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K3 voltage under load

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Harris K9RJ

K3 voltage under load

I am running my K3 off an Astron RS-35M. No load voltage at the rig is 14.0V (per the K3 display). Running approximately 100W this reading drops to 12.3V. Is this the norm? BTW current reads just under 18 amps. The amp meter reading on the Astron is way off.73 Harris K9RJ

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Harris K9RJ

Ed K1EP

Re: K3 voltage under load

I don't think that this is normal. It depends upon the voltage drop
on cable between the radio and power supply, as well as any voltage
drop inside of the radio. I actually was measuring this
yesterday. My supply reads between 13.7 and 13.8 on the K3 meter
under receive. With 100W keydown, it was reading 13.2. This was a
quick measurement and I didn't verify that the supply maintained
constant voltage (it should have as it is a 25A supply). I have
about 12" of 10AWG cable from the supply to the radio. I think that
this drop is typical or maybe even slightly high. Your drop of 1.7V
is way too high. I would inspect your DC cabling to the radio,
correct installation of your powerpoles on that cable, and the
connector pins on the KPA3 and KPAIO3.

At 6/2/2009 02:07 AM, Harris Leck wrote:

>I am running my K3 off an Astron RS-35M. No load voltage at the rig
>is 14.0V (per the K3 display). Running approximately 100W this
>reading drops to 12.3V. Is this the norm? BTW current reads just
>under 18 amps. The amp meter reading on the Astron is way off.73 Harris K9RJ
>
>
>
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Bill VanAlstyne W5WVO

Re: K3 voltage under load

In reply to this post by Harris K9RJ

I own an Astron analog power supply, and there is NO fluctuation of voltage
under full load, without load, or anything in between. That's what a regulated
power supply is supposed to do. I would say you have a defective power supply.

Bill W5WVO

Harris Leck wrote:

> I am running my K3 off an Astron RS-35M. No load voltage at the rig
> is 14.0V (per the K3 display). Running approximately 100W this
> reading drops to 12.3V. Is this the norm? BTW current reads just
> under 18 amps. The amp meter reading on the Astron is way off.73
> Harris K9RJ
>
>
>
> ______________________________________________________________
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Ed K1EP

Re: K3 voltage under load

At 6/2/2009 08:26 AM, Bill W5WVO wrote:
>I own an Astron analog power supply, and there is NO fluctuation of voltage
>under full load, without load, or anything in between. That's what a
>regulated
>power supply is supposed to do. I would say you have a defective power supply.

No, not necessarily. He stated that the 12.3V was measured inside of
the radio. That reflects any IR loss to that point and not
necessarily poor regulation on the supply. More data is necessary to
come to that conclusion.

>Harris Leck wrote:
> > I am running my K3 off an Astron RS-35M. No load voltage at the rig
> > is 14.0V (per the K3 display). Running approximately 100W this
> > reading drops to 12.3V. Is this the norm? BTW current reads just
> > under 18 amps. The amp meter reading on the Astron is way off.73
> > Harris K9RJ
> >

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S Sacco

Re: K3 voltage under load

In reply to this post by Harris K9RJ

Harris -

This is likely due to "I squared * R" losses in your DC cable; the voltage
is being reduced by the resistance of the cable. I had the same problem.

How long is it? What gauge is it? Are there any fuses or other items
in-line with it?

73,
Steve
NN4X

On Tue, Jun 2, 2009 at 2:07 AM, Harris Leck <[hidden email]> wrote:

> I am running my K3 off an Astron RS-35M. No load voltage at the rig is
> 14.0V (per the K3 display). Running approximately 100W this reading drops to
> 12.3V. Is this the norm? BTW current reads just under 18 amps. The amp meter
> reading on the Astron is way off.73 Harris K9RJ
>
>
>
> ______________________________________________________________
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Guy, K2AV

Re: K3 voltage under load

It only takes about ** a tenth of an ohm ** between K3 and power supply to
drop 1.7 volts at 18 amps. Size of wire, bad crimp in a connector, tiny bit
of corrosion, etc., etc.

AND, the tenth of an ohm may be spread out in different places.

I have three feet of #10 to the K3, and I drop from 14.2 to 13.8 at 100
watts using an Astron RS 35A I adjusted up just a teeny.

73, Guy.

----- Original Message -----
From: "S Sacco" <[hidden email]>

> Harris -
>
> This is likely due to "I squared * R" losses in your DC cable; the voltage
> is being reduced by the resistance of the cable. I had the same problem.
>
> How long is it? What gauge is it? Are there any fuses or other items
> in-line with it?
>
> 73,
> Steve
> NN4X
>
>
>
> On Tue, Jun 2, 2009 at 2:07 AM, Harris Leck <[hidden email]> wrote:
>
>> I am running my K3 off an Astron RS-35M. No load voltage at the rig is
>> 14.0V (per the K3 display). Running approximately 100W this reading drops
>> to
>> 12.3V. Is this the norm? BTW current reads just under 18 amps. The amp
>> meter
>> reading on the Astron is way off.73 Harris K9RJ
>

Joe Subich, W4TV-4

Re: K3 voltage under load

In reply to this post by Harris K9RJ

This drop is excessive. With the standard (factory assembled)
K3 power cable, I see 13.9V no load and 13.2V at 20 A with an
Astron RS-35.

I would be concerned ...

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Harris Leck
> Sent: Tuesday, June 02, 2009 2:08 AM
> To: [hidden email]
> Subject: [Elecraft] K3 voltage under load
>
>
> I am running my K3 off an Astron RS-35M. No load voltage at
> the rig is 14.0V (per the K3 display). Running approximately
> 100W this reading drops to 12.3V. Is this the norm? BTW
> current reads just under 18 amps. The amp meter reading on
> the Astron is way off.73 Harris K9RJ
>

Ed K1EP

Re: K3 voltage under load

In reply to this post by Harris K9RJ

At 6/2/2009 05:09 PM, Hector Padron wrote:
>Certainly there is mot enough evidence to blame the PS yet,he will
>have to read the drop at the PS output poles to see if is the same
>or worse,otherwise its losses at his DC cable or something lose in
>the DC line at the K3,even a cold solder can create that,but if the
>radio makes 100W all the time,why to worry?

There are a number of reasons to worry. If there is a defective
connection, it could (and will) heat up and melt (or self destruct),
causing other problems. I have seen the plastic on power poles melt
due to incorrect installation and high resistance. Typically, the
voltage to the PA is not regulated, in the sense that it uses the
voltage supplied to the radio which it assumes is regulated. It does
that because there is no room to supply a 20A regulator in the
radio. (if you want that, you will be buying a bigger and more
expensive radio) But if the voltage becomes modulated with the audio
or other parameters, you will introduce RF distortion and other
unwanted byproducts. Not a good thing either.

>
>AD4C
>
>
>"The difference between genius and stupidity is that genius has its
>limits". -- Albert Einstein
>
>--- On Tue, 6/2/09, Ed K1EP <[hidden email]> wrote:
>From: Ed K1EP <[hidden email]>
>Subject: Re: [Elecraft] K3 voltage under load
>To: "Bill W5WVO" <[hidden email]>, "Harris Leck"
><[hidden email]>, [hidden email]..net
>Date: Tuesday, June 2, 2009, 12:39 PM
>At 6/2/2009 08:26 AM, Bill W5WVO wrote:
> >I own an Astron analog power supply, and there is NO fluctuation of voltage
> >under full load, without load, or anything in between. That's what a
> >regulated
> >power supply is supposed to do. I would say you have a defective
> power supply.
>No, not necessarily. He stated that the 12.3V was measured inside of
>the radio. That reflects any IR loss to that point and not
>necessarily poor regulation on the supply. More data is necessary to
>come to that conclusion.
>
> >Harris Leck wrote:
> > > I am running my K3 off an Astron RS-35M. No load voltage at the rig
> > > is 14.0V (per the K3 display). Running approximately 100W this
> > > reading drops to 12.3V. Is this the norm? BTW current reads just
> > > under 18 amps. The amp meter reading on the Astron is way off.73
> > > Harris K9RJ
> > >
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Grant Youngman

Re: K3 voltage under load

Maybe there's too much concern to do all the hand wringing?

It all depends on what's between the PS and the radio. In my case,
for example, my 13.8v supply feeds a West Mountain Radio battery
charger (200AH of battery), and there's a drop there (.4V). then to a
WMR distribution box and on to the radio. I have 13.5v no load and
12.5v transmit at 100W. All of the wiring is #10 as short as
possible. The APP's are 45A and are properly terminated. And the
radio just keeps on chugging.

I've chosen not to be concerned about it. I may try to increase the
RS-70M output to as close to 15v as I can, but my motivation is
lacking to open up the box and try to adjust the unreachable output
adjust since nothing is broken.

Grant/NQ5T

On Jun 2, 2009, at 4:41 PM, Ed K1EP wrote:

> At 6/2/2009 05:09 PM, Hector Padron wrote:
>> Certainly there is mot enough evidence to blame the PS yet,he will
>> have to read the drop at the PS output poles to see if is the same
>> or worse,otherwise its losses at his DC cable or something lose in
>> the DC line at the K3,even a cold solder can create that,but if the
>> radio makes 100W all the time,why to worry?
>
> There are a number of reasons to worry. If there is a defective
> connection, it could (and will) heat up and melt (or self destruct),
> causing other problems. I have seen the plastic on power poles melt
> due to incorrect installation and high resistance. Typically, the
> voltage to the PA is not regulated, in the sense that it uses the
> voltage supplied to the radio which it assumes is regulated. It does
> that because there is no room to supply a 20A regulator in the
> radio. (if you want that, you will be buying a bigger and more
> expensive radio) But if the voltage becomes modulated with the audio
> or other parameters, you will introduce RF distortion and other
> unwanted byproducts. Not a good thing either.

hb9brj

Re: K3 voltage under load

When switching my K3 from RX to TX 100W FM, I measured these voltage drops:

0.03V directly at the Astron RS-35M's output
0.25V at an unused output of a WMR RIGrunner, connected to the RS-35M by a 2ft cable
1.00V as indicated by the K3, connected to the RIGrunner by a 4ft cable

By cable I mean the type supplied with the K3.

Certainly not as good as the 400mV reported by Guy K2AV.
Still better than the 1.7V reported by Harris K9RJ.
Corresponds to the 700mV reported by Joe W4TV (direct connection, no RIGrunner)

Guess the major problem resulting from voltage drop is a reduced efficiency of the KPA3.

73, Markus HB9BRJ

W8ZN

Re: K3 voltage under load

If this is a serious issue to folks as it appears to be, use a power supply with remote sense and attach the sense lines at the Powerpole at the back of the K3.

My gut feel is the DX will never know the difference.

Terry

----- Original Message -----

From: hb9brj

To: [hidden email]

Sent: Wed, 3 Jun 2009 17:59:42 +0000 (UTC)

Subject: Re: [Elecraft] K3 voltage under load

When switching my K3 from RX to TX 100W FM, I measured these voltage drops:

0.03V directly at the Astron RS-35M's output

0.25V at an unused output of a WMR RIGrunner, connected to the RS-35M by a

2ft cable

1.00V as indicated by the K3, connected to the RIGrunner by a 4ft cable

By cable I mean the type supplied with the K3.

Certainly not as good as the 400mV reported by Guy K2AV.

Still better than the 1.7V reported by Harris K9RJ.

Corresponds to the 700mV reported by Joe W4TV (direct connection, no

RIGrunner)

Guess the major problem resulting from voltage drop is a reduced efficiency

of the KPA3.

73, Markus HB9BRJ

--

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Alan Bloom

Re: K3 voltage under load

In reply to this post by hb9brj

On Wed, 2009-06-03 at 10:59 -0700, hb9brj wrote:
...
> Guess the major problem resulting from voltage drop is a reduced efficiency
> of the KPA3.

Actually, for a given power level the KPA3 probably has better
efficiency. For lowest heat in the PA, the supply voltage should be as
low as possible that still works at the selected power level. But the
system efficiency is lower because of the power loss in the cables.

Al N1AL

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S Sacco

Re: K3 voltage under load

I guess the most interesting thing is that we never heard back from Harris,
K9RJ, about his setup!

What se ye, Harris?

73,
Steve
NN4X
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Jack Smith-6

Re: K3 voltage under load

In reply to this post by Alan Bloom

I've made some measurements of my K3's efficiency versus DC supply
voltage, output and frequency at
http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm

Jack K8ZOA
www.cliftonlaboratories.com

Alan Bloom wrote:

> On Wed, 2009-06-03 at 10:59 -0700, hb9brj wrote:
> ...
>
>> Guess the major problem resulting from voltage drop is a reduced efficiency
>> of the KPA3.
>>
>
> Actually, for a given power level the KPA3 probably has better
> efficiency. For lowest heat in the PA, the supply voltage should be as
> low as possible that still works at the selected power level. But the
> system efficiency is lower because of the power loss in the cables.
>
> Al N1AL
>
>
> ______________________________________________________________
> Elecraft mailing list
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>

Alan Bloom

Re: K3 voltage under load

The graphs show: the lower the power supply voltage, the higher the
efficiency.

The reason: When you set the K3 to, say, 100W it has to put 1.4A into
the 50-ohm dummy load (P = I^2R = 1.4^2 x 50 = 100).

The DC current through the PA transistors is pretty much directly
proportional of the RF current through the transistors. Whatever DC
current the PA transistors require to achieve 1.4A of RF into the load
doesn't depend on the power supply voltage.

Since the transistor current is the same no matter the power supply
voltage, you get best efficiency (lowest power dissipation) at the
lowest voltage that is capable of sustaining the desired power level.

Al N1AL

On Wed, 2009-06-03 at 19:04 -0400, Jack Smith wrote:

> I've made some measurements of my K3's efficiency versus DC supply
> voltage, output and frequency at
> http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm
>
> Jack K8ZOA
> www.cliftonlaboratories.com
>
>
>
> Alan Bloom wrote:
> > On Wed, 2009-06-03 at 10:59 -0700, hb9brj wrote:
> > ...
> >
> >> Guess the major problem resulting from voltage drop is a reduced efficiency
> >> of the KPA3.
> >>
> >
> > Actually, for a given power level the KPA3 probably has better
> > efficiency. For lowest heat in the PA, the supply voltage should be as
> > low as possible that still works at the selected power level. But the
> > system efficiency is lower because of the power loss in the cables.
> >
> > Al N1AL
> >
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> >
> >

Don Wilhelm-4

Re: K3 voltage under load

Alan,

Your analysis is correct - BUT --

Efficiency is one thing. but it has been previously discussed that
higher DC voltages result in improved IMD.
So the "best" voltage to be used is a compromise (efficiency alone is
not the only consideration). My preference is to stay with the 13.8 volt
output of my power supply and keep the voltage drop under full load to a
minimum by using #12 or larger conductors and low drop (APP)
connectors. My vote is to stay with a "systems" approach rather than
concentrating on only one parameter. YMMV.

73,
Don W3FPR

Alan Bloom wrote:

> The graphs show: the lower the power supply voltage, the higher the
> efficiency.
>
> The reason: When you set the K3 to, say, 100W it has to put 1.4A into
> the 50-ohm dummy load (P = I^2R = 1.4^2 x 50 = 100).
>
> The DC current through the PA transistors is pretty much directly
> proportional of the RF current through the transistors. Whatever DC
> current the PA transistors require to achieve 1.4A of RF into the load
> doesn't depend on the power supply voltage.
>
> Since the transistor current is the same no matter the power supply
> voltage, you get best efficiency (lowest power dissipation) at the
> lowest voltage that is capable of sustaining the desired power level.
>
> Al N1AL
>
>
> On Wed, 2009-06-03 at 19:04 -0400, Jack Smith wrote:
>
>> I've made some measurements of my K3's efficiency versus DC supply
>> voltage, output and frequency at
>> http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm
>>
>> Jack K8ZOA
>> www.cliftonlaboratories.com
>>
>

Alan Bloom

Re: K3 voltage under load

Very true. There is a tradeoff between efficiency and distortion. The
K3 has good cooling, so for a fixed station where power consumption is
not an issue, you might as well keep the PS voltage fairly high. It
also might give you a little more power output 6 meters which tends to
run a little low.

Al N1AL

On Wed, 2009-06-03 at 23:42 -0400, Don Wilhelm wrote:

> Alan,
>
> Your analysis is correct - BUT --
>
> Efficiency is one thing. but it has been previously discussed that
> higher DC voltages result in improved IMD.
> So the "best" voltage to be used is a compromise (efficiency alone is
> not the only consideration). My preference is to stay with the 13.8 volt
> output of my power supply and keep the voltage drop under full load to a
> minimum by using #12 or larger conductors and low drop (APP)
> connectors. My vote is to stay with a "systems" approach rather than
> concentrating on only one parameter. YMMV.
>
> 73,
> Don W3FPR
>
> Alan Bloom wrote:
> > The graphs show: the lower the power supply voltage, the higher the
> > efficiency.
> >
> > The reason: When you set the K3 to, say, 100W it has to put 1.4A into
> > the 50-ohm dummy load (P = I^2R = 1.4^2 x 50 = 100).
> >
> > The DC current through the PA transistors is pretty much directly
> > proportional of the RF current through the transistors. Whatever DC
> > current the PA transistors require to achieve 1.4A of RF into the load
> > doesn't depend on the power supply voltage.
> >
> > Since the transistor current is the same no matter the power supply
> > voltage, you get best efficiency (lowest power dissipation) at the
> > lowest voltage that is capable of sustaining the desired power level.
> >
> > Al N1AL
> >
> >
> > On Wed, 2009-06-03 at 19:04 -0400, Jack Smith wrote:
> >
> >> I've made some measurements of my K3's efficiency versus DC supply
> >> voltage, output and frequency at
> >> http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm
> >>
> >> Jack K8ZOA
> >> www.cliftonlaboratories.com
> >>
> >
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Harris K9RJ

Re: K3 voltage under load

In reply to this post by Harris K9RJ

First I would like to thank all who have provided advice and comments. This is a great reflector!Second I will fully explain my setup: Astron RS-35M to a Samlex BBM-12100 battery backup module to a RIGrunner 4012 to the K3. The cable between the Astron and the Samlex is #10 and about 6'6" long. Between the Samlex and the RIGrunner is #10 about 5'6" long. Finally from the RIGrunner to the K3 was the entire #12 cable supplied by Elecraft about 5'2" long.As someone noted there is about .4v loss in the Samlex and probably a bit in the 4012. Ased on the collective advice I have removed about 8'6" of cable, only 2'3" was off the #12 wire. The results are now 14.1v receiver only load and 13.0v under full load. So I have reduced losses by a full .5v or about31.25%. I am happy with this result. Thanks again to all that provided advice. Harris K9RJ

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Harris K9RJ