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Old 05-09-2004, 12:26 AM
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StRaNgEdAyS StRaNgEdAyS is offline
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Exclamation If it's so safe, why is it called a terminal?

One of the most important things you will do when you build your planes is install your electical system.
Why is it one of the most inportant? Simply because if something goes wrong and you have a major electrical fault, you can be left with a fancy looking glider with no way to let anyone know what's going on. Yes, you may land safely, but if that safe place happens to be in the middle of the Great Sandy, then you're in deep
So, where should I start?
Let's start with how you are going to connect your cables.
Over the years, I have seen people employ many different methods to connect cables. Some ingeneous, some downright baffling. I once saw an old petrol marine engine with a leaky fuel pump that had it's ignition coil connected by a series of twisted wires. I was actually there to repair the fuel pump, but I threw the cable repair in for free.... that could have at best failed while they moored, and worst exploded at sea, leaving the occupants to swim for it.
There are two generally accepted ways of making electrical terminations, crimp and solder. Now for the record, I will not have crimp connections anywhere in my aircraft. Crimp connections are fine for domestic and automotive installations, where there is not likeley to be any major of sudden environmental changes, and the occasional corroded connector will result in nothing more than losing your CD player of at worst having to call roadside assistance. In the air a failed connection can range from annoying to disastrous. I will be soldering.
How to make a good soldered connection.
Things you will need: A good soldering iron, if you can an instant heat variey such as a scope 32V transfromer isolated unit is prefect, (no accidental burns) but any reliable one will do. Heatshrink tubing, several types and a clear one, which very handy for marking your cables. (The heat gun you use already should be sufficient to shrink this with) Solder connectors, which look similar to the standard crimp connectors, and some silicone dielectric grease is handy as well. Wire strippers, (ever wondered why electricians have a groove in between their front two teeth Ask me, I know!) and wire cutters. A can of PCB (Printed Circuit Board) cleaner is handy too, this is a spray can that cleans junk away prior to soldering.


The first thing you will need to do is cut 2 pieces of heatshrink, one in a contrasting colour to the wire insulation, about the same length as the insulator on the connector, and another clear piece about twice as long.
slide these and the insulator for the connector onto the cable, so that the insulator goes on last. Next strip the required length back on your cable, use the strippers, not your teeth, as strippers are cheaper to repair and replace. give the wires a quick twist to make the neat and hit it with the PCB cleaner and then tinn it by quckly applying heat and a solder. just enough to colour the conductors silver, you don't want great globs of solder hanging off it, and slide it into the connector. You will notice a small hole in the center of the connector's tube. sit this facing up on the cable, and apply heat to the bottom while feeding solder in to the end opposit the cables' entry point. when you see flux buble up through the hole, remove the solder and the iron in that order and allow to cool. Do NOTblow on the joint or worse, cool with water, as the solder will crystallise and make a dry joint, which will give high resistance to current and may fail.
Next Slide the insulator ofer the connector. You should feel it slip home with a definate "click" If not, spin it around and try again. next put a some dielectric grease around the bottom of the connector, and slide the contrasting heatshrink tubing over the insulator. Now get your trusty heat gun (a gas jet cig. lighter works very well too), and starting at the end near the connector, shrink it down all the way around, then move to the other end, repeating the procedure. Then shrink the middle down from the connector back, and give it a good wipe off once cooled. Now get a small length of paper you can wrap diagonally around the cable and write down what the cable leads to. wrap this around the cable, starting just below the join, and slide the clear heatshrink tubing up to cover the label completely. shrink it in place, and there you have it, one high quality terminal that you can depend upon, and you will never have to scratch you head and wonder "where does this %^&$#$ go "
Sure it takes a little longer (like 3x as long, and then some) but for the piece of mind, it's well worth it.
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Old 05-09-2004, 09:23 AM
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Thanks for the description, Strange, but I'd like to point out to readers that a VERY respected aeronautical electrical wizard, if not the guru of airplane electrical systems, Bob Nuckolls, has argued very emphatically the other way. His web site is http://aeroelectric.com/. Many of us are following his teachings and wiring schematics.

I think the basis of Bob's argument is that solder wicks up the wire. Where it stops is a potential fracture point which will not stand up well to vibration.
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Old 05-09-2004, 09:40 AM
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Radio Shack sells a small butane powered soldering iron that I have found to very handy. Starts easily, has almost instant heat and there is no running a cord all over the hangar to do a quick solder job. Just be CAREFUL around sources of ignition or leaky fuel ect. That will ruin your day.


Steve
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Old 05-09-2004, 10:24 AM
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Quote:
Originally Posted by John Slade
I think the basis of Bob's argument is that solder wicks up the wire. Where it stops is a potential fracture point which will not stand up well to vibration.
That certainly is a concern, but I think strange has addressed it with the shrink tube. That will prevent any fracture at the solder/wire joint.

I had two crimped wires fail last week in a wire harness at work where there was NO vibration at all. It looks like a slight bit of insulation was crimped with the wire and this caused the strands to fracture over time. I'll post a pic if I can. I saved the pins.
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Old 05-09-2004, 10:39 AM
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Post the pic to the aeroelectric list as well, if you can. Or i will if you wish.

Bob is bleeding edge electronics for aviation, but he is no high preist. His list has quite a few BRILLIANT people on it, and a great many learning.

Get his book and read it. If you find a flaw let him know. His list is all about open peer review of ideas.

On to crimping.

I encourage all who are doing there own electric system read and understand

http://aeroelectric.com/articles/rules/review.html
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Old 05-09-2004, 11:07 AM
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Yes Mike is correct, that is the main purpose of the heatshrink. Also, with practice, you can get a solder connector on with virtually no wicking at all. The secret is in the tinning, all you need to do it just get the solder wicking in on the end of the bare coductor, so there is just traces showing through the outside strands. There is no need to make the entire length of the stripped condtuctor silver. You will find, when it cools down and you give it a wipe, it will be silver, and what you were seeing before was the flux.
I also have to admit I have not seen Bob Nuckolls work, but I'll certainly check it out. Thanks for the link John.
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Old 05-09-2004, 11:21 AM
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Quote:
Bob is bleeding edge electronics for aviation, but he is no high preist
Actually - I'm at the bleeding edge, and I have the scars to prove it

Bob sits somewhere at the back directing. He's certainly very knowledgeable and very difficult to disagree with. Obviously he's considered the structural value of shrink wrap in his arguments against soldering. I'd agree that Bob's not a high priest, but from my lowly position in the religious hiarchy he's worth a genuflection or two.

I'm sure his discussion on soldering v crimping is around somewhere. Anyone have a link to it?
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Old 05-09-2004, 11:30 AM
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It is in my post. At the bottom.
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Old 05-09-2004, 11:35 AM
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Quote:
but from my lowly position in the religious hiarchy he's worth a genuflection or two.
Yes I've been looking over his site, and I have to admit, there is a lot of good information on there. The man certainly knows his stuff.
My preference to soldered connections is probably a result of 2 things, firstly seeing way to many crimped terminals remain happily attached too their posts while the wire that was supposed to be securly attached to it comes free. Second has to be the vulnerability of a crimped connector to corrosion, espescially if you are in a saline environment.
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Old 05-09-2004, 11:53 AM
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does anyone know how the industry(boeing etc.) does their terminals?-oops! sorry! just read the article by 'lecric bob. it says it all.
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Old 05-09-2004, 12:21 PM
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StRaNgEdAyS
Read the artical. All will become clear.
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Old 05-09-2004, 12:36 PM
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If you have to use shrink tubing and you are sincere about strain relief then use adhesive lined shrink tubing. It is heat activated and will prevent corrosion as well.
I used this stuff a lot on the boat and also on a project that had multiple connections in a wet environment without ever a failure due to moisture.
You need to buy it in large quantities otherwise it is expensive.
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Old 05-09-2004, 08:53 PM
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Yes, I did read the article, and it certainly brought my attention to some things.
I may well have been amiss in my mistrust of crimped connections. *hangs his head, duly admonished*
I really shouldn't have been so mistrusting of them, I just was.
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Old 05-09-2004, 11:50 PM
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I knew this one was going to get things going.
I am no Guru but have been around the block a few times.

I think it is fair to say that soldering and crimping BOTH have their place in aviation.

Problems I have seen with both.

With soldering :

Cold Solder Joints

Trying to WELD with solder...just won't work thats not the idea..a GOOD mechanical connection has to be made first then the solder added.

Using the wrong type of solder.

Improper flow of solder on connection. Usually with larger gauge wires.

INMHO if a proper soldered connection with heat shrink breaks due to vibration the wire should have been supported better to keep it from flapping around! Properly done, its as strong as the wire itself.

With Crimps:

Corrosion

Improper hardware for the gauge wire used.

Crip not made properly.

To get consistent results with crimping you have to have the RIGHT tool!
A cheap tool that crimps directly from grip pressure will not give consistent results. You have to have a tool that properly positions the crip and automatically applys the proper pressure when the grips are pulled.

These are just personal observations from over 30 years in electronics and aviation.

Steve
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Old 05-10-2004, 12:49 AM
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Ditto!

I'd have to agree with everything that Av1ator said.
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