[Elecraft] Highest power supply voltage for K2?

[Jack Brindle]

Guys, there are several things to consider when raising the input  
voltage to the K2 family.

First, power loss in the regulators. There are several 5V, 6V and 8V  
regulators on board. If you have a 12V source to a 6V regulator, you  
will be burning up as much power in heating up the regulator as in  
powering the circuit. At 15 volts you will be wasting twice as much  
power in the 5V regulator as the circuitry it feeds. I'm sure you would  
much rather have that power go out the antenna port or the speaker than  
to warm the case.

The other big thing to consider is the voltage rating of the  
components. Some of the electrolytics in the K2 or its various  
accessories are rated in the 15 to 20 volt range in order to keep the  
size down. Do you _really_ want to risk popping these things?

The max rated input voltage to the K2 and its accessories is 15 volts  
for a very good reason. Your K2 will last much longer if you keep the  
power supply below this level...

On Nov 29, 2004, at 11:53 PM, Tom Althoff wrote:

> 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.

- Jack Brindle, W6FB
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