Understanding coils and solenoids

Hayden · 20th October 2006, 02:03 PM

Is there any place where I can learn how coils and magnets work I have search google and here but still doesn’t answer my questions.
I made a coil with a lot of fine wire and it showed up as 1.1 ohms so I recoiled it with a bit over double the size wire and less coils and it was 1.2ohms so I rewind the coil around a ferrite bar and still 1.2 ohm how does that work? Any formulas?

also I wanted to make a solenoid too
Any help would be greatly appreciated

jneutron · 20th October 2006, 02:34 PM

I believe you are having resistance measurement issues, not coil ones. How are you measuring the resistance?

The dc resistance will follow the guage..#12 will be about 1.7 milliohms per foot, #14 at 2.73, #16 at 4.36, #18 at 6.92, 20 at 10.9, 22 at 17.5..Belden has a good chart.

Cheers, John

xplod1236 · 20th October 2006, 04:47 PM

This should be a good start. While you're there, also do a search for magnets and electromagnets.

http://electronics.howstuffworks.com/inductor.htm
http://en.wikipedia.org/wiki/Inductor
http://en.wikipedia.org/wiki/Coil

Nordic · 20th October 2006, 06:07 PM

Yep, gotta agree with John...its probably a cheap Multimeter unable to measure any finer resolutions than the 1.2 ohms you are seeing.

cliffforrest · 20th October 2006, 10:34 PM

Just touch the meter probe tips together (with no coil in sight!)

It should read zero, but it won't!

You will see the resistance of the meter leads plus the contact resistance of the probes. Easily 1 ohm for a cheapy meter, and hard to get a consistent reading.

Measuring resistance below 1 ohm with any degree of accuracy and consistentency is not easy!

Hayden · 21st October 2006, 04:19 AM

Thanks for the info
I’m not sure on the brand of the meter but it’s a fairly good one that you can download some information form the meter to a computer via an optical cable after you have analyzed a component its wasn’t cheap either about 2 years old.
How do speaker get like 500ohms and greater I ran a magnet down the center and didn’t change impedance much anyway I’ll study those links you gave me that may answer my questions.

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20th October 2006, 02:03 PM	#1
Hayden diyAudio Member Join Date: Aug 2004 Location: Mackay Australia	Understanding coils and solenoids Is there any place where I can learn how coils and magnets work I have search google and here but still doesn’t answer my questions. I made a coil with a lot of fine wire and it showed up as 1.1 ohms so I recoiled it with a bit over double the size wire and less coils and it was 1.2ohms so I rewind the coil around a ferrite bar and still 1.2 ohm how does that work? Any formulas? also I wanted to make a solenoid too Any help would be greatly appreciated

20th October 2006, 02:34 PM	#2
jneutron diyAudio Member Join Date: Jan 2004 Location: away	I believe you are having resistance measurement issues, not coil ones. How are you measuring the resistance? The dc resistance will follow the guage..#12 will be about 1.7 milliohms per foot, #14 at 2.73, #16 at 4.36, #18 at 6.92, 20 at 10.9, 22 at 17.5..Belden has a good chart. Cheers, John

20th October 2006, 04:47 PM	#3
xplod1236 diyAudio Member Join Date: Dec 2003 Location: On the couch	This should be a good start. While you're there, also do a search for magnets and electromagnets. http://electronics.howstuffworks.com/inductor.htm http://en.wikipedia.org/wiki/Inductor http://en.wikipedia.org/wiki/Coil

20th October 2006, 06:07 PM	#4
Nordic diyAudio Member Join Date: Sep 2005	Yep, gotta agree with John...its probably a cheap Multimeter unable to measure any finer resolutions than the 1.2 ohms you are seeing.

20th October 2006, 10:34 PM	#5
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	Just touch the meter probe tips together (with no coil in sight!) It should read zero, but it won't! You will see the resistance of the meter leads plus the contact resistance of the probes. Easily 1 ohm for a cheapy meter, and hard to get a consistent reading. Measuring resistance below 1 ohm with any degree of accuracy and consistentency is not easy!

21st October 2006, 04:19 AM	#6
Hayden diyAudio Member Join Date: Aug 2004 Location: Mackay Australia	Thanks for the info I’m not sure on the brand of the meter but it’s a fairly good one that you can download some information form the meter to a computer via an optical cable after you have analyzed a component its wasn’t cheap either about 2 years old. How do speaker get like 500ohms and greater I ran a magnet down the center and didn’t change impedance much anyway I’ll study those links you gave me that may answer my questions.

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