Strain Relief, relief

[MrAl]

Hello there,


As the title suggests, i need some relief dealing with strain reliefs

I have several devices that have wires coming out of them and the wires often have to flex in order to be used in a daily routine. One example is a computer mouse, which just broke the other day.

What happens is that inside the wire, right outside the strain relief, a tiny wire breaks and so the mouse stops operating completely. Sometimes if you bend the cord near the relief the mouse starts working again, until you let go.

Now this is no ordinary mouse, but a gaming mouse with a very high quality cord coming out of it. The cord is made out of silicone, and the wires inside each are made up out of many strands of very thin magnet wire. Still, this wire eventually broke inside the jacket, same as all the rest, it just took a while.

The mouse is now repaired (found the break and soldered it) but i need a more long term solution.

So the question is, do any of you have this same problem and if so how did you fix it?
In particular, i'd like some ideas about how to make a good strain relief. The kind that was on there was the plastic kind molded to the wire and it allows the wire to flex but only a certain amount.

Oh yeah, there is one catch too. I dont want to have to unsolder all 5 of those tiny wires inside the mouse so the proposed solution has to fit over the wire from the outside, without having to cut the wire. I know that's a lot to ask for, but here are some examples of what i have already considered...

1. Hot glue. A big blob right where the cord comes out of the mouse. Would work but might be too inflexible.

2. Silicone sealant. This would probably be nice, but would be harder to apply in a blob.

3. Spring. This makes a nice relief, but i would have to cut the wire or unsolder it, which i dont want to do. I also dont think a spring with wide enough coils to allow the wire to pass through (so it could be 'threaded' on) would be a good spring for this application. I was thinking more like a spring from a retractable ball point pen.

Any other ideas?

 

[ericgibbs]

hi Al,
This is one option, they also come in 'spiral' form.
HELLERMANN TYTON|632-01020|STRAIN RELIEF, PVC, 5.5/5.3MM | Farnell United Kingdom

HELLERMANN TYTON|HV2107-PVC-BK-T1|STRAIN RELIEF, PVC, 8/12MM | Farnell United Kingdom

If that fails, a good stiff whiskey will help with strain relief...

 

[3lectrokid]

twice a year i push the wire coming in from the mouse in very slightly so it puts pressure on a different point

 

[MrAl]

Hi again,


Eric:
Looks good. I can see using them for other things too. Down side is i forgot to mention that the cord is less than 1/8 inch diameter (0.125). I need something a little smaller i guess.

3lectro:
Nice idea there. Mine was a little different though, the cord was bonded to the original strain relief so i couldnt push it in farther. The inside of the mouse is very confined too, unlike my other mice. This one has several buttons and a wheel and it seems that their is no room left inside unless it hits something else like a switch or wheel. It was so cramped in there it took me 3 tries just to get it back together again without the cord hitting something else. What a pain.

 

[kinarfi]

Use silicone rtv and apply it at the end of the day, spit on you finger to smooth it out and let it hang over night to cure, another idea is to apply some electrical rubber tape, Scotch 130C, stretch it as you apply and taper the thickness. If NJ has Napa auto, go get some black or ultra black silicone, it seems to have a little different property than what's at the super market.
JEFF

 

[Dean Huster]

This was one of the great reasons that Atari made an aftermarket wireless (49MHz RF) control for the Atari 5200. I don't know that a lot of fine strands in each wire contributes to durability as much as it does to flexibility.

 

[Mr RB]

I think a solution needs to ensure the largest possible bend radius, as the metal fatigue is a function of; strand diameter/bend radius.

Normally the strain reliefs use a rubber tube that gets progressively more flexible as it gets longer to give a large bend radius. You could use successive layers of heatshrink tube to give a similar effect then support it at the case (thick end) with silicone.

Sometimes you can brute-force a strain relief off another cable, particularly audio and AV cables. Then if it is larger slide it over your cable. But you said you didn't want to unsolder all 5 wires so that rules out both my suggestions...

 

[MrAl]

Hello again,

kinarfi:
Thanks for the idea. That sounds like the simplest solution so far.

Dean:
Well i figure they dont want to use only one strand of small diameter, as multi strands will increase the tensile strength. A larger diameter would of course not bend as easy. Just to add a little more info, the center of each wire (the core) is a fine thread of some tough plastic maybe nylon, which increases tensile strength but doesnt help much with the bend radius problem (as MrRB outlined so well in his post).
I cant really go wireless at this point because i want to keep this mouse for a while longer, and i dont like changing batteries in the wireless mice. I had one one time and i had to replace the AA cells every two weeks or something like that. I hate that

MrRB:
Yes, that's exactly it. You've nailed it this time The gradient thickness should decrease with length, or like that anyway. This is how the spring works too in this kind of app.
I also thought about using a thin spring steel wire parallel to the mouse cord, and wrapping something like thread around the wire and silicone over that. Remember i want to get away with doing this without having to disconnect the wire. Alternately i may attempt a better solution next time it breaks ie disconnect all five wires from the PC board, but these knid of wires are a real pain to work with as they are very tiny and each one has it's own enamel coating. It can be done of course, but it's a real pain.

 

[Mr RB]

Try spiral wrap, it is pretty good at stopping small radius bending.

You can also wrap electrical tape, tapering in number of layers, and then secure it over the top with the spiral wrap.

Both thos solutions can be added without removing the cable, although I think you will still need silicone at the case.