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CAN Bus Communications Decoded: Splicing together new CANBus wires

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Splicing together new CANBus wires

11.10

00:00 - When we're building a new wiring harness, that's integrating CAN bus wiring into it, can be a little bit challenging.
00:06 In this module, we'll have a look at a technique that can really help us get a nice tidy and reliable result.
00:12 If you're fairly new to wiring, I highly recommend checking out our dedicated motorsports wiring course which covers splicing and everything else in between in a lot of detail.
00:22 From here on though, we'll assume you have a good understanding of the base skills involved.
00:26 First we need to think back to the discussion on CAN bus wiring in general.
00:31 In that we have a main trunk that runs through the entire vehicle and devices are connected to this trunk via shorter nodes.
00:39 Now it's time to have a look at making the connection between that trunk and those nodes.
00:45 The tricky part with splicing CAN bus wiring comes about because we're always working with a twisted pair of wires.
00:51 The key to getting a tidy result here is staggering the splices so they're not directly lying next to one another, which would create a bulky point in the harness.
01:01 Although we're going to insulate our splices, staggering them also limits the possibility of any short occurring between the CAN high and the CAN low lines.
01:09 Either open or closed barrel splices can be used with small sections of Raychem SCL used for insulation.
01:16 Your splices will always either be behind a connector or at a transition point in the harness so will be located behind a rigid booted part of the harness making sure they won't see any strain and will be nice and reliable.
01:30 I've got a fairly representative demonstration set up here.
01:33 We're going to create a small section of CAN bus wiring that's going to represent the main trunk, passing through a transition point with 2 nodes coming out of that.
01:43 So what we'd call this would be a 1 in and 3 out splice, because our trunk is going to be 1 in and 1 of those out and we're going to have 2 nodes coming off that as well.
01:55 So to show that I've got some example wire set up here, so this is pre twisted and we've got our 3 which are going to be on the outside and our 1 which is going to be on the inside here.
02:08 Now often the inside will actually be very very close to a connector body so it's quite possible that these wires won't actually be twisted because if you're placing that splice directly behind a connector body, it's going to be much easier for these sections of wire to be straight and then be pinned into the connector.
02:27 That's not going to cause any issues because those 2 CAN, the CAN high and the CAN low wires there are still very close to one another so they'll still see the same level of radiated electrical noise, so don't stress if you're performing a splice like this and you've got straight wires just being pinned into your connector.
02:45 So the first thing I'm going to do here is actually just untwist a good section of our wire, between 30 and 40 mm.
02:52 And we're just going to do that on all of these.
02:59 And then we're going to have to trim the ends of the wire to give us our stagger that we're going to need.
03:06 So then we're trimming the wires to get the staggered point where our splice is going to occur.
03:12 We've got to trim all the wires on the inside of the splice.
03:15 Inverse to those on the outside of the splice.
03:19 So that'll make a little bit more sense as I do it here.
03:22 So I'm going to start on the inside of the splice and here I'm simply going to trim our white wire which for my standard colouring scheme I have white as CAN high and green as CAN low.
03:34 So I'm going to trim the end off this white wire here and I'm going to trim around about 15 mm off because that's going to give us a good distance between our 2 splice points, they're going to be nicely staggered away from one another.
03:48 Now for all our other sections of wire here, to get those to meet up, I'm going to have to trim them the inverse so I'm going to have to trim our CAN low or our green wire.
03:58 So we'll go ahead and trim those now all the same amount.
04:13 Now we've got all those trimmed and our splices are going to meet up nicely, keeping our entire bundle nice and straight, we need to strip the insulation off the wires to give us a point to actually crimp onto that copper.
04:25 Got my Ideal stripping tool here which is excellent for the TXL wire that we're working with for this demonstration.
04:32 When I'm doing this, I might actually just need to untwist just a little bit more of that wire, just so my wire strippers have a good point to grab onto.
04:41 So we'll go ahead and get all that insulation stripped.
04:53 We've got all our wiring prepped now.
04:56 What I'm going to do is I'm going to get one of my open barrel splices installed into my crimp tool.
05:01 Now I've used 22 gauge TXL wire here so 22 gauge TXL wire has an individual CMA of the wire of 700 so all up we've got 2800 of CMA of copper to crimp together and these are, that's well within the range of the open barrel terminals I'm using here.
05:22 Talking about CMA, that's circular mill area, that's the actual area of the copper conductor strands, we do go through that in a lot of detail in our wiring course.
05:31 So we're going to get this open barrel splice installed into our tool here.
05:37 Now because I'm using our ratcheting open barrel crimp tool here, it's really nice, it'll actually hold itself in that position and that's going to keep our open barrel crimp in place and let us line up all our wires.
05:48 Splicing like this is something that would be really handy to have a 3rd hand for so if you've got a small benchtop vice or something like that, you might be able to make use of it to make the job a little bit easier.
05:57 There's a key thing we have to remember to do at this step though and that is to install our pieces of heat shrink.
06:05 Because we're dealing with twisted pairs of wire, particularly in this example on both the inside of the crimp and the outside, if we don't put our heat shrink on now we're not going to be able to tidily do that afterwards.
06:18 So I'm going to get everything lined up on our CAN high wires here.
06:24 On the outside of our crimp and then I'm going to pop a piece of our Raychem SCL over there and that's actually going to help us out as well because it's going to help keep those wires together and let you line them up to get them all into our open barrel splice.
06:45 So just holding those and squeezing them together we can get those through into our tool, double checking we've got all our copper conductors coming out the other side.
07:00 Then from this side I'm going to install our inside of the crimp.
07:06 Just double checking everything's in place there, squeeze the handles and crimp that splice down.
07:18 So looking at that, we've got a nice reliable crimp connection there, give it a bit of a tug test, I can really pull on that quite hard and it's not coming apart so that's going to be a nice reliable splice join.
07:30 We know that was going to be the case because we looked at the sizing of our open barrel terminal and we determined it was going to be correct for the size and number of wires that we're working with here.
07:40 Now it's exactly the same procedure except we're going to crimp our CAN low wires together so I'm going to install our heat shrink just here to make sure we've got that out of the way.
07:52 Get another one of our open barrel splices, just into our tool.
08:05 Get everything lined up.
08:11 And this is the point where things are actually a little bit trickier because we're performing a splice operation but we've got the rest of the wires already connected over here.
08:19 So can be a little bit tricky to maneuver your fingers around and get everything in place.
08:23 The key thing you need to be sure of though is when you've got all these wires installed into this open barrel splice and you're about to perform the crimp operation that the crimping tool isn't going to pinch any of the other wires that are in there.
08:38 So I'll just get all these in here.
08:42 Double checking everything's coming through the other side of our splice there.
08:47 Install this side.
08:54 Everything nicely lined up, when I crimp that down, the jaws of the crimp tool are going to miss all of the other wires, nothing's going to be inadvertently pinched.
09:10 So once again just having a wee look.
09:12 I've got a good reliable crimp join there that's folded over nicely, tug test, it's nice and tight and it's definitely not coming apart.
09:21 We can now slide our pieces of SCL just across those crimp joins and head over to our heat gun and recover those down.
09:46 So we've got our heat shrink recovered down there, splices are nice and tight and you can see they're staggered.
09:52 So there's no chance of any shorts between our CAN high and our CAN low wires there and it's not going to be too bulky.
09:58 Now as mentioned, joins lke this are always going to be behind a connector body, so beneath a rigid booted section or in a transition point of the harness which will also be a rigid booted section.
10:11 But you still want to keep them staggered like this as it really keeps the harness nice and slim.
10:17 As you can see, having to deal with the twisted pair does mean that the splicing is a little bit trickier but all of our same splicing rules apply.
10:24 For a professional motorsport wiring harness, I typically use 22 AWG Tefzel wire and I purchase it in a pre twisted pair.
10:33 However, the current requirements for bus wiring are very low so moving to a 24 or even 26 AWG wire is possible, provided you're working with connectors that accept these sizes of wire.
10:47 Often moving to the smaller size wire can help with the concentric layout planning as well.
10:52 For a club level spec harness, I use the same 22 AWG TXL wire the rest of the harness is mainly made up from and I twist it myself using the drill method.