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I am building a project that I can put a AA battery into a little compartment. The battery fits fine without anything else in it, but when I put a wire in, it gets tight. A solution that might work: aluminum foil.

I measured the resistance with a multimeter, and it is about the same as a wire. Is this a bad idea? (Besides the low durability of the foil) I am planning to wrap the foil in some electrical tape or similar to insulate it, except for where I am going to connect to the battery. Will it carry enough current without overheating and melting the plastic? 100mA max with LEDs, only on for 1/2 of every minute I would say during use. Fairly standard plastic, I would say and operating in a house.

P.S. The battery is 3.7v 1200mAH and a Lithium rechargeable, but may be a bit more/less voltage.

Also, I only need it for one of the two sides (+/-), and is one better to use than other?Should I change my circuit, or am I just paranoid?

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    \$\begingroup\$ The battery has the ability to provide a lot of current. What you're thinking of doing makes me nervous. Fires aren't fun, so be cautious! \$\endgroup\$ – Brooks Aug 9 '13 at 18:48
  • \$\begingroup\$ @Brooks Yeah... that's why I asked. What I'm doing is I'm controlling a IR LED with a Wii remote (has IR camera that is hackable via Bluetooth) and it will only be on when the user "clicks." It's not a flashlight, and copper/aluminum seems to be quite thermally conductive to me, but will that matter that much? As long as they're not drawing or playing a game for three hours, should it be a difference? \$\endgroup\$ – Anonymous Penguin Aug 9 '13 at 22:16
  • \$\begingroup\$ I am concerned about shorts... \$\endgroup\$ – Brooks Aug 12 '13 at 13:22
  • \$\begingroup\$ @Brooks That's why I'm wrapping it in tape. Also, I will wrap the part where the wire meets the foil: all that will be exposed is the stripped parts of each wire, the foil is wrapped completely, and it's like a "inbetween" conductor to make it fit. Plus, I only have to do it with one wire. \$\endgroup\$ – Anonymous Penguin Aug 12 '13 at 22:58
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There are things called "Flat Flex Cables", and many variations of those, that are basically the "non-Ghetto" version of what you are talking about. These are also related to "flexible circuits", which are part cable, part PCB. Essentially they are all custom flexible circuits that many people use as cables for tight spaces.

Here is a picture of an older iPhone where these cables are clearly visible (in a sort of orange-ish-brown color):

iPhone Internals

These cables are designed a lot like we design PCB's-- using the same CAD software. They are designed in those crazy shapes, and not just bent when it is all put together.

Sometimes these cables are just soldered directly to the PCB's, other times they use connectors.

With the right design, they can be capable of carrying several amps.

If you are making only one, in your garage, I would use copper tape instead of aluminum foil. It is easier to solder to, and is more conductive. Instead of "wrapping it in electrical tape", I would use two layers of thicker packing tape. Lay one layer, sticky side up, and lay the pre-cut copper foil onto it. Then lay another layer of tape, sticky side down, on top of that. Squeeze. If you want to be extra careful, use three layers of tape, with copper for +V between two of the layers, and copper for -V between the other 2 layers. That way if the copper shifts around it won't short out so easily.

Update:

Instead of packing tape you might want to use Kapton Tape. Kapton is a special tape that can withstand high temperatures-- like when you solder. So you could use copper tape/foil with Kapton on the outside and then solder to the copper after you assemble your "cable". Don't get the 1 or 2 mil thick tape, since that will be too thin for your purpose. Go with 3 or even 5 mils.

It is good to 500 deg F, which is hot enough to solder with but many soldering irons can go hotter-- so you still need to be a bit careful. But it is a lot better than packing tape in that regard.

The down side is that compared to packing tape, Kapton tape is very expensive.

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    \$\begingroup\$ I only need to solder on both edges once, and it is going to be one straight line, so I can add the tape after it is cooled. I don't need to design it or anything. One thing: how flexible is the copper tape? \$\endgroup\$ – Anonymous Penguin Aug 9 '13 at 22:06
  • \$\begingroup\$ @AnnonomusPerson The flexibility of the copper is going to depend on the thickness. The thicker it is, the less flexible it will be. You might be able to use several layers of thin copper foil, but assembly will get messy. \$\endgroup\$ – user3624 Aug 9 '13 at 22:10
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100 mA into a strip of heavy duty kitchen aluminum foil, width a few millimeters, driven by a AA battery will be just fine. If some part of the foil is too thin and generates too much heat because you're drawing amps' worth of current, the foil will act like a fuse and burn off.

I would just use a good coat of acrylic conformal coat to insulate it, rather than tape. By the time you have two layers of tape on it, you might as well use coated 28AWG wire, ("transformer wire") which is about as thin as a few layers of tape. 28 AWG transfomer wire is about 1/3mm thick, and is rated for up to 1.4 A current in chassis wiring.

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