How to determine toroid AL factor without having a LCR meter?

I have some toroid transformer cores that got mixed together. They are unmarked and the same size, and I don't have any record of the part numbers from when I bought them. Is there any way to determine the AL factor of them without having an LCR meter? I guess I could put some turns of a winding on it and put it in series with another component of known value and measure the ac voltage drop at more than one known frequency. I could then repeat the same procedure with a different number of turns. Then I could calculate the AL factor. I know that sometimes the AL factor is based on the square of the number of turns (n^2) and sometimes not , so I probably have to repeat the procedure a few times to get an accurate set of data with which to perform the calculations. Is there an easier way?

Toroid AL factor

My suggestion would be based on what you have already said. Put say 4 turns on and measure inductance then Al is half the inductance you measure.

I find resonance is the quickest way to measure inductance without an LCR meter provided you have a signal generator.

Keith

Re: Toroid AL factor

Yes Keith, I will have to build one using some sort of oscillator and a buffer amplifer. I will choose the frequency based on the AL factor being somewhere near 2000nH / n^2 since I vaguely remember it being in that vicinity, and go from there. Thank you for your input.

George
KB1PDK

Toroid AL factor

I tend to do this:



and just look for the resonant peak. You may need to juggle with the resistor value to get a decent peak. Pick the capacitor so it isn't affected too much by the oscilloscope capacitance.

Keith.

Re: Toroid AL factor

I know that sometimes the AL factor is based on the square of the number of turns (n^2) and sometimes not .

Click to expand...

Don't know where you got this, but it's wrong. It's always square respectively near to.

Re: Toroid AL factor

FvM said:

I know that sometimes the AL factor is based on the square of the number of turns (n^2) and sometimes not .

Click to expand...

Don't know where you got this, but it's wrong.

Click to expand...

True. Al is normally quoted as nH per turn squared. So if Al=100nH then one trun produces 100nH, 2 turns will give 400nH, 3 turns 900nH etc.

Keith.

Re: Toroid AL factor

Yes , that is right Keith. I don't have a signal generator nor can I afford one at the present time, so I will have to try to make the oscillator I build variable over a significant range.

Question: Are AL factors always based on the square of the number of turns or is is ever just based on the number of turns to the first power?

Toroid AL factor

I don't know of the Al being anything other than a square law - it is defined by the laws of physics (or magnetism if you prefer).

Keith.

Re: Toroid AL factor

If you have an L-meter you could use this piece of software :
mini Ring Core Calculator
**broken link removed**