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Old 10-21-2008, 07:06 PM   #1
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Default A thought on Wire

I had a thought today as I was re-wiring my SphereTC....

We all use the same wire, what appears to be thin copper/silver strands that are braided together adding up to a desired gauge...12-14. (forgive me if my terminology is wrong, but you get what I mean). Using this style of wire, it's extremely flexible which seems to be the biggest benefit.

Now my thought was this...doesn't electricity run along the outside of the wire? If that's the case, surface area would be the name of the game right? So why (aside from the convenience of flexible wire) don't we use solid 10 gauge or something gnarly like that? I realize it would be stiff and less convenient, however the surface area would be quite high and the surface of the wire itself is very smooth thus presenting less electrical resistance/distance to travel.

Unless, the hundreds of hair thin strands equate to more overall surface area...then there's nothing to argue, but does it?
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Old 10-21-2008, 07:12 PM   #2
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Originally Posted by mafiaracers View Post
I had a thought today as I was re-wiring my SphereTC....

We all use the same wire, what appears to be thin copper/silver strands that are braided together adding up to a desired gauge...12-14. (forgive me if my terminology is wrong, but you get what I mean). Using this style of wire, it's extremely flexible which seems to be the biggest benefit.

Now my thought was this...doesn't electricity run along the outside of the wire? If that's the case, surface area would be the name of the game right? So why (aside from the convenience of flexible wire) don't we use solid 10 gauge or something gnarly like that? I realize it would be stiff and less convenient, however the surface area would be quite high and the surface of the wire itself is very smooth thus presenting less electrical resistance/distance to travel.

Unless, the hundreds of hair thin strands equate to more overall surface area...then there's nothing to argue, but does it?

The surface areas add up.
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Old 10-21-2008, 07:42 PM   #3
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Have fun soldering a solid piece of 10g wire to a Motor
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Old 10-21-2008, 07:47 PM   #4
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Yes you are right that the total surface area's of all the wires add up to be like on giant wire in a small package. That is why the more strands in the wire that more current it can carry!
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Old 10-21-2008, 07:59 PM   #5
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Default

This is what we call "thinking out loud"...but yall are right, many smaller strands would equal overall area.

And I could only imagine the difficulty of soldering a solid 10g wire onto a motor...yikes!

I guess my next question is, at what point do you need more wire? If you're running 17.5, 14gauge would suffice all day, but where are the intervals for heavier wire...should heavier be on batteries and smaller on motors?
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Old 10-21-2008, 08:35 PM   #6
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Default Skin Effect not relevant for RC

This business of current only flowing on the surface of a conductor is known technically as the "Skin Effect" but it is only significant for high frequency AC currents. A brushless motor turning at 50,000 RPM has a switching speed of 5,000 times per second (50,000 RPM / 60 sec per minute ==> 833 rev/sec. Multiply that by 6 (for each of 3 phases being energized twice per rotation) gives you 5000 changes or 2,500 cycles/sec. Look at this article in Wikipedia:

http://en.wikipedia.org/wiki/Skin_effect

It shows that the skin depth for 10,000 cycles/sec is .66 MM, for 1000 it is over 8MM. So for RC frequencies the wire we have and use is fine enough that no further advantage would be accrued by making the strands thinner.
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Old 10-21-2008, 09:28 PM   #7
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Quote:
Originally Posted by katfish317 View Post
Yes you are right that the total surface area's of all the wires add up to be like on giant wire in a small package. That is why the more strands in the wire that more current it can carry!
That's correct, & that's also why all power cables are the same way. They experimented with solid wire a LONG time ago, but of course it was TERRIBLY unwieldy, so they played around more & found that a multi-stranded cable was not only more flexible, but could handle more current(which also means lower electrical resistance, something we all rely on in our cars). The only downside I believe with stranded wire is more electrical noise generated by them....
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Old 10-21-2008, 09:33 PM   #8
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Quote:
Originally Posted by mafiaracers View Post
This is what we call "thinking out loud"...but yall are right, many smaller strands would equal overall area.

And I could only imagine the difficulty of soldering a solid 10g wire onto a motor...yikes!

I guess my next question is, at what point do you need more wire? If you're running 17.5, 14gauge would suffice all day, but where are the intervals for heavier wire...should heavier be on batteries and smaller on motors?
I think it's all a matter of how much current is running through it, I doubt a 17.5 would draw all that much, so 14 AWG might be plenty. Or if you're running a 1/12 scale on 4 cells(lower voltage also means less amp draw from the motor), you can get away with thinner wire. Really, I'd only feel a real need for thicker wire with serious modified stuff on higher voltage(i.e, if you run a 3.5 motor with LiPo's then I'd use as thick as possible, & generally 12AWG works fine for that)....
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Old 10-22-2008, 06:45 AM   #9
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Bit of a shamless plug but we're an advertiser here now.... TQ Racing has been doing high performance wire since 1990 for slot cars and we've always used the thinnest strands possible both for both performance and durability: 18 gauge - 413 strands, 16 gauge - 665 strands, 13 gauge - 1,296 strands.

We have a new wire line just for RC, check out www.tqracing.com
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Old 10-22-2008, 07:45 AM   #10
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Rather than using those RC specific wire which cost a BOMB, would it be ok to use those thick car wires such as those use in real car voltage stabilizer unit ???
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Old 10-22-2008, 09:07 AM   #11
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You could, but the reason RC wire costs so much is the silicone, which is much more heat resistant for our soldering irons than the rubber/plastic/vinyl found on household or automotive audio and power wiring.
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Old 10-22-2008, 09:49 AM   #12
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I have found that not all gauges and wires are the same.

I had some 14ga flex wire that just felt funny compared to normal 14ga flex wire and sure enough there was an less copper in the wire as the braiding was done very loose and I would give that wire credit for being a 16ga wire fluffed into a 14ga. Besides the density issue, this wire had problems with the silicone jacket. Since the wire braid was spongey, the jacket became loose and would rip in sections.

I also had wire that was twisted the wrong direction in the braid causing the jacket to stick into the strands and not flex properly. The silicone was hard to clean out of the strands and soldering with wire that issue as the braid didn't loosen to solder well.
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Old 10-22-2008, 10:54 AM   #13
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The advantage of all those strands does no good for high frequency unless they are individually insulated.

http://en.wikipedia.org/wiki/Litz_wire

At the frequencies used in RC applications, it really will not help.
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Old 10-22-2008, 06:33 PM   #14
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Quote:
Originally Posted by kufman View Post
The advantage of all those strands does no good for high frequency unless they are individually insulated.

http://en.wikipedia.org/wiki/Litz_wire

At the frequencies used in RC applications, it really will not help.
True, I use Litz wire at work to wind a large induction coil for a sensor tool we use(one section of which uses about 250 turns of the stuff), & it is unique to work with(it's a real PAIN to strip & solder)....
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Old 10-22-2008, 10:50 PM   #15
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We use Litz wire to build high frequency filter chokes. I agree, it is a pain to work with, but electrically it is very nice.
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