[Elecraft] K3 12 volt current modification

[Bob Locher]

I had the same problem - that the switched output of the K3 is limited.

I have my shack set up so that turning on the K3 turns on several other 
functions including a P3, and a W2 watt meter. Also, I turn on a 12 volt 
coax relay that attaches the antenna to the rig. Everything was fine 
until I went about adding the P3 - that blew me well past the half amp 
limit.

I solved the problem a completely different way. Out of my junk box, I 
took a small project box, some RCA connectors and an automotive 12 volt 
20 amp relay designed for PC board mounting.

I mounted six RCA jacks first - two on one side and four on the other. I 
mounted the relay upside down inside the project box, using a generous 
dollop of hot melt glue.

I wired it as follows - one of the RCA jacks goes to the relay coil. 
This jack is connected to the switched output of the K3, and only pulls 
about 70 ma. The second jack goes to my 30 amp Astron power supply, and 
feeds the 12 volts DC supply to the relay common pin. (I used a pair of 
#16 wires from the Astron to the jack.) The switched output of the relay 
goes to the other four RCA jacks.

If you do this  be sure to get everything right, and to label out inputs 
and outputs.I would have liked to have different connectors for the K3 
input and the supply input to prevent mixups but my junk box came up 
short. I contented myself with good labels.

Anyhow the system works perfectly. I turn on the K3 and everything comes 
on, and I still can add more outputs to the box without fear of 
overloading anything.

Cheers/73

Bob Locher W9KNI