JST’s PH series product page has a datasheet. On the top of page 2 it shows what the contacts look like, and has a table of all of the available contacts for their PH connector:
The largest-gauge wire the contacts are rated to fit is 24AWG, which has a cross-section area of 0.205mm². FRC CAN wire, including in REV’s cable, is 22AWG, which has a cross-section area of 0.326mm². More confusingly, the cable has two wires going into each contact, making loops off of the connector. That suggests that 0.652mm² of conductor is being crammed into a contact which isn’t even supposed to accommodate a third that much. How does it all fit in?
Probably my biggest beef with the SparkMax (the fact that without this the CAN bus is a passthrough so without this bypass style connector, the CAN connection must be plugged in to work). I wouldn’t even try to make those double crimps using my gear (and I’ve got decent crimpers).
I’ve just buy them as @Weldingrod1 suggested. They started shipping with these a while back, didn’t they?
Ugh. You don’t. JST connectors are already a royal PITA to crimp even without the loopback.
You don’t actually need both sets of wire. You can just use one set and use 3-way connectors to plug it into your CAN bus. You want to keep the length of that wire short (a few inches), but it works just fine – it’s a bus, after all, and you’re just slightly increasing the length of the drop to the bus.
The short wire that used to bridge the two pairs of contacts does look very thin, so I’d guess it’s not the same size as the main wire. Also, they do make crimp connectors for different wire sizes, so it’s possible that the ones REV is using are rated for the actual cross-section copper area that they are using. I don’t have one handy to check carefully, but these have been reliable for the team that I know best.
I’m not sure why everyone is so scared of crimping - I use a cheap Amazon ratcheting crimper, and as long as you use the correct wire gauge and die sizes, JST is not hard to crimp. It’s way harder, and more expensive, to run your own mill/lathe, 3d printer, etc.
We’re here to learn skills! Spend an afternoon and make 100 garbage crimps, and then show off your superpower of infinite JST connectors. Teach new team members, help teams in the pits, etc. I promise that it is cheaper, quicker, and more reliable than ordering dozens of JST extensions and daisy-chaining them together.
I think this gets back to OP’s original question though, they want to learn how to do it but are running into a mismatch between the manufacturers specs and what is apparently available: how is Rev putting 22awg wire into a 24awg connector? If anyone’s in touch with JST that would help clear things up.
One of our parents runs an electronics manufacturing company and brought some of REVs can wires to work to examine more closely. The crimps definitely are not designed for that much wire, and do not grip the insulation properly. We started making our own with 24ga wire and the loops attached above the JST PH crimps so we are within spec on the connector.
If you can’t make your own wires, be very careful not to put any stress on the connections.
In that case, you are my new idol. I can barely see the crimps, let alone tell if the wire is in the right place. And then trying to keep the connector properly seated in the crimper while holding the wire in place while actually crimping… Nope. Far easier to buy pre-made connectors and cut the wires to size, soldering them together if need be.
And now add getting a highschool student to sit down and do 100+ crimps for practice (plus then the actual crimps for cables you need on the robot), while being completely focused and meticulous with the job at hand…
For me, spending $2.75 per Spark (even $5.50 per if you want to account for a spare cable for every Spark) is well worth not having to make these cables ourselves.
Oh we’ve definitely had issues with the V2 CAN cables from REV in the past (wires falling out of the crimps, straight out of the packaging). We just ensure to do a tug test on each cable when we get them.
I’ve managed to remove a crimp from one of 3494’s REV Spark MAX CAN Cables and get two serviceable pictures with my toy microscope and smartphone camera.
The light-green wire is the CAN wire, and the dark-green one is the loop wire.
I see two tricks that REV used to make both wires fit into the one terminal:
The loop wire is only 26 AWG. This makes the total conductor area in the crimp 0.129mm² + 0.326mm² = 0.455mm², which is only a little more than double that of the largest single wire the contact is rated to fit, 0.205mm².
They just cram the wire in there. The conductor doesn’t seem to be the limiting factor; strands from both wires are in the crimp, and the conductor crimping barrel looks to be well-formed. Rather, the insulation is the limiting factor. There’s so much insulation that the supports can’t actually go around it all; both of them actually cut into the insulation, then poke back out before bending over a bit. (I wonder how hard it was to set up an automated crimper to insert the wires like that?) The wings are also definitely not bent over as far as they’re supposed to be, but I can’t judge how tightly they’re actually holding on to the insulation.
