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

in Part 1 we introduced the topic and assembled our tools. This time, we’ll use them to make something and show how its done, step by step.

So after having gone through Part 1, we assembled our gear and have what we need to get a job done.

What are we going to do? I have an article on how to create an ultra reliable ebike battery charger (which also works as an AC charging brick for a solar generator like a Bluetti AC200P). Since I have an extra one sitting and gathering dust, we’ll make some plugs for it here. That will serve the dual purpose of giving readers of that other article a step-by-step construction guide.

What do we need to get the job done?

Everything we saw listed in Part 1. Our project device will be a Mean Well HLG320H-54A LED power supply.

The Mean Well power supply with bare wires. If purchased new retail, both ends will be stripped and tinned.

We will also need a 6-foot-long, 3-prong AC power cord with an open pigtail on the female side. Never seen one before? Don’t worry they are commonly available. Apparently a lot of construction workers tear up the cords on their power tools, so replacements are easy to find and cheap.

Lets get started.

Step 1

Size the heat shrink you will need at the very end of this process, and run it down along the wire NOW before you need it. I cannot even begin to count the number of times I have gotten wrapped up in making a cable and then realized I forgot to size and place the heatshrink for that last step. Do it now before you need to do it and before a connector is on and its too late.

The heat shrink has been added – nice and long – and you can slide it well back from the connection as needed.

Put it on the side that you can slide the furthest away from the heat gun for when we have to take that step later. You don’t want to be shrinking this one up when its out of position so it needs to be away from the heat.

Step 2

The wires on the pigtail side of the power cord are already stripped and tinned so they are easy to work with. Lets use those to teach ourselves how deep the butt end connectors are. We can trim these wires so their insulation fits right up to the edge of the metal connector insert. Once we do that, we’ll know how much we need to strip off the wires on the other side of this connection.

Dip the wire into the connector. The insulation on your wire should seat against the metal butt end connector inside. How much extra is there? Snip some off so the insulation fits right up to the end. Repeat for all three wires on the power cord.

Step 3

Next, we strip the wires that go into the other end of these butt-end connectors. The lengths we snipped down to in Step 2 give us an easy visual guide to how much we need to strip back on these wires.

A note on wire stripping: There can be a little more to it than just picking the hole that matches your wire gauge and biting in. I like to spend a little more time on the job so I don’t lose a single wire in the bundle (if I can help it).

Here’s the way I did this particular wire: I picked the 18 ga slot and was able to clamp down hard on it without damaging the wire underneath the insulation. Its a size up from where I’d get a clean, complete cut, and gave me a safe cut of maybe 80% of the insulation. Then I shifted down a size to the 20 ga slot and – very gently, clamped down on the same spot. Just a bit. While slowly spinning the cutters radially around the wire (again, just a bit). This cut the insulation without cutting any of the wires underneath. Until you get a feel for it, put the wire into a hole thats too big for it and work your way to smaller holes from there.

From there, I hand twisted the now-exposed wires so they bunch together and I’m ready for the next step.

Step 4

Crimp connectors onto the wires on the power cord. For this article I am using my new handy-dandy semi-auto crimping tool for the first time, rather than my manual commercial-grade crimper (i.e. giant pliers). The ‘semi-automatic’ part of this crimper is you just squeeze until the crimper releases, and you have a good crimp that is solid, and uniform with every other crimp you make for this job. Because of the small wire size, we can use the pink 18-22 gauge connectors.

Something to remember when you do this: While you are fumbling around the wire can slip partially or even fully out of the connector. Because of this I like to grab onto the connector with my crimper – without squishing it any just yet. Once I have it fixed in place, I use one hand to push and hold the wire end into the connector so it can’t slip back. Only then do I squeeze the bejesus out of it to make the final crimp and permanently connect the two wires.

Step 4 Complete. The semi-auto style crimper with its dual crimps was almost too big for this small 18-22 gauge connector.

Another something to remember: When doing one of these 3-wire connections, things can get awfully tight when you start finishing the connections in the next step. There may not be enough room to stuff the crimper’s jaws in between the wires to get the job done. Solve this problem by stripping enough of the plastic sheathing back from each side so you have enough open space to work with when things start getting crowded. If you can’t do that (I couldn’t here) then you’ll have extra effort in store trying to get the crimper’s jaws in the right spot while the wire stays in place inside the connector before the crimp.

Step 5

Now crimp on the wires on the other side – the charger side. This time, you have to pay close attention to which wire goes where. Since I live in the USA, our power cords do not adhere to the international standard for wiring colors. Connect:

  • The green wire on the cord to the green wire on the charger (GND)
  • The black wire on the cord to the brown wire on the charger (AC+)
  • The white wire on the cord to the blue wire on the charger (AC-)
Step 5 complete. Note the dual crimp lines on each side. The 18-22 ga crimper jaws were almost too large for this connector. You have to go right to the edge of the metal connector inside.

If you live pretty much anywhere else besides the USA, the wire colors will all match and what you connect to what will be obvious.

If you happen to screw up making one of these connections: Bite the bullet. There’s no uncrimping one of these. You have to snip off any crimped connectors at their very edge. Then snip down any wires you haven’t connected yet so they are all still the same length. Then re-strip and try again from scratch.

Step 6

Now you heat shrink the individual wire connectors. Remember the big heat shrink you put over the wire in Step 1? Make SURE you keep it well away from the heat gun while doing this. Let it get warm in the slightest and it’ll stick itself to wherever it is now, and not where you want it to eventually be.

I use my heat gun on its lowest setting, which is much slower going, but it lets me very carefully heat up my connector. I like to push the wires – and the connections – together a little, which spreads them out more or less evenly. Then I slowly rotate them around under the heat so every side of each connection gets heated up. You’ll be able to tell when you are done on each side because you will see a little bit of the internal adhesive squeeze out and form a bead on the wire. When you can see that – AND the air bubbles inside the connector disappear (this is another reason you slowly rotate while heating) you are done.

Ready to begin Step 6

Heat up each END of the connector. Stay clear of heating the center over the metal connector. That center section is where you stressed the adhesive covering by smashing the hell out of it with your crimper. If that stressed area shrinks and tears, it will expose the metal underneath, and thats a bad thing. Let the center section shrink down thanks to the indirect heat coming to it from each of the two ends. Also, if you use a manual crimper, which is much more likely to cause a tear if you are a little overzealous, then staying away from the center will let the adhesive inside liquefy and seal up the hole you created rather than spreading it open via shrinkage.

Step 7

Let the wires cool a bit. Our next step is to slide the oversized, overly long piece of adhesive heat shrink over the connection we just made. If you try and slide it over while the connectors and wires are still hot… it’ll stick to them, shrink up a touch … and you’re screwed. So walk away for five minutes and be patient.

On this power cord, I am using an extra long piece as I want this to be a strong connection. I am also using an oversized tube that will just barely shrink down to hug the power cord, which means it will be very thick once it gets to its minimum diameter. I did this because this cord is going to take abuse as its going to be pulled, coiled and stepped on. Hopefully for years (it turns out when this stuff cools after shrinking its also completely rigid, which is a good thing for protecting my connection).

Step 7 complete. That little red ring of heatshrink near the plug is just a test I did to make sure the big size I used would shrink all the way down to hug the cord.

Application of heat is the same process as it is for working the connectors. Regardless of whether or not it looks like the heat shrink has shrunk down enough to do its job, take the extra time to apply heat to the every angle of the exterior of the strip. Slowly go around all of it in even, top-to-bottom strokes. It may look like its fine halfway thru the process, but going around it and heating thoroughly it at every angle will shrink it down tight on top of the other work you just did.

And… pay attention. Keep the nozzle moving and keep it on low heat. Its a whole lot easier to melt your cord than it is to unmelt it.

And thats the end of the AC cord input side.

The Power Output Side…

We did the power input cord in step-by-step detail. We won’t need to go into that same level of detail on the output side, since its almost the identical process. But there are a couple items worth calling out.

We need step-down connectors this time

The XT60 we are using for power output is a nice beefy 12 gauge, which would need a yellow connector. The Mean Well’s power wires are 14 gauge. Thats ordinarily a blue connector. So we need a step-down (yes, I could have used a 14 gauge XT60 – I do have them in my shop – but I prefer the heavier wire).

We do the same trimming to size the wire in the connector as before. However the 12 ga wires on the XT60 have enough fudge in the 10-ga-capable wire connectors that we can leave the tinned ends on. So no need to snip them, we just take some insulation off and job done. If you can leave the ends of a wire tinned, do it and make your life easier.

Bigger connectors = more room to work with

On the 18-22ga pink connectors, we almost didn’t have enough room to work with. But with the larger yellow 10-12ga connectors that wasn’t a problem.

You can see how the crimping jaws are within the borders of the metal segment on this larger connector; ending fully to the left of the slot in the middle. Lots of room.
The connectors, after applying heat to shrink them down onto the wiring, just before having the external sheath shrunk down over them. They essentially glue themselves and the wire connection together, providing a second of three layers of stabilization to the connection.
The finished product. I used red heatshrink over the wire on the output side simply so my stock of heatshrink (red and black) gets used up at about the same rate.

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

Solder or crimp? Debate on that can be fierce. After more than 7 years of daily commute riding, I have never had a crimped connection fail. How is that reliability accomplished?

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.

A good, strong pair of industrial scissors – with tiny serrated edges on the cutting surface to grip the wire – can work in a pinch. Regular household scissors… not so much.

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 actually 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.

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.

Tinned XT90S pigtails. The green paint signifies the connector is the anti-spark variant.

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.

My box of XT60 and XT90 pigtrails, along with some pre-made extensions. Crimp two pigtails together you’ve made a cheap, short extension cord. You can see one in the center of the box (an XT60).

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?

You can find a variety of crimp-on ends. These two make up a detachable bullet connector that can be manually separated.

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.

You can buy heat shrink in little pre-cut bits, but I much prefer uncut lengths so I can snip it to exactly fit the job I am doing at the moment.

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.

For whatever reason, I don’t own a hair dryer

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).

I keep the leftmost adapter permanently on the nozzle to concentrate the heat as much as possible. This minimizes the possibility of collateral damage to nearby wiring and connectors.

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.

A quick morning’s work: A 50-foot extension out to my portable solar panels, sitting in the blazing summer sun. The short factory cable connects to a watt meter that I added to measure current, and that connects to the actual extension which leads outside to my solar panels. Created entirely from parts I already had in my garage workshop.

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