Config: ADC REF (revisited

[Robin Diane Goldstein]

wondering what this means:

with the latest beta firmware i measured the voltage across ACC pin 2
and ground and got 4.95v on my dmm...  i then set that number into
the Config:ADC REF setting.

my K3 now shows the supply voltage as being 13.6 volts, but when i
measure the supply at the output of my PS it shows 13.76...  the
cable is only about 12 inches, so that seems like a pretty steep drop.

am i missing something?  (probably something about ohms law and a
missing decimal point?)

cheers!
robin (K9RDG)
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[Brett Howard]

Well use your DMM and measure the resistance of your power cord.  Then
look at the current consumption of the K3.  Then multiply these values
together.  Good ole ohms law (v=i*r).  If you end up getting about .16V
then there is your drop...

~Brett

On Wed, 2009-08-19 at 22:38 -0700, Robin Diane Goldstein wrote:

> wondering what this means:
>
> with the latest beta firmware i measured the voltage across ACC pin 2
> and ground and got 4.95v on my dmm...  i then set that number into
> the Config:ADC REF setting.
>
> my K3 now shows the supply voltage as being 13.6 volts, but when i
> measure the supply at the output of my PS it shows 13.76...  the
> cable is only about 12 inches, so that seems like a pretty steep drop.
>
> am i missing something?  (probably something about ohms law and a
> missing decimal point?)
>
> cheers!
> robin (K9RDG)
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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[P.B. Christensen]

> my K3 now shows the supply voltage as being 13.6 volts, but when i
> measure the supply at the output of my PS it shows 13.76...  the
> cable is only about 12 inches, so that seems like a pretty steep drop.

I wouldn't be concerned about a 0.16VDC discrepancy since you're looking at
the supply voltage as measured on two separate devices at two separate
locations.

With your DMM, measure the supply voltage on both ends of the 12" power
supply cable with the K3 powered-up. If you're using the supplied cable from
Elecraft, the two readings should be very close on a 12" cable with ~ 1 A of
DC current.  Subtract the two numbers.  The subtracted amount represents the
voltage drop on the power cable.  Any remaining amount is due to: (1) a
slight accuracy discrepancy between the DMM and alignment of the K3's
internal voltmeter; and (2) any slight additional drop associated with the
APP connectors and internal K3 wiring.

Also, you may want to take the time to ensure that the APP pins on your
power connector are aligned properly.  Voltage drop on an APP connector is
highly correlated to pin alignment since there's no concentric pin/socket
friction as there is on Molex and AMP Mate 'n Lok style connectors.

Paul, W9AC

 

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