[Elecraft] Switching PS for travel with K2/100

[John Webster]

Hi Group:

Several have asked me to post results from my query
concerning a switching PS suitable for travel use with
my new K2 & K2/100.

Again, outstanding response.  This list is a GREAT
resource.  Thanks to Tom (N0SS), Bill (NA7Y),
Geoff (K6TFZ), Hank (K8DD), Don (KD5NDB),
Thomas (k8la / ys1ztm), and Ron (ZL1TW) for
their specific suggestions and advise.  [Many others
replied to my other post about adjusting the output
voltage of an Astron RS35A.  I will post separately
about that.]

Five specific suggestions were offered:

1. The Samlex SEC-1223 23/25 amp small.
2. The MFJ MightyLite"  4125 basic 25 amp small.  Or
the MFJ-4225MV same with meters and front panel
voltage adjustment. (Preferred over the Astron SS-25-M).
3. Kenwood KPS-15.  [But Samlex claims that this
is the same as their 1223, at a hefty increase in price]
4. The Astron SS-30.
5. AA4PB's SLA charger, if Battery charging alone
were the point.

Given my time constraints (I leave on Monday), I
decided to resort to the local Anaheim ham emporium.

I figured that I would get the MFJ-4225MV.  It
is small, weighs just 3.7 pounds, and most important
has meters, front panel voltage adjustments, and
multiple ways of connecting.  I figured, when not
traveling, it would serve double duty as a nifty
bench variable PS.

As murphy would have it, HRO did not have the
MFJ PS's (any of them) in stock.  They did how-
ever have the Samlex SEC-1223 on the shelf,
personally recommended it, and it was the cheapest
of the lot (under $100).  So I got the Samlex.
Amazing how time constraints make decision
making far simpler! :)

NOW for the big question.  Can the output voltage
be raised from 13.8 to 14 or 14.2v on this unit?
I opened it up and there are two trim pots VR1 and
VR2 (glued down, but adjustable I think).  Now, there
is NO circuit description or diagram in the brief
manual!  All it says is that its 13.8 VDC is based
on pulse width modulation (PWM) control.

Anybody know if I can safely adjust the output?
Has anyone one it with this unit?  If so which pot?
Can I safely experiment with the two pots?
I don't really know how PWM PS's work.

Any help would be gratefully received!

[I will repeat my question, briefly, in a separate
post, as brevity (a virtue I am not richly endowed
with) seems to be the secret predictive index of
volume of response :)]

Thanks again,

John



----- Original Message -----
From: Tom Hammond <n0ss@earthlink.net>
To: John Webster <jww@dslextreme.com>
Sent: Wednesday, July 30, 2003 2:48 PM
Subject: Re: [Elecraft] Switching PS for travel with K2/100


> John:
>
> >Any recommendations or experience with switching
> >PS for travel use with a K2 (with internal battery)
> >AND with K2/100 top for use where necessary?
>
> Check out:  http://www.radiodan.com/misc/samlex1223.htm
>
> I have used this P/S several times so far and have experienced little, if
> any, significant RFI from it. Of course, I've taken steps to ensure that
my
> antennas were removed some distance from the station itself, thus
lessening
> RFI opportunities.
>
> We used this P/S on FD this year with my K2/100 and it never even broke a
> sweat.
>
> 73,
>
> Tom Hammod   N0SS
>
>