In a parallel LC circuit, I get a very very small current reading at resonance. Apparently this is supposed to happen, but I have no clue why. Isn't current supposed to be a maximum at resonance?

In my witricity project, everyone is telling me to use a parallel LC circuit, meanwhile in my simulations I see that a series LC circuit produces the highest current and voltage. Why a parallel LC circuit then?? Can someone please explain this.

EDIT: Hey Bill, I did the series LC circuit with a 120V RMS and 159.155 Hz (this is the resonant frequency --> you can modify the frequency in the AC power supply in the simulation program). The results I got were crazy! The voltage and current rise to infinity! Unless you put in a resistor to limit it to a really high voltage and current, it will just short circuit the AC power supply.

Here's the simulation output:

Isn't this a better method instead of a tesla coil to generate extremely high voltages?? It seems like you can generate any amount of voltage desired, provided your capacitors and inductors are rated to handle that desired amount of voltage, right?

 

That relates directly to this post.

The voltage is real, but practically useless. The moment you try to tap into it it drastically reduces Q and most likely moves the resonance. The voltages across the coil and cap are equal and opposite, you are seeing the √-1 in action. I usually recommend beginners do the math just for your reaction. Interesting, isn't it. Add a resistor to limit the current, and you will still get high voltages, though not as extreme.

Like I said, a series resonant allows the resonant frequency through (a short), while a parallel resonant circuit blocks the frequency. These kind of filters have some really useful properties.

 

It would make sense for me to build a series LC circuit because it filters out all the other frequencies and only allows the resonant frequency to pass, which is what I need. I still don't understand why people are using parallel tank circuits to do this experiment. Everything positive points into the direction of a series LC circuit, yet they chose to use parallel LC circuit. Is it because

"One use for resonance is to establish a condition of stable frequency in circuits designed to produce AC signals. Usually, a parallel (tank) circuit is used for this purpose, with the capacitor and inductor directly connected together, exchanging energy between each other"

 

You can use resonance to couple two circuitw. I believe the MIT approach uses something like this to a high degree.

 

You can use resonance to couple two circuitw. I believe the MIT approach uses something like this to a high degree.

Yes I am aware of that. What I don't understand is: Which type of LC circuit is best to use to resonantly couple two circuits? Parallel (tank) or series? As far as all the input to this thread goes, the only difference is that one blocks the resonant frequency and the other allows it. My question is: Is that the only difference or is there some other properties of parallel vs series I should know?

 

Think coupling via magnetic or RF. RF does have a magnetic component, though I don't know how much difference this makes.

One nice thing about RF is it can be made extremely directional. If you use a MASER it can even be made coherent, same as a laser. Again, I don't know how this would apply to a magnetic field.

The LC circuit resonates with the RF from the antenna. You can make a loop antenna that is also the coil, I suspect this is how MIT did their trick.

 

Think coupling via magnetic or RF. RF does have a magnetic component, though I don't know how much difference this makes.

One nice thing about RF is it can be made extremely directional. If you use a MASER it can even be made coherent, same as a laser. Again, I don't know how this would apply to a magnetic field.

The LC circuit resonates with the RF from the antenna. You can make a loop antenna that is also the coil, I suspect this is how MIT did their trick.

Ah, a couple things I need to note is that the MIT guys didn't use RF to do this, but rather evanescent coupling which is non-line-of-sight so it had no directionality importance in the design. The other "loop" you see is on the secondary coil which is used for some reason to re-couple the secondary coil to a tertiary coil. I am not aware why they did that, but it is supposed to increase efficiency and save power.

In wikipedia, I took note of this line in the LC circuit article:

1. Most common application is tuning. For example, when we tune a radio to a particular station, the LC circuits are set at resonance for that particular carrier frequency.
2. A series resonant circuit provides voltage magnification.
3. A parallel resonant circuit provides current magnification.
4. A parallel resonant circuit can be used as load impedance in output circuits of RF amplifiers. Due to high impedance, the gain of amplifier is maximum at resonant frequency.
5. Both parallel and series resonant circuits are used in induction heating.

Could it be that they use parallel LC circuit because it magnifies the current in the secondary coil? But I don't understand...I thought in parallel tank circuit the impedance was maximum at resonance....doesn't this mean that no current can travel because the resistance is almost-infinite?