http://elecraft.85.s1.nabble.com/KPA-1500-Efficiency-As-A-Function-of-Input-Power-tp7644440p7644450.html
> I really do NOT understand why this data is so surprising.
> It all seems to me to be perfectly normal with the amplifier's highest
> efficiency occurring at near max output.
> Which curiously, I would assume, is the way the amp was designed.
>
> Think zero output with zero drive = zero efficiency.
> Apply some drive, read some output and the efficiency goes up from there.
>
> 73, Charlie k3ICH
>
>
>
>
> -----Original Message-----
> From:
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> Sent: Friday, August 17, 2018 8:57 AM
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> Subject: [Elecraft] KPA-1500 Efficiency As A Function of Input Power
>
> Interesting data, Charles. I assumed that running the KPA1500 (or KPA500)
> at lower power would keep the fan from running as much. I knew that
> efficiency changed with output power but I did not expect that it was this
> significant. If your data is correct there is 1000++ watts of heat to
> dissipate no matter what power level you use.
>
> John KK9A
>
>
> From: charles k5ua
> Date: Fri Aug 17 01:17:49 EDT 2018
>
> Upon further testing, I have found that the efficiency of the KPA-1500 is
> varies greatly with driving power. The following table illustrates the
> relationships between exciter power, voltage, current, power-in(voltage x
> amps), power-out, efficiency, and dissipated power.
> The following test was made with the KPA-1500 into a dummy load and readings
> from the KPA-1500 utility software.
>
> (Exciter)(Amps) (Voltage) (Power-In) (Power-Out) (Efficiency Pout/Pin)
> (Dissipated Pwr)
> 10w 29a 52.7v 1528w 375W 375/1528 = 24.5%
> 1205w
> 15w 37a 52.7v 1950w 620w 620/1950 = 31.7%
> 1335w
> 20w 43a 52.6v 2262w 861w 861/2262 = 38.0%
> 1413w
> 25w 47a 52.6v 2472w 1060w 1060/2472 = 42.8%
> 1451w
> 30w 51a 52.6v 2682w 1227w 1227/2682 = 45.7%
> 1420w
> 35w 53a 52.5v 2782w 1380w 1380/2782 = 49.5%
> 1412w
> 40w 55a 52.5v 2887w 1497w 1497/2887 = 51.9%
> 1382w
> 45w 56a 52.5v 2940w 1600w 1600/2940 = 54.4%
> 1313w
> 50w 57a 52.5v 2992w 1703w 1703/2992 = 56.9%
> 1315w
> 53w 59a 52.5v 3097w 1825w 1825/3097 = 58.9%
> 1306w
>
> The remarkable thing is that DISSIPATED POWER appears to be relatively
> constant from 375w output through 1825w output. This implies the
> KPA-1500 will need to dissipate nearly the same amount of heat at low power
> output as at high power output, if I am interpreting the data correctly. I
> would like to know from Elecraft if this is normal behavior.
>
> Charles K5UA
>
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