How To: Safe, Reliable Electrical Crimp Connections (part 1 of 2)

We’re going to add this to the growing list of topics I never thought I’d be writing about. But it seems to need discussion quite a lot, and not just in ebike circles. I come across it frequently in the world of solar generators too, from folks who have zero experience with or initiation into the necessary skill of making extension cables. So while I am typically discussing DIY ebike topics, this subject crosses over into a whole lot of other areas.

Should I Solder or Crimp?

If you know how to do a good job of soldering, chances are pretty good you already know your answer. There’s nothing incontrovertibly bad about doing a proper soldering/wiring support job. At the same time, if you make good crimps that never fail, then there’s nothing wrong with crimping, either.

Can a case be made that either method is superior? Yes. I’m going to ignore the existence of this debate and instead focus on showing my tools and methods, which have resulted in a perfect reliability record so far. You decide for yourself if you want to go this route, or another.

What Tools Do We Need?

As is always the case, your success will be entirely predicated on using the right tools for the job. A crimping tool is not a pair of pliers for instance, regardless of the fact that you already own pliers and crimpers sure do look a whole lot like pliers.

Wire cutters

I use a dedicated set of wire cutters. Yes you absolutely can find yourself a single combined tool, or press tin snips or scissors into service if you already have those. I suggest you resist that temptation. Right tool for the job… remember? I use these, which I bought from Amazon.

You can find what amounts to the same cutters with a different label on them under about a zillion different brand names. These are actually cable cutters (not wire cutters) and they serve a good dual purpose in that they also work great for cutting bicycle brake and shifter cables (did I just violate the right-tool schtick I went on about just a second ago?). The best way to make a cut is to put the wire in their jaws and use a sharp, fast hand squeeze to snip the end off lickety-split. Trying to cut slowly and deliberately will give nothing but trouble with leftover wire strands. These bigger cutters will work especially well on the 10 gauge wire that is common on ebike controller input and battery output wires.

Wire Strippers

Here again, you want a dedicated tool. I mostly use this one, again purchased from Amazon. I also have one made by Klein Tools that is marginally better… and double the price. While I like the Klein tool a little better, reality is I use the cheapie almost exclusively. So it must not be so bad, right?

Wire crimpers

Here’s where the magic happens. Its another tool you’d be tempted to not buy and just use a pair of pliers or something, but its very important to use actual crimpers. We’ll get more into why in Part 2 when we look at making crimps.

For the most part I use a 9 3/4″ manual crimper that I bought from Home Depot. I like it because I am used to it, but its probably better to use something like this Klein Tools semi-automatic crimper. It makes a uniform crimp that is perhaps more likely to leave the outer heatshrink surface of the connector completely intact – something you have to learn how to do after some experience with manual crimpers.

While the manual crimpers have been my tool of choice for years, I have the Klein tool on order right now and we’ll see how it goes when I use it in Part 2 when we get hands-on with crimping duties.

UPDATE:
One year after the above was written, I use the Klein crimpers exclusively. Both tools do the job but the semi-auto tool does it brainlessly and would certainly be easier for a beginner to master.

End Connectors (Pigtails)

So you have your wire on one side. You need a connector of some kind on the other. For an ebike, the common choice for a battery charge connection is an XT60 female connector with a 12-gauge wire. For the battery output its typically an XT90 female connector. A larger, more power-capable version of the widely-used XT60. Better yet, instead of using an XT90, make the connector an XT90S, where the ‘S’ signifies the anti-spark feature of that otherwise identical-to-XT90 version.

The cheapest way to create connector ends is to take a soldering iron and directly attach a connector to the destination wire. But an alternative shortcut is available to folks who may not be up for that, and its ideal for folks who are crimping connections. “Pigtails” – a connector professionally pre-soldered to a short length of wire – are commonly available, ready to crimp on with very little preparatory work. I use them almost exclusively.

How much preparatory work is ‘very little’? Well on a pigtail, the bare wire ends are ‘tinned’. Essentially this means the bare wire has been dipped in solder, which makes it a single piece that cannot fray. You almost always have to snip off that end bit before you strip them. But we’ll get to that in Part 2.

Wire Connectors

All of the connectors I use are 3:1 heat-shrink adhesive ‘marine’ grade connectors. There are non-adhesive connectors (usually employing a 2:1 heat shrink ratio) which you should avoid. There are also connectors that do not employ any heat shrink at all. Same deal: Stay away from them and use only the adhesive marine grade version (unless you are an experienced hand at this, in which case there’s no reason for you to bother reading this article in the first place).

Why? Well, the heat will shrink tightly around the wire insulation on each side. This firm, adhesive grip will strengthen the connector’s bond, and support it. The adhesive liquifies under the heat and then dries, forming a strong gripping bond that ends up being stronger than the plain wire. Whats not to like about that?

While there are a variety of connector types, including spades that let you screw a wire down, or bullets that let you uncouple and re-couple a connection manually, I almost always stick to butt-end connectors that just connect a length of wire to another wire. I do any form of quick-detach connections with proper connectors like an XT60 or XT90.

There are two sorts of butt-end connectors you should know about:

Straight-thru same-gauge connectors

These are pretty straightforward: You have the same thickness of wire on both sides. Or, more accurately, the thickness of one wire is within one size of the other.

Your yellow connector works for 10-12ga wire. the blue ones work with 14-16 gauge and the pink ones work with small 18-22 gauge (thats actually three sizes). But what happens when you have a bigger difference in the wires on one side or the other? You need a special kind of connector that has a smaller hole on one side.

Step-down connectors

This is the solution for connecting two wires of different sizes that exceed the ordinary tolerance of your standard straight-thru butt end connector.

The yellow connector is ordinarily used with a 12-10 gauge wire. But notice the blue band on the left? That side has a narrower opening that accepts a wire of 14-16 gauge. The right side, banded in yellow, takes the standard-for-that-connector 10-12 gauge.

The blue step-down connector has a blue stripe on the left for its normal 14-16 gauge wire. The red stripe on the right means its suited for an 18-22 gauge wire.

Here’s a connection using same-gauge connectors:

Above at left, I’ve connected a three-prong (grounded) power cord to a power input cord on an ebike battery charger I am making. The connectors have been crimped together, but have not yet been heat-shrunk. On the right is what the adhesive connectors look like after careful application of heat from a heat gun.

Notice how the adhesive covering of the connectors has not been broken or split despite being smooshed by the crimper. This is a big deal as if you split the adhesive shrinking surface, the split will widen when it heats up and make a hole with the bare metal of the connector exposed: an uninsulated path to a live connection (more on that in Part 2).

All this wire needs need now is some adhesive heat shrink covering the entire connection to finish off the job. And yes depending on where you live thats a funny looking plug. Its a ‘Schuko’ type plug and I was making a charger for someone living in the EU.

Heat Shrink

Once we completed the crimps as seen above, we need to cover it. This is to further stabilize/support the connection and protect it. For that I am using heat shrink tubing. Once again, there are two kinds of heat shrink: 3:1 marine grade adhesive heat shrink is the best. Stay away from the thinner, less sturdy 2:1 non-adhesive stuff unless perhaps you are putting on an external layer in a pretty color – over top of the 3:1 stuff – for the sake of cosmetic appearance. I have orange, green and white 2:1 heat shrink rolls for use on cable coverings for orange, green and white bikes I have built. But its just for show.

By using the thicker adhesive version you add another significant layer of protection over your connection. If it wasn’t going anywhere before (it pretty much was already unbreakable) its completely safe and protected now with a crimp, an adhesive grip on the crimp and another adhesive grip completely over top of that.

Left (above): the same plug already illustrated, with the wire now covered in adhesive heat shrink. Without looking right at it you might miss that its not a factory-made cord. See the red/black wires? That is the bare wire on the other end of that same charger (its not the same wire).
Middle: We take the two output leads on that black/red wire and graft on an XT60 plug to connect to our ebike battery. We use blue connectors this time because of the thicker 14 gauge wire.
Right: After shrinking the connectors, we slip a long length of 3:1 adhesive heat shrink over it all to strengthen and stabilize the new connection. Job done.

A Heat Gun

This is what does the shrinking. You might be able to use a hair dryer for this job instead of a proper heat gun. And it may work.

One benefit of a heat gun is you can stand it up vertically on the garage floor, so you can use it hands-free. That gives you two hands to slowly rotate what you are heating up over it, to get a uniform effect without burning or melting stuff.

This is the heat gun I use. It has two heat settings and I almost always use it on ‘low’, which is slower but gives me lots of control over what is happening (its a lot easier to melt things than it is to un-melt them).

Quality Bulk Cable

One of the spiffs of having all this cable- and cord-making gear on hand is the ability to make just about any cord your heart desires. To do that conveniently, it will pay in the long run to buy the cable you are most likely to need in a spool. Say… 250 feet of the stuff. Thats going to seem expensive until you need a 50-foot extension for your solar panels and snip-snip-poof you have what you need in 30 minutes.

Sadly, the 250-foot spools don’t seem to be available at the time of this writing, but you can still get 100 feet of oxygen-free copper wire in 10AWG for under $1 per foot. You can spend more than this for bonded, PVC-coated wire that can take the outdoor weather and even be buried.

---

Next: Part 2 of 2. How To Do The Work, Step By Step