Strain Relief for Small Wire Connectors

Question

I am working on a project where we are using 28 - 30 AWG wire with the Molex picoblade and Molex picolock connectors. Does anybody have any recommendations for strain relief for wires and connectors that are very tiny? The wires themselves should not expect any strain, but the device itself will be moving, and I'm worried about possible reliability issues if the wires are flexed near the connector.

I've already popped out a bunch of wires just connecting and disconnecting the connectors. (During actual use, the connectors should never need to be disconnected).

Thanks.

If the connectors never need to be disconnected, can you cover them with hot glue? — tcrosley, Oct 19 '15 at 17:55
That is odd that you have wires popping out. Do you mean the wires are coming out of the crimp contact? I've never had this issue with properly crimped picoblade connectors. One thing I have done on a board before is drill 2 small holes on the board with the connector, and tie the wire down with bare wire. It's nothing fancy, but worked for the strain relief I needed on 3 conductor 26 AWG wire. I use hot glue as tcrosley mentioned when I'm making test wiring that should never be unplugged and receives lots of abuse in manufacturing. — I. Wolfe, Oct 19 '15 at 19:31
@I.Wolfe I added two pictures to the question which show what I mean by the wire coming out of the connector. It looks to me like the wires are breaking right at the point where they meet the connector (and there is still part of the wire left in the crimp insert when this happens). I tried tcrosley's solution of adding hot glue this morning, but it looks to me like the issue will remain just now at the location where the wire meets the glue. I have ordered some silicone to try the same idea with a material that is less hard than the hot-glue. — Skaevola, Oct 19 '15 at 20:12
Ah yeah, the AWG of the wire is so small that the strands break under the strain too easily. You need to secure the wire somehow, behind the connector. Hot glue should work. The issue is that the wire is breaking where the insulation is stripped, so the strands are the only thing taking the strain. If you hot glue the wire back away from the connector so the strain is on insulated wire instead, it should help stop this issue. The only other method I can think of would be to tie the wire down somehow. So you would plug the connector in, and then tie the wire to whatever the connector plugs into — I. Wolfe, Oct 19 '15 at 20:16
End goal is to get the strain on the insulated portion of the wire, and away from where it crimps into the contact. Where it crimps into the connector, it has NO insulation, and is therefore much weaker, since it only has some really thin copper strands holding it in place. If you put up picture of the hot glue job, I could tell you if it looks good. — I. Wolfe, Oct 19 '15 at 20:21
@I.Wolfe A variation on I.Wolfe's method is to drill through the pcb and loop a thin tie wrap/zip tie through the board and around the bundle. This has the advantage of easier field/workshop repair. But really your best ootion is to switch to a connector with in built strain relief. — BenG, Oct 19 '15 at 20:51
Are you using a legit crimp tool, which should grab insulation as well as conductor? My experience with the smaller Molex pin inserts is that you have best success using the right tool for the right job. — Scott Seidman, Oct 19 '15 at 21:48
@ScottSeidman I am using the proper crimp tool and the connector inserts are grabbing the insulation when I crimp them. — Skaevola, Oct 20 '15 at 14:44
@BenG do you have any recommendations for small connectors (~1mm pitch) that have built in strain relief? — Skaevola, Oct 20 '15 at 14:45
@Skaevola Specific product recommendations are against the rules. But looking at the crimp terminals you have linked. They really should be fine. If the insulation is gripped properly. ie physically deformed by the wings when they fold around there should be no stress at all on your bare strands. It may be your crimper is faulty? If it is not crimping hard enough try using a pair of needle nose to finish it off. As a stress test you can do one wire and suspend it from the crimp pin with a weight tied on the other end and swing it like a pendulum. If it survives you shoukd be ok. — BenG, Oct 20 '15 at 22:12
also. can you take a close up picture of a crimped wire outside the connector? — BenG, Oct 21 '15 at 01:25

score 2 · Answer 1 · answered Oct 21 '15 at 22:33

Wires often break the way you show if they are not properly crimped. This can create a pinch point near the edge of the crimp and cause them to break easily. Are you using the correct Molex Picoblade crimper with the correct AWG pins and wire? Is your strip-length correct? Is the wire insulation diameter small enough to be captured by the crimp? (I am having this problem presently)

One thing I like to do is braid or twist the wires making more of a cable. This helps the strands act as a larger, stiffer piece of cable rather than a bunch of tiny wires.

score 1 · Answer 2 · answered Oct 21 '15 at 21:37

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I would get some water thin cyanoacrylate(crazy glue) and put a drop in each connection. It is non-conductive and should not corrode the wires but will bind them to the casing fairly well.

The advice above about better crimping should be taken. If done right you should not need the glue.

answered Oct 21 '15 at 21:37

HighInBC

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Though if doing that be careful the glue doesn't get wicked down into the connector and on to the contacts. A cold-melt glue gun would probably better than CA as it won't which into the contacts and is more flexible (CA dries solid so isn't brilliant for strain relief). – Tom Carpenter Oct 22 '15 at 01:27

Strain Relief for Small Wire Connectors

2 Answers2