I just started my electronics hobby and what I plan to do is to get some coils resonantly coupled. I do realize coils can ramp up voltage rapidly and yes I am taking safety precautions.

https://en.wikipedia.org/wiki/Resonant_inductive_coupling

My plan is to get the primary coil resonating. I thought just to use a TL494 based PWM module and square wave and then drive the coil with a BJT or MOSFET. I ordered some IRFP260N MOSFETs, but atm I just got one 2n3055 hooked up. Then just adjust the freq until I get the most voltage in the primary coil. Does this sound about right?

Then I wish to get the secondary resonating at the same freq. Secondary might be just a looped coil with a cap for tuning.

The third coil would be the load coil with a rectifier like in the wikipedia article I linked. Coils are connected only by near field transmission.

Now since I got no clue what I'm doing I already burned one TL494 module Now what I want to know what is the "proper" way to drive the primary coil with a square wave and do I need some snubbers to protect my oscillator module and the driving transistor?

I drew up this circuit for driving the primary coil, but I did not dare to hook it up yet...

https://www.circuitlab.com/circuit/y9wuxmsmf697/tesla-driver-circuit/

 

Are these air core coils or do they have a magnetic core?

 

Are these air core coils or do they have a magnetic core?

Hi!

These are air cores like described in the linked Wikipedia article chapter

"Energy transfer and efficiency"

 

I don't think that you are quite understanding the "WiTricity" process. At least...your circuit certainly isn't.

 

To drive the coil efficiently you want to use a push-pull driver that is capacitively coupled to the coil (to block any DC current if you are using a single supply voltage).

 

To drive the coil efficiently you want to use a push-pull driver that is capacitively coupled to the coil (to block any DC current if you are using a single supply voltage).

Third forum and the first intelligent answer! So I could use my module http://www.ebay.co.uk/itm/131586554657 with a pair or MOSFETs to drive the primary coil?

Could you possibly point me towards a schematic, that would not take me years to decipher? Like I said this hobby is 2 weeks old and my kungfu is not very strong yet.

 

I see no reason for PWM (pulse width modulation) in this application.
Why do you think you need it?
You just want an oscillator with about a 50% duty-cycle driving the coil.
What frequency range do you think you need?

 

The Tesla transformer is not necessarily a resonant situation. It is a step-up transformer.

 

I see no reason for PWM (pulse width modulation) in this application.
Why do you think you need it?
You just want an oscillator with about a 50% duty-cycle driving the coil.
What frequency range do you think you need?

I thought sharp DC pulses would get the coils to produce high voltage? Since I already have this module I thought I could use it? If you say "you cannot use PWM in this situation" then I will change it.

"You just want an oscillator with about a 50% duty-cycle driving the coil." Well if I connect this 44% duty cycle PWM module straight to the coil I get blue smoke. So I think I need a bit more than just the oscillator. That "more" is the part I don't have. I hope the frequency I need for resonance is somewhere between 0-300kHz because that is what the module can do.

In the simplest form I just need a circuit that allows me to connect my PWM module to the coil without the module being burnt. Then I could start ramping up the frequency to find the resonant freq of the primary.

 

The Tesla transformer is not necessarily a resonant situation. It is a step-up transformer.

So my question was "how can I get this to resonate" and your answer is "I doesn't necessarily resonate". This feels like asking NASA what is on the far side of the Moon.

 

Do you have an oscilloscope to monitor the circuit voltage as you change the frequency?

You can put a resistor in series with the coil to limit the current until you find the resonant point.
Off resonance the coil looks pretty much like a short circuit, which is likely why the module burnt.

 

You start with this circuit. The feedback comes via the secondary to the base of the transistor. The primary will have to be around the connect way.
Once you get this circuit working, you can increase the driver.

 

Do you have an oscilloscope to monitor the circuit voltage as you change the frequency?

You can put a resistor in series with the coil to limit the current until you find the resonant point.
Off resonance the coil looks pretty much like a short circuit, which is likely why the module burnt.

The PWM puts out 5V. Should the resistor be small like 500Ohms? I was wondering if it got burnt by the back EMF / voltage spikes from the coil?

Yeah I just bought an oscilloscope and I had a party when I actually got the PWM square wave out of it!

 

You start with this circuit. The feedback comes via the secondary to the base of the transistor. The primary will have to be around the connect way.
Once you get this circuit working, you can increase the driver.

Thx Colin! Do I replace the "Switch" with my PWM module's signal output? Can the secondary be just a loop with a cap and maybe a resistor? Does it have to give feedback to the circuit?

 

Thx Colin! Do I replace the "Switch" with my PWM module's signal output? Can the secondary be just a loop with a cap and maybe a resistor? Does it have to give feedback to the circuit?

I can see you don't have the slightest idea how the circuit works.

The circuit self-oscillates as a flyback arrangement and it finds its own natural frequency of operation.

Just build the circuit exactly as described and don't put any thought into the project.

 

I don't know if this idea will work but I'll suggest it.
Why not try a ZVS driver with a larger air coil(also at a smaller voltage first -5v).Zvs resonates at the tanks frequency and also produces a sine wave trough the coil.On the receiver end a similar tank can be used(omitting the centertap).

 

Thx Colin! Do I replace the "Switch" with my PWM module's signal output? Can the secondary be just a loop with a cap and maybe a resistor? Does it have to give feedback to the circuit?

I can see you don't have the slightest idea how the circuit works.

The circuit self-oscillates as a flyback arrangement and it finds its own natural frequency of operation.

Just build the circuit exactly as described and don't put any thought into the project.

I can see that you have trouble reading and understanding English. You tell me how I can put any "thought" into a circuit, that does not describe my problem? How can I know how this circuit works, if you don't tell me? I ask how to use my PWM and you give me a flyback circuit.

You think that if I had a clue I would come here to get abused by douche bags?

Yeah it is very hard to learn electronics with unabombers going full asberger mode on you with every question. It is like going to a karate studio asking to learn karate. First comment is "Why don't you try judo?" or "your belt has the wrong knot in it". Then if you ask "well could you teach me a kick" you get reply "you don't have a slightest clue about karate. It is not just kicks. It is also punches, locks and strange holds. Btw here is a picture of a TaeKwonDo fighter in a stance for you".

crutshow at least tried to help. Why is this forum here? For some nerds to look at capacitor pictures and wanking?

Now if anybody still wants to learn electronics. Do not come to this forum or at least do not ask any questions! Buy an electronics book and burn all the components you need to get a clue. Then come back and vomit on people.

One last question. How can I delete my account here?

 

There are hundreds of projects on the web showing how to make a Tesla coil.
You have not done any research or made any experimental models, otherwise you would know the circuit I presented is self-oscillating and because it finds its own frequency, the output is the best you can get.
It is pointless putting PWM into a circuit and trying to fight the natural resonances.

 

Ahh...first to explain why the PWM option does not work at resonance...
Every component is not perfect(as expected) so the used values are a bit off and they present some kind of resistance.
You can try using a ne555 is astable mode aka PWM generator (plenty of calculators online) to generate your pwm at a frequency let's say f.
Even if the IC produces the desired frequency your tanks(L-C parralel setup ) won't perfectly match.a parallel LC tanks resonating frequency formula is 1/(2pi*sqrt(L*C)) where L and C are provided in SI units(Henry's and Farad's).
So to overcome this there are self oscillating circuits that set their frequency by using the tanks frequency.
Above I explained in lay terms.
One such circuit is a ZVS driver(zero voltage switching).Such a driver usually has other kinds of uses...but is a selfoscilating circuit that has a sine wave trough the 'main' coil. So I assume that if a similar tank is used as a receiver it might just work as you want.
A ZVS drivers pro feature: can switch a lot of power.
For starters you should further look at how such circuit works...I've seen it references also as Mazilli driver....popular name is ZVS driver.
Note....zenners and gate pulldowns are for serious high power implementations.Anyway it's not exactly easy to make a driver like this to work without experimentation...so I suggest you use a protected power supply(one that has some kind of current limiting...a PC power supply fits in ...I personally use one to power mine)
Work from here...it's the first time probably someone tries to use this circuit for an application like this.So some test will be needed.
Good luck.