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| Electrical contacting on aluminium busbar |
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| David Hess:
--- Quote from: damien22 on February 27, 2019, 11:20:36 am ---Would stainless helicoil thing be a good solution ? Unfortunately we cannot bolt as the bar lay flat on an insulator to which they are fixed and on the other side the PCB are mounted. --- End quote --- Helicoils would prevent the threads from bring ripped out of the relatively soft aluminum or copper but I have never heard of them being used for conductivity. --- Quote ---The PCB does contact with the bars so most of the current would go through there. --- End quote --- Be careful about crushing the printed circuit board material. --- Quote from: coppercone2 on February 27, 2019, 01:55:01 pm ---How much does a damn bus bar cost in the scheme of a fucking train even if you consider a order of magnitude cost increase??????? MTA is already going to fuck it up with unknown unpredictable means, don't make it worse. Train fires suck. They can burn in tunnels etc. --- End quote --- During World War 2, the copper bus bars from the substations and power houses along the Columbia river were replaced with silver bus bars and armed guards were assigned to protect them until they could be replaced with copper again. |
| Gregg:
Aluminum bus bar is used extensively in large mains switchgear and even home breaker panels because it is cheap and light weight. There are thousands of variations of alloy, conductivity and hardness available and a designer needs to choose wisely. Most of the large current aluminum bus bars I have seen are tin plated at the factory to minimize the problems with connection conductivity. There is nothing inherently wrong with properly designed and implemented aluminum bus bar installations; it is the branch circuit wiring that causes many of the aluminum wiring related problems and copper clad aluminum is just as bad. Quality commercial and industrial aluminum bus bar systems use bolted connections and are designed so that expansion and contraction will not stress the connections. If you can't easily get a nut on the back side of your bus bar, look for PEM nuts or press fit nuts similar to these: https://www.ebay.com/i/173438526393 Helicoils are great for some purposes, but I personally don't think they are suitable for bus bar application. In any case, as already mentioned, the bolt should not be considered as a conductor. |
| kony:
Stock material in -T6 temper if it is some 60xx alloy or in -H18 if you go after highest conductivity (EN AW 1050), electroless nickel per ISO 4257 (at least 15um, ~10% P content) and fuck it. There is nothing nonstandard at it, even for aluminium alloys, and any good plating shop serving electronics industry will be capable of that. Don't forget to keep the bolted connections under preload, prefferably not just by the screw torque, but by some other means as well - best case disk spring washers. Especially if there is PCB pads in the stack-up of the fastener, the common laminates will creep badly over time! Alodine or other conversion passivation is wrong here, so are dissimilar metals inserts. Also be VERY wary of tin plating on busbars (regardless of base metals) - whiskers are a big deal here and can turn your gear into big plasma ball in short few years. |
| MagicSmoker:
--- Quote from: kony on March 02, 2019, 09:59:55 pm ---Stock material in -T6 temper... --- End quote --- Finally someone gets it! 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; I'm not sure how popular Belleville washers are in the EU, though, so Nord-Lok are an excellent - albeit more expensive - alternative. I also agree that directly threading the bus bar - even with Helicoil inserts - is not ideal, but it can work just fine for small small ring terminals such as #6 (M3) through #10 (M5); once you go past 1/4" (M6), though, you really can't generate enough clamping force with threads in aluminum (unless the bus bar is unusually thick). I also agree that alodine is not an appropriate choice of surface finish as it's effectively an insulator. |
| T3sl4co1l:
Ahh-- not quite! Conical washers are indeed springy. They're perfect for this: a short-throw, high-force spring. Nord-Lock aren't conical or domed, as far as I know. So they don't take up any spring force. They do prevent unscrewing -- very important in high vibration (especially high shear) applications, but only useful when the bolt and base metal can be relied upon to not creep or stretch. They're also rather expensive AFAIK, so are best reserved for these cases when they're needed. There's also wave washers, though they tend to be softer than cone washers. Split washers, by the way, are literally no good at all: as a spring, they crush at even less tension than wave washers do, and in tests, they perform as well, or poorer, than plain old flat washers! Which is often worse than no washer at all, because they add another friction surface and can make the joint easier to move. FR-4 can creep or flow under pressure, too (especially at high temperature). If you're making high current bolted connections to PCB, consider using spring washers there, too! Tim |
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