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Switches... Screw or push-on
A quick search did not produce an results sooooo....
About to dive into wiring and I need order pieces-parts. What are the pluses amd minuses of switches with screw terminals vs switches with push on tabs. I hope this is not the cousin to the primer debate.... |
I vote 1/4" fast-on's.
They are so much easier to work on when you have everything in place. Also they are easier to insulate. Use some good connectors with the insulation, or some heat shrink over the connector. |
I also decided to go with fast-on after waffling back and forth during the design phase. Once you push a few of those connectors onto the tabs you will realize how well they hold. The quality connectors aren't like the ones from radio-shack, they hold on Tight!!
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Swithches
Seems to be thread drift. I believe your question was about switches.
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http://www.bandc.biz/electrical-switches.aspx |
I'm a big fan of the Honeywell 2TL1- xx switches, available in all configurations including locking. They are what were used on almost every jet I worked on and are virtually failure proof, waterproof, dustproof etc..
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Faston's for me...use the proper terminal and it will never just fall off.
I don't like screw terminals because they are hard to work with and if one gets loose, you may not know it till it is too late. |
Honeywell TL series
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They are very robust, mechanically and electrically. Much more so than commonly used commercial grade switches I've seen (e.g. those from B&C). They have a rock solid look and feel (think military or airline cockpit). They conform to a standardized (milspec) set of mechanical and electrical specifications. So, why is that beneficial to us experimental guys? In this case, simply for standardization and future availability of replacement parts. As these switches are used in practically every military and commercial airplane produced in the western hemisphere, they will remain available for decades to come. Whereas commercial grade switches like those sold by B&C might be just as good (or not), but product lines come and go quickly, and a particular one is less likely to continue to be available in the same specifications, form factor etc. over the lifetime of the airplane. Think spare parts 10 to 20 years down the road. Also, Honeywell is not the only producer of these milspec switches. Eaton also has their own line of switches that conform to the same milspecs, and are mechanically and electrically interchangeable (drop-in compatible) with the equivalent Honeywell switches. And finally, these milspec switches really are NOT very expensive if you shop smart. First and foremost, DO NOT just blindly buy them from aviation-related vendors. From what I've seen, you'll pay 2x to 3x what they go for elsewhere. Go download the product datasheet from Honeywell, identify the part numbers you need, and Google search them to find many other non-aviation vendors who sell them. And if you want a pretty good shortcut to a one-stop-shop, Allied Electronics tends to have very competitive prices on these and carries a wide selection. That's where I got mine. |
Those switches are $44!!!! Wow.
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I prefer switches with screws and ring terminals crimped onto the wires. Never had one come loose yet if you tighten it properly and use a lockwasher.
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http://www.alliedelec.com/search/pro...x?SKU=70120168 When you get into more complex multi-pole, multi-throw, locking toggles, etc. they will obviously be somewhat more. And if you don't shop around for the right vendor, you can pay A LOT more. |
Expensive
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That's the beauty of building an RV. Everyone gets to choose what to buy and install. Have fun. Buy reliable parts from respected vendors, and be happy with your selection. It's your airplane. You only have to please yourself. |
I heard 'lectric Bob speak at Oshkosh a few year ago about exactly this. He advocated using inexpensive, off the shelf parts like B&C sells and then replacing the switches after 10-15 years. For $100, you can replace all the switches in a typical homebuilt periodically and achieve system reliability that likely exceeds that of expensive mil-spec switches.
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Use whatever you want, quality stuff usually costs more, but to me (and most of my customers will agree) it's worth it. 8 years, 1300+ hrs, 100% Dispatch reliability. |
Lectric Bob..... also explained why push on connectors were a superior electric connection.
I purchased all of my switches from Granger rated for AC. I used these switches in my propane truck. This switch was cycled over 40 times a day, five days a week for fifteen years. And NOT one failure. This was an AC rated switch on a DC load. Part # 4X849 about $6 each. |
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I look at switches the same way as any instrumentation - it needs to work. If it doesn't matter if it works or not, you probably don't need it and should consider getting rid of it. TODR |
Getting back to the original question:
Both push on and screw on terminals work fine and do not often fail. I use both on my aircraft. Both work!. When do I use screw on .. when I have a linear group of switches or circuit brakers that are all tied together by a copper bus. You drill holes, then use screws though the bus (with lock washers). If you use pushons you will have many more connections that could fail.Also, not as clean looking. Just my 0.02 cents. |
Forces and spec sheets....
The 1/4 inch Faston PIDG terminals are great, but some care needs to be taken installing and removing the terminal from tabs.
For 22g wire the minimum commercial crimp "pull out" force is 8 pounds, while the maximum "pull the terminal off the tab" force can be as high as 18 pounds for the first use. So... don't pull on the wire to remove a terminal from a tab....:) Numbers here - http://www1.futureelectronics.com/do...CS/42067-1.pdf |
Component reliability, system reliability, and dispatch reliability
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All switches can fail. Not necessarily at the same rate, nor for the same reasons, but they all can and will eventually fail (though most will outlive your airplane). System reliability is a function of the reliability of the individual components under their respective operating conditions, but also the design of the system to prevent single component failures from taking down the system or large portions thereof. That's a whole topic in itself that I won't get into here. But the point I wanted to make is the following. Even if you assume for the sake of discussion that the commercial grade switches from B&C are equally as reliable as the milspec switches (doubtful, but assume it for the sake of discussion), the milspec switches still have the advantage of ubiquity as I described above (post #7). Walt hit the nail on the head in referencing the objective of achieving good dispatch reliability. Part of that is reducing the failure rate by various means, including use of good quality of components. But another less obvious part is ensuring serviceability and minimizing down time when failures do occur, both at home and away, both at present time and in the future for the lifetime of the airplane. When you experience a failure 10 years from now and 1000 miles away from home (away from your personal stash of spare parts), the local mechanic or avionics shop is likely to have the standard milspec switches on hand, not the B&C flavor of the day from ten years prior. That's when that extra $100 spent upfront to use milspec switches in your panel (a drop in the bucket on a ~$100K airplane I might add) will have more than paid for itself, in getting you back on your way with minimum delay. P.S. There was recently a thread discussing standard external power connectors versus Piper-style connectors and other possibly effective but non-standard contrivances, where I advocated using the standard connector for essentially the same reasons I'm advocating the milspec switches here. Dispatch reliability. When the s*** hits the fan at the most inconvenient time and place, consider what resources will be most likely available to get you back on your way. |
Thank you for all your inputs which I do value?. In the interest of fairness, I plan to use half screw on and half Faston. I also intend to complete the rest of my airplane without priming any more.
I?m now schizophrenic and so am I |
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I pulled about 30 of them off the forest of tabs by pulling on the wire. Not a single one of them pulled the wire out of the connector. Some had to be pulled very hard to get em to come off. Sold me on good connectors, good crimp tools and Faston connections. |
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Just be careful when the tabs are new and unused and be aware that the smaller gauge wires have lower pull forces...:) |
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All my switches are fast-on terminals - I wouldn't do it any other way. |
A bit of thread drift:
Several years ago, I had multiple switch failures of the Carling switches in my RV-9A (switches bought from B&C). Working with Bob Nuckolls, and after much discussion and failure analysis, we established that the riveted connections on the Carling switches were working loose, increasing resistance and causing a chain reaction of failures due to overheating. The worst offenders were switches used for non-resistive loads: strobe circuits, landing light circuits and (wow!) master switch (alternator field) circuit. The master switch failure led to overvoltage in the charging circuit. The strobe switch failure led to charred wiring and a burnt finger. I replaced all of my Carling Switches with similar Honeywell TS switches and the failures have stopped. It was a lot easier working with fast-ons when upside down under my panel! You can Google this on the aeroelectric list if you wish. This study was pretty definitive. Failing switches are not just an inconvenience-- they are a flight safety problem. |
I used Otto T7 series with 1/4" Q.C. terminals. Price= $9-25. 25,000 cycles inductive load and 50,000 cycles resistive. I use similar terminals in the HVAC field and as long as they are tight going on, they hold up good pulling 25 Amps. Much quicker for troubleshooting later too.
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