How can i lower from 18vac to 12vac?

Thread Starter

Ian Vella Baldacchino

Joined Oct 20, 2019
1
I have a similar situation i have an 240vac to 18vac transformer but i need 12vac for the Christmas tree fiber optic rotating motor and light. 5W 12vac required. How can i lower from 18vac to 12vac?
 

Dodgydave

Joined Jun 22, 2012
8,389
You can use a light dimmer on the Primary side to lower the output voltage, or if you can unwind some of the secondary side is better.
 

TeeKay6

Joined Apr 20, 2019
382
I have a similar situation i have an 240vac to 18vac transformer but i need 12vac for the Christmas tree fiber optic rotating motor and light. 5W 12vac required. How can i lower from 18vac to 12vac?
Considering the complexity of circuitry to reduce the voltage and the time/effort to implement, I suggest that the more prudent solution is to simply buy another transformer. A 5W wall-wart transformer should not be very expensive and would be a "clean" solution.
 

Tonyr1084

Joined Sep 24, 2015
3,578
Some AC motors will run on DC as well. I think they're called "Universal" type motors. If yours is capable of operating on DC then you can use a bridge rectifier / filter capacitor feeding into a buck converter to drop the power down to 12 volts.

However, I suspect your motor is probably a shade pole induction motor. In that case DC won't work.
 

AnalogKid

Joined Aug 1, 2013
8,103
You can use a light dimmer on the Primary side to lower the output voltage,
That would lower the RMS value of the voltage, but not necessarily the peak value. Not sure how the motor would respond, but depending on the LED regulator circuit it might have high enough peaks to cause some problems.

Full disclosure, I've never looked at a power transformer secondary with a scope when the primary was driven through a TRIAC dimmer. Hmmm...

ak
 
Full disclosure, I've never looked at a power transformer secondary with a scope when the primary was driven through a TRIAC dimmer. Hmmm...
You basically need Phase Angle Firing with current limit to operate into a transformer. Before my time at work, some temperature controllers worked operated into a Variac and some did not. I wired them all with current limit, used 25 A I2t controllers and added a load fuse.

Then they didn't blow fuses that cost $25.00 USD each, so it helped a lot.

Later, I suggested a programmable temperature controller and a DC power supply. Well 7 of them.
 

danadak

Joined Mar 10, 2018
3,577
Of course resistors always can work, if load is stable and fixed. Very in-efficient
and heat generating. Or use a small light bulb, automobile 6V system,
again not very deterministic and power waster.

Regards, Dana.
 

MisterBill2

Joined Jan 23, 2018
3,874
The best solution will indeed be to get a different transformer. But using a series resistor can also work fairly well. No, it will not be efficient but it can work well.
 

DarthVolta

Joined Jan 27, 2015
116
Have you popped open the transformer? If you were super super lucky, it might be easy to unwind/cut some winding off. But the way things are made, that would probably more effort than it's worth.
 
Subtract 6.3 V. You might be able to find one of these transformers surplus. The secondaries will either add or subtract when placed in series
 

dendad

Joined Feb 20, 2016
3,006
Or, if there is room on the secondary, wind extra turns on it and connect the 2 secondaries in anti-phase.
 
Top