How to know when an LC circuit hits resonance

[sophiecentaur]

In a series LC circuit, in a parallel circuit it is at minimum at the resonance frequency.

The current through the inductor peaks; the L and C are doing exactly the same think in both cases. This is the problem with using 'simple' terms like series and parallel. The only way to avoid talking at cross purposes is to refer to an annotated diagram.

 

[gary350]

<< Post edited slightly by the Mentors >>

First things first. Buy a good meter you don't need to over pay for a good meter. I bought a nice meter on ebay it came from China and cost me $76 free postage. It reads, inductance, capacitance, ohms, frequency, volts, amps, etc.

Just because a part is marked to be a certain value does not mean it really is. Some parts of 20%, some are 10%, some are 5%, some are 1% value. If your capacitor says 45uf it could be off 20% plus or minus. If you have a collection of parts test the value of 20 or 30 capacitors all marked 45uf see if you can fine 1 that really is 45 uf. You may need to solder several smaller capacitors in parallel to get exactly 45 uf.

Check your coil you need to know its real value. You can hand wind your own coils to get the value you need. You can add or remove turns to a factory made coil to change its value. You can put 2 or more coils in series to get the value that you need.

Once you have parts with the correct value solder them together then use your meter to check the resonance frequency.

There are formulas for finding resonance frequency. You can build a band pass filter or a filter that blocks the target frequency.

Get free TVs on Craigslist they are full of good free electronic parts. Remove the circuit boards and other useful parts then trash the rest. Lots of good aluminum heat sinks, wires, power resistors, capacitors, mosfets, and more.

 

[jim hardy]

original question was

Can anyone teach me how to calculate the resonant frequency.

1/2π√(LC) http://hyperphysics.phy-astr.gsu.edu/hbase/electric/serres.html

but you have to figure out what are L and C.

The current through the inductor peaks; the L and C are doing exactly the same think in both cases. This is the problem with using 'simple' terms like series and parallel. The only way to avoid talking at cross purposes is to refer to an annotated diagram.

That's a great point. We tend to take for granted our basics.
My Freshman EE textbook highlighted in bold print:
"The Voltage gain of a series resonant circuit can kill you."
"The Current gain of a parallel resonant circuit can kill you."

Those gains will be Q , which equals ratio X / R .
So if OP is studying a real circuit he needs to find both its reactance and its resistance.

I was relieved to see he's exciting it with a signal generator not his wall socket. A fellow can get hurt.

old jim