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Source? for12 volt telephone answering machines

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Posted by Frank T on July 25, 2004, 11:04 pm
Hi all,

Does anyone know of a source for a 12 volt DC answering machine?  We live
off-grid, with a Trace SW2512, and on search mode it doesn't find too much
to run very often.  Our lighting was wired years before the inverter arrived
in our lives, so it is all 12 vdc, as well as our Dankoff water pump, our
Sunfrost fridge, and our sound system.  So the inverter comes on only to
power appliance use, i.e., computer, washing machine, kitchen stuff, etc.

Keeping the inverter up and running just to power a phone answering machine
is enery consuming, as well as tricky.  We have to turn on something, just
to 'trick' the inverter, when we go to work for the day, and want the
answering machine on.

I'd love to find a new/or/used 12 voltdc machine, but don't know which
companies make one.  Perhaps an RV or trailer supply?

Thanks in advance for any suggestions!

Frank Tettemer
Living Sol ~ consultation, design & building
Killaloe, Ontario
(613) 756-3884
Creating healthy, energy efficient, sustainable homes and cottages

Posted by Ray on July 25, 2004, 10:51 pm
Lots of phone answering machines run on DC.  They are powered with those
large square transformer plugs that you see on so many electronic items
nowadays.  On the plug, and often on the electronic item itself, there
is a label that will give you the voltage and available (on the
transformer) or required (on the electronic item) amperage.

Look around for a phone that requires twelve volts.  The ones at radio
shack will probably work fine.

If you are a little adept with electronics, it's not difficult to use a
regulator to knock the voltage down from twelve to nine, six, or four
volts as needed.  You lose some efficiency if you use a standard linear
regulator, though.

Ray Drouillard



Posted by Ecnerwal on July 25, 2004, 11:06 pm

Nah, just look for any of the (many) machines that use a wall-wart to
supply them with DC. If you are lucky you might get one that uses 12V -
I have one or two that use 9V, which can be supplied by either a
somewhat wasteful but very cheap voltage regulator (excess burned off as
heat) or a more expensive (and still not "perfect") DC-DC converter (or
more accurately, DC-AC-DC converter).

And/or, one with a back-up battery...

Cats, Coffee, Chocolate...vices to live by

Posted by Loren Amelang on July 26, 2004, 7:38 pm
 On Sun, 25 Jul 2004 23:06:10 GMT, Ecnerwal

None of the follow-ups warned about a potential killer defect in this
scheme. Some phone machines (including an otherwise very nice
Panasonic I used to have) ground their internal circuitry directly to
the _wrong_ side of the phone line - the side that is at -48VDC
relative to earth ground (at least in the US). They rely upon the
transformer in the wall wart to isolate the internal circuitry from
the power source ground. Replace the wall wart with a non-isolated DC
power source, and you let out all the magic smoke.

Before you say my phone wires were reversed, I tried that - the
machine could not detect an incoming ring without the -48 to power
ground connection.

Apparently most machines do not have this problem, or more people
would have noticed it. But a quick test with an ohmmeter would be


Posted by Gordon Reeder on July 27, 2004, 4:08 am

Unusual, since a completely isolated phone line interface is
possible to design.  In fact all computer modems are fully
isolated.  Transformer in the voice circuit and an
opto-isolator in the ring circuit.

Just my $.02 worth.  Hope it helps
Gordon Reeder
at: myself.com

Where is George Bush leading this country
and what are we doing in this hand basket??

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