[Elecraft] ASTRON RS-20A

Fri Dec 5 19:29:00 2003

Ron,

Thanks for the updated info.  I was having problems getting to Astron's web 
site when I was typing that, and I was working off of faulty "Grey RAM."

Tim Raymer
73 de KA0OUV

At 12:35 12/05/2003 -0800, Ron D'Eau Claire wrote:
>No, it doesn't "push" an Astron 20 amp supply to drive a K2/100 at all. An
>Astron 20 amp supply is LOAFING well within it's mfg's specs when driving a
>K2/100.
>
>The K2/100 demands intermittent currents up to about 16 A at 100 watts (mine
>runs 16 amps at 108 watts 'wide open'). That's total drain for the K2 and
>KPA100. And those are intermittent peak currents up to 16 amps.
>
>The ASTRON 20 amp supply is rated for 16 amps continuous! So even if a K2
>were to draw 20 amps at full power, it would still be within the "normal"
>working range for the Astron 20 amp supply.
>
>The K2 can only make full power output (and consume about 16 amps of
>current) with fairly low duty-cycles - SSB peak or CW (if you don't want to
>see the KPA100 smoke, you'd better not hold the key down too long in CW
>mode).
>
>That's why Elecraft recommends a 20 amp supply. What seems to catch people
>is the comment in the KPA100 manual about using a supply rated at 20 amps
>"or higher". What they are saying is that if you have a supply with a higher
>current rating it won't hurt your K2/100, but it is not any 'better' to do
>so.
>
>Remember, the K2/100 is de-rated for high duty-cycle loads like PSK, etc.
>Which drops its current demands well below the peak levels, so a 20 Amp
>Astron is "loafing" under any set of conditions that the K2/100 can
>withstand.
>
>But, even if I wanted to see my K2/100 melt down by putting a book on the
>key until it died, the Astron 20 would still be running within its current
>ratings. You'll understand if I don't want to demonstrate that. However,
>when I first built my KPA100, I only had a Ten-Tec 11 amp (ICAS) supply on
>hand. It ran the K2/100 just fine for a couple of weeks at full power before
>I picked up my Astron 20. I kept an eye on the heat sink temperature and it
>stayed well within it's normal operating range. Clearly, the Ten Tec supply
>was build like an Astron - lots of excess capacity.
>
>If you put a good-quality but too small supply on a K2/100, what you will
>most likely see is that the rig will suddenly shut off when you go above a
>certain power level. Most supplies have a "crowbar" circuit that shuts off
>the output if a certain current is exceeded. That protects the supply from
>damage in the event of  an accidental short.
>
>Where the 35 Amp supply might be handy is if you wanted to run several rigs
>from the same supply. Driving a K2/100 wide open, a 20 amp Astron has about
>4 amps continuous current capacity for other things. IF you need more than
>that, the bigger supply might be better.
>
>With the bigger supply come more weight, much stronger magnetic fields that
>must be kept away from the K2, and  more noise. The big ones tend to "hum"
>noticeably because the field around the transformer vibrates the case.
>Personally, I prefer two or three smaller supplies to one BIG one.
>
>Ron AC7AC
>
>
>
>-----Original Message-----
>I went with the VS-35M for mine....  What drove my decision was that the
>K2/100
>would be pushing the RS-20 beyond the 100% rated load and into the
>50%ICAS.
>
>Tim Raymer
>73 de KA0OUV
>
>
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Timothy A. Raymer               <[email protected]>
Missouri Department of Health   <[email protected]>
and Senior Services