[Elecraft] ELPAC Power Supply

[Lyle Johnson]

Hello Ron!

> When faced with firing off all of those big relays in the KAT100, it
> allows the voltage to droop about 4 volts below normal for about 1/2
> second. That causes problems for the K2 controller. That right?

Long answer:

It allows the +12V to droop to about +4 volts for about 450 mSec.  The
brownout detector in the KAT100 MCU sees that its Vcc is below +5V nominal,
so it stops working.

During this time, the K2 CPU can't handshake with the now-silent KAT100 CPU,
so it fails to detect its presence.

Short answer:

Yes :-)

> It looks like the regulator wasn't designed to respond to such large
> transients quickly enough for this application...

It appears that my supply doesn't respond well at all.  Even a 60 Hz
switcher (using an SCR on the priomary) would respond in 16.7 mSec.  To take
450 mSec to figure it out is really, really bad.  I frankly suspect I may
have a bad supply.  But it seems to works OK when it runs the K2, although I
haven't fully characterized it under that condition since I have the KBT2
installed and always ON.

The *real* question becomes:

Is KK7P's ELPAC supply typical, or is it a defective supply?

> ..That may well be a
> problem with many supplies that do not have a large capacitor at the
> output. Indeed, putting a BIG capacitor across the output may take care
> of the problem, provided the regulator can supply the current to charge
> it up when the supply is first turned on without damage.

Yes, the supply could be modifed (if it is a design problem) or repaired (if
it is a defect in my particular supply).

With no schematics, and at under $20 to buy it in the first place, it's not
worth much time or trouble.

But I would be interested to know if other ELPAC supplies have this problem,
or if I am just lucky :-/

***

In normal operation, my KAT100 runs on the supply that also runs the KPA100,
and has no problems at all.  As Wayne pointed out, this is just something
uncovered during testing, and it may or may not be typical of the ELPAC
supplies.

Worst case, a note in the troubleshooting section of the KAT100 manual could
say "If the K2 doesn't recognize the KAT100, be sure the power supply
voltage doesn't droop when the K2 is turned on."

73,

Lyle KK7P