[Elecraft] KPA-1500 Efficiency As A Function of Input Power

[john at kk9a.com]

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