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flat copper coil...?

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LAN_403

RateReducer

Thu Jun 20 2013, 08:46PM

Registered Member #4603 Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159

Hi. Has anyone tried to make a coil with flat copper? I have some flat copper laying around... 37 x 0,1mm. I would wind it with a foil between the copper layers.

just like this. ------ = foil _____=copper

--------
_______
--------
_______
BARREL
--------
_______
--------
________

I hope this is understandable...
Shall i give it a try or is this idea just stupid?

Thomas W

Fri Jun 21 2013, 12:09AM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

I assume by foil you mean a insulator.

I wouldnt think it would be that effective, as its just like winding one turn then another turn ontop of it, the ferther away it is from the barrel, the less effective it is i guess, so i think just winding normally would be much more efficient..

RateReducer

Fri Jun 21 2013, 08:39AM

Registered Member #4603 Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159

I tried it with the whole flat copper. I used it "as it is" wound around a mounting from a choke. It worked but i think it is very inefficient...

Now i want to wind a common coil. How does the perfect current waveform through the inductor look like?
A huge positive peak with nearly no ringing? 1ms duration?

Wizzup

Fri Jun 21 2013, 09:24AM

Registered Member #3302 Joined: Sun Oct 10 2010, 02:21PM
Location: Finland
Posts: 42

I used this simulator to design my coilguns coil:

The authors site is down so I thought I could upload it there because it is very handy, it includes projectile simulation aswell.

The simulator is pretty tricky to use because it has no failsafes for bad values, so if you for example set the projectile weight to zero the whole program will crash so be careful.

Here is an example of a coil I made for my old 240J cap bank:

RateReducer

Fri Jun 21 2013, 04:09PM

Registered Member #4603 Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159

Thanks! I tried a "quick and dirty" setup @ 270J. 170 turns 1mm wire. Shoots through 6mm plywood

I think i will try a 2 Stage design soon...

Yandersen

Thu Jul 11 2013, 09:50PM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

I do dream about flat copper coil! I want to see at least one in action ever! I found that the tighter the coil wound the higher it's inductance is: take the same wire of the same length, rewind it tightly and nicely turn-to-turn forming the coil of the same length and internal diameter - and induction become higher. FEMM agrees, it is true. The performance of the coil is greatly depends on an inductance to resistance product (heat losses are smaller in tightly wound coil and even pull force is stronger). So the less the air gaps and insulation trash inbetween the copper, the higher efficiency can be achieved from the coilgun. Comparing insulated round wire to a flat copper with a top layer of insulation we have over 20% more copper in a coil. Such benefit may even allow us to use aluminium foil instead of copper wire to lower gun's weight without drop in coil efficiency. But I would prefer copper flat tape of coil-width, insulated. If only I have one...
It would also easier to wound: 2cm flat tape of 0.1mm thickness is electrically equal to wire of 1.6mm in diameter, but so much more flexible! This will allow to wind tightly-packed mechanically rigid coils.

Just recently I found the path to flat copper tape - it turned to be used as EMI supression shielding material and can be bought at digikey for example:

But the best option will be an insulated tape. Anyone knows the sources?

klugesmith

Thu Jul 11 2013, 10:19PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

1. Re. winding with copper strip (ribbon) vs. wire.

The strip coil will behave exactly the same as a wire coil of the same metal, if they have the same ID, OD, length, and number of turns.

And as I've said many times before:
Within that coil volume, you can trade off the wire area against the number of turns, with NO effect on magnetic field strength and duration.
Provided that you make a complementary trade off between capacitance and voltage, and have the same stored energy. This is like rewinding motors or transformers for different voltage/current tradeoffs, with no change in efficiency or conductor mass.

As Yandersen said:
Strip has the possibility of getting a better "fill factor", to reduce the average radius for a given cross-sectional area of conductor.
And with only 1 turn per layer, it's much easier to make nice pretty windings.

2. Here is another source of copper strip:

Yandersen

Thu Jul 11 2013, 11:00PM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Slug repelling copper tape? Smart! :) Will try Home Depot, I guess...
What about the insulation then? Using a scotch tape as an insulator for a bare copper tape may not be an optional solution - both tapes have almost the same thickness, so no copper density benefit may be achieved then. Moreover, the voltage the insulator has to sustain is tiny-small: for a coil of 1cm in thickness wound with 0.1mm-thick tape (resulting in 100 layers) fed with 450V will result in 4.5V between any pair of adjacent turns - almost nothing, so insulation layer can be even thinner than round wire usually have. So it makes sense to just apply some nail polish on one side of a copper tape to make insulation strong enough to protect turns from short-circuiting?

klugesmith

Fri Jul 12 2013, 12:58AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Here's one way to improve the fill factor with thin metal foil.
Use two or more layers of metal (electrically a single conductor), then one layer of insulation.
That has the same effect as winding with thicker wire.

Here are some ideas for getting thicker strips of conductor (aluminum, not copper).
- painted slats from a scrap Venetian blind
- painted aluminum sheet made for gutters or roof flashing - need to slit it to a useful width.
- a large aluminum beverage can, cut in a helix.

Aluminum from those sources is likely to be alloys significantly less conductive than the commercially pure element. (Same might apply to copper foil, copper pipe, etc. if not specified for electrical use.) I would always start by measuring the sheet resistance, in milliohms per square, of a sample. From that and the thickness, we can get the bulk resistivity.

I expect that permanent electrical connections can be made by soldering to the aluminum. Will soon be trying that for a personal project using a couple of these coils:

Anyone have any recommendations for fluxes & solders?

Ash Small

Fri Jul 12 2013, 12:06PM

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

klugesmith wrote ...

I expect that permanent electrical connections can be made by soldering to the aluminum. Will soon be trying that for a personal project using a couple of these coils:

Anyone have any recommendations for fluxes & solders?

There are a few ideas in this thread:

Adhesive copper tape could be used, as it is conductive. You could then solder to the copper, depending on the application.

EDIT: the video in the last post looks like it might be exactly what you want.

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