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Prewired harnesses?

10 Posts



Administrator
Shoreham EGKA, United Kingdom

I was just working on finishing the pin mapping and measuring the cable lentghs for a new audio panel and 4 place stereo intercom.
I love the idea of using a pre made wiring harness but this “hub” thing these guys are providing looks very interesting.

Switzerland

Agree. I wonder how it is made internally: PCB or spaghetti?

LSGG, LFEY, Switzerland

You can get PCBs made in China amazingly cheaply. I have just ordered five 4-layer boards, 10×10cm, with about 400 component places, gold plated, 4/4 rules (0.004 tracks 0.004 spacing) for US$70 total including courier delivery. The company, JLCPCB, is somewhat famous for stating they cannot speak English and will never read instructions on the layers, so you have to get the gerber data 100% right, but nobody argues with the price.

So, all this company has to do is draw the wiring diagram, autoroute the PCB, and order the boards. I use 25 year old schematic and PCB design software (Orcad SDT/386 and Protel PCB 2.8, with the Specctra autorouter) and it would be dead easy. Autorouting time would be seconds.

What you could not get that way is shielded wires, unless you used a lot of ground planes, but the crosstalk would be minimal.

So it’s a strong possibility, especially looking at how thin the box is.

Administrator
Shoreham EGKA, United Kingdom

I’ve recently used PCBWay (another Chinese outfit) for mine, they seem pretty good at doing the pre-production checks. I actually got the boards back in about a week.

Andreas IOM

There is a lot of them; I used to use ITEAD but nobody gets close to JLCPCB price-wise.

Anyway in this case it doesn’t matter if the board is $100. It would be a clever solution.

The main challenge I see for the avionics shop is working out the wire lengths.

This has the potential to really damage the avionics installation business. They would be making money more or less only on the dealer discount on the supply of the equipment.

Administrator
Shoreham EGKA, United Kingdom

These guys are essentially exploiting the economy of scale by offering standard harnesses they can order by the hundred. If I were wiring a flying test platform for avionics, I would certainly consider using this arrangement; I am not so sure about wiring for day-to-day use – after all, connectors are known points of failure, and there is also the extra weight (not just from connectors, but also from extra cable length, as they probably make them long enough to fit many different aircraft, and possibly from extra wires in the harnesses, as they need to cover different use cases). Finally, I think the $5000 price the guy in the video was quoted for the custom harness is probably the result of not shopping around and being, ahem, less than clueful in aircraft systems.

LKBU (near Prague), Czech Republic

Having connectors readily mounted on both ends, will possibly hinder the installation of the cables?

Ultranomad’s points are valid: this solution doubles the number of connectors which increases weight and decreases reliability.
We must however consider that human-assembled one-off cables may or may not be as well made as machine-produced standard cables ? I really like the idea of making the cables generic and putting all of the custom interconnection work in PCB.

I think I will go for this on my next avionics job….

LSGG, LFEY, Switzerland

I am not sure that the extra connectors degrade reliability significantly. It depends on how well they are done, and on the connector quality.

Administrator
Shoreham EGKA, United Kingdom
10 Posts
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