JST Connector Crimping Insanity

[Edit] Since I published this article, Tom Nardi at Hackaday wrote an article entitled “The unnecessary? Art of Connector Crimping” about my article where he pointed out that I am not the first person to come to that conclusion.  He made reference to several useful things

  1. JST is not a Connector


Last week I was using a CY8CKIT-062-BLE PSoC 6 development kit with a Digilent PMOD-HB5 connected to the PMOD port.  Specifically, I was using the PMOD HB5 as a solid state switch to drive a higher voltage, higher current than the GPIO on the PSoC 6 can drive.  In order to do this I needed to connect to the “6-pin JST connector for direct connection” which is on the right side of the board in the picture below.

Digilent PMOD HB5

But, what I might ask, is a JST Connector?  And, how might you make a connection to it.  Well, this where the insanity starts.  The first thing that you will discover is that “JST” stands for Japan Solderless Technology and that they make about 50,000 different types of connectors.  The next thing that you will discover is that all around the internet on the maker websites you will find people referring to connections as “JST” and acting like there is only one type of JST connector.  Then you will discover that there are tons of youtube videos that “show” you how to crimp JST connectors, and that most of them are absolute crap, particularly if you are 50 years old can barely see the freaking crimp connectors.  Finally, you will discover that there are a boatload of crimping tools that range in price from $10 (for a crap pair of pliers) to $500 (for the OEM JST Crimpers)

For this article I am going:

  1. Tour the common version of the JST connectors, where they are used.
  2. Consider not crimping
  3. Show pictures of a proper crimp
  4. Show some JST crimping tools
  5. Take you through my crimping procedure – which seems to work
  6. Some other videos/resources

Honestly the whole thing is pretty annoying.  The crimps are a bit hard to make and there is this inherent assumption everywhere that you should have just “known” how to do this.

I will also observe that the “JST” problem extends to some other crimp connectors including “Molex” and “Dupont” (which has a crazy history).  I will write about these other two types later on.

The JST Connector Series

Series Pitch Wire Connector Use
PH 2.0 24 JST PH Connector Digilent PMOD HB5
SM 2.5 28 JST SM Connector Adafruit Adafruit NEOLED
SH 1.0 28 JST SH Connector Spark Fun QWIIC 
XH 2.5 22 JST XH Connector Some batteries
ZH 1.5 26 JST ZH

Consider not Crimping

The first thing that I will say about the crimping process is that you should consider not doing it.  It is possible that purchase pre-crimped wires which will then easily slip inside of the connector housing to create almost any combination you might want.  Here is a pile of the the raw wires with crimps on one end:

JST PH Connector

And here are some that are pre-made into 6-pin connections.

JST Connector

A Good Crimp

So… you really want to make your own crimps?  OK.  Before I tell you HOW to do a good crimp, I want to show you what you are trying to do.  When you buy the crimp connectors, they will come on a metal strips which are meant to go through a machine that automatically crimps wires in China (obviously we are going to do it manually).

JST Connector

Each crimp connector has two sets of wings, which you will bend during the process.  One set holds the wire and the other holds the insulation.  Here is a zoom of some of the connectors where you can see the wings.

JST Connector

In the picture below you can see that there are two sets of wings.  The set in the middle crimps the raw wire.  The set that is near the strip is for the insulation.

JST Connector

Here is a picture of what we are trying to achieve with the crimp.  You can see that the inner crimp grabs all of the wires and the outer crimp grabs the insulation on the wire.

JST Connector

Once you have the wires crimped they will snap into a plastic housing that gangs them together.  In the picture below you can see that on the backside of the crimp connector there is a little piece that is bent up.  That will snap under the little plastic tab on the housing.  (it is a 2-pin housing)

JST Connector

In this picture you can see another view of the piece of metal that is bent up to grab the plastic.

JST Connector

Once you stick the crimp connector into the housing it will look something like this.  When you push the wire into the housing you will get a very satisfying little click (assuming you haven’t destroyed the crimp connector metal too much)

JST Connector

Crimping Tools

I bought a range of tools, but these tools from a Japanese company called “Engineer” seemed to be the best.  These tools are less “efficient” because you have to crimp twice, once for the wires and once for the insulation, but they seem to be easier not to screw up with.  The difference between PA-09 and PA-20 is the range of crimp sizes that you can do.

Engineer PA-20 & PA-09

I bought these two tools from Amazon for about $20… and they crimp both sets of wings at one time… but I have not had good luck with them.

IWISS Crimper

The actual JST crimper is really cool, but it had better be for $470.  I haven’t tried it because the Engineer PA-09 worked so well.  It can crimp both sets of wings at the same time and automatically positions the crimp connector to the exact right place.  But it also only works for one type of connector, in this case the JST-PH

JST WC-240

JST Connector Crimping Procedure

I would not say that my process is canonical, but it works.

(1) Start by stripping the end of your wire, then giving it a little twist.  I use a stripping tool called a “Knipex 12 42 195”.  The strip should be about 2-3mm

Knipex Stripper

(2) Then break off a crimp connector from the strand.  Hold it in your left hand and stick the wire wings into the 1.6mm section of the tool.  You want to make sure that the outer insulation wings are not in the crimper, meaning we are only going to crimp the inside wings on the first crimp.

JST Connector

Here is a picture where you can see that things are all lined up.

JST Connector

Dont crimp yet, but push down a little bit to hold the crimp connection in place while you use your left hand to pick up the wire.

JST Connector

(3) Insert the wire into the crimp connection.  The plastic insulation should end at the edge of the crimper (it should not stick into the connection).  In my experience, the insulation is too big to go into the connection and the side of the crimp tool keeps it from going in.

  JST Connector

(4) Then crimp it… and you will have something that looks like this.  You can see that the strands of the wire are under the newly folded wings… and the outer wings are still open.

JST Connector

(5) Use the end of the crimper to bend the out wings in just a little bit so that it can fit into the crimp tool.  Just make them so that they are parallel.

JST Connector

(6) Next put it in the crimp connection into the 1.9mm slot (from the other side) & crimp.

JST Connector

Now you should have a crimped connection

And here is a short video of me completing a JST Connector crimp

In my experience the thing that go wrong when crimping a JST Connector are

  1. I over crimp and bend the crap out of the connection
  2. I strip either too much or not enough wire
  3. I dont push the wire in far enough, which ends up with me not crimping insulation.