[Elecraft] KPA/100 displays wrong PS current (much lower)

[Don Wilhelm]

Ioannis,

The current display on the K2 indicates only the current for the base 
K2, not for the K2 and KPA100 combination.
That is why you set the CAL CUR to 3.50 amps even though the KPA100 will 
draw much more current.

Yes, the KPA100 does have a scaling on the amount of RF voltage that is 
being detected.  That is used for power control and has nothing to do 
with the current displayed.  The result of that voltage is sent to the 
VRFDET signal in the K2 (Voltage of the RF Detected).

73,
Don W3FPR

On 4/24/2016 12:05 PM, Ioannis Kassotakis wrote:
> Just finished building the KPA-100 for my S/N 2102 K2 (MCU v. 2.03D, KPA
> 1.06)
> The K2/100 does not display the correct 13.8 V power supply current (by
> taping Display) when it switches to HI POWER (>10 Watts).
> I used a DMM in series to accurately measure the PS supplied current while
> checking the K2 display at several power settings . Later, I also measured
> the KPA TP1 voltage which is the I sense input to the KPA-100 processor.
> For several power settings I got:
> PWR (Watts) - PS Current (DMM) Amps - K2 Current Display Amps - KPA/100 TP1
> (mV)
> RX-0.4 - 0.44 - 0 <x-apple-data-detectors://0>
> 1.0- 1.72- 1.76 -0
> 5.0 - 3.3-3.3 - 0
> 10- 3.8 - 3.8 - 0
> 15- 4.5 - 1.01 - Not measured
> 20- 5.4 - 1.02 - 100
> 40 - 7.0 - 1.20 - 250
> 60 - 8.5 - 1.28 -380
> 80 - 9.5 - 1.41 - 500
> 100 - 10.3 - 1.48 - 580
> 111 - 10.8 - 1.54 - N/A
> The measurements were done at 40 m (7.100) at CW to a dummy load through
> KAT-100.
>
> It seems to work fine a LO PWR (<11 Watts) but appears to have a scaling
> issue, when the PA switches On to HI PWR mode.
> According to the schem (p.61) I Sense is supposed to vary 0-5 V for 0-32 A,
> so the TP1 figures seem to be rather low.
> Is this a known issue? Is it possible that I have a failed U7 or Q5 ?
>
>