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gbalkam
Post  Post subject: Resistance and conductivity in twisted wire?  |  Posted: Sun Sep 25, 2016 8:52 pm
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So here is the scenario.

I need a spring. I have to make said spring since I can not find one to buy. This spring has to retain its springiness AND be conductive to electricity. In other words, hold its shape after repeated compression and have a low resistance.

I find copper, though highly conductive, does not maintain its shape well, being to soft. Stainless steel, while very good at keeping its shape and returning to that shape after compression, isn't very conductive (has a fairly high resistance compared to copper)

So what would happen if I twisted copper and stainless steel wire together? Would the resistance be lower than the stainless steel and more springy than the copper? OR would the stainless steel keep its springiness and the copper act as a conductor, being the path of least resistance?


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Pong
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 7:31 am
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The copper would fight the steel, mechanically.

Maybe use brass. It comes in different hardnesses, or you can "work" it by hammering to harden further. I'm guessing this is part of a switch. Do you really need a coil spring here?


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marnixR
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 9:55 am
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in fact, speaking of steel, stainless is about the worst choice for (electrical and thermal) conductivity - plain low carbon steel, or maybe better spring steel (i.e. with high silicon content) would be better in both strength and conductivity

if you want better conductivity with improved strength some sort of brass or bronze might be a better choice
if you don't mind going some more exotic materials Cu-Al or Cu-Be alloys might be a good choice, although I don't know how readily available they are

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gbalkam
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 4:09 pm
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it is actually for a spring in the 510 positive connector of a ecig mechanical device. It goes inside and acts to put pressure on the bottom of the atomizers + lead. The body of the device acts as - contact. WHICH requires batteries to be in perfect condition (no nicks or tears in the liner)
So it has to be strong enough to be springy, and conducive so it doesn't interfere with the resistance. Im trying a diy copper plating on a stainless steel spring i made by coiling some wire. They would be pretty cheap to buy.. if i could actually find one.


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marnixR
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 5:21 pm
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does it have to be stainless ? because standards aren't usually made of stainless steel, but high silicon spring steel - but this shouldn't prevent it from trying to plating it with copper

however, you better make sure your copper layer is of suitable thickness and quality (e.g. not too porous) otherwise your electrical conductivity would be that of the underlying steel and possibly damage the copper layer by local melting

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gbalkam
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 5:29 pm
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no, it doesn't have to be stainless steel, I just happen to have a bunch of 20ga stainless steel wire. Like 160ft of if.
Im trying to find something I can get easily, is very conductive *or as conductive as possible* and will make a good, long lasting spring.

http://imgur.com/a/HKVgC


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gbalkam
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 6:27 pm
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Ok I've tested a couple stainless steel coils, and a copper one, both of course are to soft. I'll have to check out the hardware store and see if they have any kind of hardened wire. Suggestions for springiness and conductivity, but easy to get?


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gbalkam
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Mon Sep 26, 2016 6:40 pm
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So back to the first post, but for a different reason..

Using copper and stainless steel as examples, since one has a very low resistance, and one has a relatively higher resistance. If I take 2 equal lengths and twist them on a drill until they break (probably at the drill chuck) how will that effect the resistance of the twisted wire?

I already know that 20ga stainless steel wire (25 inches) twisted with 21ga NiChrome (25 inches) comes out to 20 inches of twisted SS+NiCr.

What i really need to know, is how does an electric current travel across this new wire, through the entire wire, or just through the copper?
and what would happen if i used 2x 25 inch strands of copper and 1 strand of stainless steel. Im trying to find a working formula to calculate in advance, the resistance of twisted wire containing more than one type of wire. I know that twisting 2 equal strands will half the resistance. (like 2 strands of 21ga NiCr= 1/2 resistance of 1 strand)

it is kind of a question of.. do the 2 wires work as 1 to conduct or does the majority of current only flow across the wire of least resistance?


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marnixR
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Tue Sep 27, 2016 8:08 am
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aren't you creating an electrolytic cell between your copper and your stainless steel wire, thereby inducing corrosion in the stainless steel part of the wire ?

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Pong
Post  Post subject: Re: Resistance and conductivity in twisted wire?  |  Posted: Tue Sep 27, 2016 8:22 am
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So I imagine this spring doesn't need much range. In that case a coil spring is overkill. Like why a lightbulb socket doesn't use a coil spring.

How about a little flat of brass, folded almost over. Or shaped into an arch that gets flattened under pressure?


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