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Inductance

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Najwan

New Member
I do not have an inductance meter and therefore am looking for an alternative approach to measuring inductance of a wire of unknown resistance (i am unsure how to obtains its resistance).
This is because I wish to construct my own inductor coil of a certain number of turns, that which will give me a specific inudtcance value (to work in high frequency)
 

JimB

Super Moderator
Most Helpful Member
Measure the resistance with an ordinary DMM.

As for the inductance, there are various methods you could use, but first, what frequency are you going to use and what inductance.
It helps to know these when deciding on a method for measurement.

JimB
 

Najwan

New Member
Values

Frequency is 100kHz
Inductance value is 570mH
We intend to wind the wire around a core i.e. we will not buy a ready made inductor.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Najwan said:
Frequency is 100kHz
Inductance value is 570mH
We intend to wind the wire around a core i.e. we will not buy a ready made inductor.

Do you have all the details of the core?, this is crucial to calculate the potential inductance - most coil winding calculations are for air cored coils (which avoids knowing the spec of the core).

Probably the best thing is to wind 100 turns around the core and measure what inductance you get - you then can simply calculate the number of turns required.

There are various ways of measuring the inductance, depending what you have available - inductance bridge (if you have some fixed known inductors to compare against), build it in an oscillator and measure the frequency (assuming you can measure frequency?), measure it's reactance at a specific frequency (scope or AC millivoltmeter).

What are you trying to do, and how accurate does the inductor need to be?.
 

Najwan

New Member
Help!

1. Do not have an inductance meter, I do tho have a DMM.
2. How can i use that (the DMM) to calculate inductance when this is all I have:
a long piece of copper wire, with which i plan to wind a core (toroidal core) a certain number of turns by hand so i was hoping for a number much smaller than a 100!
like i said earlier, we wish to use it at high frequency n i was told it best to build the inductor to withstand this, rather than purchasing one from a shelf.

Using for example a bread board wit simple components such as resistors or watver can u guide me step by step in measuring the inductance?
 

ClydeCrashKop

Well-Known Member
Most Helpful Member
WIRETRON.COM sells wire. They have a nice free program that tells you gauge dimensions, resistance per foot, safe amperage, etc. WIRETRON.EXE I don’t think it will calculate inductance but maybe it would help
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Najwan said:
1. Do not have an inductance meter, I do tho have a DMM.
2. How can i use that (the DMM) to calculate inductance when this is all I have:

Does it include a frequency meter?.

a long piece of copper wire, with which i plan to wind a core (toroidal core) a certain number of turns by hand so i was hoping for a number much smaller than a 100!

As you have the core, the manufacturers datasheet will probably tell you winding details?. For the frequency you mentioned expect a LOT of turns, which is why I suggested winding 100 and measuring.

like i said earlier, we wish to use it at high frequency n i was told it best to build the inductor to withstand this, rather than purchasing one from a shelf.

You specified 100KHz, this is a very low RF frequnency, not a high one at all - I don't see yopu reasoning for not buying one?.

Using for example a bread board wit simple components such as resistors or watver can u guide me step by step in measuring the inductance?

Like I mentioned before, there are various options, depending what you have available - but, for a start, what is it for? - you keep mentioning 'high' frequency, then specifying a 'low' frequency. So tell us EXACTLY what you're trying to do!.
 

Russlk

New Member
You don't want to use a toroid because winding hundreds of turns by hand is too tedious to contemplate. Use E cores with a bobbin. You can turn the bobbin with a drill and wind many turns in a few minutes.
 

chemelec

Well-Known Member
Nigel Goodwin said:
Does it include a frequency meter?.



As you have the core, the manufacturers datasheet will probably tell you winding details?. For the frequency you mentioned expect a LOT of turns, which is why I suggested winding 100 and measuring.



You specified 100KHz, this is a very low RF frequnency, not a high one at all - I don't see yopu reasoning for not buying one?.



Like I mentioned before, there are various options, depending what you have available - but, for a start, what is it for? - you keep mentioning 'high' frequency, then specifying a 'low' frequency. So tell us EXACTLY what you're trying to do!.

100Khz is a high frequency, compared to audio frequencies.
Admiditly compared to RF Frequencies, 100 Khz is a low frequency, But Hi and Low, Is a Relative thing .

It sounds like there trying to making a choke for a Switching supply.

Personally I would suggest they give more Details so we can advise them further, than Buy a proper choke for their application.
 

Hetal

New Member
group partner

chemelec said:
100Khz is a high frequency, compared to audio frequencies.
Admiditly compared to RF Frequencies, 100 Khz is a low frequency, But Hi and Low, Is a Relative thing .

It sounds like there trying to making a choke for a Switching supply.

Personally I would suggest they give more Details so we can advise them further, than Buy a proper choke for their application.

hey every1 .. i am actually najwans lab partner.. for this project. i guess Nigel already knows me as i am into programming and she has the hardware to handle... well yes we are makin a choke for a buck converter. we have got a value of the inductance to be 570uH . though we have the inductor of that rating, we have been told to make a choke..... we have a DMM with a dc power supply and waveform generator.. we have 2 copper wires of different thickness(unknown .. we dont even know the awg rating since we had got it from an electrical shop)..we also have a core..

it is difficult to get a bob pin here and ordering a inductor .. would take us almost one week for it to be delivered..

there is one way that i have read for measuring the resistance of the copper wire is by series resistance method.. connect a known resistance. with a wire of a certain lenght.. measure the voltage across the known resistance and theereby .. we can find the value for the wire.. however i have a question regarding that???.... does the length of the copper wire ..matter ? my second concern is .. on a breadboard i am connecting the voltage supply again using copper wires(insulated ones ) will they create errors in the reading ???

however if there is another method..to determine. the resistance of the copper wire.. would be better .. thannks..
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Do you have the manufacturers datasheet for the toroidal core?, that should give you winding suggestions - but the resistance of the wire makes no difference to the inductance, although you obviously need low resistance thick wire to handle the current (but this is basically down to the gauge of the wire used).
 

Hetal

New Member
nope...

since it was difficult getting the core.. we went to an electrical shop and got it removed .. from one of the circuit boards.. so we dont know the .. specs of the core ..too.. well we dont know the awg ratings of the .. copper wire.. .. so is it possible to determine without them ?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hetal said:
since it was difficult getting the core.. we went to an electrical shop and got it removed .. from one of the circuit boards.. so we dont know the .. specs of the core ..too.. well we dont know the awg ratings of the .. copper wire.. .. so is it possible to determine without them ?

I don't see how you could calculate without knowing the specs on the core?, you can only wind a few turns around it and measure it, this will give you the ratio of turns to inductance.

But if all you have is a DMM you're going to struggle to measure it's inductance!.
 

audioguru

Well-Known Member
Most Helpful Member
Everything seems to be hard to get or is completely unknown in some countries. Then we are asked what did we do 100 years ago. Why??
 

Najwan

New Member
Now what?!

I am stranded with an unknown AWG copper wire and an equally unknown core. I stil lack an inductance meter and time is of the essence.
What is the most time effective means to rectifying this, taking into consideration financial constraints, to construct this inductor?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Najwan said:
I am stranded with an unknown AWG copper wire and an equally unknown core. I stil lack an inductance meter and time is of the essence.
What is the most time effective means to rectifying this, taking into consideration financial constraints, to construct this inductor?

As I've already told you TWICE, wind some turns around the core and measure it's inductance, OR buy a suitable ready made coil!.

As I've also told you previously, there are various methods of measuring inductance, depending what you have access to! - just a DMM though isn't likely to be enough!.
 

JimB

Super Moderator
Most Helpful Member
All I see in this thread is lots of unknowns and a lot of confusion.

There is wire of an unknown gauge.
There is talk of measuring the resistance of the wire. USE THE DMM, it has resistance ranges doesnt it?
Yes the length of the wire will affect the resistance, double the length and you will double the resistance.

The core for the inductor is totally unknown.
Wind some wire on there and measure the inductance.
You will need a LOT of turns, like Nigel said earlier, try 100 turns to start with. If it is a torroid core, have fun.

To measure the inductance, put a resistor in series with the inductor and connect them to the output of your waveform generator (set to sinewave).
Measure the voltage across the resistor and the inductor, do some maths and find the inductance.
Beware: you will have to use a low frequency, I doubt if the DMM will work above a couple if kHz, if that. And remember the voltage across the resistor and inductor will be 90deg out of phase with each other.

Does this help?

JimB
 

Najwan

New Member
Hmm

Am sory Nigel that you had to repeat yourself and thank you jim for the tips. N ofcours a hearty thanks to you Nigel as wel.
 

chemelec

Well-Known Member
Hetal said:
hey every1 .. i am actually najwans lab partner.. for this project. i guess Nigel already knows me as i am into programming and she has the hardware to handle... well yes we are makin a choke for a buck converter. we have got a value of the inductance to be 570uH . though we have the inductor of that rating, we have been told to make a choke..... we have a DMM with a dc power supply and waveform generator.. we have 2 copper wires of different thickness(unknown .. we dont even know the awg rating since we had got it from an electrical shop)..we also have a core..

it is difficult to get a bob pin here and ordering a inductor .. would take us almost one week for it to be delivered..

there is one way that i have read for measuring the resistance of the copper wire is by series resistance method.. connect a known resistance. with a wire of a certain lenght.. measure the voltage across the known resistance and theereby .. we can find the value for the wire.. however i have a question regarding that???.... does the length of the copper wire ..matter ? my second concern is .. on a breadboard i am connecting the voltage supply again using copper wires(insulated ones ) will they create errors in the reading ???

however if there is another method..to determine. the resistance of the copper wire.. would be better .. thannks..

The Best way to determine the wire Gauge is to use a Micrometer or a Vernier to measure its diameter. Than look at a wire chart to get the actual wire gauge.

Also, There is no way you can measure the inductance with the equipment that you have.

And Unless you know the Specifications on that core, you will not be able to wind that choke properly.

Also 570uH sounds a bit high for the inductance.

*** How did you come up with this value?

About the best I could do woyld be to mail you a choke, but the closest value I have that would be suitable for your application is a 400 uH one. And it would probably take a week or more for tyou to get it.

Gary
 
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