Hello,

I have been experimenting with various wire and pvc tubing to create my first inductor, (this is for a tesla coil) and I am a bit stuck as when tested with an LCR meter my coils draw 0.01 milli henrys at best.

Please see below with what I have done in the experiment thus far:

Materials:

* Various PVC piping
* 0.5mm copper wire from an electronics store
* general copper wire from a hardware store
* LCR meter
* Breadboard tank circuit with inductor connected to a 100 pico Farad capacitor, inturn connected to an oscilloscope and function generator to determine the resonant frequency of the circuit and thus L, the inductor.

Results:

1. Cut a PVC pipe with L - 40mm, D - 27mm, R - 13.5mm and made 30 turns of the hardware store wire to create L1 and ran it in the breadboard circuit explained above. Resonant frequency came out at 299.984 kHz therefore L1 was calculated at 2.8 mH.

2. Took the same inductor, L1 and checked it with an LCR meter and it read 0.01 of a mH. Bought an inductor (L2) with a known value of of 0.5 mH and it read 0.5 mH on the LCR meter.

3. Uncoiled L1 and recoiled it with the 0.5mm copper wire from the electronic store, retested with the LCR meter and still read 0.01 of a mH.

What could be wrong here? Is the way I've coiled the inductor or is it the wire?

Your thoughts are appreciated.

 

Resonant frequency came out at 299.984 kHz therefore L1 was calculated at 2.8 mH.

Did you take the input capacitance of the scope, and the breadboard capacitance, into account when doing the calculation?

 

This calculator says your 0.5mm wire coil would be 0.024mH so your resonant frequency measurement system would seem to be very wrong.

 

Yes, Ive worked it out.

I didn't take into account the capacitance of the breadboard and scope.

The calculator you provided Albert is accurate because I made a larger coil (120mm length this time) and it registered 0.03 - 0.04 milli henrys on the LCR which is about right.

As this is my first time putting one together I didn't realise how little inductance air core coils have.

 

Usually magnet wire is what is used for inductors. It is very doubtful that you could procure magnet wire from a hardware store, but possibly from an electronics store. These days a bulk spool of magnet wire is not widely available.

Magnet wire is enameled wire, that is, solid copper wire with a thin coating of enamel.

A software program identifying turns and dimensions of a coil to obtain a certain inductance value almost certainly assumes magnet wire.

Regular insulated wire with a relatively thick plastic insulation doesn't allow each winding to be in close proximity to the next one that makes possible higher inductance and a reduced total length of wire than regular insulated wire.

Disregard all of this if you do in fact have magnet wire.