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K3 - How much supply voltage is too much?

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Ross Primrose N4RP

K3 - How much supply voltage is too much?

I have a surplus laptop switching supply that's 15V @ 5A. Is that too
high a voltage to run my 10W K3 on routinely?

Thanks, and 73, Ross N4RP

--
FCC Section 97.313(a) “At all times, an amateur station must use the minimum transmitter power necessary to carry out the desired communications.”

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N5GE

Re: K3 - How much supply voltage is too much?

>From Page 8 of the K# owners manual, Revision D9, Dec. 7, 2010:

"Supply Voltage and Current
13.8 V nominal (11 V min, 15 V max). 17-22 A typical in TX for K3/100, 3-4 A
typical in TX for K3/10. 0.9A typical RX (less sub receiver). When using reduced
supply voltage (< 12 V), power output should be reduced (e.g. 70 W at 11 V)."

73,
Tom
Amateur Radio Operator N5GE

On Tue, 10 May 2011 13:54:01 -0400, Ross Primrose N4RP <[hidden email]> wrote:

>I have a surplus laptop switching supply that's 15V @ 5A. Is that too
>high a voltage to run my 10W K3 on routinely?
>
>Thanks, and 73, Ross N4RP

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Amateur Radio Operator N5GE

Jim Brown-10

Re: K3 - How much supply voltage is too much?

In reply to this post by Ross Primrose N4RP

On 5/10/2011 10:54 AM, Ross Primrose N4RP wrote:
> I have a surplus laptop switching supply that's 15V @ 5A. Is that too
> high a voltage to run my 10W K3 on routinely?

If it were my radio, I would add one or two silicon diodes in series
with the positive lead to reduce the voltage to about 14 volts. For a
10W K3, I'd guess that 5A diodes would be just fine.

If it's a laptop supply, I would also be concerned about RF noise that
it might produce.

73, Jim K9YC
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Ross Primrose N4RP

Re: K3 - How much supply voltage is too much?

On 5/10/2011 3:13 PM, Jim Brown wrote:
> If it were my radio, I would add one or two silicon diodes in series
> with the positive lead to reduce the voltage to about 14 volts. For a
> 10W K3, I'd guess that 5A diodes would be just fine.

I'd thought about that as a possibility. Heat could be an issue,
especially if I want it to be easily portable, at 5A, that's about
3.5W/diode assuming a 0.7V drop.

> If it's a laptop supply, I would also be concerned about RF noise that
> it might produce.

I'm concerned about it too, but the laptop supply is already in hand,
and without a laptop, so it's worth a try. I know the old desktop PC
supply I'm using now has broadband noise at 7.070-7.080, so maybe this
one will be better (and definitely a lot smaller!).

73, Ross N4RP

--
FCC Section 97.313(a) “At all times, an amateur station must use the minimum transmitter power necessary to carry out the desired communications.”

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alsopb

Re: K3 - How much supply voltage is too much?

Roger,

You should see the crummy "DC" waveforms put out by typical laptop
switching supplies. I bought a bunch at a recent hamfest. Put each one
on a 'scope to observe the output. One had a 0.5 volt sawtooth
superimposed over the DC value. Another have ringing with introducing a
swing of over a volt in magnitude around the DC value. I tested at zero
and full load. None of these problems went away. The rest were far
from clean. Some were IBM branded.

No way would I put my rig on one of these beasties.

I don't know how laptops manage to tolerate them.

The only other thing is yes were hamfest items and could have all been
rejects or something.

For what it is worth, I did find one good supply but it was for a Kodak
printer. However, it put out 25 volts. The output was very clean at
all levels of load.

73 de Brian/K3KO

On 5/10/2011 19:35, Ross Primrose N4RP wrote:

> On 5/10/2011 3:13 PM, Jim Brown wrote:
>> If it were my radio, I would add one or two silicon diodes in series
>> with the positive lead to reduce the voltage to about 14 volts. For a
>> 10W K3, I'd guess that 5A diodes would be just fine.
>
> I'd thought about that as a possibility. Heat could be an issue,
> especially if I want it to be easily portable, at 5A, that's about
> 3.5W/diode assuming a 0.7V drop.
>
>> If it's a laptop supply, I would also be concerned about RF noise that
>> it might produce.
>
> I'm concerned about it too, but the laptop supply is already in hand,
> and without a laptop, so it's worth a try. I know the old desktop PC
> supply I'm using now has broadband noise at 7.070-7.080, so maybe this
> one will be better (and definitely a lot smaller!).
>
> 73, Ross N4RP
>

-----
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Checked by AVG - www.avg.com
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N5GE

Re: K3 - How much supply voltage is too much?

In reply to this post by Jim Brown-10

If I had paid 1,500USD or 1,700USD for A K3 10W rig I don't think I'd risk
putting anything but a real power supply on it. Wall warts are not (in my
opinion) real power supplies.

Look at this:

http://www.mfjenterprises.com/Product.php?productid=MFJ-4125

And it's reviews:

http://www.mfjenterprises.com/Reviews.php?productid=MFJ-4125

http://www.eham.net/reviews/detail/1895

And if you get a KPA3 later you won't have to get another one...

73,
Tom
Amateur Radio Operator N5GE

On Tue, 10 May 2011 12:13:33 -0700, Jim Brown <[hidden email]> wrote:

>On 5/10/2011 10:54 AM, Ross Primrose N4RP wrote:
>> I have a surplus laptop switching supply that's 15V @ 5A. Is that too
>> high a voltage to run my 10W K3 on routinely?
>
>If it were my radio, I would add one or two silicon diodes in series
>with the positive lead to reduce the voltage to about 14 volts. For a
>10W K3, I'd guess that 5A diodes would be just fine.
>
>If it's a laptop supply, I would also be concerned about RF noise that
>it might produce.
>
>73, Jim K9YC
>______________________________________________________________
>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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Amateur Radio Operator N5GE

Mel

Re: K3 - How much supply voltage is too much?

In reply to this post by Jim Brown-10

Probably been addressed, but the switching supplies all have a feedback loop to
set the output voltage. I would look for it and determine the voltage divider
and reduce the value on the output/top side by 10% using a parallel resistor.
This makes the switcher think it is producing too much voltage and will lower it
accordingly. Measure the voltage without a load. It should reduce your voltage
by about 1.5 VDC. Making it 13.5.. Give it a try before just adding diodes.
It has worked for me on two surplus supplies. Good luck.

Mel, K6KBE

________________________________
From: Jim Brown <[hidden email]>
To: [hidden email]
Sent: Tue, May 10, 2011 12:13:33 PM
Subject: Re: [Elecraft] K3 - How much supply voltage is too much?

On 5/10/2011 10:54 AM, Ross Primrose N4RP wrote:
> I have a surplus laptop switching supply that's 15V @ 5A. Is that too
> high a voltage to run my 10W K3 on routinely?

If it were my radio, I would add one or two silicon diodes in series
with the positive lead to reduce the voltage to about 14 volts. For a
10W K3, I'd guess that 5A diodes would be just fine.

If it's a laptop supply, I would also be concerned about RF noise that
it might produce.

73, Jim K9YC
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Kurt Pawlikowski

Re: K3 - How much supply voltage is too much?

In reply to this post by alsopb

Brian,

Laptops "get away with it" because they use their internal battery
like a capacitor. And, they're not really too susceptible to noise in
general. Nature of the beast...

Regards,

kurtt

Kurt Pawlikowski, AKA WB9FMC
The Pinrod Corporation
[hidden email]
(773) 284-9500
http://pinrod.com

On 5/10/2011 15:32, Brian Alsop wrote:

> Roger,
>
> You should see the crummy "DC" waveforms put out by typical laptop
> switching supplies. I bought a bunch at a recent hamfest. Put each one
> on a 'scope to observe the output. One had a 0.5 volt sawtooth
> superimposed over the DC value. Another have ringing with introducing a
> swing of over a volt in magnitude around the DC value. I tested at zero
> and full load. None of these problems went away. The rest were far
> from clean. Some were IBM branded.
>
> No way would I put my rig on one of these beasties.
>
> I don't know how laptops manage to tolerate them.
>
> The only other thing is yes were hamfest items and could have all been
> rejects or something.
>
> For what it is worth, I did find one good supply but it was for a Kodak
> printer. However, it put out 25 volts. The output was very clean at
> all levels of load.
>
> 73 de Brian/K3KO
>
> On 5/10/2011 19:35, Ross Primrose N4RP wrote:
>> On 5/10/2011 3:13 PM, Jim Brown wrote:
>>> If it were my radio, I would add one or two silicon diodes in series
>>> with the positive lead to reduce the voltage to about 14 volts. For a
>>> 10W K3, I'd guess that 5A diodes would be just fine.
>> I'd thought about that as a possibility. Heat could be an issue,
>> especially if I want it to be easily portable, at 5A, that's about
>> 3.5W/diode assuming a 0.7V drop.
>>
>>> If it's a laptop supply, I would also be concerned about RF noise that
>>> it might produce.
>> I'm concerned about it too, but the laptop supply is already in hand,
>> and without a laptop, so it's worth a try. I know the old desktop PC
>> supply I'm using now has broadband noise at 7.070-7.080, so maybe this
>> one will be better (and definitely a lot smaller!).
>>
>> 73, Ross N4RP
>>
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1325 / Virus Database: 1500/3628 - Release Date: 05/10/11
>
> ______________________________________________________________
> 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
>

David Gilbert

Re: K3 - How much supply voltage is too much?

Didn't someone here not too long ago post some information on the
unreliable voltage regulation of many wallwart/laptop supplies? Maybe
it wasn't this reflector. In general, though, I believe the thread
mentioned that many of those supplies assume a load, and under no load
conditions the voltage often went up several volts. The K3 has it's own
internal voltage regulators, but I'm not sure I'd want to subject them
to that sort of over voltage at turn on.

Dave AB7E

> On 5/10/2011 15:32, Brian Alsop wrote:
>> Roger,
>>
>> You should see the crummy "DC" waveforms put out by typical laptop
>> switching supplies. I bought a bunch at a recent hamfest. Put each one
>> on a 'scope to observe the output. One had a 0.5 volt sawtooth
>> superimposed over the DC value. Another have ringing with introducing a
>> swing of over a volt in magnitude around the DC value. I tested at zero
>> and full load. None of these problems went away. The rest were far
>> from clean. Some were IBM branded.
>>
>> No way would I put my rig on one of these beasties.
>>
>> I don't know how laptops manage to tolerate them.
>>
>> The only other thing is yes were hamfest items and could have all been
>> rejects or something.
>>
>> For what it is worth, I did find one good supply but it was for a Kodak
>> printer. However, it put out 25 volts. The output was very clean at
>> all levels of load.
>>
>> 73 de Brian/K3KO

Don Wilhelm-4

Re: K3 - How much supply voltage is too much?

David,

I have many times commented negatively on the use of unregulated wall
warts for use with any radio because the no load (low load) voltage can
be substantially greater than the rated voltage (the specified voltage
is only at full load). Many 12 volt wall warts will develop 17 volts or
more at no load. Those power supplies intended for laptop computers may
do the job, but still, I shudder at using them unmodified, and that does
not speak to any potential spurious responses (some call them "birdies")
coming from the power supply.

Regulated wall warts are a different matter (birdies not considered) -
if they will provide the required current at 13.8 volts or so, then
there is no harm in using them, but the availability of 13.8 volt
regulated wall-warts is close to zero at the sources I normally use - it
seems all the available ones with sufficient current that I have located
are unregulated.

Use wall-warts and computer power supplies at your own peril. For me, I
would not subject any radio to such a power source. With the K3 in
particular, if one has spent upwards of $1.5k for the radio, then why
"go cheap" on the power source. Spend a few extra dollars and obtain a
good 13.8 volt power supply - you will be more satisfied in the long run.

73,
Don W3FPR

On 5/10/2011 9:04 PM, David Gilbert wrote:

> Didn't someone here not too long ago post some information on the
> unreliable voltage regulation of many wallwart/laptop supplies? Maybe
> it wasn't this reflector. In general, though, I believe the thread
> mentioned that many of those supplies assume a load, and under no load
> conditions the voltage often went up several volts. The K3 has it's own
> internal voltage regulators, but I'm not sure I'd want to subject them
> to that sort of over voltage at turn on.
>
> Dave AB7E
>

Johnny Siu

Re: K3 - How much supply voltage is too much?

Very true indeed. The price for a decent regulated dc supply has dropped for the past years.

Sent from my iPhone 4

Don Wilhelm <[hidden email]> 於 2011年5月11日上午11:44 寫道：

> David,
>
> I have many times commented negatively on the use of unregulated wall
> warts for use with any radio because the no load (low load) voltage can
> be substantially greater than the rated voltage (the specified voltage
> is only at full load). Many 12 volt wall warts will develop 17 volts or
> more at no load. Those power supplies intended for laptop computers may
> do the job, but still, I shudder at using them unmodified, and that does
> not speak to any potential spurious responses (some call them "birdies")
> coming from the power supply.
>
> Regulated wall warts are a different matter (birdies not considered) -
> if they will provide the required current at 13.8 volts or so, then
> there is no harm in using them, but the availability of 13.8 volt
> regulated wall-warts is close to zero at the sources I normally use - it
> seems all the available ones with sufficient current that I have located
> are unregulated.
>
> Use wall-warts and computer power supplies at your own peril. For me, I
> would not subject any radio to such a power source. With the K3 in
> particular, if one has spent upwards of $1.5k for the radio, then why
> "go cheap" on the power source. Spend a few extra dollars and obtain a
> good 13.8 volt power supply - you will be more satisfied in the long run.
>
> 73,
> Don W3FPR
>
> On 5/10/2011 9:04 PM, David Gilbert wrote:
>> Didn't someone here not too long ago post some information on the
>> unreliable voltage regulation of many wallwart/laptop supplies? Maybe
>> it wasn't this reflector. In general, though, I believe the thread
>> mentioned that many of those supplies assume a load, and under no load
>> conditions the voltage often went up several volts. The K3 has it's own
>> internal voltage regulators, but I'm not sure I'd want to subject them
>> to that sort of over voltage at turn on.
>>
>> Dave AB7E
>>
> ______________________________________________________________
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