Wiring Harness Design.  Daisy-Chain?? - Page 1
Forum section: electronics / projects

author: rantonides
author_rank: Contributor
timestamp: October 17, 2012, 07:05:09 pm
content: I'm new to designing wiring harnesses. I work mostly in industrial, so up to now, I've used din rail, terminal blocks, etc, but now I've designed a compact machine that will have some quantities, so I need to design a wiring harness, but have no experience in doing so.I think I want to use the Mate-N-Lok type connectors.I have one cable with 12 conductors that needs to break out to 8 other cables.2 of the conductors on the 12 conductor cable need to go to each of the 8 other connectors (These are +V and GND). Do I daisy-chain these wires on each of the 8 connectors? How do I do this? Can I put 2 wires in a crimp pin? Is there a cleaner way or more reliable way to do that?Thanks for your help.

author: Bloch
author_rank: Unknown
timestamp: October 17, 2012, 08:42:24 pm
content: Quote from: rantonides on October 17, 2012, 07:05:09 pmSure you can it have ben done in pc forever.one example

author: Rerouter
author_rank: Super Contributor
timestamp: October 18, 2012, 12:06:52 pm
content: 2 wires in most crimps is a very reliable method, while it comes down to your costings a little here are a few small modifications i make to my looms that make them last a little longer,twist the 2 wires together,lightly tin the wires with solder, so they keep shape,cut to length (for a good twist you always need about 8-10mm of stripped wire, while the crimps normally only need 3-4mm)crimp so the wires sit side by side, each of the tabs folding over a seperate wire,melt solder into the front of the smaller tab crimp so it flows in a little,slide over a piece of heatshink over the crimp so it starts at the smaller tabs and goes down the wires about 12mm past the end of the crimpif you must tape the looms, leave 80mm from the plugs before taping them,while most of that is stress relief, any test lead or loom i have made following that has lasted 4-5 times over the standard twist crimp (solder optional)

author: PuterGeek
author_rank: Regular Contributor
timestamp: October 18, 2012, 06:47:20 pm
content: Like so many other things, it depends.Quote from: rantonides on October 17, 2012, 07:05:09 pmWhat type of machine is it and what is its operating environment?If it is a PC like device you can do things that would be unacceptable in an industrial application. If it is diesel powered even the industrial techniques aren't adequate.I worked for an industrial diesel engine control panel and harness OEM for 10 years. Industrial engines are commonly attached to the powered equipment (pump, generator, etc.), mounted on a skid, a control panel bolted to the engine and a harnesses added to complete the power unit. The unit is then expected to survive outdoors for several years in all climates with an occasional pressure washing if it is a rental unit. The vibration (up to 10 Gs), temperature extremes (-40 to +85C), chemicals (diesel fuel, oil, antifreeze, caustic cleaners, etc.) and UV radiation quickly degrade most 'standard' components.Doing it the way we did would be gross over kill for a PC but using Cat 5 and DB connectors would be a total fail for an industrial diesel engine.What kind of quantities and who is making the harnesses?If you are personally making 5 to 10 a month is one thing but a thousand a month by a contract harness contractor is another. Splicing wires is added work if you are hand assembling a few harnesses at a time but ultrasonic wire splices are better for an automated harness contractor.Automatic wire stripper/crimpers support double crimps (2 wires in a terminal) but only on one end of the wire, it is slower and more likely to have a fault. Ultrasonic wire splices are a better choice in that environment.Quote from: rantonides on October 17, 2012, 07:05:09 pmYou can put several wires into a single terminal with a few a limitations. You have to use stranded wire, the total conductor cross section must not exceed the terminal's capacity and the total insulated diameter must not exceed the insulation support crimp capacity. Trying to get more than 2 or 3 wires is a handling challenge but it might be a good choice in some cases.Most (all?) Mate-N-Lok terminals have an insulation support which is crucial if the machine will see ANY vibration! Solid wire will fail from metal fatigue caused by vibration. Stranded wire is effectively solid where crimped or soldered and the insulation support provides a strain relief to protect the joint. The soldering and heatshrink recommended by Rerouter is not necessary with the insulation support crimp.A good quality crimp joint is air tight and just as good as a solder joint (better in some ways). The key is 'good quality' which means crimp tooling designed for the terminals being crimped. A highly experienced assembler can make do with a generic open barrel crimper but the right tooling is always more efficient.Good quality also means using the correct terminal for the wire size. Different terminals are usually available for different wire cross sections and sometimes different insulation or seal diameters. And there are frequently different plating options (unplated, tin, silver, gold, etc.) and/or terminal materials (brass, bronze, etc.).Soldering creates special problems because the solder wicks up stranded wire under the insulation. In that case adding heatshrink may be necessary even with insulation support. Soldered terminals in a wire harness are rarely necessary except for rockets and high performance aircraft.I hope that helps answer your questions. Let me know if you need more info.

author: free_electron
author_rank: Super Contributor
timestamp: October 18, 2012, 07:39:15 pm
content: yuo may not want to daisy chain forever ... the current draw on an intermediate node can cause voltage drops at the end... and the inductance in the cabling can be enough to cause voltage spikes at the end of the cable too.use star connections from the power source to each load