[Elecraft] Power Cord Questions

[Fred Jensen]

On 3/9/2012 6:37 PM, Lee Buller wrote:
>
> I am rebuilding the power cord from my RM35M to the K3.
>
> Questions.....
>
> 1.  Do you need fuses to be in both the positive and negative lead?  Or, since I
> am a "fixed" station, can I get away with one fuse in the positive lead?
> Currently, I have both leads fused.

Physics and EE challenged student here -- one fuse, in the positive lead 
if you never -- ever -- take your K3 into a vehicle.
>
> 2.  What length should the power cord be....considering that there will be some
> power consumption (voltage drop) in the line which is longer than shorter?  My
> current length is over 6 feet.

Short.  Shorter is even better.  Minimize the number of connection 
points going to and from the radio.
>
> 3.  Should the fuse(s) be mounted at the radio or at the power supply?
> Currently, mine are right at the power supply.

Doesn't really matter ... unless things in your configuration are going 
to move.  If things move, shorts can happen in many places.  You really 
want the short to happen "after" the fuse, so I'd put it as close to the 
power supply as possible, just on general principles.
>
> The reason why I am rebuilding the power cord is that I am getting somewhat of a
> voltage drop on key down.  According to the K3, the voltage is at 13.8 but goes
> to 11 volts at key down at 100 watts....around 21 to 22 amps.

Well, "Over 6ft" could be a kilometer or so, but for a reasonable shack 
length, that's a little more than expected.  There's a couple of tenths 
volt drop in the K3 to the voltage sensor.  The problem with fuses in 
moderately high current applications is that the fuse connections often 
offer a lot of voltage drop themselves.  The automotive spade lug fuses 
in their appropriate holders tend to be lower resistance than the 
in-line guys, but that sometimes involves additional connections.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org