jrd wrote:

Hi, I have a device that requires 12vac but need to use 12vdc as a
source. Is this possible? I see all kinds of 12vdc inverters around but
they all provide 120\240 vac
Been looking high and low and can't find a power supply or inverter on
the market that will do what i'm looking for. Starting to think its not
possible. I guess something like a variac off the power inverter might
drop the voltage down from 120vac to 12vac but thought there must be
some other way. Also tried looking for a "variable" dc to ac inverter
but they dont seem to exist either. I need under 1 amp on the 12vac.
thanks

What kind of device is it? It may well have an internal rectifer and
you could simply tap in with DC after that point?

-Bill

"jrd" wrote in message
...
Hi, I have a device that requires 12vac but need to use 12vdc as a source.
Is this possible? I see all kinds of 12vdc inverters around but they all
provide 120\240 vac
Been looking high and low and can't find a power supply or inverter on the
market that will do what i'm looking for. Starting to think its not
possible. I guess something like a variac off the power inverter might
drop the voltage down from 120vac to 12vac but thought there must be some
other way. Also tried looking for a "variable" dc to ac inverter but they
dont seem to exist either. I need under 1 amp on the 12vac.
thanks

Unless you are in a car or mobile (and a battery is your only power source),
a standard filament transformer (120 VAC to 12.6 VAC) will do the trick
(available at Radio Shack). There are also inexpensive wall-warts (new and
surplus) that actually supply 12 VAC to SOME devices, although a majority
are 12 VDC

gb

Hi, I have a device that requires 12vac but need to use 12vdc as a
source. Is this possible? I see all kinds of 12vdc inverters around but
they all provide 120\240 vac
Been looking high and low and can't find a power supply or inverter on
the market that will do what i'm looking for. Starting to think its not
possible. I guess something like a variac off the power inverter might
drop the voltage down from 120vac to 12vac but thought there must be
some other way. Also tried looking for a "variable" dc to ac inverter
but they dont seem to exist either. I need under 1 amp on the 12vac.
thanks

In article , jrd wrote:
Hi, I have a device that requires 12vac but need to use 12vdc as a
source. Is this possible? I see all kinds of 12vdc inverters around but

Depending upon the type of load, you could make an inverter out of a
60Hz oscilator and a cheap car stereo amplifier. This would not work for
a large motor such as a drill or mixer due to heavy startup drain,
but a small motor such as a clock, old tape recorder/vcr, telescope
positioning unit (clock drive) etc would do fine.

The trick is to get a good 60Hz sine wave. Besides an resistor/capacitor
oscialtor, which would be fine for most things that are not truely
time critical, you could do a digital thing with a multiple of 2 such
as 32768kHz (common clock/watch frequency) and a counter circuit to
cut the pulses down to one every 60th of a second. You would then need
to smooth the square waves (pulses) into sine waves and then amplify
them to your 1 amp at 12 volts.

Geoff.


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: 972-544-608-069 IL Fax: 972-2-648-1443 U.S. Voice: 1-215-821-1838
I may be an old fart, but I'm a high-tech, up to date old fart. :-)

An inexpensive approach is to use a $29.95 inverter, purchased at one of the
auto parts stores on sale, then use a 120 v to 12 volt transformer. That
will give you what you want for about $35 - and give you 120 volts in your
car for other things.

You could build you own inverter, but at that price it is hardly
worthwhile - unless you need smething smaller.

Colin K7FM


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In article , jrd wrote:
Thanks for the input guys. Looks like i will go with the inverter to
transformer for the 12vac. Seems to be really the only way. Any idea how
clean the output off the transformer would be? How clean is the output
directly off a power invertor. The 12vac that i need is for an audio
application.

You still haven't answered the question about what you want to run.

If it's for an audio application, it's probably because the device is
producing a bipolar supply inside, for +/-15V op-amp circuits. And it
is probably somewhat sensitive to supply input noise, if it is typical of
typical consumer-grade audio gear.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Thanks for the input guys. Looks like i will go with the inverter to
transformer for the 12vac. Seems to be really the only way. Any idea how
clean the output off the transformer would be? How clean is the output
directly off a power invertor. The 12vac that i need is for an audio
application.
tks
COLIN LAMB wrote:
An inexpensive approach is to use a $29.95 inverter, purchased at one of the
auto parts stores on sale, then use a 120 v to 12 volt transformer. That
will give you what you want for about $35 - and give you 120 volts in your
car for other things.

You could build you own inverter, but at that price it is hardly
worthwhile - unless you need smething smaller.

Colin K7FM


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its for a stereo generator to convert mono to stereo for my recording
hobby. The generator requires 12vac
tks
Scott Dorsey wrote:
In article , jrd wrote:

Thanks for the input guys. Looks like i will go with the inverter to
transformer for the 12vac. Seems to be really the only way. Any idea how
clean the output off the transformer would be? How clean is the output
directly off a power invertor. The 12vac that i need is for an audio
application.


You still haven't answered the question about what you want to run.

If it's for an audio application, it's probably because the device is
producing a bipolar supply inside, for +/-15V op-amp circuits. And it
is probably somewhat sensitive to supply input noise, if it is typical of
typical consumer-grade audio gear.
--scott

"Any idea how clean the output off the transformer would be? How clean is
the output directly off a power invertor. The 12vac that i need is for an
audio application."

If the power supply is converting back to dc, it should not be a problem.

The only time it would be of concern is if something gets into the audio
section by transfer outside of the desired path. I would try it and you
will probably find that it is fine.

I have used miy inverter for various projects and never found that the less
than perfect sine wave caused any problems.

73, Colin K7FM



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"jrd" wrote in message
...
its for a stereo generator to convert mono to stereo for my recording
hobby. The generator requires 12vac
tks

The stereo generator likely takes it to a rectifier / capacitor inside the
unit to produce DC anyway ..
you could tap (and feed 12 vdc) beyond the rectifier (and maybe capacitor) -
if it was a straight 12 vdc conversion.

gb