Your Experience with Reliable Connections? - Page 1
Forum section: electronics / projects

author: Alaezae
author_rank: Contributor
timestamp: August 05, 2020, 10:03:21 pm
content: Hi,I’m currently involved in a robotics project and I had a question. The number one thing we struggle with electrically is reliability. It seems like all the connections we make (whether that be wire to wire or wire to board) fail once the robot starts moving. It’s generally not a problem with the service loop in the wire, it’s more of an issue of the type of connector we’re using. They either vibrate apart or break at the wire over time, and this cannot happen. As far as reliability of connections goes, what connectors generally stay together on a moving vehicle?

author: OM222O
author_rank: Frequent Contributor
timestamp: August 05, 2020, 10:22:23 pm
content: Wire to wire: porperly solder and add heat shrinkWire to biard: proper cage type screw terminals (the ones that have a movijg jaw) not the cheapo spring leaf one. As a general rule of thumb the cage types are usually in a green plastic housing and the spring leafs are blue.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 05, 2020, 10:26:55 pm
content: Are you perhaps cutting your wires a bit too short, inducing stress on parts of the wiring? Having some extra wire may alleviate things.

author: TimFox
author_rank: Super Contributor
timestamp: August 05, 2020, 10:56:44 pm
content: When your connector connections break at the wire (under vibration): do the contacts include the extra crimp section to secure the insulation while the other crimp secures the wire? The automotive connectors are probably a good example of how to make connections in a vibrating environment.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 05, 2020, 11:17:40 pm
content: As implied by the previous posts the key is to have mechanical support for the wire separate from the electrical joint. That's after you get through making a proper electrical joint, either with solder or appropriate screw terminal.Several methods.For wire to wire twist the wires tightly together before soldering, or shrink wrap, or ...For wire to board mechanical clamp on insulation, or hot glue, or lace tie downs to board or ...Solder has horrible mechanical properties and copper is malleable, so any mechanical stress on the electrical joint can cause failure. You need to make the joint move as an entity, eliminating that mechanical strain. The second clamp in many connectors to grip the insulation behind the joint helps and is good enough in many situations, but most insulation is an elastic material and passes some amount of motion. You may have to go further.Remember the numbers game you are playing. I am sure you have dozens, and possibly hundreds of connections. 99% reliable joints aren't good enough. With three dozen joints that predicts an overall reliability of only about 70%.Automotive wiring systems are fairly good for this. Look at what they do. Aircraft are better. If you can, look at their methods. Both in person and in the form of specifications.

author: jmelson
author_rank: Super Contributor
timestamp: August 06, 2020, 01:25:56 am
content: All these cheap header and single-point contact (Molex, for instance) are not reliable under vibration. DB-style connectors, when screwed together are pretty reliable.Jon

author: tooki
author_rank: Super Contributor
timestamp: August 06, 2020, 02:06:21 am
content: Quote from: Alaezae on August 05, 2020, 10:03:21 pmWhat connectors are you using now?

author: Alaezae
author_rank: Contributor
timestamp: August 06, 2020, 03:24:27 am
content: We use these crappy barrier strips for connections. I tried adding ferrules to see if that would help but the problem is the screw keeps coming out. Those barrier strips are really cheap and crappy and I’m using them to daisy chain a CAN bus. As far as I’m concerned, they need to go. I just don’t know what to replace them with.I appreciate the advice with soldering, the problem is that the components we are forced to use fail so often. I really need a connection where I can make a quick disconnect. We are forced to use these components because of specific regulations, not what I would choose but I can’t do anything about it.I’ve tried using Molex connectors and they work okay, if you screw up the crimp though you’re boned. Or if you have to redo something the tool to get the contacts out is terrible (and painful, I’ve stabbed myself with on more than one occasion). They do have the ability to lock together which adds a whole lot of reliability, they are just time consuming and difficult to implement.I would use automotive grade connections, I just can’t find out where to get them for cheap. I have a VERY tight budget for this project. The crimpers alone can cost $500, which is more than I can justify spending for this application.I just want to know if anyone knows of any connector types which are cheap and have relatively cheap crimpers. I do appreciate the advice on mechanical support for the connections, I will certainly implement it!

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 06, 2020, 04:10:03 am
content: I have been successful searching Mouser for automotive connectors and then sorting by price. Tons of choices and I don't have model numbers for what I bought. 8 pin connector bodies were a couple dollars and pins are a few cents. While it would be nice to have the proper crimper, with care you can use inexpensive universal crimpers. If you want you can solder the crimped connection. (this statement will bring down the fire from many but I haven't encountered problems).

author: OM222O
author_rank: Frequent Contributor
timestamp: August 06, 2020, 07:55:07 am
content: If you want quick disconnect: T tap connectors + spade commectors. No soldering, no stripping, nothing.

author: jfiresto
author_rank: Frequent Contributor
timestamp: August 06, 2020, 04:13:11 pm
content: Quote from: Alaezae on August 06, 2020, 03:24:27 amWhich ones? I asked Digi-Key to search for "Molex connector" and they returned over 137thousandresults.

author: TimFox
author_rank: Super Contributor
timestamp: August 06, 2020, 05:12:26 pm
content: With huge-range companies like Molex, I miss printed catalogs. Perhaps Molex' on-line catalog is easier to use than the DigiKey search engine.

author: tooki
author_rank: Super Contributor
timestamp: August 06, 2020, 11:39:18 pm
content: If only. It’s arguably worse. Molex’s website is a fooking mess. (Not as bad as TE’s, though.)

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2020, 01:09:40 am
content: Crimp terminals for connectors need to include a strain relief section which crimps over the insulation like Molex connectors commonly have.For very high current connections, I like to bolt ring terminals together.

author: Wendy_Preston
author_rank: Contributor
timestamp: August 07, 2020, 07:20:00 am
content: Now, please don't blast me for mentioning our own company's connectors - but high-reliability is kind of our bread-and-butter. We supplied Datamate connectors to NASA for the Robonaut...https://www.harwin.com/connectors-hardware/high-reliability-connectors/On a more general basis, I'd say you need to consider at least the following features:Some sort of fixing between mated pairs. Jackscrews, screw-loks, bayonet locks, latching - something. This will prevent the vibrating apart. Depending on how often you need to disconnect the pair will help you with your choice of fixing feature and how quick or easy it is.Backpotting, cable hoods, heatshrink - some form of additional strain relief on the cables at the rear of the connector. This is one of the more vulnerable spots over long-term vibration. As elsewhere mentioned as well, make sure there is a bit of slack in the cable loom - but not too much that it's flapping around.On that note, consider cable management near the connection, like cable tying it to a fixed part so it vibrates with the rest of the build rather than against it.Other solutions are available

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 07, 2020, 09:08:48 am
content: Soldering and vibration are not friends as it was stated earlier.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 07, 2020, 04:03:21 pm
content: Quote from: Wendy_Preston on August 07, 2020, 07:20:00 amNot to hijack this thread, but are those Gecko connectors suitable for board to board connections too?

author: tooki
author_rank: Super Contributor
timestamp: August 07, 2020, 07:29:52 pm
content: Well they say so right on the product page (“ideal for stacking”), so I would say “yes”.

author: Alaezae
author_rank: Contributor
timestamp: August 07, 2020, 08:58:07 pm
content: I looked at the Harwin Connectors, I like them. Definitely expensive at $20 for one of those circular connectors, but certainly in problematic areas it is something to consider. Thanks for everyone’s help, I think the main thing is mechanical support and some sort of lock. I’m still going to try and avoid solder. Thanks!

author: tooki
author_rank: Super Contributor
timestamp: August 07, 2020, 09:12:37 pm
content: If you give more info, like what kinds of wire you’re using, current capacity requirements, space constraints, etc., it might be easier to make concrete suggestions.

author: Wendy_Preston
author_rank: Contributor
timestamp: August 14, 2020, 08:07:20 am
content: Quote from: Mr. Scram on August 07, 2020, 04:03:21 pmSorry for not replying on here earlier Mr Scram, but I'm only on once a week, apologies! And yes,Geckois definitely suitable for board-to-board. We have applicable options with bothlatches and screw-loks. If you need to disconnect them at any time, latches will need side access (to reach in and press the latches), screw-loks will need rear access to unscrew. Both styles are tested forvibration and shock.If you need any help with these, do please reach out to one of ourTechnical Experts!Quote from: Alaezae on August 07, 2020, 08:58:07 pmUnfortunately Alaezae, yes, they are not the cheapest connectors on the market - they are priced to reflect the processes, development, higher level of test & inspection and quality materials that we need to utilise to make a micro-connector withstand the environments that it does. There are more expensive options available too. But seriously, we find our connectors have good traction in larger companies with planes, racing cars, medical or other vibration issues - for hobbyists and start-ups, it might not be an option unless other lower-priced options have already failed.

author: cmcraeslo
author_rank: Regular Contributor
timestamp: August 17, 2020, 09:40:37 am
content: Soldered wire-to-board connections work perfectly (tested in real life in various rough environments for many years, but have not gone to space with them). Trick is to use long enough wires so they don't stress the boards/joints and properly fix them on the board somewhere, so the only thing moving/stressing the joint is the weight of the wire from fixting point and the joint (leaded). If you have such vibrations that this method fails, then you the connectors will be the least of your worries.If you use modules that are constantly plugging/unplugging, make them with integrated wires and use a wire-to-wire connector like automotive Amphenol ATM series. We use it like that and hadnt had a failure due to the wiring.

author: max_torque
author_rank: Super Contributor
timestamp: August 17, 2020, 11:36:04 am
content: Quote from: cmcraeslo on August 17, 2020, 09:40:37 amDirectly soldering wires to a pcb is a real no-no unless you can absolutely anchour the wire to the pcb independantly of the solder joint! What i have found works is two plain holes through which the wire is threaded like a snake and then soldered to a surface mount pad, or poked into a plated through hole and soldered. Here it is critical that only just enough solder is used to anchour the conductor to the PTH, but not so much that the solder wicks up the wire! ANY solder in any bit of unsurpported wire that can flex in any way WILL result in a very early life failure.With the "wire snaked though the pcb first" trick, you can also use an adhesive to help retain the wire to the pcb, and if necessary, also probide a second set of holes through which to thread a zip tie to strain relieve the wire bundle.All of this takes up a fair bit of pcb real-estate of course

author: RJSV
author_rank: Super Contributor
timestamp: August 18, 2020, 03:09:16 am
content: Datamate Connectors, (seen in recent posts), even three of those, what quantity could you use up, in six months, or worse: how many failures are OK, in six months, say?I did testing, Systron Donner, Concord, CA. Any failure could have disabled an engine fire detection!Or, less bad, cause a false alarm, turn the airliner back to airport. Yeah, I guess I got attitude, with safety issues.Map your failures, aggravation. What if some key Engineers QUIT, over that. If it was a good subject to ask, then try spend that, out. Just monitor things.Can connectors be changed, with later package ?Or is this a less formal setting ? My job, got pretty up-tight, with 379 $ for one, Mil-spec 9 pin conn.

author: cmcraeslo
author_rank: Regular Contributor
timestamp: August 18, 2020, 07:31:11 am
content: Quote from: max_torque on August 17, 2020, 11:36:04 amExactly. This works great in real life (tested this method in all kind of motorsport applications and hadn't had a failure). Using fancy connectors with incorrect tools for crimping the cables, brings a lot more trouble than this method.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 18, 2020, 03:54:05 pm
content: You might look into the plastic circular connectors from TE connectivity. Relatively inexpensive and have most of the features that make the MIL-SPEC and very expensive connectors good. I have had good luck with them, but have not used them in a severe environment.The other thing to think about is to do what the serious players in the reliability game do - they test their approaches, both in the design phase to find weaknesses but often also in assembly/fab to weed out latent failures/manufacturing defects and the like. Some of the early work on this was gathered by a guy named Willoughby, a google search on Willoughby templates will bring up a lot of good history and material. While the details of implementation have in many cases moved on from Willoughby the concepts are good.Doing this quantitatively with calibrated vibration stands and the like is difficult and expensive. There are many traps and it requires a lot of knowledge and experience to do it right. But a qualitative form is relatively easy and can rapidly find the weak points in your approach. Something as simple as an eccentric wheel driving a platform with a couple of loose weights that can bang a bounce around can do the trick. Again, a google will find ideas and concepts. Just be aware that there are two serious risks in the qualitative approach. First, you may be under stressing your UUT, and will find more defects in the field, just as you are currently. Second, you may be overstressing, and consuming the life of your unit or outright destroying it needlessly.You can try to split the difference between the qualitative and quantitative approach by doing the instrumentation you can afford on your device in a competition. Shock sensors, accelerometers and the like. At affordable levels these will be poorly calibrated, limited bandwidth and have other problems. But they can give a rough idea of the correct environment, and you can compare that with what you see on your banging/clanking screening machine to find if you are in the right order of magnitude (or two, these things are really tough to nail down).

author: TimFox
author_rank: Super Contributor
timestamp: August 18, 2020, 04:46:23 pm
content: I like the "CPC" connectors mentioned here, especially the lower-density ones that are rated for higher voltage. The locking collars work very well.One thing to watch out for, however, is that sometimes you don't insert the barb-locked pins far enough; then they get pushed back when the connectors are mated. Test each one individually by pulling on the wire after insertion.

author: Maxoverdrive
author_rank: Contributor
timestamp: August 18, 2020, 04:56:51 pm
content: whatever the connector family you will selected , a matched crimp tool is mandatory and crimp tools are generally costly tools , that a parameter to check before to select a model of connector , other solution is hollow base with solder as MIL-DTL-26482Some mil connector as MS3111 can be very reliable they are available in true Mil specs and industrial specs which are far affordable in price .