Best source for copper bars?

[chaster]

Well, I've got 230 LiFePO4 batteries on order from Headway (part of the group buy) and now I'm thinking about how to best connect them up for my pack. I'm thinking copper bus bars with holes for the screws (since we're getting screw tops). I found this site:

http://store.electrical-insulators-and-copper-ground-bars.com/copper-barstock-metric.html

I also was searching around for copper set screws (for series connections) but haven't had any luck...

What does everyone else do?

Chaster

 

[pvorlicek]

Chaster:

I'm also in on the group buy of Headway. Those bars you link to seem quite thick (3 mm minimum). I was planning to use some copper strapping that I had leftover from a plumbing project:

(http://books.google.com/books?id=1SFklbi-m5gC&pg=PA35&lpg=PA35&dq=plumbers+copper+hanging+strapping&source=bl&ots=HdDzVg_08m&sig=6QTvlPJPQSolaXOTT6ge93aUDJM&hl=en&ei=7l0ISp6ICIX2tAOCkajzAQ&sa=X&oi=book_result&ct=result&resnum=1)

or just purchase some 1 to 2 mm material and cut to size with tin snips. I'm expecting to run no more than 30 AMPS through my set-up.

I'll need some help in some other areas and will post a separate email. This will be my 1st battery pack project!

 

[frodus]

you can use nickel as well.... copper can corrode .... I've seen people use both. Welded packs use nickel for the most part. Aluminum is ok, but a little more lossy and can oxidize.

Eric, a close friend is a mechanical engineer and he said its cheap to get things waterjetted... just give them the cad model, and tell them what material. Can be turned around in a few days, and everything is tight tolerance. Thats how I'm doing mine.

 

[XRuss]

frodus: para two above. what?

 

[frodus]

xruss: your question is ambiguous... what do you mean "what"?

 

[BatteryMooch]

I use McMaster-Carr (http://www.mcmaster.com) for copper sheet/bar/rod and bronze hardware and BoltDepot (http://www.boltdepot.com) for bronze hardware (bolts, nuts, washers).

 

[bobmcree]

i use coax shield braid. i have also used brass strips which can be purchased at most hardware stores. auto parts stores usually have brass shim stock in various thicknesses.

 

[XRuss]

Sorry frodus, I withdraw my what. Me thinks I should keep my eyes open and my keyborad shut. Cheers OM. XRuss

 

[frodus]

No, I was just wondering what you were referring to... I can explain if there's something unclear.... we're all gonna be building packs soon

 

[XRuss]

Travis, Yea, I know. Some of that para two is Wiserdspeek to me. I'm a long way from being up to speed on this stuff.
But thats ok cus I am sure there will be lots of chatter on pack building with HWa cells, So my speed will pick up mucho fast if I just keep EO&KS. Hang in.....Russ

 

[frodus]

I'll elaborate for you, not a problem. Waterjet is a way to cut metal... its kind of like lasercutting material. You have to draw it on the computer with AutoCAD and export files for the machine. The machine takes those files and cuts out the 2-dimensional shape out of metal sheet. You just tell them what material, give them the file and away she goes.

Essentially, you have a battery layout, and you need to connect the ends together in a format that gets you the voltage and Ah you need. I was just saying that for larger pack configurations like Chaster (eric) and myself, we would likely want to cut large busbars out of material, but to save time (because there are alot of plates) we could get them waterjet. This way they're custom done for our pack.

You might only be connecting 1 battery to the next battery... Whereas eric and I are putting multiple batteries in parallel and connecting those to the next parallel group.

 

[XRuss]

Got it Travus and thanks. Over and out

 

[dak664]

I was planning on using copper flashing, or is that not a good idea? Stamping a ridge in the middle to give some flexibility and damping between cells. For more thickness copper pipe straps from a plumbing store could also be flattened.

 

[frodus]

don't get me wrong, not saying copper is bad, just giving alternatives as well

We used copper pipe hanger before for my SLA pack... worked great.

 

[bobmcree]

copper flashing would be fine. copper has very low resistance but it corrodes easily. this is the reason pcboards are coated with tin and usually solder after that. anything that seals the copper is fine, but if you just lightly plate the contact ends of the copper straps with solder or tin, corrosion elsewhere does not reduce conductivity. the problem is when bare copper contacts another metal like the battery stud, and there may be electrolytic corrosion along with the oxidation. brass does not have the same problem and is not much less conductive. 1 mm thick copper or brass (.040 is plenty for 50A in my experience.

 

[chaster]

I don't know enough to properly dimension my connections (that's why I have Travis/Frodus giving me advice) but my pack could be seeing several hundred amps flowing through it, so I want to make sure the connections can handle that.

The waterjet cutting sounds like a nice clean solution Travis. Also, Kale has a source who has been doing laser cut gears for him for pretty competitive (cheap) prices. Might be another way to go. Would it be worth investigating designing the fuseable links into the bars...? Dunno.. Just a thought...

Eric

*EDIT* Changed "breakers" to "fuses"...
*EDIT 2* Changed "fuses" to "fuseable links" (DOH!)

 

[frodus]

you could do that, but I don't see a point in putting breakers build into the bars... i guess it all depends on how much work you want it to be

 

[julesa]

Fuses between parallel cells could protect the rest of the group if one cell developed an internal short. My pack's not going to be big enough to justify the effort though.

 

[frodus]

at that point, fuses get expensive, and its better to waterjet/etch/lasercut "fuseable links" on the plate so they melt if one cell fails and dumps the current from the other n-number of cells.

 

[julesa]

at that point, fuses get expensive, and its better to waterjet/etch/lasercut "fuseable links" on the plate so they melt if one cell fails and dumps the current from the other n-number of cells.

That's what I thought he meant .... oh he edited his post s/breakers/fuses/

 

[chaster]

at that point, fuses get expensive, and its better to waterjet/etch/lasercut "fuseable links" on the plate so they melt if one cell fails and dumps the current from the other n-number of cells.

That's what I thought he meant .... oh he edited his post s/breakers/fuses/

Actually, that IS what I meant. Fuseable links... Not Fuses... Not breakers... (sorry folks, I'm not an EE, I'm an AeroE/MechE, so my electrical knowledge is... limited... to say the least.. and I get mixed up with the terminology...)

I meant, if we're getting these things waterjetted/lasered/whatever, perhaps we should just get the fuseable links done in there too while we're at it. I don't think it would cost much more... maybe the same cost even...

Chaster

 

[MitchJi]

Hi Bob,

copper flashing would be fine. copper has very low resistance but it corrodes easily...
...the problem is when bare copper contacts another metal like the battery stud, and there may be electrolytic corrosion along with the oxidation. brass does not have the same problem and is not much less conductive. 1 mm thick copper or brass (.040 is plenty for 50A in my experience.

So brass connected to the copper won't be a problem but nickel might be?

 

[bobmcree]

Hi Bob,

copper flashing would be fine. copper has very low resistance but it corrodes easily...
...the problem is when bare copper contacts another metal like the battery stud, and there may be electrolytic corrosion along with the oxidation. brass does not have the same problem and is not much less conductive. 1 mm thick copper or brass (.040 is plenty for 50A in my experience.

So brass connected to the copper won't be a problem but nickel might be?

my experience is that because copper oxidizes so easily that any time it is exposed to air there will be corrosion. brass does it too but more slowly. a bigger problem is galvanic corrosion from dissimilar metals in contact. this will be much worse in areas where there is more salt in the air. there is a good chart showing which metals will corrode when used in contact at
http://www.roymech.co.uk/Useful_Tables/Corrosion/Cor_bi_met.html

the table shows no potential for corrosion with copper to brass contact, while there is potential with nickel to either one. of course if you make very good electrical contact and use something like dielectric grease to exclude the moisture necessary for corrosion you will be much better off.

 

[HAL9000v2.0]

I did it like this. It took me 2 hours for 44 pieces...

 

[Sacman]

my experience is that because copper oxidizes so easily that any time it is exposed to air there will be corrosion. brass does it too but more slowly. a bigger problem is galvanic corrosion from dissimilar metals in contact. this will be much worse in areas where there is more salt in the air. there is a good chart showing which metals will corrode when used in contact at
http://www.roymech.co.uk/Useful_Tables/Corrosion/Cor_bi_met.html

the table shows no potential for corrosion with copper to brass contact, while there is potential with nickel to either one. of course if you make very good electrical contact and use something like dielectric grease to exclude the moisture necessary for corrosion you will be much better off.

Very interresting info on Bi-Metallic Corrosion from that link. Thanks for that. So what kind of metal is used on the screw terminals of our Headway cells? And if we wanted to sellect a metal that's closest to it on the Galvanic Series list (to reduce this Bi-Metallic corrosion effect), what metal should we choose for our connection straps?