Copper sheet and strip - use for DIY high current PCBS? - and good source

[PStechPaul]

I am building a prototype for a high current (20-30 amp) battery powered DC-DC converter, and I was considering using strips of copper sheet for the high current traces. I found some material in my odds-and-ends metal that is 0.036" (0.9 mm or 19 gauge), but I decided to use bare #16 AWG copper wire. However, it may be good to use some copper strip even for the actual PCB, to avoid wide traces or extra heavy material.

I found some copper flashing at Home Depot that is listed as 3 ounce copper and 0.007" thick, but according to what I found, 3 ounce (per square foot) is actually 0.00375" (3.75 mils). The description shows that it has a paper backing that probably adds to the thickness. Also, the roll is 2 pounds, with an area of 13.3 square feet, which would indicate that it is only 2.4 oz. The cost is about $20/lb.

Here is a chart of common gauges, weights, and thicknesses:

http://www.alascop.com/pdf/sheet_gauge_charts.pdf

Lowes has a 4" x 5" piece of 0.025" copper for $9: https://www.lowes.com/pd/The-Hillman...-Metal/3478155

While searching for information of copper weight and thickness, I found what seems to be a good source of copper sheets and strips: http://basiccopper.com/

They have bargain packs of assorted pieces for as low as $6-$10/pound, and a good range of foil, strips, and sheet from 0.001" to 0.040". Also a nice guide to various gauges and recommendations for usage and tooling:

http://basiccopper.com/thicknessguide.html

For current-carrying capacity of copper strip, I have a wire gauge chart that uses various means to determine what is allowable. For 211 circular mils/amp, a 0.025" x 1/4" strip will handle 23 amps. For 0.24 watts/square inch (for free convection), this size will handle 35 amps.

Here is my spreadsheet for wire sizes and ampacities (including bus bars):

http://enginuitysystems.com/pix/elec...s/WireSize.xls

[Sparky_NY]

Some roofing supply houses stock copper sheets. I bought one a few years back for a repair job for a friend and saved some of the scraps just in case a project appears one day. I would guess its maybe 50 thou thick.

[Juiceclone]

I've found at least when repairing pcb's with high current areas, that just using appropriately sized wire jumpers instead of the copper traces works well. ....Maybe redesign to use wires where necessary??

[darryl]

I have some copper foil at 6 thou thickness which I've used for transformer winding. It's especially handy when you have an existing primary on an assembled transformer and you don't want to or can't take it apart. Prep was tedious as I had to cut the long strip from a roll, then roll it out to flatten the edges etc, then apply an insulation to one side. I found a packing tape that was under 2 thou thick and applied that, leaving some overlapping the width of the copper. After attaching a leadout it's a matter of threading it through the core and making a one turn wide winding. It's a lot easier to wind the copper strip than to thread a #12 wire through turn after turn-

A one inch wide strip of copper 6 thou thick is about equivalent to 12 gauge wire.

[alanganes]

I've found at least when repairing pcb's with high current areas, that just using appropriately sized wire jumpers instead of the copper traces works well. ....Maybe redesign to use wires where necessary??

On a similar note, in the past I have used plain old solder-wick as a replacement for traces that had burned off of PC boards I was repairing. It is available in a range of sizes and once it is anchored in place, you can saturate it with solder to keep it from oxidizing.

[38_Cal]

You can get brass and copper sheets for hobby use from K&S Metals, http://ksmetals.com/30.html. Specific thicknesses and dimensions.

[darryl]

I've used regular bare copper wire to build up pc board traces for higher current carrying capacity. That keeps the width of the trace down and also gives a way to terminate the ends of the traces in a suitable way- often a screw or bolt like a regular terminal block. The wire is formed into a loop at that point and soldered to the trace.

I've also seen where copper sheet is used and is stood up on edge where it has to travel around on a pc board. At the ends it's folded under so it's flat to the board and a similar screw terminal is made. This allows the traces to run close together around the pc board, and it's easy to bend them to suit, while maintaining very low resistance.

[PStechPaul]

Thin, flat conductors are better for high frequency, because of skin effect. My design will use 50-100 kHz, at which skin depth is 0.008 to 0.012", so anything thicker than 0.025" is wasted.
http://www.rfcafe.com/references/cal...calculator.htm

There are bus bars for PCBs and they are sometimes two layers laminated for power and ground distribution:

http://e-fab.com/products/pcb-stiffeners/



They are also used for mechanical stiffening. I might be able to use short pieces of solid wire, maybe 18 or 16 AWG, soldered to a strip of copper and able to be connected to the PCB with multiple thru-holes.

http://www.fci.com/en/products/power...tribution.html


http://stormpowercomponents.com/cust...FccDhgodpFQPrA

[J Tiers]

The busbar is going to be better for you.

1) Minimal PWB area used

2) Since usually there are 2 traces carrying current, they minimize inductance (if insulated for your voltage so they can be used). Side by side strips in one plane are largely wasted, as the current crowds at the near edges because that is minimum energy. Refer back to that Dixon paper from Unitrode/TI. So if you use strips as traces, put them on different layers and run together.

Strip may be good for transformer windings, though. But if you use it there, make sure to have the thickness less than skin depth so as to minimize effective AC resistance, again per Dixon.

[Paul Alciatore]

Paul,

They make copper foil with adhesive backing for PCB use. You can get it from electronic suppliers:

http://www.mouser.com/Search/Refine....pper+foil+tape

Just cut and paste.

[PStechPaul]

That is only 1 ounce copper, about 1.2 mils thick. I have a roll of copper foil tape with adhesive backing. But it is too thin for high current use:

http://www.banggood.com/6mmX20m-Copp...l?rmmds=search


Something much better is Vector bus strips. I have some of that somewhere. It is a bit expensive ($16/10 strips):

http://www.mouser.com/ProductDetail/...TS50xNNeaIwrCy


http://www.mouser.com/ds/2/424/New%2...5-78-10025.pdf

It is 0.017" thick and 0.08" wide, and each piece is 14" long.