OT: wall wart for RX-only PS?

[DOUGLAS ZWIEBEL]

OK folks, I do own a pair of K3 and a K2...but I also own A Yaesu
FT817.  Here is my question....

I want to set this up away from the shack, but still in the house, for
RX only (when I'm not in the shack).  I have a RS wall wart rated at
14 watts (12v, 500ma).  Is there any reason why I should NOT use this
as the PS?

Thanks,
de Doug KR2Q
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[n7ws]

Hum?

--- On Sun, 12/6/09, DOUGLAS ZWIEBEL <[hidden email]> wrote:

From: DOUGLAS ZWIEBEL <[hidden email]>
Subject: [Elecraft] OT: wall wart for RX-only PS?
To: "Elecraft Reflector" <[hidden email]>
Date: Sunday, December 6, 2009, 2:30 PM

OK folks, I do own a pair of K3 and a K2...but I also own A Yaesu
FT817.  Here is my question....

I want to set this up away from the shack, but still in the house, for
RX only (when I'm not in the shack).  I have a RS wall wart rated at
14 watts (12v, 500ma).  Is there any reason why I should NOT use this
as the PS?

Thanks,
de Doug KR2Q
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[AC7AC]

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[K1LI]

Doug,

Many (most?) wall warts are unregulated. They may present a much higher
voltage than the indicated output when they are not under load. I recommend
you check the no-load voltage to be sure you don't fry something in the
FT817. You could, of course, put enough resistive load across the output of
the 'wart to bring the voltage into a "safe" range when the radio is off.
--
73 -- Brian -- K1LI

On Sun, Dec 6, 2009 at 4:30 PM, DOUGLAS ZWIEBEL <[hidden email]> wrote:

> OK folks, I do own a pair of K3 and a K2...but I also own A Yaesu
> FT817.  Here is my question....
>
> I want to set this up away from the shack, but still in the house, for
> RX only (when I'm not in the shack).  I have a RS wall wart rated at
> 14 watts (12v, 500ma).  Is there any reason why I should NOT use this
> as the PS?
>
> Thanks,
> de Doug KR2Q
>

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[Mel]

Hello Doug,

Most of the wall warts are just rectified AC.  Very little if any filtering.  I would not advise it unless you put it across a battery, however, I would be more comfortable getting a surplus laptop switching power supply and adjust the voltage down to 13.5 VDC or so.  Most of the laptop supplies are about 15 VDC and VERY good on filtering and capacity.  I
used two silicon diodes in series to drop the voltage to run my 817 on both RX and TX.  It was the size of a double deck of cards.  I got mine for $15.  Good luck.

Mel, K6KBE


--- On Sun, 12/6/09, Wes Stewart <[hidden email]> wrote:

From: Wes Stewart <[hidden email]>
Subject: Re: [Elecraft] OT: wall wart for RX-only PS?
To: "Elecraft Reflector" <[hidden email]>, "DOUGLAS ZWIEBEL" <[hidden email]>
Date: Sunday, December 6, 2009, 2:01 PM

Hum?

--- On Sun, 12/6/09, DOUGLAS ZWIEBEL <[hidden email]> wrote:

From: DOUGLAS ZWIEBEL <[hidden email]>
Subject: [Elecraft] OT: wall wart for RX-only PS?
To: "Elecraft Reflector" <[hidden email]>
Date: Sunday, December 6, 2009, 2:30 PM

OK folks, I do own a pair of K3 and a K2...but I also own A Yaesu
FT817.  Here is my question....

I want to set this up away from the shack, but still in the house, for
RX only (when I'm not in the shack).  I have a RS wall wart rated at
14 watts (12v, 500ma).  Is there any reason why I should NOT use this
as the PS?

Thanks,
de Doug KR2Q
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[John Lonigro]

Doug:
Check the voltage coming out of that wall-wart.  Very few of them are
actually regulated.  It might put out approximately 12V at 500 ma, but
it might be closer to 20V when you aren't drawing much current.  As
previously noted, hum might also be a problem.  You could still use it,
but you need to put a regulator and a couple of capacitors on the
output, to eliminate damage to the rig as well as hum.

73's,

John AA0VE

DOUGLAS ZWIEBEL wrote:
> I want to set this up away from the shack, but still in the house, for
> RX only (when I'm not in the shack).  I have a RS wall wart rated at
> 14 watts (12v, 500ma).  Is there any reason why I should NOT use this
> as the PS?
>
> Thanks,
> de Doug KR2Q
>
>  
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[Jim Brown-10]

On Sun, 6 Dec 2009 14:21:47 -0800 (PST), Mel Farrer wrote:

>Most of the wall warts are just rectified AC.  Very little if any
>filtering.

We have a lot of power interruptions up here in the Santa Cruz
mountains, thanks to storms, falling trees, and wild fires. Rather
than buy a lot of commercial units, I have put together a bunch of
little home-brew back-up power supplies for most of this gear. I
simply find suitable batteries at swap-meets and use a wall wart as
a float charger, with a parallel feed to the equipment. To avoid
overcharging the battery, I carefully match the "normal" charging
current so that current into the battery falls into the "trickle"
range (5% -10% of the 10 hour discharge rate). This tends to work
quite well. When power drops, our internet router, AC powered
phones, Ethernet switch, etc. all continue to work just fine, even
through relatively long outages. Likewise, my 12-14v ham gear runs
on a couple of big Costco deep cycle batteries that are charged from
a little 10A supply. Again, charging current is kept below that
which could degrade the batteries. They won't run a big amp, but
they do fine to keep K3s and a VHF rig running.  

73,

Jim K9YC


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[Geoffrey Mackenzie-Kennedy]

Doug,

As Mel has suggested a laptop supply is an option, I used one to power my K2
in RX mode 24/7 over a period of almost 3 years during a propagation study.
The supply I used outputs 15V @ 500mA, so I used a LM317 regulator after the
supply to obtain the required output voltage for the K2 and a VHF converter.
The LM317 is not a low dropout regulator, but I had some in my junkbox.

73,
Geoff
GM4ESD


Mel Farrer <[hidden email]> wrote:



Hello Doug,

Most of the wall warts are just rectified AC. Very little if any filtering.
I would not advise it unless you put it across a battery, however, I would
be more comfortable getting a surplus laptop switching power supply and
adjust the voltage down to 13.5 VDC or so. Most of the laptop supplies are
about 15 VDC and VERY good on filtering and capacity. I
used two silicon diodes in series to drop the voltage to run my 817 on both
RX and TX. It was the size of a double deck of cards. I got mine for $15.
Good luck.

Mel, K6KBE












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