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Avionics connector types and crimping tools

Partly inspired by WilliamF’s quest to properly design wiring, I’m trying to get my head around the various connectors used in aviation.

Can someone point me at a list of the most common connector types, just so I know what is called what when I see it when I finally take a peak behind the panel?

Speaking solely about the non-RF side of avionics, is there a single crimping tool that will do the various connector types commonly found? Or at least a single tool with different dies?

I’ll appreciate recommendations for reasonably priced hobbyist quality tools that actually get the job done. I don’t want a cheap tool that isn’t going to work, I’d rather know I can’t have one cheaply. Looking more for “buy it now” than “save search and wait for auction to come up” type of thing.

I understand that RF and high current connectors will need a different tool – recommendations are also welcome.

Ideally when all is said and done I’d like to be able to attempt to make a harness for an audio panel. The portable one I have now is a safety reducing device. And yes, I know I’ll more than likely end up ordering the harness with the panel anyway ;)

tmo
EPKP - Kraków, Poland

In my little experience there are several types of pins (high density & low density?). I remember using this tool https://www.aircraftspruce.com/catalog/elpages/edmolittleblue.php and different positioners (K41, K42 and K13-1 I think) and it covered all my avionics needs (Garmin, JPI, etc).

If you do an audio panel you’ll need to be careful about shielding. If you’re looking for techniques this matches what I’ve been “taught” (I’m nowhere close to being a pro):

Stock up on these solderless sleeves!

Actually a nice step-by-step thread with pictures would be great and would probably attract a lot of (positive) criticism from the pros on this forum.

I was taught to crimp, with the correct crimping tool, rather than solder, whenever possible. In multi strand wire, solder will wick down the strands, and stiffen the stranded wire, which may then break at the end of the wick when it flexes. Better that the wire flex to the crimp connector.

Use the crimp connector recommended by the crimp manufacturer. Connectors should be crimped, rather than squashed over the wire. Cheao crimping tools tend to squash, rather than correctly curl and crimp a connector over the wire.

At a Cessna aging aircraft presentation in Wichita many years ago, the theme was expected to be structure. Instead, though structure was discussed, Cessna presented that aging aircraft should have their wiring inspected and probably replaced. This has been my experience too. For the rebuilds I have done, I have generally rewired, or at least replaced all the crimp connectors if the wire is otherwise in very goo condition. It’s worth the effort not to chase faults later. I was surprised years back, while flying a fairly new Caravan, to smell electrical smoke, and see sparks coming from under the panel, from just over my knees. ’Turns out an original Cessna crimp had failed, and the load carrying wire was making intermittent contact and arcing. Happily, the fault was in a location easy to find and repair, but that convenience is rare! Do it right the first time!

Home runway, in central Ontario, Canada, Canada

Steinair are one of the go-to places for electrics and avionics in the amateur build scene and they have a great collection of videos online here. In particular, take a look at this one



on the common connector types.

Top Farm, Cambridgeshire, United Kingdom

Justine’s nightmare fly-in is one where soldering versus crimping is discussed, and actually she had been to one of those She now asks for an assurance that this topic will not come up again…

Sadly as you see in above link there isn’t a single crimping tool, by a very long way. Fortunately you can pick up good examples of most crimping tools on Ebay (often US Ebay) for perhaps 1/10 of their new price.

RF work often uses crimp connectors too but often it is soldered, because the solder versions of the connectors are much more available and are often much cheaper.

High current connections can also be crimped but it can be hard to find the right terminals in small quantity. OTOH you may need a really big soldering iron.

A lot of the debate around this revolves around whether the installer can or cannot solder. Many cannot solder but also soldering is hard or dangerous in a confined space, often working upside down and then you don’t want a blob of molten solder dropping into your eye. If you can solder well and especially if you have the opportunity to wire stuff up at home, a lot of avionics wiring can be done really neatly.

Another thing is that a lot of avionics shops work in unheated hangars, and if the temp is -5C outside, the poor buggers will be freezing their balls off and can’t possibly do soldering with their fingers shaking with the cold. I remember some Annuals done in such a hangar and felt really sorry for them.

The other bit of the debate is vibration resistance – see the above link. Pilot_DAR is spot on about solder wicking up the strands and causing a failure point right there. However this will fail only if there is repeated movement, and while this is generally true in GA avionics, it is not necessarily the case if the installation is done well and the wire is correctly supported as it leaves the connector. If you use heatshrink sleeving on the joints then you can support the wire quite well too.

As an old hand with a soldering iron, since around age 6 (1963) I am predictably biased towards soldering but my experience is that while soldered joints never fail (unless subjected to gross environmentally induced corrosion) crimped joints do seem to become intermittent after some decades.

I don’t think solderless sleeves for joining wires are a particularly useful thing, except where you don’t have soldering access. If you can solder (the usual IF) it is easy to solder wires together and heatshrink over them.

I’ve done a lot of avionics wiring… some pics here.

In GA one sees a lot of crappy connectors – here. There is no point in using these, especially when you can pick up the milspec circlar ones on Ebay, unused.

Another thing is that avionics wire gets unusable (for new work) after some years – see here. You can strip it but it won’t solder. It will of course crimp but I wonder if the joint will last. So avoid using old (say 30 years old) avionics wire, tempting as it may be because the stuff is damn expensive.

One of the annoying things is that most avionics use connector types which cannot possibly be wired up with the wires correctly supported. For example you may have a 50 pin connector and the hole in the shell is only 15mm. You can’t possibly do it unless it is just single wires passing through the hole. So if any of the wires need shielding (and if doing the job right, most wires will need shielding if you want to avoid issues like this!) you have to terminate the shield well outside the connector.

Molex connectors (shows in the video above) are IMHO best avoided. They guarantee problems some years down the road.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Fortunately you can pick up good examples of most crimping tools on Ebay (often US Ebay) for perhaps 1/10 of their new price.

Yes indeed, and in fact, there is no absolute need to buy the super-expensive TE/Daniels/whatever military-grade tools anyway. Their only advantage is that they are relatively foolproof, while with industrial-grade ones (at one-fifth the price) you need to understand what you are doing. Just don’t use consumer ones. Industrial ones of Chinese origin (from Aliexpress) may be good – specifically, the frames are generally fine, but the dies need to be selected carefully; I have about 12 different dies from China, and most of them are good, but I spent some time gathering information on them. I wouldn’t hesitate to recommend them as the second set that you haul around and aren’t afraid to lose.

Peter wrote:

High current connections can also be crimped but it can be hard to find the right terminals in small quantity. OTOH you may need a really big soldering iron.

For soldering really thick ones (e.g. starter battery wiring), electric soldering irons are usually inadequate (except the really powerful ones that look like a hatchet), but a small torch works wonders.
For crimping, a hallmark of a good high-current terminal is the presence of small ribs or knobbles inside the barrel (e.g. TE SOLISTRAND). Also, seamed and seamless barrels require different dies to crimp.

Peter wrote:

Another thing is that avionics wire gets unusable (for new work) after some years – see here. You can strip it but it won’t solder. It will of course crimp but I wonder if the joint will last. So avoid using old (say 30 years old) avionics wire, tempting as it may be because the stuff is damn expensive.

An old oxidised wire can actually be fixed with the right kind of flux, but non-corrosive ones tend to be toxic (e.g. hydrazine).

Last Edited by Ultranomad at 27 Mar 11:17
LKBU (near Prague), Czech Republic

I’ve been soldering for years too (in fact, I spent most of yesterday and some of this morning building a remote DDS VFO for a radio using point-to-point wiring since I doubt I’ll be able to get a PCB made any time in the next 2 months).

However, nearly all the time on the aircraft I’d rather crimp. Even brand new aircraft wire doesn’t solder easily (it conducts away the heat far faster than normal PVC coated wire making it hard to get a good joint). Crimping takes a fraction of the time and if you have a good crimp tool (not one of those £7.99 from Halfords jobs, but a decent one bought from an electronics tool supplier) you can teach a chimp to crimp. I can make perfectly nice soldered joints for aircraft wiring, but I can crimp a connection in about a tenth of the time and with a tenth of the fuss. (Not to mention my hangar is “off the grid” so I have to listen to the racket of a generator if I want to solder anything in the field).

Some times you need to solder (the centre pin on BNC/TNC connectors, and many of the higher grade RF connectors are designed to be soldered) but the centre conductor of RG400 solders to a BNC centre pin very easily, and the connector’s design means that the soldered joint will never get moved once the connector is assembled.

Last Edited by alioth at 27 Mar 11:53
Andreas IOM

JLCPCB claim to be up and running.

Administrator
Shoreham EGKA, United Kingdom

While a skilled operator can produce a high quality soldered joint it takes time, try to repeat this operation for the two hundred and twenty-second time in a day and quality is likely to fall.

This is why having the correct crimp tool is the only option for consistent quality and time saving.

If you have if you have a lot of connections to make and a limited time to do the job you probably need to buy a crimp tool to keep the quality high enough after all trying to repair a broken connections in an installed rack is a very time consuming and expensive.

An expensive crimp tool is very cheap if it provides reliability.

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