So, I will try crutschow way and put a small voltage through them, as I can’t read the resistance on my meter at the moment, and that seems a simple way to find out the difference.

If you put a small DC voltage across both of them in series, then you want to measure the voltage drop across each of them, not use the resistance setting on the meter.

 

Years ago I had a need to test simple batteries. I used a DC motor and an old bottle cap along with a short piece of plastic. I mounted the bottle cap onto the motor shaft. Using one battery I would spin the motor and touch the short piece of plastic to the ribbed side of the cap and LISTEN for the tone. A higher tone meant a stronger battery. I did this with all the batteries under test and sorted them from the highest tone to the lowest (strongest to weakest). I'm wondering if you can build a simple audio tone generator and simply listen for which has the higher tone. Now here's the part I'm not certain of - the 33 µH coil will produce the higher tone - I think! You're building a sort of audio-scope. You can't see the tone but you can hear the difference, provided the frequency is in the audible range. And no - I don't know off hand just how to build one. But I imagine it can't be that difficult.

 

I don't think you would be able to make an oscillator in the audio range with a 33 uH inductor. Even at 10Khz it would require about 7.7 uF to resonate with 33 uH. I think the circuit would have too low a Q with those values to oscillate.

Les.

 

I don't think you would be able to make an oscillator in the audio range with a 33 uH inductor. Even at 10Khz it would require about 7.7 uF to resonate with 33 uH. I think the circuit would have too low a Q with those values to oscillate.

Les.

I was suggesting a tuned circuit to provide a resonance peak, with the lower peak belonging t the higher inductance. Using a sound card application to provide the frequency is about as non-technical as I can get. And the reading of frequency only needs to be adequate to see higher and lower. It seems that the TS does not have equipment, but given the presence on this site, must have some sort of computer. Making an oscillator is far more complex, so I did not even consider that

 

If the TS has a a radio that covers the medium wave broadcast band he could build an oscillator with the inductors that would oscillate at about 1 Mhz. The 100 uH coil with about 250 pF or the 33 uH with about 770 pF would oscillate at about 1 Mhz. He should be able to detect the frequency when the radio went quiet as it was tuned across the frequency.

Les.

 

If the TS has a a radio that covers the medium wave broadcast band he could build an oscillator with the inductors that would oscillate at about 1 Mhz. The 100 uH coil with about 250 pF or the 33 uH with about 770 pF would oscillate at about 1 Mhz. He should be able to detect the frequency when the radio went quiet as it was tuned across the frequency.

Les.

A single capacitor that produce frequencies in the BC band would be simpler, but my impression is that an oscillator would be a bit too complex for the TS.

 

If the TS has a a radio that covers the medium wave broadcast band he could build an oscillator with the inductors that would oscillate at about 1 Mhz. The 100 uH coil with about 250 pF or the 33 uH with about 770 pF would oscillate at about 1 Mhz. He should be able to detect the frequency when the radio went quiet as it was tuned across the frequency.

I like this idea.
I was thinking about going the sound card route, but have a iPad and didn’t want to connect it to a electrical circuit through the head phone socket. I know it will probably be okay, but it was the probably that scared me!
This radio idea seems simple and don’t mind the probably on that!!!
Can someone design me up the circuit I need to do this?

I am surprised by the amount of comments this has had, I suppose these are one of the harder things to test for the simple minded like me.
I also think I might order me of those testers that test alsorts of things off eBay for a tenner as this might make life simpler in the future.

 

I like this idea.
I was thinking about going the sound card route, but have a iPad and didn’t want to connect it to a electrical circuit through the head phone socket. I know it will probably be okay, but it was the probably that scared me!
This radio idea seems simple and don’t mind the probably on that!!!
Can someone design me up the circuit I need to do this?

I am surprised by the amount of comments this has had, I suppose these are one of the harder things to test for the simple minded like me.
I also think I might order me of those testers that test alsorts of things off eBay for a tenner as this might make life simpler in the future.

You will be amazed at some of the questions that draw a hundred responses. Of course, in this thread not having any test equipment makes the task a bit more challenging.
As for taking a signal from the earphone connection on an ipad, the 1000 ohm resistor would provide protection, and the only external connected device would be the digital voltmeter. So no risk there. I don't suggest risky ventures!

 

Okay, maybe I will try both and see.

Can you give me a circuit diagram I will need to do this?

 

I described the circuit once, here it is again. First, the unknown inductor and a capacitor connected in parallel, and then a resistor in series with that connecting to the input from the earphone plug. The other end of the parallel connection goes to the common of the earphone plug. The meter connects across the capacitor-inductor pair. The resistor can be from 1K to 10K ohms, the capacitor can be from 4.7mfd to 10Mfd, any voltage rating is OK.

 

I described the circuit once, here it is again. First, the unknown inductor and a capacitor connected in parallel, and then a resistor in series with that connecting to the input from the earphone plug. The other end of the parallel connection goes to the common of the earphone plug. The meter connects across the capacitor-inductor pair. The resistor can be from 1K to 10K ohms, the capacitor can be from 4.7mfd to 10Mfd, any voltage rating is OK.

Do you mean something like this?

 

Do you mean something like this?

I believe very much like that. With the ac voltmeter connected across the inductor capacitor pair. That is what I was describing. Now the effort is to get the siund function to deliver a frequency to the earphone jack. You can do that with an earphone connected to verify that it is doing what is wanted, which is delivering a tone..That will be the hard part, from what I see.

 

I was going to suggest using a simple oscillator circuit using an LM393 comparator IC but when I tried it the frequency was about 20% lower than the calculated value for resonance. I think this must be due to the loading effect of the oscillator circuit. This would make it unreliable for use by the TS.

Les.

 

I was going to suggest using a simple oscillator circuit using an LM393 comparator IC but when I tried it the frequency was about 20% lower than the calculated value for resonance. I think this must be due to the loading effect of the oscillator circuit. This would make it unreliable for use by the TS.

Les.

TS is only trying to determine the difference between 30uH and 100uH not accurately measure them.

 

Hi Albert,
This is the circuit I thought of suggesting.


With a 100 uH inductor and a 220 pF capacitor the resonant frequency should be about 1.07 Mhz. In the oscillator it produced around 800 Khz.
I checked the resonant frequency by feeding just the tuned circuit via a resistor from a signal generator and monitoring the voltage across it with a scope. It resonated at about the calculated frequency. The calculated frequency if the 33 uH inductor is used with a 220 pF capacitor is about 1.87 Mhz so I would expect the oscillator to oscillate at about 1.4 Mhz.
If the TS wants to try I suggest grounding the input pins (Pins 5 & 6) on the unused half of the LM393 . It may also be worth adding 100 nF ceramic capacitors in parallel with the electrolytics . (I did not do this.)
While I had the scope and signal generator out I tried to get the 100 uH inductor to resonate with a 3.3 uF mylar capacitor (Calculated resonant frequency 8.76 Khz.) to see if MisterBill2's suggested method would work. I could detect no resonance either with the inductor and capacitor connected as a parallel or series tuned circuit. I don't think you could go much higher than this frequency and detect a peak listening through headphones.

Les.

 

The original concept was, and still is, to see which frequency is higher, using the same capacitor, so that the only variable is the inductor.using different capacitors for each makes it a bit less certain.

 

TS's problem may be solved with multimeter and simple circuit:

 

And the purpose of the diode D1, across the coil is??

 

And the purpose of the diode D1, across the coil is??

Measuring voltage enters to coil in the form of powerful short square pulses
(see diagram below), therefore without diode EMF of coil self-induction
interferes with the normal functioning of circuit.

 

OK, and thanks for the explanatio. I had been thinking that the waveform was a bit different. It makes perfect sense now.