PWM Fragility

[Guru]

We know that PWM cables break easily, but why? What makes them so fragile? And is there a way to just buy new heads instead of entire cables if a cable 'breaks'? We've been through 3 'broken' PWM cables, 2 of which were working properly.

[sciguy125]

What are you doing to them? We've never had any of the cables break unless they were abused or not manufactured properly to begin with. The only real problems we've actually had with them is the connector on the Victors.

[Alan Anderson]

I concur with Phil. I don't think there's anything particularly fragile about a PWM cable, and they don't "break easily" in my experience. The last one I remember failing was due to being accidentally Dremel'ed in half.

[Dave K.]

Originally Posted by Guru

We know that PWM cables break easily, but why? What makes them so fragile? And is there a way to just buy new heads instead of entire cables if a cable 'breaks'? We've been through 3 'broken' PWM cables, 2 of which were working properly.

This is what I bought to do custom cable construction and appear to be identical to the connectors IFI uses on their cables.

FCI Bergcon series connector:

65039-034, 3 pin housing
47715-000LF, female pin (there are quite a variety available, this one is for 22-26AWG, tin-lead contact, high force. Gold contacts also available.
48116-000, male pin, 22-26AWG.

Mouser has stock and good pricing.

Note that the IFI supplied ables appear to use gold plated contacts, and while I'd normally recommend that, the tin pins can work well enough for the short life that the robot will see that you can shave a few bucks on your budget by going with the cheap pins.

While the $1000 crimp tool would work well, you may find another crimp tool that will also work. I have an old Waldom tool that is designed to fold over the crimp pins in a double "U" shape that works well on the contact crimp, but not so well on the strain relief crimp. Its a bit tedious but I do trust the resulting connection.


Out of the four IFI supplied cables I tried to use this year, I have found two cables that were bad. I didn't bother to see which wire or end was bad. One was a hard fail, the other intermittent.

The likely problem is with a poor crimp rather than a broken wire, but I have yet to put them under a microscope to QA them. This sometimes occurs if the wire isn't properly stripped and the crimp gets a bit of insulation rather than copper.

The pins release from the housing quite easily by gently lifting the little plastic side latch and then pulling the wire out. If it doesn't slide out easily, the latch isn't up far enough. Use the tip of an X-Acto knife or jewler's screwdriver.

Repair may be possible with a small (i.e. 15W) soldering iron and a tiny bit of solder to bond the copper to the contact. I recommend a Metcal iron with a small tip and some 0.015" dia. solder, and using a microscope to inspect your work. My point here is that this is deft work and it takes a light touch... a little solder will go a very, very long way... don't over do it.

[Al Skierkiewicz]

Originally Posted by Guru

We know that PWM cables break easily, but why? What makes them so fragile? And is there a way to just buy new heads instead of entire cables if a cable 'breaks'? We've been through 3 'broken' PWM cables, 2 of which were working properly.

Guru,
There are several types of commercially available PWM cables. They are made with different types of wire with the really thin wires being the more fragile. Unfortunately the small wire size is not taken into consideration by the manufacturer. The types that are available with the red, white and black wires are particularly robust. You can purchase the wire, pins and blocks from Digikey and there is a slightly expensive crimp tool you want to buy. It is made by Molex and the Digikey # is WM9999-ND for about $60. This tool can crimp pins and jacks for virtually any connector with a two crimp design. (crimp over the stripped wire and then crimp over the insulation.)
I would be concerned if you have damaged more than one of the PWM cables though. Someone is being really rough. If you have experienced intermittant connections at the Victor end or the cable and thought your cable was bad, it might be that you had not fully inserted the cable into the Victor. This is a tricky operation and a fully inserted plug will have only 1/8" extending above the Victor body. It takes some experience to get it in so be patient.

[Dave K.]

Originally Posted by Al Skierkiewicz

Guru,
There are several types of commercially available PWM cables. They are made with different types of wire with the really thin wires being the more fragile. Unfortunately the small wire size is not taken into consideration by the manufacturer. The types that are available with the red, white and black wires are particularly robust. You can purchase the wire, pins and blocks from Digikey and there is a slightly expensive crimp tool you want to buy. It is made by Molex and the Digikey # is WM9999-ND for about $60. This tool can crimp pins and jacks for virtually any connector with a two crimp design. (crimp over the stripped wire and then crimp over the insulation.)
I would be concerned if you have damaged more than one of the PWM cables though. Someone is being really rough. If you have experienced intermittant connections at the Victor end or the cable and thought your cable was bad, it might be that you had not fully inserted the cable into the Victor. This is a tricky operation and a fully inserted plug will have only 1/8" extending above the Victor body. It takes some experience to get it in so be patient.

Al,

That's the one I've been using and it does make the terminal to wire crimp just fine, but the insulation gripper takes a little more patience because the terminal's fingers are a bit off axis... but it can be made to work and is certainly cheaper than FCI's $1000 tool.

The Manufacturer's part number for the Molex crimp tool is 63811-1000.

Mouser currently has them for $38, Jameco for $43, and Digikey for $51.

Thanks,

[Guru]

Thank you guys, we had this problem last year, too, but it was probably because of improperly plugged PWM cables. We were thinking of making our own cables and the info you gave us has been greatly appreciated.