[Elecraft] K3 power supply recommendation

[Edward R Cole]

Wes,

As that may be (it depends on ambient air temp), most hams are not 
transmitting key-down for extended time.  In the communication 
industry the duty-cycle for Tx to Rx time is assumed to be 10%.  Most 
FM equipment is equipped with time out timers that stop continuous 
transmission after 3-minutes.  Since I will assume you are not 
talking about FM or AM or digital modes like WSJT, the class of 
service is ICAS and not CCS.  The Astron 35 will handle 25amps quite 
nicely.  25a x 13.8v = 345w.  This is probably way above the typical 
100w RF CW/SSB radio dc load.  If the amplifier runs at 60% 
efficiency it will draw 167w (about 12amps).  Add the load of the 
radio this probably is not more than 17amps.  You can probably add a 
VHF radio sitting in Rx and still not exceed 25amps (and that is only 
drawn in transmit 10% of the time of use).

If you run any of the modes that are CCS then adding some air cooling 
is not a bad idea.  I have fans on my high power VHF and UHF amps to 
just have a bit more tolerance to heat.  I do use them for FM 
somewhat, and also are used as drivers for WSJT-eme for the 8877 
final.  Duty-cycle of WSJT (JT65) is 50% (one minute cycles of 
key-down followed by one-minute receive).  This is hard-duty on ham 
equipment so lower the RF power if you run these.  I run 55-60w on my 
150w amp to drive the 8877 to 1300-1400w.

My station Astron 50M is fused at the distribution panel for 30A so 
never exceeds this in any mode.  I have a lot of equipment running at 
the same time.

73, Ed - KL7UW

From: "Eugene Balinski" <eugeneb at nni.com>
To: Wes Stewart <n7ws at yahoo.com>,elecraft at mailman.qth.net,
	garyk9gs at wi.rr.com
Subject: Re: [Elecraft] K3 power supply recommendations
Message-ID: <web-493727653 at admin.nni.com>
Content-Type: text/plain; charset="ISO-8859-1"

Another vote for the RM-35. I have had mine for over 30
years.  Not an issue.

Note however that Astron over specs their power supplies.
  They claim that the RS-35 will do 25A continuous.  It will
not.  It gets too darn hot.  Given the heatsink, it should
do about 20 continuous.   This is with static air cooling,
no forced air.