[Elecraft] K2: power-on current spike

Tue Jan 6 14:22:00 2004

I checked the fuse info again and there is a misprint on the Bussmann =
data sheet. The (I^2)t rating for a similar fuse is=20

5A^2s. So, although the normal cap-charging inrush current could be =
high, it does not continue long enough to open the fuse. As a reality =
check the amount of energy imparted to the fuse while charging a 22uF =
cap to 12 volts is 1.6 mJ. The data sheet shows the short-term energy =
needed to open the fuse is about 400 mJ. So, I don't think the normal =
inrush current can open this fuse after all.

  Dave=20

-----Original Message-----
From: drcuthbert=20
Sent: Tuesday, January 06, 2004 9:04 AM
To: 'Tom Arntzen LA1PHA'; [email protected]
Subject: RE: [Elecraft] K2: power-on current spike

I have looked into the fuse issue. I ran some simulations and with these =
parameters:=20

2' cable from a gel cell being switched into a 22 uF cap with an ESR of =
100 milliohms.
6' cable from a gel cell being switched into a 22 uF cap with an ESR of =
100 milliohms.

I see a peak of 50 amps with the 2' cable and an I squared t of about =
0.016. I checked some fuse types and some 2A fast acting glass fuses =
open at only 0.005 (A^2)t. So, it is entirely believable that your fuse =
is opening. Can you give me the type and model number of fuse?

I will measure my K2 when it is complete. I am assuming that the =
mechanical power switch (that's soo 1980s!)is switching the gel cell =
into a 22 uF caps. Are there other, larger, filter caps? Much modern =
equipment uses active switching. One advantage is that "soft" switching =
can be implemented to avoid this sort of thing. And besides high inrush =
current, hard switching can cause massive voltage overshoot- in this =
case I see overshoot to 18 volts.

    Dave

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Tom Arntzen LA1PHA
Sent: Monday, January 05, 2004 2:37 PM
To: [email protected]
Subject: Re: [Elecraft] K2: power-on current spike

Hi Trent!
Just a shot in the dark.
Have you checked if the electrolyte capasitor C13 and C15 on =
controlboard is put in the right way?
They have enough capasitance to draw high current during chargeup if =
mounted the wrong way.
Hope I hit the spike here.
Enjoy.
Tom LA1PHA

----- Original Message -----=20
From: "Trent - KD7WUR" <[email protected]>
To: <[email protected]>
Cc: "Trent - KD7WUR" <[email protected]>
Sent: Monday, January 05, 2004 1:56 AM
Subject: Re: [Elecraft] K2: power-on current spike

> Thanks to those who responded (incl. Tom, Don, and Jim).
>=20
> I'm in the middle of phase 2 build-out, so I can't do powered-on tests =
just
> at the moment, but I've double checked everything mentioned (shorted =
power
> connector, reversed relay, diodes, electrolytic caps, etc.), and I am
> scouring the board for solder bridges.
>=20
> I doubt it's any of the major parts (reversed diodes and the like) or =
it
> would be a *continuous* problem (read "exhibited during normal =
operation,
> not just power-on").  It *could* be something relay-related since =
those are
> energized during the power-on reset sequence.
> Howdy All!
>=20
> I'm building up my K2 (what a delight[*] this kit is) and have been =
having
> problems with power-line fuses:
>=20
> Once powered up and running in Stage 1 tests/alignment, the rig runs =
0.06 -
> 0.10 A (depending on day/nite, dot/bar, etc. settings) which is =
exactly what
> the manual says to expect.
>=20
> However, the 2A fast-blow fuse I had in the power line (directly fed =
from a
> hefty 12V gel-cell) blew IMMEDIATELY the first time I tried to power =
up.  I

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