[Elecraft] Additional Observations on K3 Power Issue

[Fred Jensen]

On 11/22/2013 2:07 PM, pastormg2 at verizon.net wrote:
> Hi Guys, I checked the Power Supply Voltage and the K3 gave me these
> readings. On receive it reads 13.9 volts but on Transmit/Tune it
> reads 13.4 volts. Plus, the Amps on receive is .89 to .91 and on
> transmit it is 11.23 to 11.25 amps. Could it be that I have a power
> supply issue? I find it hard to believe the the power supply voltage
> would drop on transmit. Help!!!  Mark Griffin, KB3Z

How, and with what, did you measure the power supply voltage?

Did you use the display in the K3 or did you measure it with an external 
voltmeter?

Did you measure it at the power supply terminals or at the radio?

How long is your power cable from the supply to the radio?

Are you using one that came with the K3 from Elecraft?

What size is the wire?

Does your power cable have one or more in-line fuses in it?

I'm going to guess at the first answer:

You said, "...and the K3 gave me..." so I think you measured with the K3 
display.  Unless you are using very very heavy wire for your power cable 
and it is verrrry short with no fuses, a 0.4V drop at 10+ amps is to be 
expected.  It's actually pretty good.  I doubt you have a power supply 
problem.  In fact, I doubt you have any problem at all.

The K3 reads the supply voltage through the power cable which isn't a 
perfect conductor and has some resistance.  Applying a little of Ohm's 
arithmetic, it appears you have a 0.4V drop with a current difference of 
10.36A which suggests the resistance in your power cable is 0.0386 ohms.

I think there's a good chance that you're trying to pick fly poop out of 
the pepper, and your K3 is being a very good K3.  CQ WW CW just started, 
go have some fun and work some new ones. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org