Crimping JST PH Connectors (Shallow Thoughts)

Crimping JST PH Connectors

(With a cheap imperfect tool)

I've written about the several neat boards I recently ordered from Adafruit.

But when I ordered, I was confused about which connectors were which, and didn't end up ordering all the connectors I needed.

Adafruit calls the connectors they use "Stemma", and (I realized too late) they have a helpful page called What is Stemma? explaining the different connectors. I had ordered several of the small ones, "Stemma QT", more technically a 4 Pin JST SH, which were perfect for connecting a Feather board to a CO2 meter. But I hadn't realized that the bigger board, the PyPortal, needs a larger connector also called Stemma, more technically a JST PH.

It turned out to be hard to find JST PH connectors with wires already attached ("pigtails") and what I found were impressively expensive in lots of two or three. I imagine I might want a fair number of JST PH, especially the 2-connector type used for batteries. So I ordered a boxed assortment of 2, 3 and 4-pin JST PH connectors and a crimp tool.

I made sure to get a crimp tool that specifically said it handled JST PH and got good reviews despite being cheap: an SN-58B from a company called Ancwoony.

While I waited for it, I watched a few videos on JST crimping. But when the tool arrived and I tried my first few crimps, it wasn't nearly as easy as in the videos, and some of the video advice didn't work.

I'm sure the procedure is different for every crimp tool and connector, but I learned a few tips for the crimper I have.

First, although the video I was following inserted the whole metal part of the female connector into the crimp tool, that doesn't work at all with my crimp tool, because it ends up smashing the end of the connector that's supposed to receive the pin from the male connector, as well as the spring-loaded clip that holds the metal part in the plastic holder, into a solid metal mass that's good for nothing.

Second, I found that I couldn't squeeze the crimp tool all the way (to where the jaws unlock), because that somehow ended up cutting the wire. The result looked like a good crimp, but as soon as I inserted it into the plastic, the first time the wire is wiggled it breaks right off. I thought at first that I had cut the wire when I stripped it, but I was using stranded wire and it's pretty obvious when you've cut too close with the stripper on stranded wire, and it happened repeatedly even when I was super careful with the stripper.

But then I discovered that my crimping tool was adjustable! I moved the adjustment dial two clicks toward - and the problem went away.

Here's the procedure that worked:

Strip a very small amount of insulation from the wire, just a couple of millimeters.

Set up appropriate magnification: I use a couple of pairs of high-mag reading glasses because that's the only way my old eyes can see anything that close and that small.

Holding the metal connector by the end that will eventually receive the pin from the male connector (the end with the spring clip on it), insert the connector into the stripper partially, making sure that the spring clip is still outside the crimper. Insert it just barely enough that the part that should crimp around the wire is inside the tool; you don't want to crimp anything beyond that point — in contrast to what web videos show.

(If you look carefully at the inside of the tool's jaws, you can see that it has two parts side by side, one of which is a little smaller than the other. This is supposedly so that the larger side crimps around the insulation, while the smaller side crimps directly onto the exposed wire. Nice theory, and that's what the videos all said, but that doesn't work with JST PH and my crimping tool, because if you insert the connector far enough that the insulation part is past the middle of the jaws so that it's on the side with the larger crimp, the other end of the connector, the part with the spring clip and the pin receiver, will be inside the smaller crimp area and it will be destroyed when you close the jaws. A tool that's actually well designed for JST PH would probably have jaws half as wide as this tool, but I don't know how you find out something like that before mail-ordering one.

I hold the connector in my left thumb and index finger, the crimper in my right hand with the jaws pointed straight at me. The open jaws on the connector that will wrap around the insulated part of the wire should point up, and the bottom of the connector will be resting on the protruding, concave upward, smallest tooth of the crimper.

Once it's lined up nicely, close the crimper a couple of clicks, just enough that it barely holds the connector in place (it will still be quite loose). The point of keeping it loose is that it lets you see a little bit of the connector between the teeth of the crimper — so when you insert the wire, you'll be able to see the end of the insulation. If you close the jaws too far to begin with, you'll have to guess how far to insert the wire.

Take hold of the crimper handles with your left hand. With your right hand, carefully insert the wire, jiggling it so that the end of the insulation is just about at the left edge of the part of the connector that needs to wrap around it.

When the wire insulation is in the right place, gently squeeze the handle the rest of the way. (Before I found out the tool was adjustable, this step involved carefully feeling the point where the resistance increased, and not going beyond that point.)

When crimping to larger wire, it may be difficult to get the insulation into the jaws of the connector and you might have to wiggle it a little and move it up toward where the jaws of the connector are the most open. But if you do that, it works even with fairly fat insulation.

It's still a fiddly process, mostly because those metal pieces are so darn small! But I've made several connectors now, and I'm pleased with the end result.

Tags: hardware, maker, electronics
[ 13:34 Dec 14, 2025    More hardware | permalink to this entry | ]