Crimp connectors provide an easy and convenient way to connect electronics while still allowing for them to be removed and swapped without having to reach for a soldering iron and desoldering wick. While browsing one’s favorite cheap shopping site, you may get the impression that all one has to do to join the world of crimp-awesome is order a $20 crimp tool and some assorted ‘JST’ and ‘DuPont’ (a Mini-PV clone) connectors to go with it. After all, it’s just a bit of metal that’s squeezed around some stripped wire. How complicated could this be?
The harsh truth is that, as ridiculous as the price tag on official JST and Mini-PV crimping tools may seem at hundreds of dollars each, they offer precise, repeatable crimps and reliable long-term stability. The same is true for genuine JST, Mini-PV and Molex connectors. The price tag for ‘saving a buck’ may end up being a lot higher than the money originally saved.
A Cautionary Tale
Back in December of 2007, air conditioning units installed at motels and apartments began to catch on fire, seemingly by themselves. All of these AC units were manufactured by a single Texan company: Goodman Co. After multiple of reports of units catching on fire, it was deduced that it must have been faulty power cords from a new supplier: Tower.
After a recall of units with Tower-supplied power cords, the following legal battle and investigation tried to pin down the cause of the fires. Using units which had not caught on fire yet, the cause was tracked down to the flag connectors that were crimped on the stranded wires of the power cord. Due to insufficient pressure applied during crimping, spaces were left within the flag connector that increased the contact resistance.
Drawing of large amounts of current, this would thus lead to rapid heat development and ultimately fire. The Tower factory used not the specified AMP crimping machines, but improperly configured knock-off machines that created improper crimps. Here the decision by Tower to save a few bucks ultimately lost them a lot of revenue, and endangered life and property.
The essential element of a good crimp is that of plastic deformation: the natural plasticity property of the materials in question and whether this plasticity is fully used to get a solid contact, but not (destructively) exceeded or – as in this case – barely used.
What the earlier example makes clear is that you have to be very cautious about exactly what you are buying: not just the tools, but also the components. One great example here is that of knock-off connectors, which one may amiably refer to as ‘DuPont Syndrome’, after a cheap clone of a much better connector, that became better known than the original.
According to Matt Millman, Berg Electronics introduced their Mini-PV connector in the 1950s. This is a connector that might be mistaken for a ‘DuPont’ connector, but is in fact a much better connector, with a bi-metal design including a BeCu leaf spring that is still produced by Amphenol today, including for the US military and other branches of the US government.
Berg Electronics was purchased by DuPont Corporation in 1972, making it a division of the latter. This might explain why when during the 1990s cheaper, Mini-PV-inspired clone connectors began to appear (including those manufactured by Harwin with the M20), it became known as ‘the DuPont connector’, even though it is mechanically different from the Mini-PV connector.
Since then, clone manufacturers have not only began to produce their own version of ‘the DuPont’ connector, but also of JST’s offerings, including their XH, PH and other ranges. Tolerances, materials used and other specifications like coatings are hereby anyone’s guess, especially when purchased from anonymous sellers on the aforementioned cheap shopping sites.
The problem with using dissimilar metals in the connectors is that of galvanic corrosion. While this is rarely an issue in the short term, the use of differently plated connectors on a PCB and the wiring harness is likely to lead to a build-up of failures after a number of months to years, depending on the environmental conditions. Without knowing the exact specifications of the connectors and wiring used in a project, this becomes a significant risk and should absolutely be avoided when long-term reliability is important.
Squeeze Metal Not Budgets
Much like with saving a few bucks on cheap knock-off connectors, it is essential to be aware of the issues with cheap crimping tools, which come primarily in sub-par crimping results and occasionally faulty crimps that may go undetected by the untrained eye. As a case in point let’s take a look at a better-than-most crimping tool for ‘JST’ and ‘DuPont’ – which yours truly also recently obtained – and which Matt Millman reviewed and compared: the ‘Preciva PR-3254’:
As the owner of a genuine Berg/DuPont Mini-PV crimping tool, Matt was able to do a side by side comparison of both tools, as well as their crimping results. The most important detail that Matt noted is that the PR-3254 has the correct die shape, as the top of the section for ‘DuPont’ has to be an ‘O’ shape, rather than a ‘B’ shape, which is the correct shape for a JST crimping tool.
Unfortunately it’s not entirely the right shape when you look closer. The problem appears when the jaws close, the resulting space is more of an oval than the circle of the DuPont crimping tool:
While the resulting crimp is acceptable, it does crush the insulation when using AWG 24 (0.205 mm2) wire, and with AWG 28 (0.0810 mm2) wire the insulation is crimped fine, but the force on the wire itself was insufficient. This could lead to increased contact resistance and other issues.
When reviewing another budget crimping tool (IWISS SN-025) that claims to be targeting ‘DuPont’ connectors, Matt found it to be somewhat better than the PR-3254, but as usual should not be used for any critical applications. Unless one is interested in becoming another entry in the list of irresponsible manufacturers alongside the likes of Tower, it might be a good idea to pony up the cash for something like the official Harwin M20 Z20-320 crimping tool for a mere $460 new.
Features offered by these tools include such niceties as a wire stop so that you cannot insert the to-be-crimped-connector too far, as well as various guides inside the dies that help to stabilize the connector before and while it is being crimped. This has as immense benefit that each crimp is likely to be as close as perfect as possible, whereas with manual (non-ratcheted) tools and budget crimping tools there is a certain level of skill required to get even acceptable results.
The Bottom Squeeze
Perhaps the most important take-away from all of this is that before even getting into the nitty-gritty of crimp connectors and associated tooling, it is essential to understand the basics. Both to avoid getting saddled with components and tools which are not up to the task they were purchased for, but also to prevent worse. Even if it’s ‘just’ a hobby project, having some confidence in the medium- and long-term reliability of one’s crimps is very desirable.
Although crimping connectors should and can be quick and nearly effortless, having poor quality components and/or tools is sure to waste the time of anyone involved. When it comes to picking either, it all comes down to a conscious choice: get Harwin M20 Mini-PV clones, or gamble on what a random seller on AliExpress had in stock that day? Is an IWISS or Preciva tool the right choice because it’s ‘just for some tinkering’, or might a faulty crimp lead to potentially very ugly consequences?
Naturally the easy answer is to just splurge on e.g. the official Harwin, JST, and Molex parts and tools, but even if one finds the crimping tools used on EBay or so, that is still a lot of money to invest in what is likely to be ‘just a hobby’, and where failure is non-critical. As long as one is aware of the limitations of the parts and tools used, there probably is no real bad choice, other than perhaps using a disgustingly cheap crimping tool that positively mauls the connector and/or wire.
[Heading image: A whole bunch of crimping tools. (Credit: Matt Millman)]