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A kit is a kit

Got my MGL stuff this week from Parts for Aircraft in the UK. One of the boxes is an ECB (electronic circuit breakers). Along with the ECB unit, MGL sells a switch kit (although the end user may use his own switches and LEDs). On all the pictures in the info they look nice and complete, and I thought I would order so I didn’t have to do lots of soldering and stuff. I should have paid more attention to the word “kit”


ENVA ENOP ENMO, Norway

I too would have been surprised to receive a bag of bits instead of what’s in the photo:-

I see what you mean… you need to solder it all together.

Soldering is easy (for someone who can do it) but to me it looks like those indicators need to be spaced just right off the PCB, which implies some sort of a jig to hold them in place.

Assembling that IDC connector (in a vice) is also a bit of fun… make very sure the individual wires are lined up.

I hope there is no vibration because the IDC connector has no strain relief.

Administrator
Shoreham EGKA, United Kingdom
I hope there is no vibration

In an aircraft? Piston powered? You can go on hoping… But frankly, I think soldering might suffer from vibration at least as much as connectors of that kind. I always learned crimped connections are much more reliable than anything soldered, in our kind of environment.

EBZH Kiewit, Belgium

We did that before e.g. here

My view is that crimping is more reliable in reality but not because the joint is better (it certainly isn’t) but because you don’t get the solder wicking up between the wire strands and creating a weak point there. If the cable is properly strain relieved then soldering is fine; better IMHO. So with soldering one uses heatshrink sleeving but the job then takes ages. Crimping is much faster.

But even a crimped joint will break or come loose eventually because a lack of a strain relief merely postpones the inevitable. I recall one avionics guy spending a week or two re-doing about 1000 crimped joints in the front of a King Air. He never found the bad one but having re-done the lot, the problem was gone

The bottom line is just cost. Decent connectors cost money, and wiring up a milspec circular connector takes ages…

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

So with soldering one uses heatshrink sleeving but the job then takes ages

You can say that again. Especially when soldering the larger gauge wires – you really have to make sure everything comes up to temperature to avoid a bad solder joint (cold joint) and it requires quite a bit of patience. Doing all the new wiring for my new radio installation took me pretty much an entire weekend of slow patient work (and it was a straightforward single radio install!) I lost count of how many heatshrink sleeves I put on!

Last Edited by alioth at 16 May 19:17
Andreas IOM

Peter wrote:

I hope there is no vibration because the IDC connector has no strain relief.

The wires (or the flat bands) weigh close to nothing, so I don’t really see any vibration issues. They are used only to drive a LED and a digital input (on/off), no current at all to speak of. In any case, a strain relief would be simple to make by simply bending it double and use strips. I’m a bit more worried about corrosion, but I guess there is nothing there that a normal marine multispray won’t fix.

ENVA ENOP ENMO, Norway

A conformal coating should do it.

Whether I would use an IDC connector on a plane at all, is another matter. They are pretty reliable in industrial electronics but there is normally no vibration or corrosion. Also there is a huge variation in price (10:1) for apparently the same connector, and this is at least partly related to the quality.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Whether I would use an IDC connector on a plane at all, is another matter.

I am in fact a bit worried about what the CAA will say about this as well to be honest. It is very “non-aircrafty”. But then again, they are not part of the traditional analog circuitry as such, they are part of a low ampere digital system.

I got the book “The AeroElectric Connection” a couple of years back. It covers the basics, but doesn’t really cover any of the more modern things at all (Nothing about LEDs, engine/general data acquisition systems, EFIS, EMS, CAN bus, distributed digital gadgets and so on). It’s all very low ampere digital things, and most problems (from what I have gathered) are due to electronic noise. If I wired everything like that book suggests, the whole aircraft would be a digital noise amplifier/emitter.

ENVA ENOP ENMO, Norway

From the bits I have seen, and I don’t want you to take this as a criticism, the homebuilt world is full of IDC connectors.

When you are making a $1000 piece of kit (which does the same apparent job as a $5000 certified version) you just can’t use $100 milspec circular connectors. Something has to give.

The interesting Q might be how the car business has achieved very high levels of reliability while keeping everything absolutely rock bottom dirt cheap. The standard techniques are

  • sealing everything from moisture (including little o-rings in the connectors)
  • mounting PCBs properly (max suppression of flex/resonance modes)
  • avoidance of mechanically flimsy and limited-life components (e.g. electrolytic caps)
  • really robust protection from spikes on the supply (mainly from the starter motor)

But not many “spare garage” outfits know about this.

Administrator
Shoreham EGKA, United Kingdom
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