# get 12 volts AC from 12 volts DC

Discussion in 'Beginner Electronics' started by Gazz, Dec 28, 2006.

1. ### GazzGuest

Should be simple to do, but can't find a circuit....

Got a disco ball type lamp that has an AC motor inside it, it's fed by a 12
volt AC input at 500Ma, standard wall wart.

Want to use this thing in a vehicle that only has a 12 volt DC supply, i
know i could get a small inverter and run the wall wart that way,
but i want to do away with the wall wart, so i need to convert 12 volts DC
into 12 volts AC... at around 50 hertz, with 500 milliamps current capacity
max.

Can this be done simply, and cheaply, i imagine a 555 timer will feature
somewhere in the circuit, but can anyone point to a circuit i can build that

2. ### Ross HerbertGuest

Since you want 50Hz I assume you are in UK/Europe where the normal
mains supply is 220-230V 50Hz.

The easiest way to get the fan working from a 12V vehicle batteryt is
to use a dc-ac inverter which will produce 230Vac at 50 Hz and then
use your normal 12V ac plug pack (wall wart).

Something like this
http://www.justoffbase.co.uk/s.nl/it.A/id.34411/.f?sc=16&category=94701

3. ### PeterDGuest

Are you 100% sure the motor is AC? Low voltage AC motors are not
common. Check to see if there is not actually a rectifier to convert
the 12 VAC to DC for the motor...

That's 6 watts. Plan your 555-driven power transistors accordingly.

Wouldn't worry about sending a square wave into an ordinarily sine
wave driven motor, since it's got heavy inductance built in.

5. ### GazzGuest

deffo a 12 volt AC motor, one of those syncronomous motor thingies, turn
very slow and they will turn in either direction, depends which part of the
AC wave it gets when turned on, or if you stall it by hand it'll reverse.

Thos fiber optic xmas trees that change colour use the same thing,

Could use an inverter, but seems a bit of a waste just for a small load, the
inverter will be pulling more power to run it's self than it'd be providing.

6. ### Ross HerbertGuest

True, but unless there is some new way to convert 12V dc into ac then
an inverter is the only option. Since nobody (almost) needs 12V ac at
50Hz then all the inverters you can buy produce mains supply voltages
only, that leaves you with little choice.

7. ### PeterDGuest

That being the case, the cheapest solution would be the smallest 12 to
120 volt inverter you can find. I see them (usualy 50 or 75W models)
from time to time for under \$20, and just think--you can use it for
other things too! <bg>

If you insist on building your own, then probably a 555 running a 60
hz square wave into a transformer using a power transistor might be
the easiest solutio. Probalby only a few parts.

8. ### defaultGuest

You "could" wind (rewind) a center tapped winding for the motor -
shaded pole or synchronous induction types and use a push/pull
oscillator to drive the winding with 12 volts. They use a single coil
to excite the armature - that coil can be rewound with a center tap
and become part of two transistor p/p oscillator - works great but not
easy to do.

More hassle than its worth - but fun and educational

9. ### JackGuest

Here is a link to a circuit that should work for you.
It's a schematic and parts list of an inverter that converts 12 volts dc
into 12 volts ac and then steps the 12 volts ac up to 115 volts using a
transformer. All you need to do is use a 1:1 transformer in place of the
step up transformer in the plans and you will have 12 volts ac.

http://www.aaroncake.net/circuits/inverter.htm