Yes yes and yes. Amps are designed with the fixed output matching
network chosen for a value of impedance and energy transfer to be at
"rated power". Running any amp at reduced power then does not confirm
to the design of the output matching network and the efficiency
decreases. You aren't doing any favor to yourself, the amp, or others
to run the amp otherwise.
73
Bob, K4TAX
On 8/17/2018 8:24 AM, Charlie T wrote:
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: elecraft-boun...@mailman.qth.net <elecraft-boun...@mailman.qth.net> On
Behalf Of j...@kk9a.com
Sent: Friday, August 17, 2018 8:57 AM
To: elecraft@mailman.qth.net
Cc: char...@k5ua.com
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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