[Elecraft] K3 shuts off

[Tom Hammond]

Mike:

Sounds to me as if his P/S is going into a momentary over-current protection.

When this state occurs, it is in response to a request for the P/S to provide
current in excess of that for which it was designed to supply.  For instance,
if the P/S built-in over-current protection circuit is designed to provide
22A (sightly more than the rated 20A) of current) but the device connected to
it is requiring 23A of current, the over-current protection will immediately(!)
drop the output voltage from 14 V down to somewhere around 0.3-0.6 VDC and
the resulting current will go to zero (or nearly zero anyway).  You can
demonstrate this on a P/S with over-current protection by intentionally
shorting the two main power cables together.. BUT DO NOT DO THIS UNLESS YOU
ARE CERTAIN YOUR P/S HAS OVER-CURRENT PROTECTION BUILT-IN.  Although most
'modern' supplies DO offer this feature, some may not, and shorting the leads
on a supply which did NOT offer it, might be somewhat DISASTROUS....!!!

Anyway... if your K3 is asking for even a little bit more current than the
P/S can supply, the supply will shut down for an INSTANT... until it thinks
the overload has been removed (as when no excessive current is being drawn)
and then it'll normally immediately return to full output voltage/current
again.  Of course, by that time, the K3 appears to have shut down and then
remained off (as a result of the built-in 'brown out' firmware in the K3!!!).
The 'brown-out' firmware senses when the K3 has suffered even an instantaneous
loss of power and will place the K3 into a state of suspended animation until
power is fully cycled off/on via the [POWER] button. It's a protective measure.

The solution to your friend's problem is one of two options:

  1 - Purchase a heavier-duty supply which can supply 25A 
(intermittently) before
      it goes into over-current protection...

  2 - Reduce requested power output (probably only required on certain bands
      which require just a bit more drive to produce 100W output) and live
      with the existing P/S.

Personally, I'd run with option #1.

Now, to being able to SEE this problem, to confirm that it exists...

The switch from normal operation to over-current protection can be so fast that
neither meters nor digital displays will not catch it. Neither will 
your eyes...!
BUT if you can hang a scope across the DC output from the P/S, set it 
to a very
SLOW SWEEP SPEED, so you can see a single trace run across the 
screen, and THEN
put the rig into TX at 100W of requested power, IF the problem is a momentary
over-current problem, you'll see the instantaneous drop of voltage 
easily on the
o-scope trace.

Good luck,

Tom Hammond   N0SS


At 21:47 12/12/2009, you wrote:
>I was at a friends today, looking at his K3. It's in the 1000 range of
>serial numbers, not a kit.
>
>If power is set above 95-96 watts, the rig shuts down instantly when you
>transmit (at least in CW and if you press the TUNE button. Didn't try it
>on any other modes).
>
>His power supply reads 14.6V, it's a 20A supply, but we didn't read it
>under load. Does the K3 have the ability to display voltage and current
>draw?
>
>I downloaded and installed 3.68 firmware, but the problem was there before.
>
>Clues and hints, please?
>
>73, Mike NF4L
>
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:Elecraft at mailman.qth.net
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html