[Elecraft] K3 - How much supply voltage is too much?

[Mel Farrer]

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 <jim at audiosystemsgroup.com>
To: elecraft at mailman.qth.net
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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