[Elecraft] K3 Display voltage?

[Don Wilhelm]

Tom,

You do have a problem.  I recommend that you first check the voltage 
during transmit at 100 watts at the power supply terminals.  If there is 
more than a few tenths of a volt drop there, you will have a power 
supply problem - the power supply terminals have connections on the 
inside as well as the outside and they must be tight and free of 
corrosion.  A few milliohms of resistance at 18 amps will create a 
significant voltage drop.

Next thing to investigate is the power cord and its terminating 
connections.  The APP connectors are quite good as long as the crimp to 
the wire is tight enough to be what is considered 'gas-tight'  If there 
are any doubts about the quality of the crimp, solder the connectors.  
Whatever termination you use on the power supply end is suspect too, the 
same criteria should be applied as for the APP connectors - good crimps 
or solder if there is any doubt.  Be certain the power cord is tight on 
the power supply output terminal bolts.

Lastly, if the power cord is much longer than it has to be, shorten it, 
every inch of wire has some resistance.  If you need to use a long 
length, consider using #10 wire instead of the #12 supplied by 
Elecraft.  Don;t get me wrong, #12 is entirely adequate if all other 
conditions are good, but 5 feet of #12 does have  8.1 milliohms 
resistance, but the return path also adds to the voltage drop, so the 
entire resistance is 16.2 milliohms which translates to 0.3 volts drop 
at 18 amps due to the copper.  The drop using  #10 wire will be about 
2/3 of that seen with #12.

 From all that, you should conclude that the most significant voltage 
drop from light load to 18 amps load will be in the connections, but 
about 0.3 volts will be contributed by the wire.

73,
Don W3FPR

TMorton wrote:
> All this talk about TX IMD and monitoring voltage, etc got me to check 
> out my K3. I usually run @ 50w into small amp and I see 13.7V on rcv and 
> 11.5 while xmit. If I run the power up to 100w, I see 13.7 and 10.8; do 
> I have a problem? I am using an unmetered Astron RS-35 into our standard 
> 220v house supply.
> 73
> Tom
> CX7TT
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