[Elecraft] Re: RS 50 supply

[Ken Lotts]

I guess I should report that I have an RS-50A.

I find it to be a pretty nice analog PS overall.  I found mine on Ebay and
landed it for about $100 after shipping etc..  As luck would have it, the
large filter capacitors were totally shot.. One had blown its guts out like
a volcano all over the inside of the cabinet (previous owner probably hooked
it to a variac?).  The large (2 X 50,000ufd) caps are rated for only 25V and
the rectifiers supply it with just over 22V so the RS-50 wont withstand much
of an AC over voltage situation very well.

There is a trimmer pot on a circuit board that allows tweaking the voltage
up and down..  On mine, the board was mounted with the components pointing
down so it was a bit hard to get to the trimmer..   I replaced the bad caps
and mounted the board right side up so that the trimmer was easily
accessible and  tweaked it to put out exactly 13.8V.   I have considered
adding metering and variable voltage etc to it since the schematics show
that it is very do-able for little expense but what the heck... it just sits
under the bench and all I want from it is clean & stable 13.8VDC.

I have not stressed it to see how stiff it is at high current loads but it
is VERY stiff at the light loads.  It has no fan so it is totally silent
(very nice!)

On the flip side, the output wiring is 10 gauge wire and the output
connector is just a couple of bolts.  To be honest the 10 gauge wire is home
runned from two spots and I am pretty sure that it would be OK for 37 amps
but.. I am not sure that doubled up 10 gauge wire and a pair of bolts would
be my choice if I was truly going to draw 37 amps continuously 24X7. (the
RS-50 is "rated" by the manufacturer at 37A).

Duracomm sells some nice switching power supplies.  I found a NIB DPS-55
power supply (13.8VDC 55 amp) on Ebay and landed it for about $90 after
shipping.  The output connectors on it are clearly designed for continuous
duty at it's rated load.  I measured the inside diameter of the holes that
accept the output wires at .314 inch.. very adequate for 1 or 2 gauge wire..
I have not done much testing yet since I don't have anything that draws that
much current.  I can report that the output voltage was an impressively
accurate 13.801 VDC right out of the box as measured on my Fluke 189
multimeter.  It has a fan but it is supposed to only turns on when the
temperature exceeds 115 F and the docs say that it generates "little" heat
until 70% load, so I _guess_ the fan would not run very often below 38 amps.

I know of a Broadcast engineer K6AER in Colorado who happily uses a DPS-75
(13.8VDC 75 amp) for all his 13.8V ham radio needs.  So it is probably
pretty clean.

Ken Lotts
aa7jc


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