[Elecraft] K3 Voltage drop

[Don Wilhelm]

I think 0.12 ohms is a lot and is not normal.  10 feet of #12 wire has a 
resistance of only 0.016 ohms.
A good, tight-fitting connector should add about 1 milliohm each - don't 
forget there are two connections for each "connector", you have to count 
the one in the return path too.  There is more than 0.1 ohms to locate, 
and at 22 amps, that is a lot.

I suspect bad connections that have a lot more resistance than that 1 
milliohm - note that the PowerPole specs show a contact resistance from 
0.0001 to 0.000578 ohms which is less than 1 milliohm for a properly 
assembled APP connector.

Don't forget to look at the connections inside the power supply too.  
Sometimes the terminals become loose and it does not show on the outside.

73,
Don W3FPR

On 2/27/2012 11:58 AM, Ron D'Eau Claire wrote:
> 2.8V at 22.5 amps is 0.12 ohms total resistance in the cable, connectors,
> etc. That's rather normal.
>
> That's why those cables between your 12V car battery and starter motor are
> so big.
>
> One approach used to maintaining voltage in spite of the unavoidable ohmic
> losses is to run a third wire for the voltage regulator sense circuit to the
> load. That way, the regulator is adjusting the voltage to maintain the set
> value at the load, not at the output of the power supply.
>
> Be aware that if anything interrupted that connection, the power supply
> would go to maximum voltage with serious consequences to the rig and any
> other equipment connected at the far end. Also, a voltage sense circuit can
> be rather sensitive to RF pickup which may cause the circuit to increase or
> decrease the voltage.
>
> 73, Ron AC7AC
>
> -----Original Message-----
>
>
>
> This really got me curious.  I was in the NAQP RTTY Contest.....and decided
> to
> look at the voltage on my K3.  I checked the meter on the RM-35A, but those
> meters are not very good.  The volt meter says 14.5 volts.  NaH!    So, I
> went
> to the K3 internal meters and got the following
>
> 100 watts out
> 22.5 amps
> 11 volts
>
> 13.8 volts key up.....
>
> 11 volts seems low to me.  So, I might have to do some checking out as well.
>
> Lee
> k0WA
>
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