output stage alone is typically about 50%, but
there are other circuits in the transmit section that must be added and
brings the overall efficiency of the transceiver down even more.
So yes, the input power required is about 3 times the output power.
A KPA500 running on 120 volts just about maxes out a 15 amp circuit, and
that is 1800 watts input. The K3 will need about 300 watts additional.
That means your UPS should be rated at least 2500 watts, but 3000 would
be more reasonable because it seems you have other gear in the ham
station that needs to be supported as well.
73,
Don W3FPR
On 8/30/2017 7:16 AM, MaverickNH wrote:
> As mentioned in another thread, I'm running my shack on a UPS that is rated
> 1500va/900w. With my K3S/100 and other hardware plugged in on the same input
> the UPS often max's out at 900W at < 100W on the K3S. Typically, the
> baseline with K3S on RX is ~350W and it spikes over 900W with TX at 100W and
> the UPS limits output. So it seems 100W isn't 100W.
>
> I'm looking to switch in another UPS rated 2200VA/1320W, or 420W higher, for
> use with the KPA500/KAT500 I just acquired from another forum member. so
> from a 100W station to a 500W station. Might this work or is the increase in
> watt TX not equal to the watt drawn?
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