# DC power to small AC motor?

Discussion in 'Electronic Basics' started by Sepp Spenlinhauer, Oct 20, 2004.

1. ### Sepp SpenlinhauerGuest

Hi - I am hoping someone can help me....

I have some small "Christmas light turners" (the kind you replace a light in
your Christmas light set with and it spins your ornaments on the tree)
I am trying to drive those motors from a DC power source (batteries) as part
of a mobile display.
I only need about 3 volts AC (not sure of the current - can't be much)

I have looked a LOTS of DC/AC inverter circuits but they are all designed
for 110volts.

ANY help here is really appreciated - I am getting down to the wire on
finishing this project.

Thanks SEPP!

2. ### peterkenGuest

Try building a circuit generating a square wave of say 5V-50Hz and use a
small 1:1 transformer or a (big enough) coupling capacitor
For low energy I'd try the latter
For a simple 1:1 transformer you might use an 'off the shelf transformer'
having 2 identical 6V "outputs", use one as input and the other as output,
thus ignoring the 110/220V connections

Hi - I am hoping someone can help me....

I have some small "Christmas light turners" (the kind you replace a light in
your Christmas light set with and it spins your ornaments on the tree)
I am trying to drive those motors from a DC power source (batteries) as part
of a mobile display.
I only need about 3 volts AC (not sure of the current - can't be much)

I have looked a LOTS of DC/AC inverter circuits but they are all designed
for 110volts.

ANY help here is really appreciated - I am getting down to the wire on
finishing this project.

Thanks SEPP!

3. ### Sepp SpenlinhauerGuest

Sounds like a good idea - Do you know where I can find a schematic or parts
list to do that?

Thanks SEPP!

4. ### Tam/WB2TTGuest

Sepp,
First I would make sure that the motor won't run on DC. If not, the simplest
thing is to get the 110VAC inverter, and a 6.0 or 6.3 v CENTER TAPPED
filament transformer (1 amp transformer should be more than enough). Connect
the motor between the center tap and either one of the other output leads.

Tam

Tam

5. ### peterkenGuest

My answer before was of course inspired by reading you are using a battery,
so a DC supply
Otherwise you *might* consider using the transformer Tam suggests, it's alot
simpler of course

To build a 50/60Hz oscillator you might just use a simple 555 integrated
timer, schematics are all over to find
Output current *might* be enough for driving directly what you want

IF using the suggested 1:1 transformer *DON'T* forget clamping diodes,
otherwise you might damage the 555 due to voltage spikes

good luck

Sounds like a good idea - Do you know where I can find a schematic or parts
list to do that?

Thanks SEPP!

6. ### Kim ClayGuest

Try a 555 timer operated around 50% duty running on 5VDC or so.
See: http://www.uoguelph.ca/~antoon/circ/555dcac.html

For a ~3VAC output drive the 555 from 4.5V to 6V DC.
The typical 555 is rated for a 200mA Max output drive.

For a </=100mA load (maybe a single motor?) forget the whole output
circuit connected to pin 3. Just connect a 1000 to 4700uF cap to pin 3
(cap pos(+) to pin 3) & connect the load from the other end of the cap
to ground.

For maybe 500mA or better use the 2 transistor drive in the drawing &
connect your load in place of L1/T1 (connect motor from the output cap
negative to ground). Depending on the current needed by the motor you
may be able to drive 2 or more motors with this arrangement.

The output capacitor needs to be larger with larger loads.
1000uF= 2.65 ohms at 60Hz, 3.18 ohms at 50Hz
2200uF= 1.2 ohms at 60Hz, 1.45 ohms at 50Hz
4700uF= 0.56 ohms at 60Hz, 0.68 ohms at 50Hz
10000uF= 0.26 ohms at 60Hz, 0.32 ohms at 50Hz

For a rather nice tutorial on the 555 visit:

Experiment a little with the 555 supply voltage & its output capacitor.
In this circuit R4 changes the frequency from ~69Hz (R4= 0 ohms) to
~47Hz (R4= 50K).

Happy Holidays - Kim Clay

7. ### JoergGuest

Hi Sepp,

You could build a simple blocked oscillator using an old transformer
core. To see how that is done check National's AN-288. Has to be 60Hz
though, not the high frequency they suggest. If you can find an old
transformer with enough symmetrical taps you may not even have to wind
anything.

Other than that, even a 74HC chip as an oscillator could work. They'll
go down to 3V easily and you can parallel gates for more power as long
as they are all in the same package. If it all hums or buzzes too much
you might need some low pass filtering so that the familiy rendition of
Silent Night is not disturbed by noises.

Regards, Joerg

8. ### Rich GriseGuest

If there's not some kind of control circuitry involved, and if you've
verified that it's 3VAC, it's probably 60Hz from the line. That is,
if there isn't some kind of electronic speed control. If that is the
case, then just get a 6VCT transformer at Radio Schlock and use half
the winding, and you're done. ;-)

Cheers!
Rich