Resistance of materials?

[GreenTeam]

A while back, during my learning via hands on experiments i constructed a teensy stator. I had used what i think was about a 0.15mm enamelled magnet wire scavenged from a 3 speed fan. It came wrapped around a plastic rectangular bobbin. I had unwound it all onto a empty coil holder to gauge how much there was. I decided to build a 8 coil single phase stator. And with a continuity test, the signal only made it maybe 5 coils at most before the continuity failed. The coils were 450 turns each. I was under the impression that copper wire had to be like maybe ten miles before resistance failed. Is there a common rule of hand for how many feet or meters wire at a certain gauge can be until resistance is to much?

[richhagen]

Hi, resistance is additive, you can integrate the resistance over the path of the conductor to determine the overall resistance.  There are other properties such as impedance (resistance + reactance), inductance, capacitance that impact signal propagation.  I wrote a wire resistance calculator a long time ago, if I can find it I will see if I can upload it.  I wrote it for looking at the lead wires for solar panel arrays and it is only for resistance, but it may have some value for you in determining the resistance of your coil.  It is an .exe program I wrote in visual basic around 15 or more years ago. Note that it is an executable file and some computers may give warnings for such upon downloading.  You can fill in any two of the values to calculate the third.  For a hundred fifty feet of .15 square mm wire, I calculated 5.26 Ohms for example.  If you measure with DC you should be close to this value with your copper wire, AC impedance in your coil will be much higher as you would need to add the reactance.    Rich

It looks like the link survived the transition to the current forum software: 
http://www.otherpower.com/images/scimages/742/WIRECALC.exe

[Mary B]

A while back, during my learning via hands on experiments i constructed a teensy stator. I had used what i think was about a 0.15mm enamelled magnet wire scavenged from a 3 speed fan. It came wrapped around a plastic rectangular bobbin. I had unwound it all onto a empty coil holder to gauge how much there was. I decided to build a 8 coil single phase stator. And with a continuity test, the signal only made it maybe 5 coils at most before the continuity failed. The coils were 450 turns each. I was under the impression that copper wire had to be like maybe ten miles before resistance failed. Is there a common rule of hand for how many feet or meters wire at a certain gauge can be until resistance is to much?

You have a bad connection between coils is my guess... if you cast in the connection points dig them out and take each one apart. I am guessing you missed taking the enamel off the wire for one coil...

[Adriaan Kragten]

The formula for the calculation of the Ohmic resistance of a copper wire with a length l (m) and a cross sectional area A (mm^2) is given in my public report KD 679 as formula 22. The formula is valid for metric sizes. So first you have to determine the wire thickness d (mm) and so the cross sectional area A (mm^2) for a certain gauge number. You must take the copper diameter so not the diameter including isolation. All my public reports can be found on my website: www.kdwindturbines.nl at the menu KD-reports.

[Scruff]

Calculations assume factory-fresh materials and proper job terminations with suitable terminal torque. I've fallen victim to using lightly crusty cabling from the scrap pile on a few occasions. Specifically with Ah counting device accuracy.
On the other hand if the wire is too long then a DMM is not always accurate because it's only running a 9V partially depleted battery.

I find voltage drop load testing to be the most accurate.