# Transformer for electromagnetic induction

#### inductive

Joined Jan 11, 2016
2
Hello,

I am doing a project to prove electromagnetic induction can be used to drive a simple 4.5V DC motor. Setup is as follows.

Input: 120V to 12V AC stepdown transformer
Primary coil: 100 turns of 24AWG enameled copper wire wound around a galvanized nail 6" long
each end of primary coil is connected to the 12V AC transformer
voltage measured is about 6.64V (Problem 1: Why is that voltage lower than 12V?)
Secondary coil: 100 turns of 20AWG enameled magnet wire would around another galvanized nail 6" long
distance between primary and secondary coil 1cm
voltage measured at secondary coil is about 0.75V (Problem 2: Why is the voltage so low? is it because the inductive coupling is very lossy)

Next step is to connect the secondary coil to a rectifier and then the DC output of the rectifier to a 4.5V motor. I think I need a capacitor to smooth out the DC from the rectifier before going to the motor.

what I am doing wrong in Step 1? Any insight/education will be much appreciated.

#### AnalogKid

Joined Aug 1, 2013
11,027
In step 1 the resistance of the wire is so low that it is trying to short out the secondary of the transformer. What is the output current rating of the transformer. If you know this we can guide you on how to make a safe primary coil.

ak

#### BR-549

Joined Sep 22, 2013
4,928
Problem 1. As ak says.....not enough impedance in coil #1.

Problem 2. Two separate coils can exchange information, but for power transfer you need a common flux and a common core.

Think toroid.

#### inductive

Joined Jan 11, 2016
2
Thank you for the responses. It is a 20VA transformer. So 20/12=1.67A.

BR-549: more clarification:
circuit1: 120v-12V transformer connected to primary coil
circuit2: secondary coil+rectifier+motor
the idea is to induce enough power from the primary to the secondary to run the motor. so i cannot have a common flux and core. are you suggesting that the secondary coil should be a toroid?

#### BR-549

Joined Sep 22, 2013
4,928
"the idea is to induce enough power from the primary to the secondary to run the motor."

You, Tesla, and everybody else want's to do that.

Some people think that Tesla figured out, how to do this.

As far as I know, a strong field, with hi u media, and a close distance is needed.

The flux has to be converged in the media.........to act like a common core.

#### #12

Joined Nov 30, 2010
18,224
i cannot have a common flux and core.
Consider this: The core is air and the flux must be traveling through it or your second coil would show nothing for voltage.
The problem is that this is a dreadful way to try to transfer power. The air coupling is just too weak to allow much energy to transfer between the inductors.

#### AnalogKid

Joined Aug 1, 2013
11,027
the idea is to induce enough power from the primary to the secondary to run the motor.
It sounds like you are trying for a version of wireless charging, only running a small motor rather than charging a cell phone. If so, that basically is an air-core transformer. The shape and alignment of the two coils is critical. At 60 Hz energy transfer is going to be very low.

ak

#### tcmtech

Joined Nov 4, 2013
2,867
The first thing I see is you are trying use two galvanized nails for transformer cores which is a poor choice being nails are made tempered carbon steel that has very poor magnetic properties for use with alternating current electromagnetic fields not silicon steel that has good magnetic properties for alternating current electromagnetic fields.

Second given the nails shape it puts the majority of its magnetic flux lines out the ends which will make its ability to magnetically couple with the other nail much less effective.

Third given your power source and the large voltage pull down your primary coil has far to low of impedance and is overloading the transformer so would suggest adding a few hundred more turns of wire to it to improve its impedance and reduce the overloading issue.

If it was me I would be making the two halves of your transformer out of laminated iron sheets from an old ballast or old transformer in a 'U' or 'C' shape and have them pointing at each other with a air gap between them. By using the correct materials in the correct layout transferring a few watts of power from the primary to secondary coil with an inch or so of air gap between their cores should be possible.