Electronics > Projects, Designs, and Technical Stuff
Electrical contacting on aluminium busbar
Mechatrommer:
--- Quote from: damien22 on February 27, 2019, 07:14:53 am ---Now there are two issues, one is the electrical contact, because of the oxidation of the material which is an issue for the electrical contact and another is the strength of the material to avoid the bar to be bend during manufacturing.
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i think you over complicating things. i think oxidation will only form on exposed part, if there will be oxidation on the contact, it means you've made not a good contact so you may revise your assembly technique. if bending is an issue, why dont use thick wire and find suitable tap to it? people have done bolt nut tap with no issue at much larger current, i think its the de facto standard... if you really concern, just solder them, problem fixed... now where's that high voltage nutter? why dont he chime in to give some good and practical advice, safety-wise advice, rather than keep breaking somethings ::)
MagicSmoker:
--- Quote from: T3sl4co1l on March 03, 2019, 04:02:23 am ---...
Nord-Lock aren't conical or domed, as far as I know. So they don't take up any spring force. ...
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Nord-Locks develop tension in the bolt through cam action. More specifically, by interlocking wedges on opposing washer faces with the wedges arranged such that unscrewing the bolt increases the tension on it (at least for the first few degrees of rotation). However, you are correct that they aren't recommended for materials which will experience significant creep after tightening. So, soft metals like unhardened copper or aluminum, especially if they are less thick than the bolt diameter. Also not recommended for cost-sensitive applications, as they are, indeed, bloody expensive. I only used them for the 1/2" bolt holes on dual-hole 4/0 compression lugs; a case where, contrary to the Mythbuster's mantra, failure was not an option.
--- Quote from: T3sl4co1l on March 03, 2019, 04:02:23 am ---Split washers, by the way, are literally no good at all...
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Also true, at least for bolts under, say, #10 (M5) in diameter. Split-ring lockwashers can be okay for non-critical use on 1/4" (M6) or larger bolts. I tend to prefer internal tooth lockwashers for general purpose application, myself.
--- Quote from: T3sl4co1l on March 03, 2019, 04:02:23 am ---FR-4 can creep or flow under pressure, too (especially at high temperature)....
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Very, very true! In fact, I don't think any kind of washer can accommodate the amount of creep a PCB will experience even at temperatures well below the glass transition. Either use a screw terminal standoff (e.g. - Keystone Electronics 7787) or a soldered-in male quick-disconnect (e.g. - Keystone Electronics 1287) for high/moderate current wire to board terminations, respectively.
David Hess:
--- Quote from: MagicSmoker on March 03, 2019, 12:32:50 am ---The type of lock washer most commonly used in the US for high-reliability bus bar applications is called "Belleville." It is a conical in cross-section with radial ribbing or teeth.
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I would love to use Belleville washers more for power transistor mounting but pricing and availability has always been a problem.
--- Quote from: T3sl4co1l on March 03, 2019, 04:02:23 am ---There's also wave washers, though they tend to be softer than cone washers.
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When it matters, I end up stacking wave washers to get enough force.
coppercone2:
how about lockwire?
I have been meaning to get lockwire pliers.
Pretty sure you can modify hex insert bolts to accommodate lockwire too. What I am thinking is to drill a small hole in the busbar, braze on a peg with a hole in it, then lockwire the washer to the peg.
OM222O:
why are you trying to manufacture the bars with such weird dimensions? usually for longer runs, you would use a plate shape rather than a square (6x7 is almost a square) and you can make runs like this without a problem using copper:
this also gives you a lot more width for your connections. as you mentioned, you're struggling with a single M4 screw! I suggest using 10 screws in parallel next to each other per PCB as it provides a lot better contact with the PCB as well as the bus bar, makes it easier to manufacture the bars and is also safer in case one of the screws fails or isn't making proper contact, as well as reducing the load to 12A per screw rather than 120! there would be a ton of voltage drop and heating of the screw with 120A passing through it and it won't last long at all! just make sure to use a washer on both sides which ensures there is good grip and you will be fine. I attached an example of the PCB which you might want to use:
Obviously make the thick copper zones (light blue) on both sides for a more even distribution and also add some vias for stitching just to be on the safe side.
One single M4 screw is a terrible idea and you will have lots of issues with it.Also if you make your plates out of copper, you can add plenty of flux and burn it with a torch to get rid of the oxidization but I'm not sure if the same can be done for aluminium. copper also oxidizes a lot more slowly than aluminium (a few days compared to a few minutes!).If you can, drill the holes in the positions with a smaller bit, let's say M2.5 instead of M4 so you have the correct positions. then just before installing the PCB, drill and tap the holes to the correct dimension. This way you can make sure there is no oxidization during installation. I'm not an electrician but this issue has already been solved by others :P I hope this answer helps.
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