K3 Transmit current drain

[k6mgo]

This is a follow-up to my post of yesterday, about the excessive current drain on my K3 in Transmit. Here is my original post:

I was playing around with my K3 and MFJ 4225 switching power supply, when I
noticed a strange thing. As you increase the power output, the input current
rises very quickly. Example:
in Receive mode, the K3 was drawing 2 amps.
In Transmit mode, CW, SK key down, at 1 watt out, it was drawing 4 amps
5 watts out, it was drawing 5 amps
8 watts out, it was drawing >6 amps
15 watts out, it jumped to 15 amps
30 watts out, it jumped to 20 amps

Didn't want to increase the power anymore, but, this seems excessive to me,
anyone else ever notice this?

Would appreciate any comments on this matter,

73, Bill, k6mgo

Thanks to the many who pointed out that the K3 draws a high current even at low power once you get above the 12 watt level, due to the bias for the power amp. I never considered this, and so when I made up a power cable to operate indoors with my MFJ 4225 switching power supply, I used a single light weight lamp cord at six feet long and a cigar lighter plug for the power cord. My reasoning being I would only operate low power, not more than 30-35 watts indoors with my antenna right over my head. So, either the lamp cord was too light, or the cigar lighter plug had too much drop for the current being drawn, and so the current meter in the K3 was indicating 20 amps being drawn at only 30 watts output.
Once I fixed the power cord by using two #18 ga. lamp cords in parallel to spade lugs rather than the cigar lighter plug, the K3 now draws 11.73 amps @ 12.7 volts, with 35 watts output,  from the MFJ 4225 power supply, which seems more normal than the previous 20 amps at the same power out setting.

I hope my experience saves someone else some grief.

73, Bill, k6mgo  


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