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

[Charlie T]

It's normal.

Even at zero output, (keyed ON but with no drive power) the idling current
required to obtain linear class amplification will cause significant power
dissipation in the final, regardless if its solid or hollow state.

73, Charlie k3ICH




-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
Behalf Of charles at k5ua.com
Sent: Friday, August 17, 2018 1:18 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] KPA-1500 Efficiency As A Function of Input Power

Thanks for the replies.

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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