Motorola mc micro power connector

I have designed a 3D printable plug for the Motorola MC Micro radio. The design cab be downloaded on Thingiverse here :-
https://www.thingiverse.com/thing:4457417

The design has a few close tolerance parts to ensure the pins fit well in the connector. Depending on the printer the holes may need to be enlarged or made a little smaller. The plug itself is not a snug fit inside the socket and relies on the connectors to provide the friction to hold it in place so there is a little room to enlarge or shrink it before printing but I have also made the tinkercad project accessible if anyone wishes to modify the design themselves :-
https://www.tinkercad.com/things/4f8kZqtST4c

The crimps used inside the plug are Molex 5.08mm commonly used in PC power cables as in the photo below. So you can either buy a lead and remove the pins from it or purchase the crimps separately but these can be fiddly to assemble if you don’t have a crimping tool.

I bought the crimps on ebay and crimped them myself as I didn’t want to have to join the wires. I got them from https://www.ebay.co.uk/itm/Male-Female-PC-Power-Supply-Peripheral-Connector-Crimps-Molex-PSU-5-08mm/232573051969

Selecting the correct cable for the plugs is quite critical. In order to be able to have the crimps grip and hold the insulation properly you will want cable with an outside diameter of between 1.9 and 2.5mm. That is quite small considering the radio can draw in the region of 8-9A. In that size range you could get something like https://cpc.farnell.com/pro-power/14-0-2rbcopper50m/cable-figure-8-14-0-20mm-r-b-copper/dp/CB17492 which has a cross sectional area of 0.44mm. At 8A you are going to get a voltage drop in the power cable of 0.6V per meter (reference https://www.12voltplanet.co.uk/cable-sizing-selection.html) which is going to become significant at longer distances.
This is one of the reasons that you can see in the final photo that I chose to make an adaptor lead. The length of the adaptor is kept relatively short in order to minimise the voltage drop along the thinner cable.

The first step is to check that the pin crimp fits snugly. It is not quite round and in one direction it will be a loose fit and in the other it will be tighter. This orientation gives the best fit.

There could up to around 8-9A going through the contact when transmitting so it needs to be a good tight fit. It is probably a reasonable contact but of you flatten the end just a fraction it will be a lot better. Flatten in he orientation shown below so the naturally wider part becomes a little wider.

Next crimp the connectors. Start with the pin you have just squashed and crimp the ground wire to it. I had a crimping tool and found the ‘AWG 18-22’ setting worked well as you can see in the above photo. You could use a pair of pliers but it would be difficult to get the crimp as neat and small enough to fit in the back of the plug and you would probably want to add some solder.

Put the pin in first and then the socket. When pushing in the socket connector make sure it is orientated so that the pin naturally likes to twist into the correct orientation in order to make inserting the plug easier.

When the socket is inserted it will push in most of the way and them seem to stop in the position shown below. There are small barbs on the socket and you can grip the cable just behind the metal and then push it the rest of the way in and it will be a good tight fit.

That’s it pretty much assembled. When removing the plug the pin will tend to try to pull out of the socket. This isn’t a problem but you can add a bit of glue or put on some heat shrink (the stuff with adhesive if you have it)

Finally I prefer to have the plug almost a permanent fitting so I made it into a short adapter lead with a XT30 connector at the other end so if I wan’t to disconnect the radio I can just unplug the XT30 instead.