Re: flat copper coil...?
Thomas W, Fri Jun 21 2013, 12:09AM

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..

Re: flat copper coil...?
RateReducer, Fri Jun 21 2013, 08:39AM

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?

Re: flat copper coil...?
Wizzup, Fri Jun 21 2013, 09:24AM

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:

Re: flat copper coil...?
RateReducer, Fri Jun 21 2013, 04:09PM

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...

Re: flat copper coil...?
Yandersen, Thu Jul 11 2013, 09:50PM

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?

Re: flat copper coil...?
klugesmith, Thu Jul 11 2013, 10:19PM

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:

Re: flat copper coil...?
Yandersen, Thu Jul 11 2013, 11:00PM

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?

Re: flat copper coil...?
klugesmith, Fri Jul 12 2013, 12:58AM

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?

Re: flat copper coil...?
Ash Small, Fri Jul 12 2013, 12:06PM


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.

Re: flat copper coil...?
Yandersen, Sat Jul 13 2013, 06:48AM

As far as I know Al can not be soldered in an open air due to instantaneous forming of Al2O3. Whatever I tried did not work - joint easily breaks after cooling even if it seems OK.
The only option I see is an electrical welding - connect both pieces of aluminum to the charged cap and make a sparky contact. Do not try it with thin aluminum foil - roll a corner of it to form a thicker chunk.
But I would recommend a mechanical contact - roll a tip of a foil over thick copper wire and clamp it into smg like a steel "U" pressurizing the mesh with plains as hard as possible to destroy oxide inside for better contact and prevent wire from sliding out.

Re: flat copper coil...?
Ash Small, Sat Jul 13 2013, 08:40AM

This video shows how to solder aluminium, using the correct flux and a tin/copper solder.



The notes accompanying the video are here:

Published on 9 Oct 2012


INDOFLUX AX-39. Aluminium Soldering Flux.(external Flux)
Solder To Al Sheet And Bulb Cap.
Can Be Applied in Solder Wire Flux Core. (ALUBOND Product)

Excellent Invention made by R&D Departement.

Aluminium Soldering Flux.
For :
Aluminium sheet, Light Bulb Cap soldering. Tin Solder Flux for Aluminium.
Using Torch, or By High Watt Solder.

Indonesia product.

ISO 9001-2008, TUV Rheinland, Certified Manufacturer.

Re: flat copper coil...?
Signification, Sat Jan 31 2015, 01:28AM

I toyed with this idea a while back, when, at first glance, I wondered if a single long flat turn (the length of the entire gun) acted as more than a single-turn loop of wire. I concluded that that there was no difference in the number-of-turns variable (N) for foil or wire.

Also, it occurred that the connections to the two wide end terminals of this coil should be such that the current flows 'into' and 'out of' the entire width of the flat ends--perhaps a large-gauge stranded wire "flattened out" and the strands soldered along the width of the copper edge ends. BUT--this may be a little tricky to implement on the 'buried' inner end layer which is somewhat inaccessible and should lie flat along the barrel !!

Has anyone thought about the inherent capacitance in this type of 'inductor'? In fact, it looks more like a (multi-layer cylindrical) capacitor.

Re: flat copper coil...?
hen918, Sat Jan 31 2015, 02:28PM


When the inductance is that low, I don't imagine that the tiny capacitance will make any difference to anything. Think of the milli-farads that you are putting into the coil. The capacitance of the coil will be in the order of pico-farads.

Re: flat copper coil...?
Signification, Sat Jan 31 2015, 10:01PM

...so that is milli-Farads to pico-Farads: a NINE magnitude order ratio of applied to parasitic capacitance...OK !!