K3 High Current Warning on 10m

[akiwi ham]

On 28.010 while in Tune a high current warning came up then a 15A fuse
went in my Astron power supply. My MFJ-259 shows SWR less than 1.5 at
this frequency. The antenna is a new SmallIR.
I have since operated my FT-897 on the same antenna and frequency. I can
key down at 100W as often as I like and for as long as I like and
nothing bad happens. Rig indicates a low and stable SWR putting out 100W.
This seems to suggest something related to the K3. Has anyone else
experienced this?

Bryan, ZL1NI
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[KeithWE6R]

Try calibrating the watt-meter on 10m, or set the K3 to only 90 watts or
so on 10m. It is probably actually putting out more than 100w and I have
seen some draw excessive current on 10m when it you go above 100w.
Keith

On 4/6/2012 1:05 AM, Bryan, ZL1NI wrote:

> On 28.010 while in Tune a high current warning came up then a 15A fuse
> went in my Astron power supply. My MFJ-259 shows SWR less than 1.5 at
> this frequency. The antenna is a new SmallIR.
> I have since operated my FT-897 on the same antenna and frequency. I can
> key down at 100W as often as I like and for as long as I like and
> nothing bad happens. Rig indicates a low and stable SWR putting out 100W.
> This seems to suggest something related to the K3. Has anyone else
> experienced this?
>
> Bryan, ZL1NI

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[Malcolm-2]

"Bryan, ZL1NI" <[hidden email]>
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Subject: [Elecraft] K3 High Current Warning on 10m
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On 28.010 while in Tune a high current warning came up then a 15A fuse
went in my Astron power supply. My MFJ-259 shows SWR less than 1.5 at
this frequency. The antenna is a new SmallIR.
I have since operated my FT-897 on the same antenna and frequency. I can
key down at 100W as often as I like and for as long as I like and
nothing bad happens. Rig indicates a low and stable SWR putting out 100W.
This seems to suggest something related to the K3. Has anyone else
experienced this?



Hi Bryan,

This is caused by the supply voltage at the K3 being below 13.8 Volts because of the
current being drawn to provide the RF power out on the higher frequencies. The K3 will
draw a higher current to try and put out the higher power thus compounding the problem.
The voltage drop can be due to using wire that is too thin,  oxidised connectors and that
includes the fuse connectors or a power supply with insufficient capacity or poor regulation.

I would try measuring the voltages when keying say 50 Watts. Measuring the drop along
each wire of the cable should show where the problem lies.

Regards

Malcolm
G0MIC

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