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PDM Installation & Configuration: Working With Large Gauge Cable

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Working With Large Gauge Cable


00:00 - We've talked quite a bit about how a PMU can selectively power up and monitor the current being drawn by other electronic devices but we haven't talked about how we supply the PMU itself.
00:11 In this course module, we'll have a look at how this is usually done, the materials and tools required and the key elements that we need to be aware of to ensure a tidy, reliable result.
00:20 While each individual system that we power from the PMU might have a relatively small current draw the sum of all these individual system currents can often reach 100 or more amps.
00:30 This is the current that will be flowing into the PMU main supply connection, before it gets distributed around to all those individual systems.
00:38 As such, this main power supply cable to the PMU needs to be of sufficient size to pass this current continuously without overheating.
00:46 Linked below this module is a chart of cable size versus current handling capacity which can be used as a guide for sizing this main supply cable.
00:54 Of course in order to do this we need to know the amount of current that your system is going to draw overall.
00:59 While we'll most likely not have a 100% complete value for this, we should be able to estimate it from the components in our system as well as the information in our earlier determining current draw course module.
01:11 I would suggest to err on the side of caution here and size that main supply cable larger if possible.
01:17 The way I approach this is to size that main large power supply cable to handle the maximum input current that the PMU is specified for which will be listed in the PMU documentation.
01:28 This will give you flexibility down the line to attach more components to the PMU and know that that input supply cable will be up to the task.
01:35 There's another key factor to consider when sizing this cable and that's the physical connector that's on the PMU.
01:41 In the case of a PMU having a threaded stud connection, we'll need to source a ring terminal with the correct combination of stud mounting hole diameter and cable crimp end for our size of cable.
01:52 Almost all combinations of these are available.
01:55 In the case of the PMU having a specific connector, such as a Radlok a SureLoc or an Autosport, your choice of cable size may be defined by this connector because it'll only accept a specific size of cable.
02:07 When we build an EFI system wiring harness and we need to connect a single ECU pin to multiple locations, we can use splices within the harness to accomplish this easily and reliably.
02:19 The same is not usuallly the case when we're working with large gauge cable and we tend to rely on crimped ring terminals and bolted connections.
02:26 An example of this might be a race car with a battery mounted in the boot, the engine in the front and the PMU mounted in the middle on the transmission tunnel.
02:35 We're going to have to use a large gauge cable to make the connection from the battery to the starter motor as well as to the PMU input supply.
02:43 We'll assume in this example that the engine is a high compression V8 and the starter motor will draw a substantial current, around 300 amps at peak.
02:51 The PMU we've installed in this vehicle is an Ecumaster PMU16 which has an M6 threaded stud for that main supply connection.
02:59 In this case I'd run a 50 mm square cable from the battery to an insulated firewall pass through stud.
03:07 This stud has threaded sections on either end that the main cables can make a connection to.
03:11 50 mm square cable would be run from the battery to the passenger cabin side of this stud using crimped ring terminals at either end.
03:20 The PMU16 has a maximum input current of 150 amps so I would size and run a 25 mm square cable also from the passenger cabin side of this stud back down to the PMU in the transmission tunnel.
03:34 The engine bay side of this stud would have a 50 mm square cable, making a connection to the starter motor.
03:41 This pass through start is therefore also acting as a distribution or splice point for the main battery connection.
03:47 The reason we do this with bolted connections is that permanent splices for larger cables like this simply aren't available.
03:54 It increases the flexibility and makes the assembly of the entire system much easier.
03:58 Whenever you're making a bolted connection like this, I advise using a Nyloc nut for fastening because if this connection vibrates loose, it may start making an intermittent connection which could damage connected electronic components.
04:10 It can also lead to a lot of heat.
04:12 Another benefit of this approach is that large gauge cable with insulation rated to higher temperatures is very expensive.
04:18 And if in this instance we needed that temperature rating on the starter motor cable, it'd only have to be that shorter section from the bulkhead stud to the starter motor that's in the engine bay.
04:30 The longer run from the battery to the bulkhead would not likely be exposed to the same temperatures and could be built out of less expensive cable with a lower temperature rating.
04:38 I'll show an example now of assembling a larger gauge cable so you can get a good idea of the process.
04:43 Crimping larger gauge cables like this is always a closed barrel crimp and there are two main crimp methods for this, being an indent crimp or a hex crimp.
04:52 Whenever possible, I suggest using a hex crimp as it tends to give a tidier more symmetrical result that is easier to slide an insulating boot over.
05:00 The first thing we'll have a look at are a couple of different types of larger gauge cable that you're likely to encounter when working in this field.
05:08 I've got a section here of pretty standard single wall insulative cable.
05:14 So this is 35 mm square cable, so we've got 35 mm squared of actual copper area and we've just got one layer of insulation there.
05:24 Another section of cable I've got here is still 35 mm squared so same amount of copper in here but we've now got two layers of insulation.
05:33 Now the reason cable like this exists is it can give an indication if this cable is suffering from abrasion.
05:40 If this is mounted somewhere and it's constantly rubbing up and down on something, it's eventually going to wear through and you'd be able to see that as a white witness mark because we'd see that inner insulation poking through the abraded away outer insulation there.
05:55 Now any situation where a large gauge battery cable is going to abrade through and end up touching on a vehicle body or an engine component is actually really serious.
06:05 Large gauge cables like this are often not fused, they could be coming directly from the battery, hopefully we've got some sort of isolator in that circuit there but they can take a lot of current and they heat up very quickly and very very readily will lead to a fire at that location.
06:24 So for this reason whenever we're working with large gauge cables like this, we want to make sure that our crimped connections at the end are really solid, nothing's going to come loose and our cables are securely mounted along the vehicle, making sure they're not going to abrade.
06:37 This is the reason why I like going with firewall passthrough studs like the one we've got here as opposed to putting a gland in the firewall and running the cable through.
06:48 A passthrough stud like this, although it is a little bit of extra work to install because we need to drill the hole, make the mounting holes for the stud itself and then we've got to make the two separate cables on either side, does tend to give a tidier and more reliable result so I do suggest going with these whenever you've got to make a transition through a firewall in a vehicle.
07:08 We'll have a quick look at the crimping tool we're going to use for this.
07:11 So there's definitely a difference in scale on this crimping tool when we're talking about crimp tools that we would use for say an ECU wiring harness.
07:20 It's a much larger tool and it's going to have much larger crimp pressures at the end here.
07:25 We've got good mechanical advantage, nice strong crimp jaws and this is a hex crimp tool so it's going to crimp down nice and evenly around our ring terminal here.
07:35 You can get these in a hydraulic form as well so it's a hydraulic ram situation that you pump.
07:42 They tend to work reasonably well, the relatively inexpensive ones you can buy from the likes of Ali Express actually do quite a good job, the only real issue I've had with them is that hydraulic ram leaking over time.
07:57 Now when we're building a large battery cable like this, all our same crimping rules for a smaller scale harness still apply.
08:06 So in particular what we're going to talk about there is going to be the copper engagement length or how much of this insulation we're going to stip off to interface with our terminal.
08:15 Those same rules apply that we're going to need to strip off enough of our insulation here that we have full copper engagement.
08:24 So we want to see our copper strands here protruding all the way to the very end of the connector.
08:30 That way when we crimp this down on the barrel terminal section here, we know we're going to have a crimp into complete copper and we're going to get really good fusing there and it's going to be nice and solid.
08:40 Another concern, which is exactly the same again is that when we strip this insulation off, we don't want the end of the insulation butted directly up onto the end of our ring terminal because then when this flexes, it's going to put unnecessary strain on things.
08:56 So we want to keep a wee gap there, around about 1 mm is what I'd aim for.
09:00 We are going to use a small piece of Raychem ATUM over this that we're going to shrink down afterwards and it's going to seal everything up as well.
09:09 I've chosen Raychem ATUM in this instance because it does retain a little bit of its flexibility once it's shrunk down and that can just help that cable get a little bit more reliable in the long term.
09:19 Now the other end of this cable here, we're going to use a Radsok connector.
09:25 So this style of connector here has a large gauge terminal on it that interfaces with a particular style of terminal and you can get these in a lot of different types.
09:37 This is an insulated firewall passthrough stud so that's going to get mounted on the firewall by these 4 mounting holes, it's going to have a bolted connection on one end and then this is simply going to plug in on the other.
09:48 Now these are really quite reliable, they're a really firm connection, they're positively locking as well so when they're in place you can't actually unplug them without pressing this wee red button on the end here and then they come apart.
10:04 The other main benefit with using a connector style like this is that you get rotation of it as well and that can really help with cables coming into it from different angles and preventing strain on our larger gauge battery cables.
10:19 So really good unit, I would suggest using these whenever you're going through the firewall of a vehicle.
10:26 Right so we'll get into building this cable.
10:28 So the first thing I'm going to have to do is strip back some of our insulation.
10:32 I'm just going to check that our cable is cut nice and parallel on the end there, which it is on both ends so that's looking pretty good.
10:39 You'd want to use quite a large gauge cable cutter when you're cutting cable like this.
10:44 Smaller side cutters and stuff aren't really going to be up to the task so a larger gauge cable cutter will get you a really nice parallel cut on the end there.
10:53 So simply sizing this up.
10:57 You can get specific ring cutters for ringing these, making a circular cut around it to remove the insulation.
11:06 I've found that just a simple box cutter actually does a really good job so that's probably the way I would recommend going as opposed to shelling out for one of those ring cutters.
11:16 So I'm just going to line this up with around about 1 mm gap just between the end of our ring terminal here to where our insulation is going to end, making sure that our copper is protruding all the way to the very end of our terminal there and I'm just going to make a wee witness mark like so.
11:35 Just make a wee bit of space here so we can get things lined up with our knife here just on that witness mark and then with a setup like this if we just turn that cable against that knife blade like so, we can get a nice parallel even cut around that right in the spot where we need it.
11:58 Then if the cut hasn't gone all the way through, you can just bend this a little bit and that insulation will separate and then you can remove that section just like so.
12:08 Just a quick test fit on our terminal here, we can see we're going to get excellent copper engagement, we've got it all the way to the end of the terminal here and we've got just the right gap.
12:18 Now one thing you definitely want to do as you're getting to the point of picking up the crimp tool and actually performing a crimp like this is just take a quick step back and think about the insulation boots that are going to need to go on this cable.
12:31 Now for the first crimp on a cable like this, you sort of get a free pass because the other end is going to have nothing on it so you're going to be able to still get those boots into place.
12:43 Definitely not the case for when you're crimping on the other end of it, you've got to make sure everything's in place because there's usually not a situation you can fit those boots on afterwards.
12:51 If it's a particularly long cable as well, say running from the boot of a vehicle up to the firewall, definitely pays to pop those on now so you're not having to slide them all the way down the entire length of the cable.
13:03 So in this instance we're going to use our Raychem ATUM, we'll just leave that to one side for the moment because I'll be able to pop than on for the other end when we're done.
13:10 Just get that fitted up and we're going to do this operation, sometimes it can be really helpful to have someone hold this for you while you perform your crimp because we are dealing with quite a large weighty, hefty tool.
13:25 I've got a vice mounted here for the bench that we're going to use, that'll just make things a bit easier for us.
13:30 So on our crimp tool here we've got our hex dies in the end, so these are what are going to come together onto our terminal which will be in there and actually crimp it down.
13:42 Now we've got some numbers on these, currently this is in the 50 mm squared spot.
13:48 Now this is a terminal for 35 mm squared cable so I'm going to turn these around until we find the 35 mm squared dies right there, just do the other side as well.
14:04 Right there.
14:06 And that's going to be our first crimp operation that we're going to do.
14:11 Now when we're working with general purpose tools like these, and cable ends like these, they're not specifically designed to be used with one another because they are general purpose so what I suspect that we're going to find is that we'll crimp this down with the 35 mm dies and it's actually not going to give us quite tight enough of a crimp and I'm going to have to go down one crimp size on our tool there and re crimp this, just to get that compression that we're really going to need.
14:39 That is really normal when you're working with larger gauge battery cable like this, particularly with those hydraulic tools that I mentioned briefly earlier, they come with different dies that have all got sizes on them.
14:51 Those sizes are an excellent starting point but it's absolutely a case of performing the operation, observing and evaluating the results and iterating from there.
15:03 So we'll get our cable end here just mounted in my vice like so.
15:11 So this is what's known as a 35-8 cable end because it's for 35 mm square cable and it's got an 8 mm hole so it would go into an M8 stud.
15:22 So I've got this far enough out from my vice that I'm going to be able to get my crimp tool in just next to it here.
15:29 So we'll get my cable set up in place, making sure we're all the way to the end there and we'll crimp that down.
15:46 OK so we've got our first crimp operation completed there and you can see I've spaced it just in between this end flange here and here just on the actual barrel section here and it's not what I would call an acceptable crimp, there's not enough compression there and I would think if I was to put enough pressure on this, I'd actually be able to pull that off.
16:09 We can confirm that we've got really good copper engagement so it's going all the way past our crimp point but we're going to have to go down one die size and tighten that up.
16:18 So we'll just take our tool here and set that to 25 mm square dies like so.
16:31 Must have missed, there we go.
16:34 Just pop this back in our vice to make things as easy as possible.
16:41 And we'll crimp that down one more size.
16:44 Now when I'm doing this, I absolutely want to make sure that I am lining up the hex with the existing hex crimp that we've undertaken, so we've got that lined up there, crimp that down.
17:07 So having a look at that one there, you can see that crimp has tightened up a lot but it's actually embossed 25 which was on the back side of the jaws here so we know we've got really good compression there.
17:17 We have had a little bit of it squeeze out at the end here which is not incredibly desirable but it's not going to cause us any issues in this particular application so that's going to be essentially cold welded together now, totally compressed and there's absolutely no way that's going to come out of there.
17:34 It's going to give us perfect electrical conductivity as well.
17:37 These terminals, although they look silver, they are actually made out of copper, they're just plated, zinc plated so we do have an excellent copper to copper connection there.
17:47 Now I mentioned it earlier that we need to make sure that we get our insulative boot materials on here now so we're going to slide that into place, that's going to end up coming all the way up here over our ring terminal here so we can actually get that almost all the way into place.
18:07 Just slide that over, good tight fit so that's actually going to shrink down really nicely.
18:14 Get our other one in place as well 'cause there's going to be absolutely no chance of getting that on once our Radsok is crimped on here.
18:22 So I'll just pull that out of place.
18:25 Now key concern when we're building a battery cable like this is the orientation of the two ends.
18:31 This isn't something you really strike with EFI wiring harnesses because all the wires are very small and you're able to simply twist them but it's not the case when you're building a battery cable like this, everything's a bit larger gauge, little bit less flexible so if we were to crimp on this end in the wrong orientation and it needed to actually be 90° from there, this cable's actually going to be quite hard to twist 90° and it's probably going to end up not laying nicely like we had designed in the engine bay.
19:00 So you want to make sure you're getting that orientation correct.
19:04 Now this cable here is actually for our SR86 racecar and it's going from a firewall stud down to the starter motor.
19:11 So when we were sizing this up on the vehicle, it became apparent that we needed the flush end of this stud, so that's the end of this that's in line with the cable, needing to be offset 180° from our Radsok so we're going to assemble the cable that orientation, that's going to cause it to lay really nicely in the engine bay.
19:32 So same procedure as before, we will use our knife to mark the amount of insulation that we're going to need to strip off here.
19:41 Now although it looks like this barrel only goes to this black plastic flange here, if we look down the end, we can see that it actually goes quite a bit deeper.
19:49 So that's going to let us size, we'll strip off insulation to leave us a bit of a gap at the end here and then we'll be able to get that millimetre that we're looking for for that good strain relief.
20:02 So we'll make a wee witness mark just again where we need that to be.
20:07 And we'll get that lined up.
20:13 And remove that section of insulation.
20:27 Just like so.
20:36 Get that terminal in place.
20:38 So when we crimp this on, we definitely want to make sure that we've got that wee gap at the end there and that our orientation is going to be correct.
20:46 Now on this Radsok connector we've got a witness hole here so that is for confirming after the crimp operation has been completed that we had full copper engagement because our crimp is going to happen in this section here and if we can see copper past that, we know that that crimp has happened on the right amount of copper.
21:04 So I'm going to get this terminal mounted into our vice now, get our cable set up in the correct orientation.
21:12 My crimpers here are still set to 25 mm squared and I suspect that we're going to find the same issue with when we crimp this down is that we're going to start with our 35 mm squared because this is for 35 mm squared cable.
21:27 But looking at it, this wall thickness here, I don't think that's going to get us a completely adequate crimp so we'll likely end up back in the same spot but we will start with our 35 mm.
21:45 So we'll get our Radsok into our vice here.
21:49 Just holding it firmly, making sure we're going to have enough space here to get our crimp tool in but also making sure we're not crushing anything.
21:57 Now our cable can go in.
22:01 Get that nice and straight and then make sure that our orientation is correct.
22:06 Then one last double check at this stage that we do have our heat shrink on here for insulating afterwards.
22:12 Which we do so we are good to crimp down.
22:19 So looking at this crimp join here, it is as we expected in that it hasn't given us quite the amount of compression that we need.
22:27 I can actually still, this cable's quite firm and tight in here now but it does move around so definitely not what we're after, we're going to have to go down that extra die size.
22:36 So we'll get these set up and get that done.
22:47 So having a look at this one here now, we can see we've got really good compression, absolutely fused in there, no way it can possibly come out, we can see all of our copper strands through our inspection hole here and our inspection hole hasn't been ovalised either so we know that there's not going to be any stresses through the copper where it comes up into the plastic section here so that's going to be a really reliable join for the entire life of this cable.
23:14 We can slide our boots into place now and fire up the heat gun and get those shrunk down.
23:27 So that's our completely assembled battery cable there, going to be rock solid reliable for the life of the vehicle, nice tidy result as well, still going to plug in nicely to our Radsok, on the firewall, down to the starter motor and that's really going to look quite excellent.
23:42 So you can see that while the tooling and the size of gear that we're working with is a bit different to EFI or body wiring harness construction, the same rules and standard of work should be applied.
23:53 If you're looking for your crimped connections to be tidy and reliable so that they will last the life of the vehicle.
24:00 In this module, we've discussed working with the larger gauge supply cables required for starting, charging and power distribution supply systems.
24:08 PMU supply cables should be sized to handle the maximum specified input current of the PMU or to interface correctly with the connectors that have been supplied with the PMU.
24:19 High current supply cables that make a direct connection to the battery must always be supported along their run length to ensure that they won't be damaged by abrasion.
24:27 We use bolted joints that act as distribution points to allow us to make the required connections, as well as easing the construction and installation process.

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