http://elecraft.85.s1.nabble.com/Silent-power-supply-for-a-K3s-tp7652889p7653154.html
Interesting data, Don. I wonder if there is any information about
resistance variations between soldered and crimped terminals. One might
with time since oxygen could get between the strands. A good solder job
should wet the wire through and (additionally) exclude oxygen. This
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> After consulting copper wire tables and typical connection resistances,
> I can present the following analysis for a 20 amp load:
>
> Often hams power their 100 watt transceivers through DC distribution
> devices such as a RigRunner which will contribute to the voltage drop.
> Also in-line fuses will contribute to voltage drop.
>
> Connection resistance contributes .05 volt loss under a 20 amp load for
> each contact point, you have 6 contact points in the path for a fused
> RigRunner plus two in the APP connector at the transceiver, plus the
> connection to the power supply for a total of 10 contact points. You
> have to consider the negative path as well as the positive. So that is
> a total of 0.5 volts of the total voltage drop.
>
> By contrast, a 5 foot length under a 20 amp load of #12 wire has 0.1588
> ohms (in both conductors) for a voltage drop of 0.3176 volts, and #10
> wire a drop of 0.1998 volts.
>
> So conclusion is that while increasing the wire size can reduce the
> voltage drop, the main contributor is in the power distribution system.
>
> A path direct from the power supply terminals can be expected to have a
> 0.5 volt drop with 5 feet of #12 wire to the inside of the K3. and #10
> wire can have a 0.4 volt drop - the difference is only slightly
> significant.
>
> Conclusion - in a 5 foot power cable run, the difference between #10 and
> #12 wire is only 0.1 volts (0.05 volts in each of the positive and
> negative leads) - the major contributor is the number of contact points.
>
> So for those who choose to measure the voltage drop from the power
> supply terminals to the APP connector on the outside of the K3, you
> should measure about 0.2 volts in each conductor with #12 wire and 0.15
> volts with #10 wire. If it is much more than that, check your power
> supply connection tightness and your crimp connections.
>
> Run the transceiver direct from a power supply using ring terminals
> instead of routing through a power distribution accessory.
>
> 73,
> Don W3FPR
>
> On 6/12/2019 6:29 PM, Bob McGraw K4TAX wrote:
>> Regarding "heavy gauge wire", I suggest one measure the voltage drop
>> using a DVM connected direct between the power supply Pos terminal and
>> the radio Pos terminal. Likewise do the same for the Neg DC line. Put
>> the radio in CW mode and close the key for rated output. If one finds
>> more than 0.25 volts drop in either the Pos or Neg line, I'd say that
>> attention to the power cable and connectors would be in order. Also
>> measure between radio ground and power supply ground. Again a voltage
>> value greater than 0.25 volts indicates attention to the power
>> distribution system and station equipment grounding is needed.
>>
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