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I need to connect a power supply to a device. The power supply provides 24V on a 2-pin Molex Mini-Fit Jr. header. The device has a 9-pin female D-Sub connector as input of which 3 pins are GND and 3 pins 24V.

My idea would be to use a 6-conductor able and crimp three conductors together into a single terminal. The conductors would be 26 AWG each (cross-section area of 0.129 mm^2); for a total cross-section area of 0.387 mm^2. I would then use a 18-24 AWG crimp terminal; which should be OK if it was a single-conductor cable.

Questions:

  • Is this the recommended approach? If not, what would you advice?
  • Should I be aware of any reliability issues? Can these be controlled or mitigated?
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  • \$\begingroup\$ Just be aware to have the crimping process be optimal, then your crimp terminal fits tight to D-sub connector to avoid heating. shouldn't be reliability issues. \$\endgroup\$
    – Fernando Baltazar
    Jul 24, 2020 at 16:19

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First let me say that at one point it was my full-time job to design cable harnesses and documentation for these, and to outsource the production to sub-contractors who specialized in manufacturing cable-harnesses.

Is this the recommended approach? If not, what would you advice?

No it is definitely not the approach I would recommend

If you pair multiple wires in one crimp terminal then you can no longer trust the holding-force specification of the crimp, nor can you be sure of the crimping resistance or current rating if you do that..

Crimp terminals might seem like a simple/primitive technology, but in reality good quality crimp terminals are meticulously designed to work with a specific type and gauge of wire.

Should I be aware of any reliability issues? Can these be controlled or mitigated?

Yes if you choose to combine multiple wires into one crimp then you absolutely need to be wary of reliability issues. And no they can not be mitigated if you use this approach, in fact I can promise you that you will have reliability issues.

The approach I prefer, and the approach that the sub-contractors I have used also preferred, is to use a solder-connector instead of a crimp connector, and solder three wires unto the same terminal, rather than trying to crimp a terminal around three wires.

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  • \$\begingroup\$ What about soldering [the three] wires into one terminal after crimping? I do this occasionally (single wires also) for added reliability. \$\endgroup\$
    – rdtsc
    Jul 24, 2020 at 11:59
  • \$\begingroup\$ I was afraid of that. Unfortunately Molex Mini Fit only has crimp terminals. That means that I will need a soldered splice somewhere in the middle to go from 1 conductor to 3. Not my preferred solution, but might be the best way forward. \$\endgroup\$
    – Andrew
    Jul 24, 2020 at 12:26
  • \$\begingroup\$ @Andrew Yes if you absolutely have to connect 3 wires to one mini-fit terminal then a Solder splice is the proper way to do it.. That said I have used mini-fit and similar connectors a lot and what I have often done in this situation is to just use a connector with more terminals and connect one wire to each terminal, then just short those connections on the pcb.. But if you are making this for a pre-existing system then you have to make do with what you've got.. \$\endgroup\$
    – user173292
    Jul 26, 2020 at 15:23
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    \$\begingroup\$ @rdtsc I would not recommend that approach, using both does not make the joint twice as good, but could easily compromise it instead.. One of the most common failure modes of these types of crimp terminals is that if the terminal is too stiff at the crimp then the wire breakes just above the crimp. Soldering the wire to the terminal would just make this type of failure even more likely. Crimp terminals are actually a fairly complex technology, and if you dont use it the way it is intended then you also dont get the expected performance. \$\endgroup\$
    – user173292
    Jul 26, 2020 at 15:35
  • \$\begingroup\$ I need/want to do the same thing (for a hobby project, not commercial production—injecting power into a run of LEDs) and I was thinking of crimping multiple wires into the power/ground pins of a JST SM connector. What solder connectors are similar size to a JST SM that I might use? \$\endgroup\$
    – Robert Atkins
    Jan 19 at 10:24

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