Make Your Own Snap Together Electrical Connectors December 16 2013
Whoever said “consistency is the hobgoblin of small minds” never tried to build anything. Or fly a plane, launch a rocket, collect data, write code, or test a hypothesis. If you've ever tried to take apart a piece of carpentry that was put together with whatever assorted nails and screws the carpenter had on hand, you already know what I'm talking about. And usually, the one who will later have to take apart, fix, tweak, etc. your projects is you. So be kind to your future self and put things together consistently, in a way that makes them intuitive to work with in the future.
It's easy enough to standardize the physical connectors in a project (e.g. build your whole robot with just one or two sizes of nut/bolt holding it together). But what about power and electrical connections? It's obviously better in some places to have plug style connectors so you can swap out parts, reconfigure and so on without having to cut wires or heat up a soldering iron. And for consistency it's best to use the same kinds of connectors throughout your project. But, most power connectors are molded onto a cable in a factory. The only way you can put one of these connectors on the end of a cable you already have is to buy a cable with that connector on it, then cut the connector off and splice it onto your cable.
Don't build kludgey connectors like this!
There's a much cleaner solution called Powerpoles. You crimp the metal contacts onto the ends of your wires and slide them into colored plastic housings. Each housing is hemaphroditic: the resulting Powerpole can connect to any other Powerpole instead of 'male' and 'female' connectors that only connect to their opposite. Powerpoles were developed for the ham radio community, but they are useful for all sorts of applications. For Yeti Solar, we have standardized all our parts to connect with Powerpoles. The friendly, lego-looking, color-coded connectors make it easy for customers to connect whatever parts they need, even if they know nothing about electricity. More tech-savvy customers can easily add Powerpoles to other 12V gadgets to connect, hack, and mod our products. The fact that anyone can put together cheap ($0.14/contact, $0.39/housing) professional quality connectors at home, with minimal tools, has a decentralizing and democratizing effect.
The quick and dirty way
The basics are pretty simple: crimp a contact onto the end of a wire. You will need a tool with good mechanical advantage, like channel-locks. Align the contact with the housing so the little lip at the end of the contact will go over the end of the flat spring in the housing. Slide it into the housing until you hear it click (meaning it's properly seated on the spring in the housing), and use. The tongue and groove on the side of the housing means you can make multi-contact connectors with whatever configuration you need. Just make sure all of them are configured the same; for example I always slide the tongue on a positive housing into the groove on a negative. If you are just putting together a couple of Powerpoles, this may be enough.
But, if you are making a lot of them, using them in critical applications, or want to avoid trouble in the future, there are a few tricks to getting consistently good performance that I have learned by putting together thousands of them:
There is a relatively inexpensive ratcheting crimping tool called a TRIcrimp ($40) that will produce much better crimps than you can achieve with pliers/channel locks (and much easier; your tendons will thank you). Instead of squeezing the contact flat over the wire, it presses a groove into the top of the contact, thus reducing its diameter and pulling the contact tight around the wire.
This ratcheting tool makes a neat, easy crimp
If the strands of stranded wire are all parallel inside the contact, they can slide out no matter how well you crimp it. You can pull the contact off with finger strength. If instead you coil the strands into a spiral, there's an irregular surface for the crimped contact to hold on to.
Straight strands pull out easily. Spiralled strands do not.
If you are using thin wire, it's going to be loose in the contact, and it will be hard to get a good crimp. If two diameters of wire will fit in the contact, strip twice as much wire and double it back. If four diameters will fit, strip four times as much wire and double it back twice.
Fold up wire as necessary to fill the contact
It takes a decent amount of force to push the contact into the housing so it clicks. The weakest point in any Powerpole assembly is the place where the contact meets the wire insulation. It will always bend there first. Not only can this be frustrating when you are trying to slide the contact into the housing, it's also where the wire is likely to keep bending any time the connector is under stress. Eventually, it can snap through metal fatigue. And, Murphy's law states that this will happen at the worst possible time. The solution is to use adhesive lined heatshrink (also called 'double walled heatshrink') to reinforce and armour over the joint. This is essentially a DIY equivalent to the strain relief on factory-made connectors. To ensure that the contact will still fit in the housing, you should use the smallest diameter heatshrink you can (for the 15 amp Powerpole contact, use 1/8 inch diameter heatshrink). If it's a really tight fit, a tiny dab of any lubricant (even cooking oil) will work wonders.
The joint is a weak point. Armour it with heatshrink.
You can 'merge' wires at powerpole connections. Two or more wires can go in the same contact if they are thin enough (strip back about twice the length of wire that will fit into the contact so there is room to heatshrink over and still fit it in the housing). This is handy if, for example you have several wires from a component that need to be connected to ground.
Merging two wires into one contact
You can also 'fork' wires using Powerpoles. Strip the insulation off a wire in the middle, double it back and insert into a contact, then also put a contact on the end of that same wire (much faster than soldering a 2:1 connection in the wire).
First strip insulation midwire, then fold and twist.
At this point, you may be thinking it would be simpler and faster to just solder the contact onto the end of the wire rather than going through the whole process outlined above. The thing about soldering though is that stranded wire can suck up that solder like a straw, turning an inch or two at the end solid. That turns the weak point where the contact meets the wire insulation into a solid piece, which makes it much more brittle and failure prone. Plus, you can twist, crimp, and heatshrink a dozen contacts in the time it would take just for your soldering iron to heat up.
note: this article is being simultaneously published at Make Magazine