[Elecraft] Traveling Power Supply for KX2?

[James Bennett]

Before the thread is terminated, I thought I'd toss in my two cents worth. My family and I will be heading to the southern Philippines for several weeks in April. I'll be operating 40-10 meters, CW, SSB, JT65, JT9 QRP with my KX3/PX3 as DU8/W6JHB. My initial plans were to bring a LiFePo4 battery and charger with me. But, with all the other stuff we are taking, including my Canon DSLR and a bunch of lenses, weight became an issue. 

I decided to use the internal KX3 battery bank when no mains power was available, and when it was, I wanted a lightweight power supply. Something that would run the KX3 and PX3, plus be able to charge those internal batteries. I ordered from Pro Audio Engineering the Kx33 unit. Wow - what great customer service. Ordered it this past Thursday - it was delivered today, Saturday! And, I had mentioned that I was planning on using it in a portable operation. When Howard from PAE heard that I was going to be portable, he surmised (correctly) that I would be using some sort of end fed antenna. He noted that quite often that sort of antenna generated common mode RFI that might cause issues in the power supply, so he tossed in a clamp on mix 31 ferrite to help avoid problems when I'm 7,500 miles from home!

This afternoon I hooked up the Kx33 to my rig and gave it a try. I was surprised to see the receive-only voltage showing 14.1 volts on the KX3 display. Nice. I fired up JT9 on 160 meters with the KX3 driving a KXPA100 at 40 watts. The amp was running off a separate power supply, so the Kx33 only had to supply current for a lightly loaded KX3 and PX3, but in that 100% duty cycle mode, the voltage dropped only 100 ma. That impressed me - very nice regulation.

Bottom line for me is that this power supply was well worth the money. And the fact that it will run on 110 or 220 makes it an ideal unit for my upcoming vacation, as the Philippines is a 220v country.

73, Jim

Jim Bennett / W6JHB
Folsom, CA

>> On Mar 17, 2017, at 3:13 PM, Josh Fiden <josh at voodoolab.com> wrote:
>> 
>> On 3/17/2017 6:07 AM, Dave B via Elecraft wrote:
>> (Often low cost brittle plastic things from
>> the Far East.)
> These are *all* low cost plastic things from the far east!
>> In this case, as the PSU is intended to be used with a device that has
>> exposed metallic parts connected to one side of the DC lead, I suspect
>> (I admit that I do not know for sure) that the AC input to that PSU
>> should include a safety ground, connected to (among other things) the
>> transformer inter-winding shield.
> The safety regulations pertain to the power supply, not the target device. So, it doesn't matter whether the radio has exposed conductive parts. Safety ground on the AC line input is not necessary either, however, design requirements change if you don't have it. The concern is isolation between high voltage line input and low voltage output, and the result of component failures. This specifies clearance & creepage distances, insulation types, rating of capacitors which bridge across line or from line to load, etc.
> 
> [K9YC: I should say "protective earthing" rather than "ground" so I don't get in trouble for improper use of the term!]
> 
> The shield (winding or foil) between windings in the transformer is not for safety or necessarily connected to earth. This is for EMI and reduces common mode noise passing from primary to secondaries. An adapter like the KX33 would be flyback topology, so a transformer shield (if present) would be connected back to the primary switching MOSFET's source pin, not ground.
> 
> Incidentally, the safety regulations are pretty well harmonized between USA and most of Europe. For example, this type of power adapter falls under UL60950 which is identical to IEC60950.
> 
> 73,
> Josh W6XU
> 
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