K3 Display voltage?

[CX7TT]

All this talk about TX IMD and monitoring voltage, etc got me to check
out my K3. I usually run @ 50w into small amp and I see 13.7V on rcv and
11.5 while xmit. If I run the power up to 100w, I see 13.7 and 10.8; do
I have a problem? I am using an unmetered Astron RS-35 into our standard
220v house supply.
73
Tom
CX7TT
_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Julian, G4ILO]

Tom CX7TT wrote

All this talk about TX IMD and monitoring voltage, etc got me to check
out my K3. I usually run @ 50w into small amp and I see 13.7V on rcv and
11.5 while xmit. If I run the power up to 100w, I see 13.7 and 10.8; do
I have a problem? I am using an unmetered Astron RS-35 into our standard
220v house supply.

I should say so!

I suppose you are using the internal voltmeter in the VFO B position? For me it reads 13.9V off-load (DMM reads 13.94V at the PSU output terminals). At 100W key down on 20m, rig draws about 18.5A, voltage drops to 13.5V. This is using a Diamond GSV3000 PSU and the standard weedy K3 power cable, cropped down to the shortest length possible to get from A to B, no more than a couple of feet.

[Craig Smith]

<>  I usually run @ 50w into small amp and I see 13.7V on rcv and
<> 11.5 while xmit. If I run the power up to 100w, I see 13.7 and 10.8; do
<> I have a problem? I am using an unmetered Astron RS-35 into our standard
<> 220v house supply.

You definitely have a problem, Tom, but it has nothing to do with the power
supply you are using.  You have excessive resistance somewhere in the DC
distribution between the power supply and the K3.  Either your cable is
using conductors that are too small in diameter, the cable is too long, or
you have a loose connection somewhere.  First of all, if you have any
connections such as a terminal strip or binding post, make sure that they
are screwed down tightly.  Also check your solder or crimp connections.

The K3, like all 100W class rigs, will demand peak currents in the range of
20 amps.  Distributing this amount of current without excessive voltage drop
takes care.  I use an Astron 30A switcher here and have the nice and
convenient RigRunner type PowerPole distribution/fusing panels for most of
the equipment in the shack.  But for the K3 power feed I go directly from
the power supply to the K3 with only 3 ft of AWG 10 cable, and only see a
couple tenths of a volt change from zero load to 100W CW key down.  This is
what you should be aiming for if you want maximum performance from the rig.

I will take this opportunity to opine further, since this is an important
issue for me.  Remote sensing is almost always used in industry when
delivering this amount of current over distances of two feet or more.  It is
amazing that the amateur market has not used this simple and effective
solution.  All it requires is a small twisted pair cable along side the DC
cable.  I don't even think there are ANY power supplies marketed for amateur
use that include remote sensing capability!  It would only add a couple
dollars to the cost.

Thinking in broader terms for the future, we are at or have exceeded the
technical capability of a nominal 12V input power system.  It is time to
think about higher voltages for rigs used in the home environment, perhaps
48V.  If there ever is a K4 (never say never, Wayne and Eric ;>), please
design for 200W with an internal or dedicated eternal Elecraft  higher
voltage power supply!!!

            73
                    ... Craig  AC0DS


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Don Wilhelm-4]

Tom,

You do have a problem.  I recommend that you first check the voltage
during transmit at 100 watts at the power supply terminals.  If there is
more than a few tenths of a volt drop there, you will have a power
supply problem - the power supply terminals have connections on the
inside as well as the outside and they must be tight and free of
corrosion.  A few milliohms of resistance at 18 amps will create a
significant voltage drop.

Next thing to investigate is the power cord and its terminating
connections.  The APP connectors are quite good as long as the crimp to
the wire is tight enough to be what is considered 'gas-tight'  If there
are any doubts about the quality of the crimp, solder the connectors.  
Whatever termination you use on the power supply end is suspect too, the
same criteria should be applied as for the APP connectors - good crimps
or solder if there is any doubt.  Be certain the power cord is tight on
the power supply output terminal bolts.

Lastly, if the power cord is much longer than it has to be, shorten it,
every inch of wire has some resistance.  If you need to use a long
length, consider using #10 wire instead of the #12 supplied by
Elecraft.  Don;t get me wrong, #12 is entirely adequate if all other
conditions are good, but 5 feet of #12 does have  8.1 milliohms
resistance, but the return path also adds to the voltage drop, so the
entire resistance is 16.2 milliohms which translates to 0.3 volts drop
at 18 amps due to the copper.  The drop using  #10 wire will be about
2/3 of that seen with #12.

 From all that, you should conclude that the most significant voltage
drop from light load to 18 amps load will be in the connections, but
about 0.3 volts will be contributed by the wire.

73,
Don W3FPR

TMorton wrote:

> All this talk about TX IMD and monitoring voltage, etc got me to check
> out my K3. I usually run @ 50w into small amp and I see 13.7V on rcv and
> 11.5 while xmit. If I run the power up to 100w, I see 13.7 and 10.8; do
> I have a problem? I am using an unmetered Astron RS-35 into our standard
> 220v house supply.
> 73
> Tom
> CX7TT
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft   
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com 
> Version: 8.0.176 / Virus Database: 270.10.14/1918 - Release Date: 1/27/2009 7:26 AM
>
>  

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Julian, G4ILO]

Craig D. Smith wrote

Thinking in broader terms for the future, we are at or have exceeded the
technical capability of a nominal 12V input power system.  It is time to
think about higher voltages for rigs used in the home environment, perhaps
48V.  If there ever is a K4 (never say never, Wayne and Eric ;>), please
design for 200W with an internal or dedicated eternal Elecraft  higher
voltage power supply!!!

The K3 was designed with portability in mind, hence the decision to make it a 12V radio. However I guess that many (if not most) of them have never moved from the owner's shack.

Since the K3 PA is a separate module that could have separate power connectors on the rear panel, couldn't someone make a higher voltage version as a drop-in replacement? I guess the lack of a commercially available power supply would deter many potential buyers, but I'm sure I recall mention of a matching K3 power supply being offered some time back, so perhaps this could be one of its options.

It's be quicker than waiting for a K4.