Bob G3VVT wrote "...a string of 1N4000 series 1A diodes could bring down the
voltage to what you require..."
I'm glad you mentioned it Bob. It's my favorite way to drop a DC supply a few
volts down. I have four 10amp rectifiers here which would give me 2.4V
drop..17.2 - 2.4 = 14.8.
The wall wart is rated at 15VDC but as Don pointed out the regulation on these
things is pretty poor and under no load I was experiencing 17VDC. Under a 1
amp load the voltage was 15.1. Since most of the time I'm not transmitting
under load I was hesitant to apply it until I checked here.
The manual that came with my K2 when discussing the output capacity of the PA
stages states on page 102 of the Theory of Operation...
"The transmit strip is conservatively rated to provide excellent reliability
and immunity to high SWR. The same push-pull final could be pushed to over 40W
on the lower bands."
This is what let me to believe there might be some leeway. I doubt they were
talking about trying to draw 4 times as much current to get the 40W but to run
it at a higher voltage than was in the specs.
I just need something to keep the battery charged while I'm at the cabin. I
didn't want to bring my 10AMP boat anchor supply so the wall wart was a small,
though less than optimum, solution.
I'll eventually add Don's smart charger hookup to help extend the life of the
battery.
Thanks to all who answered.
73 de Tom K2TA
----- Original Message -----
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED] ; elecraft@mailman.qth.net
Sent: Monday, November 29, 2004 9:29 PM
Subject: Re: [Elecraft] Highest power supply voltage for K2?
In a message dated 30/11/04 02:01:23 GMT Standard Time, [EMAIL PROTECTED]
writes:
What is the absolute highest safe voltage you can pump into the K2 before
you start overheating the regulators etc?
Most manufacturers seem to give 16V as the upper sustained voltage limit for
DC input on 12V equipment. The 2SC1969 PA transistors are rated at this in
their data sheets and the regulators seem to come out at 25V as their maximum
input so should not represent a problem.
Faced with the situation you have with 1.2V above the 16V normal limit a
string of 1N4000 series 1A diodes could bring down the voltage to what you
require. Normal forward voltage drop comes out somewhere near 0.6V per diode,
so two in series would probably fit the bill. Used this technique to power a
Sony 2001 SW broadcast radio I had in the Middle East for over 20 years needing
4.5VDC power source.
Bob, G3VVT
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