[Elecraft] K3 - Power cable voltage drop

[shull2805 at gmail.com]

At what point does a drop in input power become significant?  Does a 1.0v loss translate to 10 times less output power than a 0.1v loss?  

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On Behalf Of Bob McGraw K4TAX
Sent: Saturday, December 28, 2019 1:07 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] K3 - Power cable voltage drop

Actually 1 ohm of total resistance from a 14V source and a 20A load would be more than excessive.  More like a 0.01 ohm is 0.20 volt drop for 20 amps.   I x R = E

View it as 3 series resistors across a 14 V source.   R-1 is the DC POS lead resistance, the radio which is a variable resistance as R-2, and
R-3 which is the DC NEG lead resistance.  Therefore, the voltage at the radio is equal to the IR drop being the sum of R-1 and R-3.

73

Bob, K4TAX

On 12/28/2019 11:26 AM, Michael Walker wrote:
> For measuring voltage drop.. I would measure the voltage drop from the 
> Plus lead of the Power supply to the plus lead on the back of the 
> radio while in full load TX (FM or RTTY).
>
> It should be less than 0.1 or 0.2 of a volt.
>
> Then, do the same on the Negative Lead.  You should see the same 
> answer (assuming Negative DC doesn't find an alternative path).
>
> Those numbers should add up to the same voltage drop total.
>
> As a reminder.  It only takes 1 ohm of loss in the cable/fuses to 
> significantly impact your full power out.
>
> Mike va3mw
>
>

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