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More wire improves efficiency of a coil?

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Yanom

Sat Oct 20 2012, 02:29AM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
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Posts: 158

Ash Small wrote ...

They run it through a bath of varnish. If you heat the wire/varnish it will dry very quickly. you just have a roller under the varnish, and roll it from one spool to another.

hmmm, varnish. Where can I get this varnish? is it possible to do this at home? What I'm thinking of here is taking a roll of aluminum foil and cutting the roll (without unrolling it) into segments about 1" wide, then removing the cardboard tubing and insulating the loosened coil. I now have a coil of thin, wide, flat aluminum wire.

Would that work?

Ash Small

Sat Oct 20 2012, 09:12AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yanom wrote ...

hmmm, varnish. Where can I get this varnish? is it possible to do this at home? What I'm thinking of here is taking a roll of aluminum foil and cutting the roll (without unrolling it) into segments about 1" wide, then removing the cardboard tubing and insulating the loosened coil. I now have a coil of thin, wide, flat aluminum wire.

Would that work?

You want a good quality enamel based varnish. I have used a yacht varnish in the past, eg 'International' Toplac or Japlac clear varnish.

You would need to feed it from one spool, into the varnish, then onto the other spool, drying it between the varnish bath and the second spool.

Some commercial enamelled wire is coated more than once for improved insulation.

Sulaiman

Sat Oct 20 2012, 10:33AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

The resistivity of aluminium compared to copper is about 1.7
(e.g. 1m of 1mm2 copper wire = 17 mOhm, aluminium = 29 mOhm, approximately)

one reason that overhead power cables use aluminium is due to weight,
copper is about 3.3 times denser than copper,
so for a given current aluminium is about 1/2 the weight of copper.
the actual cost calculations are complex
(metal cost, support structures, tensile strength, corrosion, skin-depth ...)
but I don't think any this applies to small amateur coilguns.

I've never been able to solder aluminium wire with 'normal' solder
so you'd have to crimp the connections or buy special solder.
I can't imagine aluminium wire being useful for a coilgun.

The de-gaussing coil for some crt used enameled aluminium wire
- must have been cheaper at one time.

Regarding the original question, I agree with Steve Conner,
the wire size will be the last thing to decide,
discharge capacitor energy/voltage/capacitance,
switch capability,
projectile size/material/weight/energy
then coil size and inductance will determine the current, hence wire size.

For an electromagnet the factors are different,
for a given flux density and area, operating with a given air gap
it comes down to Watts dissipated in the coil!
high voltage/low current/many thin turns or low voltage/high current/fewer turns
it always works out to be 'magnetic force' x operating distance = Watts.

Yanom

Sat Oct 20 2012, 12:47PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
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Posts: 158

Ash Small wrote ...

so Ive got to coat it and then dry it with a hairdryer?
will polyurethane sealant for woodworking do the trick?

Ash Small

Sat Oct 20 2012, 02:32PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yanom wrote ...

so Ive got to coat it and then dry it with a hairdryer?
will polyurethane sealant for woodworking do the trick?

I imagine polyurethane will be ok. What does it say to use for cleaning brushes or for thinning it?

Yanom

Sat Oct 20 2012, 02:54PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

Ash Small wrote ...

I imagine polyurethane will be ok. What does it say to use for cleaning brushes or for thinning it?

mmm, I don't know. Does it have to be thinned?
Anyway, the stuff I found in my garage was in fact not polyurethane but this stuff:

1350744868 4659 FT145405 Img 20121020 095210

there's also roof waterproofing sealant in there.

Ash Small

Sat Oct 20 2012, 03:18PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Tung oil is no good. (at least I don't expect it is.)

You want a varnish that requires white spirit for thinning/brush cleaning (eg polyurethane).

You won't need to thin it.

Yanom

Sat Oct 20 2012, 05:18PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

Ash Small wrote ...

Tung oil is no good. (at least I don't expect it is.)

You want a varnish that requires white spirit for thinning/brush cleaning (eg polyurethane).

You won't need to thin it.

ok, I'll get some of that. And a hairdryer is good to dry it once it gets polyurethane'd?

Ash Small

Sun Oct 21 2012, 05:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

A hairdryer should do it, but it will be slow going.

You could try heating the wire before dipping it, and also warming the varnish.

It does dry fairly quickly if it's heated.

Yanom

Sun Oct 21 2012, 06:54PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

Ash Small wrote ...

A hairdryer should do it, but it will be slow going.

You could try heating the wire before dipping it, and also warming the varnish.

It does dry fairly quickly if it's heated.

mmm. ok. What if I dunked the entire coil in varnish, then hairdryered it a bit, then left it out to dry? Would that work? doing it one segment at time seems tedious, but if that's the only way to do it...

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