K3 and K2 AC Input Power

[John W2XS]

There was a mention a while ago about a JA contest where the efficiency was measured at the power supply input and compared to the transmitter output.

I bought one of those little $20 “Kill-a-Watt” meters to measure AC Input Power. The meter gets plugged into the AC wall socket and then the device to be measured gets plugged into the meter. It reads out in volts, amps, and watts.  I used the watts setting. It also measured the line frequency and the power factor and KWH.

Here are the results with my K3 and K2. I have an Astron RS-35A supply. At first, I was a little surprised at the total AC power. But I had never before considered the efficiency of the power supply itself. I used the rig’s voltage and current displays to calculate the DC input power for the rig itself.

K3 Receive Total AC Input Power = 35 W.
K3 display says 13.8 V and 1.08 A which = 15 W.
Therefore the Astron is dissipating 35 W – 15 W = 20 W.

By the way, the Astron supply all by itself with no load measures 11 W.

K3 Transmit (100 W output) Total AC Input Power = 396 W.
K3 display says 13.3 V and 17.4 A which = 231 W.
Therefore the Astron is dissipating 396 W – 231 W = 165 W.

So the K3 is 43% efficient (100 W output divided by 231 W input) but the system is only 25% efficient (100 W output divided by 396 W input).

I repeated the measurements for the K2.  I used what the display said and did not take into account the voltage drop of the internal diode.

K2 Receive Total AC Input Power = 17 W.
K2 display says 13.2 V and 340 mA which = 4.5 W.
Therefore the Astron is dissipating 17 W – 4.5 W = 12.5 W.

K2 Transmit (10 W output) Total AC Input Power = 69 W.
K2 display says 12.6 V and 2.8 A which = 35 W.
Therefore the Astron is dissipating 69 W – 35 W = 34 W.

I measured the AC input power for a few other things in the shack:

Drake SSR-1 receiver = 10 W
Hallicrafters S-85 receiver = 73 W
Hallicrafters S38-E receiver = 28 W
Drake R4-A receiver = 61 W
Redsun RP2100 receiver = 4 W
Holmes electric heater = 1400 W

We could calculate the efficiency of the receivers using, say, 1 W audio output.  But you probably have more information at this point than you really wanted. hi hi.  Next to be measured here will be the TV sets and the computers.

73,

John W2XS