# Re: [Elecraft] Issue 12 re Astron Power Supply

Using a fused Rigrunner to connect from the K3 to a power supply can cause excessive voltage drop. There are 6 points of contact. The APP contact to the rigrunner itself (2 contacts, the negative must be considered as well). There are 2 at the fuse contacts, and there are 2 at the the cable connecting the output of the Rigrunner. Add an additional 2 for the connection to the K3 - that makes a total of 8. If you consider a 1mohm contact resistance (a practical estimate), then you have an 0.008 ohm resistance between the power supply and the K3. At 17 amps current draw for a K3 at 100 watts, the expected IR drop with that configuration is 0.136 volts due to contact resistance alone. Add to that the resistance of the wire (#12 wire at 20 degC of 1.558 ohms per 1000 ft.), you have an additional 3.116 milliohms resistance in a 5 foot cable of #12 wire - for a total of over 1.0 volts from the #12 wire.
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In other words, the total contact resistance of the 8 powerpole connectors is not as great as the resistance of 5 feet of #12 wire.

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Yes, connect the the K3/K3S directly to the power supply for best results, but if you connect through a Rigrunner,, expect some added voltage drop.
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The voltage drop through properly assembled APP connectors is low but not zero.
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73,
Don W3FPR

On 4/16/2018 4:51 PM, Joe Subich, W4TV wrote:
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```On 2018-04-16 4:26 PM, hawley, charles j jr wrote:
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```So 4 sets of power pole connectors plus 2 fuses.
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Even if the power pole connectors are assembled perfectly and
mated with optimum tension, the resistance in just the four
(15 A) power pole connectors in the negative lead is equivalent
to nearly 40 feet of #12 copper wire!

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```The voltage at the rig, K3, now drops a volt when putting out 100
Watts.
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With the equivalent of 50 feet of power cable (4 connectors plus a
10 foot physical cable), I would not be surprised.  Assuming 20A
in transmit (on 15A power poles!), a 1V drop represents 0.05 Ohms
of total circuit losses .... that's pretty good for 10 feet (x2)
of cable plus eight connectors (4 in the + lead, 4 in the - lead)
and the switching device (probably a Schotkey diode).  However,
the 0.05 Ohms in the negative lead is probably ten times higher
than in a braided bonding connection directly from the K3 chassis
to the power supply chassis.

I'm surprised that only 75% went through the ground path - that
indicates the ground path has 1/3 as much resistance as the "right"

73,

... Joe, W4TV

On 2018-04-16 4:26 PM, hawley, charles j jr wrote:
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About 75% went thru the ground path. The 10 ga to the rig went from Astron to a battery switching device in case of power outage, to rig runner and to rig. So 4 sets of power pole connectors plus 2 fuses. I’m thinking of changing some of that too. The voltage at the rig, K3, now drops a volt when putting out 100 Watts.
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Chuck Jack
KE9UW

Sent from my iPhone, cjack

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```On Apr 16, 2018, at 3:14 PM, Wes Stewart <wes_n...@triconet.org> wrote:

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I would hope that "much of the current..." wasn't really much.  The direct conductor from the negative terminal of the power supply to the radio should carry the majority of the supply current,
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Wes  N7WS

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```  On 4/15/2018 7:38 PM, hawley, charles j jr wrote:
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This thread prompted me to check out my Astron vs35m. It had a small black wire from -V connected to the bottom of the chassis. Perhaps it could be called a case or cabinet...more importantly, it’s what the green wire from the line cord is connected to. I disconnected the black wire. When it was connected, much of the current that would have passed thru the negative power wire from the power supply to the rig was shunted thru the green power cord wire, the ground buss bar, and other ground connections.
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Chuck Jack
KE9UW

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