[bwjunkie]

I was looking at this stuff to see if I could make some bus bars / battery interconnects. I have some retail for most of my batteries, but I'd like to be able to make more, anyone already been down this road?

at 20mil how many leafs should be sandwiched together for 1 - 500 amp?

http://basiccopper.com/20-mil-copper-strip-2in-10ft.html

josh

 

[dougingraham]

It looks like 2 layers would close to 1/0 cable in resistance. But it is 2 inches wide. One inch wide would be 4.1 layers. For 2/0 equivalent it would be 2.6 layers of 2 inch wide or 5.2 layers of 1 inch wide. This is based on the diameter of the wire being equivalent to the .04 sq inch cross section of the copper ribbon. 4 layers would be 0.08" thick. 5 layers would be 0.1" thick. These thickness pass the reasonableness test to me.

For short periods of 500 amps 1/0 equivalent should be fine. For short periods of up to 1000 amps 2/0 should be acceptable.

Assuming 1 inch wide and 4 layers you get only 5 ft of usable material for your $46. If your straps are 3 inches long this would give you 20 straps. If they are 4 inches long then only 15 straps. Split the diff and your straps will cost around $3 each excluding shipping. It would be better if they were tin or nickle plated as well because bare copper oxidizes.

 

[bwjunkie]

hmm okay thanks, that helps!

If I buy some of their "bulk" options I can get it to below half that price, but gotta spend $500. I wonder if a band saw would be good here or some sort of rolling cutter?

 

[Karter2]

20 mil soft copper you could cut with scissors ! ( well "tin snips" )
But a shear or sheet cutter would be ideal.

 

[kennybobby]

Use a shear press to cut the sheet into strips. Band saw would take a long time and waste quite a bit of material.

 

[McRat]

McMaster-Carr is never the cheapest, but they have good service.

A 100 foot roll of 0.016" x 1" wide copper ribbon is about $120.

http://www.mcmaster.com/#catalog/120/3792/=qwc9bl

 

[McRat]

As you can see, there is also thicker, thinner, wider, and narrower.

Your best value at mcmaster is the 0.016" x 1". Any decent cutting tool will cut this like butter.

 

[McRat]

As far as power goes, to pass 300+ amps, GM uses multi-layer copper ribbon that is 0.078" thk x .679" wide x >36" long. So a full inch wide should OK for 500amps? A circuit board calculator tells me no, but how does GM do it then?

That's why I got the copper ribbon.

EDIT: No matter what I look at, nothing agrees with GM battery cable dims. But I did read that if the connector ends are silver plated, it has a higher rating.

 

[Duncan]

As far as power goes, to pass 300+ amps, GM uses multi-layer copper ribbon that is 0.078" thk x .679" wide x >36" long. So a full inch wide should OK for 500amps? A circuit board calculator tells me no, but how does GM do it then?

That's why I got the copper ribbon.

EDIT: No matter what I look at, nothing agrees with GM battery cable dims. But I did read that if the connector ends are silver plated, it has a higher rating.

It boils down to
How many volts/watts can I afford to lose
How hot will it get

I am using 0.5mm x 20mm copper strips with the terminals 42 mm apart

That will have a resistance of 0.072MilliOhms

I use two strips on top of each other so that is 0.036 mOhms
Each of my strings has 10 of these so - 0.36 mOhms
(The other connections are cells nose/tail)
Each string has a max current of 240 amps (15C) - 0.08 volts drop
Not significant in a 130v string
(four strings in my pack)

Each will produce 2 watts of heat

Again not a problem for the 10 seconds I can use 15C
This drops to 1 watt for "continuous 10C"

Copper is easy to cut, the best way to make the holes for the bolts would be with a hole punch

I used wood cutting drills
The type that look like metal drills except they have a point and two sharp outer tips

I found they made much nicer holes than proper metal drills

I get 0.4 mOhms for your GM strips - so 0.2 volts drop and 100 watts at 500 amps

 

[dougingraham]

As far as power goes, to pass 300+ amps, GM uses multi-layer copper ribbon that is 0.078" thk x .679" wide x >36" long. So a full inch wide should OK for 500amps? A circuit board calculator tells me no, but how does GM do it then?

That's why I got the copper ribbon.

EDIT: No matter what I look at, nothing agrees with GM battery cable dims. But I did read that if the connector ends are silver plated, it has a higher rating.

You are not pulling 300 battery amps continuous. Your max duration at that current would be perhaps 20 seconds and the only time you will see that would probably be up a steep hill trying to go faster than the law allows. What will happen is something else in the car will be getting hot and the motor controller will turn down the amps. In your example the equivalent diameter of a flat copper bar that is 0.078" thick by 0.679" wide would be 0.2597". This is slightly larger than 2 gauge wire (0.2576"). Lets call them the same since resistance. 2 gauge wire has a resistance of 0.1563 ohms per 1000 feet. This means that for your 3 foot piece of flat cable the resistance is 0.0004689 ohms. At 300 amps that piece of bar stock will show a voltage drop of 0.14 volts and will be generating 42.2 watts of waste heat. This is spread out over a piece of material with a lot of surface area. If it went on for minutes you would see a rather warm area. But we know that it cannot in any reasonable driving scenario do that. What about typical highway cruising power levels. 300 wh/mile at 60mph is a power level of 18000 watts. With a 360 volt battery pack this is a current of 50 amps. So how much waste heat is generated at 50 amps? The voltage drop at 50 amps is 0.02345 volts giving 1.17 watts spread out over that 3 foot length. This is minimal and why that size was chosen. In a typical acceleration event you only see the 300 battery amps for a second. The cables on the motor side of the controller are heavier than this as they see the higher currents for longer periods of time.

Hope that helps.

 

[McRat]

Sidebar - I took my desk scissors, made for paper, and easily cut 0.4mm x 25.4mm with them 10 times. No problems. Westcott "titanium" scissors.

http://www.amazon.com/Westcott-Stra...53&sr=1-1&keywords=westcott+titanium+scissors

$5 each shipped.

EDIT - I used a wall stapler and stapled it to a 2x4.

However, I broke my wife's cheezy plastic stapler trying to staple it.

An heavy duty paper punch will put holes in it, and a paper cutter will shear it. However these aren't chinese stuff.

 

[evmetro]

Here is a thread about making bus bars with copper strips

http://www.diyelectriccar.com/forums/showthread.php/bus-bar-size-and-material-84801.html

 

[bwjunkie]

Cool I think I'll order $50 worth , looks about the same, roughly .08 to .12 cents per square inch of 20 mil is a fair price. Also the roofing rolls on ebay seems to usually be laminated which would probably be bad,