When it comes to reliable system operation, choosing the right connector is key.
The right connector can make your system smaller, lighter, and easier for the user to handle. It's not a place to take shortcuts, as the right connector system can help avoid the high price of recalls, repairs, and lost customers. Conducting adequate research on the connectors and cables must be done at the beginning of a systems design process to produce the optimal design. Follow these 10 steps to research the ideal connector early in the design phase and you can positively impact the design, usability, and cost structure of your entire device.
Electrical needs
Defining the electrical voltage and current requirements each contact will carry is the first step to selecting the ideal connectors for your device. You have to ensure that you not only have the right number of contacts, but that the contacts can carry the power demands of your application. The size of the contact and the wire dictate the contact's current-carrying capability. Contact spacing, insulation materials, and the geometry of the insulator used to isolate the contacts dictates the voltage rating.
Table A
To ensure that you design in the proper connector, it's important to dig deep and understand how a manufacturer specifies their connectors' current ratings and operating voltages. Their test data should reference a test standard, informing you exactly how their testing was conducted. Not everyone uses the same testing criteria, so ensure that you understand how these specifications were derived. When you are reviewing current ratings, take note of the "temperature rise" spec, which indicates how much heat will be dissipated at a specific current value. You should also confirm that the contact will support the conductor size that you've selected. A non-compatible conductor could cause overheating issues, leading to premature connector failure (see table A).
Adding functions
After you identify the electrical requirements, determine whether other functions can or should be added to your connector. Hybrid connectors are usually custom-designed, but if you have the time to work with a manufacturer to develop a specific hybrid connector to exactly meet your needs, it can be worth the effort. The results will provide the end user with fewer connections and cables to manage. Try to source a single connector that can carry more than one of the following: power, signal, coax, fiber, liquid, and/or gas. The most common types of hybrid connector are the all-electrical versions that offer several larger pins for power and a high-density group of smaller pins for signals. The industry is moving to smaller, denser, and often more rugged multi-use connectors, and this approach could lead you to a device that's easier to use and more cost efficient.
Termination types
Termination types have a direct effect on the assembly process and the ability to seal a connector. Connectors with solder contacts are typically easier to seal against moisture ingress, while crimp contacts may offer better field reparability. There's a trade-off between the two, so the final decision on which termination type to use is often made after discussions with your manufacturing and design groups. It's important to know exactly how and where the connector will be used, and whether field reparability is a requirement, as this decision has a significant impact on the assembly equipment and processes used in manufacturing.
Environmental sealing
If the connectors will be used in harsh operating environments, check the manufacturer's IP (Ingress Protection) rating for sealing to dust and water at various depths and operating time frames. Make sure you understand the end-use environment for your connectors, and then compare that scenario with the details behind the manufacturer's IP rating (more information about IP ratings can be found here). Most of the IP designations have specific conditions, but the IP68 rating may be defined differently by each manufacturer.
I've encountered numerous failures of the large rectangular modular connectors offered by LappUSA, Weidmuller, Harting to name a few that do not stand up to real use. This year I've personally witnessed four different incidents where the connectors permitted water to enter.
Going to higher ratings than are strictly necessary is sometimes necessary to get the protection desired.
IP69K is a high pressure high temperature environment that better represents industrial food processors. IP67 sensors were simply not holding up.
As I design CNC machinery, I just want a connector that is already attached to the type of wire I need. So, I end up looking over countless catalogs for the perfect option. Often I end up having to build the harness myself. I am truly tired of doing that. All I need is a DB9 with 18 awg wire, shielded, twisted pair, 6 feet long. Is that so hard to manufacture?
Anyway, price is also a concern. With proprietary connectors, you often end up stuck with one vendor.
How in the world is a crimp on pin connector field repairable? REplacing a damaged pin would require cutting of the crimped on pin, making that wire in the cable too short to use. When I was an application/support engineer I would solder the crimp pins on for those 28 and 36 pin MS connectors with the individually inserted pins. The result was that I could replace a damaged pin in just a few minutes instead of needing to fight with stores for 2 hours to get a replacement cable assembly.
It is certainly true that connector choice can break a product and render it totally user unfriendly.
I think for the average assembler the crimp connections are much more reliable. They probably don't need replaced as often. Also, what is the most common failure mode in a soldered pin connection? I would guess that wire breakage where the solder wicked up into the wire. If so, the wire would have to be shortened in that case too.
For my early years in the industry I ran the Service Department for an agricultural equipment manufacturer. The environment was hostile, to say the least, but I quickly found that nearly all of the failures were switches, potentiometers and connectors. Semiconductors rarely failed, but anything electromechanical was bound to be damaged by vibration or user input. Not only were connectors an issue, but providing strain relief on cables without damaging the cable under vibration was an issue too. Connectors became such a problem that we decided to do without them at one point and used terminal strips. This wasn't an installation friendly approach, of course, but it did solve the problem.
When I played in a band connectors were always the first component to fail, too. Smoking was still legal in Chicago Blues clubs back then, and a layer of brown goo accumulated on all connectors. Switched 1/4" connectors were the worst with the switch contacts quickly failing with a layer of cigarette goop. Line Out and Insert connectors typically had this type of connector, so the quick stage fix was always to shove a loop back cable in the offending channel and see if this fixed the problem.
I also found that MTA connectors used as interconnects would fracture solder joints on circuit boards during thermal cycling. This happened quite a few times on newer Fender amps (why many musicians favor point to point wiring). The solder will expand and contract at much greater rates than the steel pins in the connector during thermal cycling and eventually the solder joint fractures around the connector pins. Later when I worked at an appliance controls company the same thing was happening to our oven controls and my stage experience paid off in finding a solution.
A poorly soldered connection to a wire is certainly a potential for failure, far moreso if there is not a good degree of strain relief. My experience with soldering is that if it is done right, the solder does not wick up the strands more than the conductor diameter. Greater wicking indicates that too much heat was applied to the connection and to the wire. But the most important part is indeed the strain relief that prevents flexing at the connector pin. No question about that.
I have to agree. Having spent over 15 years providing technical support for products in industrial environments, connection issues were by far the most prevalent. This is not the area to take shortcuts. Connector design, fabrication, backshell, wire gage and level of sealing are all important to get right.
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