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Coils

Number of messages: 11

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adept
Colorado, United States

Why do coils have resistance? This make no sense to me.

Posted 8 Nov 2009 06:56 AM

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bigGlittlestar
United States

Are you refering to ignition coils?

Posted 8 Nov 2009 05:10 PM

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edward_t
North Carolina, United States

All things have -some- resistance, otherwise you have found that wonderful thing tons of physicists have been looking for called a "super-conductor" that will allow us to use electrical power generated in far away places. It is my understanding that all the "super-conduction" materials we have so far found require amazingly low temps to work as superconductors.

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Posted 9 Nov 2009 01:52 AM

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adept
Colorado, United States

Im talking about contactor coils. a long copper strand of wire that is wrapped into a tight "coil". If you stretch the wire straight it reads 0.2 ohms on my meter. but when its wrapped up into a "coil" it has 46 ohms resistance. Why?

Posted 9 Nov 2009 02:21 AM

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bigGlittlestar
United States

OK I think I understand the question and I think I am going to give you the correct answer or something close to it.

Control cards put out low voltage signal to that coil, the resistance slows the voltage passing through it and allows it to build to whatever the voltage range is for the coil to pull that contactor closed.

Simplest example I can think of is a garden hose allowed to flow freely only allows water to come out of the open end a foot or two. Now put a spray nozzle on the end of the hose. That now puts resistance and makes that water flow through a smaller orafice and now the water will spray twenty feet.

I hope I explained that correctly, its been about twenty years since I went to basic electric school. If I didnt hopefully someone will correct me.

Oh and the increase in resistance from end to end to coiled together is just surface contact. The more wire touching itself just concentrates the resistance.

Modified 10 Nov 2009 08:43 AM
by poster.

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edward_t
North Carolina, United States

I think I might have answered the question of; "but when its wrapped up into a "coil" it has 46 ohms resistance. Why?"
with a question;
would a short answer work?; "electro-magnetic induction".

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Posted 10 Nov 2009 09:21 PM

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griffman_23
Michigan, United States

Issues like this are why using the famed "Ohm" setting on your meter is fairly useless, unless testing for shorts to ground, or power to frame or other dead shorted areas. I've been mis-led by Ohm readings myself, so I prefer a voltage drop method. Plus this is better applied any because you're able to tell if the coil fails under full load, instead of that 0.3 Volts that you're meter puts through it.

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--Just an opinion from some punk ruining the world--

Posted 14 Nov 2009 09:56 AM

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edward_t
North Carolina, United States

to me, testing for shorts to frame with an Ohm meter is one of the first tests I do, and I notice GE says to do this and to voltage load test the battery before ANY other troubleshooting is done, so for that reason, I find the Ohm meter a pretty damn valuable tool, and not "fairly useless" as fixing these 2 problems ofter makes the rest of the troubleshooting considerably simpler, and whatever the repair was to "last longer".
I think BigGlittleStar is a bit confused when he says; "the increase in resistance from end to end to coiled together is just surface contact.
The wire in a coil has a slight amount of insulation on outside of the wire itself and so is not electrically "touching" the other wires, (otherwise you would have a shorted contact point and not a coil) and the Ohm meter's own current is what is creating the induction that reads a higher amount of resistance when coiled.
Big G also said; "The more wire touching itself just concentrates the resistance". ahh, no. that would be a series circuit, and this is discussing a VERY simple single circuit.
now, if my term of " "electro-magnetic induction" is as correct as "electromotive and counter-electromotive force" is maybe worth discussion...
I would also note that while he is correct that it takes more current (not JUST voltage) to initially pull in a coil, it is not as correct to state that -every- controller uses battery voltage and then cuts down the amount of voltage used to hold in the contacts. there are/were plenty of controllers that just used battery voltage all the time.

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Modified 16 Nov 2009 08:46 PM
by poster.

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griffman_23
Michigan, United States

Edwardt--I must have misspoke myself. I also check for shorts to frame, and for that the ohm setting is the best tool. But when trying to toubleshoot components, I've found it quite misleading. Thats what I was refering to with the "fairly useless" comment. And as for your electro-magnetic induction, I haven't heard that term since college, so please remind me as to what that is, if you could.

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--Just an opinion from some punk ruining the world--

Posted 15 Nov 2009 07:25 AM

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edward_t
North Carolina, United States

this may not be the best place, [nor I the best teacher, especially on a Saturday night] to explain what the explanation of induction is,
Try wikipedia; "en.wikipedia dot org/wiki/Electromagnetic_induction"
if if that is clear as mud, let us know, and maybe we can do further work at helping you visualize the phenomenon of a coiled wire having a higher resistance reading than the same wire laid out straight and not in proximity to any other current carrying devices...

?since when do they let people who been to college work on forklifts? [just joken]

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Modified 15 Nov 2009 11:32 PM
by poster.

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bigGlittlestar
United States

Ed T, thanks for the correction. I was never top notch when it came to electrics. If I had the book I could hold my own and as I said in my earlier post, its been a long time since basic electric class.

Posted 16 Nov 2009 03:40 PM

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