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Practical Wiring - Professional Motorsport: Potting Electronic Components

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Potting Electronic Components

14.52

00:00 - If we're always aiming for every extra ounce of reliability we can get with a motorsport wiring harness, occasionally we need to eliminate a sensor or actuator connector that may not be up to our requirements.
00:11 Most OEM automotive connectors will handle the heat and chemicals they may see in a motorsport application but it is the much harsher vibrations they will be subjected to that will cause them to fail.
00:23 If we cannot replace the sensor or actuator that we need to connect to with a model that has a more motorsport orientated connector, we can look at attaching our own wiring pigtail to the connector pins, potting that connection point and then installing a connector on the other end of that wiring pigtail that will withstand the conditions much better.
00:41 The term potting refers to filling a cavity or void with a solid compound to help with resistance to shock and vibration.
00:48 For our application it means that we're going to permanently attach wires to the connector pins of a sensor or actuator with solder and then pot the connector body on the device with the same epoxy compound that we used when recovering a sealed boot onto our wiring harness.
01:05 Important to check when considering undertaking this process is that the connector body on the item in question forms a sealed cup that can hold the potting compound while it cures.
01:15 Often connector bodies will have small holes at their base which will let the potting compound leak out.
01:21 If this is the case, it might be possible to seal those from the outside with some Kapton tape.
01:26 We'll have a look now at an example of a variable reluctor engine position sensor that by default accepts an OEM Sumitomo style connector.
01:35 In a high vibration environment these connectors are known to be suspect and a suspect connection on a critical sensor monitoring engine position and speed absolutely must be avoided.
01:46 The first thing I'm going to check with our variable reluctor position sensor here is that that connector body is sealed.
01:53 And I can see around the base of the sensor here there's no holes, so that is gonna form a nice sealed cup to hold our potting compound which is gonna give us our strain relief on our solder join.
02:03 You also need to make sure that you clean everything really thoroughly.
02:06 Particularly if the sensors you're using are second hand like the ones we have here are.
02:12 They were covered in quite a lot of grit and grime but brake clean and isopropyl alcohol are both really good solvents to use, get in there with some compressed air as well and you will get that nice and clean.
02:22 We're going to need to prepare the wires that we're going to solder onto our connector pins here.
02:28 In this instance because this is an engine position sensor, we're going to be using shielded cable so I have a section prepared here.
02:34 I've simply gone through and removed the outer shield jacket from a section around about 25 millimetres long at the end here and then stripped the inner conductors back as well.
02:45 Baring around about 10 millimetres of those copper conductor strands.
02:49 We're actually going to bend those copper conductor strands around to face back in the direction of our wiring pigtail.
02:56 And I'm doing this now as the next step we're going to undertake is actually to tin these and I don't want the tinning, because the solder will wick up these wires slightly, to cause a strain point right at that bend.
03:10 So I'm gonna bend these back now and get our soldering iron heating up and then we're going to tin these copper conductor strands.
03:17 We've gone through the tinning process in a good amount of detail in the wiring fundamentals course but simply the aim of the game here is to get a good coating of solder onto your individual conductor strands.
03:29 So I'm just gonna go ahead and tin these wires nicely now.
03:42 Like we've done with our wires there, we also need to tin the connector terminals on our engine position sensor here.
03:50 Now this can be a little bit tricky depending on how deep those terminals are down in the cup.
03:55 These ones are actually fairly deep so often you can need quite a slimline soldering iron to be able to get in there on one side of that terminal and get your solder on the other side of that connector pin.
04:05 Really important when you're doing this is that you do it as quickly as possible as you don't want to transmit too much heat down those connector pins.
04:14 So I'll get this process done, just simply going to hold my soldering iron in place with the bevel of the soldering iron there against one side of the connector pin, and apply solder to the other side, and do this as quickly as possible.
04:27 And you want to make sure that you avoid melting the connector body with the soldering iron as well.
04:44 Now we've got our terminals tinned and our wiring prepared and those copper conductor strands tinned, we're going to solder the two together.
04:52 Now with these copper conductor strands bent over like they are, this wiring can sit into the connector body here and it's going to be a very quick process to simply pop our soldering iron down there, reflow all that solder and make a really nice reliable connection between those points.
05:10 The sticking point with solder is that you are turning our stranded wiring into solid core wiring which is something we always want to avoid as vibration is what we're trying to mitigate here and solder connections are extremely prone to cracking from vibration.
05:25 This is where our potting is going to come in, as once we have our wires connected into the sensor here, we're going to loop them around to give us a wee bit of strain relief there and then we're going to fill that entire cavity with our epoxy compound, that's going to give us the resistance to vibration and final strain relief that we need.
05:42 So I'm going to get my wiring in place now and get those soldered onto our connector pins.
06:04 Got my wiring in place now.
06:06 I'm just going to turn my soldering iron off and move it out of the way to make sure we don't burn ourselves on it.
06:17 And we can have a look at how we're gonna loop this wiring around to make sure it's nicely strain relieved before we inject our potting compound into that connection terminal there.
06:26 What you're looking for when you're looping the wiring around in here is that you're not manipulating the point where the wires turned at a 180 degree angle where the copper conductors were exposed, but we are manipulating further up here where we still have our stranded wiring.
06:41 And essentially we just want to make sure that everything makes a couple of direction changes inside there to make sure it's nicely, gonna be nicely strain relieved and we overall, we want our wiring pigtail to be exiting the centre of that connector body.
06:57 Now in our application here, because we're using our shielded wiring, it's already nicely bundled together but at this point if you were using individual wiring, you would contain those all together with a bit of Kapton tape down near the connector body here and undertake your twisting process, just to get those wires nicely bundled together.
07:16 We're going to put a bit of DR25 sheathing onto our pigtail now and we want to get the end of that all the way down into our connector body.
07:25 As when we pot that we want the potting compound to make a connection to that DR25.
07:31 To make sure that is going to be the case, I'm going to go ahead and actually abrade the end of our DR25 shrink tubing before we've got it in place and recovered down as I'm not gonna have access to get in there once it's in place.
07:44 So I'll go ahead and get that abraded now.
07:54 With the end of our DR25 abraded there, we can get that into place.
07:59 In this instance this is 3/16th DR25 as that's gonna give us a nice shrink down onto our shielded cabling here.
08:06 So we can easily get this sheathing into place, making sure that we slide it all the way down into that connector body.
08:12 This is also going to have the added benefit of as I'm sliding it past the point where our outer jacket of this cable ends, it'll insulate the connector pins in here from any errant strands of that shield connection braid.
08:27 We have trimmed them back pretty close as you want to do, but just every extra little bit of protection you can get in there is going to be good.
08:34 Now we can get our heat gun out and recover this shrink tubing into place.
08:48 Got our DR25 sheathing recovered onto our wiring pigtail here.
08:52 Nicely abraded down this end so our potting compound is gonna make a really good strong bond to that DR25 inside the connector body.
09:01 Next part of the process is going to be getting our potting compound into place, so we're going to need to mix that up.
09:07 Once again just a scrap plastic bag like this one makes a really good mixing surface for that potting compound as it does get very very messy and does like to get everywhere so if you can mix it up, get it into your syringe and then throw out that plastic bag, you're gonna be keeping your workspace much tidier.
09:25 Need to have a wee look here and estimate the volume that we're going to be actually filling up here.
09:32 And make sure we squeeze out enough potting compound to fill that void completely.
09:38 I always err on the side of too much at this point as the potting compound isn't hugely expensive so I'm not concerned about a little bit of wasteage.
10:14 Got my syringe of potting compound ready now, we're going to get this into place into our connector body.
10:19 Before I do that though I just need to adjust the orientation of the sensor and the vice here to make sure that it is pointing directly up as we want it to form a nice sealed cup to hold that potting compound.
10:32 So we'll just get that into place, trying not to manipulate that wire too much as we don't wanna weaken any of those solder connection points.
10:39 Something you're going to need to be conscious of is keeping your wiring pigtail in the correct orientation as it's leaving your sensor body.
10:46 So in this instance we're going to be wanting it to head straight up and be central in that connector body.
10:51 To do that I'm going to use a little bit of tig filler rod here.
10:54 I'm simply going to get it in the vice in between that sensor body, but I'm only clamping very very lightly and can bend it into place next to our wiring pigtail here and cable tie those together.
11:09 With our wiring pigtail secured in place, we can get our potting compound into place.
11:14 You want to start at the bottom of that connector cup here and work your way out towards the top and that's gonna help you avoid getting any air bubbles in there.
11:53 We've got all of our epoxy potting compound in place there.
11:55 Working from the bottom up ensuring we've got no air bubbles or inclusions in there.
12:01 That's going to take around about 24 hours to completely cure so you want to leave it in this orientation for that time to make sure your wiring pigtail's going to be at the correct orientation as it exits the sensor body.
12:14 The potting compound also self levels quite well so you will end up with a nice smooth surface on the face of your connector body there.
12:22 Once our potting compound has completely cured, we are going to boot this connection point as well and that's going to give us just a little bit of extra strain relief again from our connector body here to our wiring.
12:34 We're going to be using some Raychem SCL for that.
12:36 We've given our potting compound a good 24 hours to set up now.
12:40 And it really has cured up nicely.
12:43 It's holding everything nice and tightly in place there and doing its job of ensuring that those soldered connections can't vibrate free in relation to the terminal pins.
12:53 So that's gonna be making a really good connection ensuring they're gonna be reliable for the life of this sensor.
12:59 We're now going to use a small piece of Raychem SCL to boot this connection point here, just really tidy up that appearance.
13:07 We're not looking for any sealing with this boot as such as all our sealing is being taken care of by our potting compound with our DR25 extending into that connector body.
13:17 It's really just going to tidy up the appearance and give us a little bit of extra support where this wire harness does exit that connector body.
13:25 Got a piece of Raychem SCL here and it's just the right size to fit over this connector boot quite tightly actually, but that's good as it means it's going to shrink down nice and tight and it's going to shrink down onto our wire harness branch there as well.
13:43 Additional to this, I'm making sure that when I recover this into place, it's going to recover onto a section of that DR25 that we had previously abraded, just that potting compound's gonna bite into that and stay nice and solid.
13:57 So I'll turn the heat gun on and we'll get this recovered now.
14:09 With that cooled down now, that SCL's giving us a nice booted connection there just making sure the potting compound on the inner wall of that SCL has made complete contact with our DR25.
14:19 Everything's gone nice and rigid and it really does look pretty tidy holding everything in place.
14:25 Potting sensor and actuator connector locations like this can also be a useful skill to have if you need to repair a device that's suffered minor damage to the connector body but is still serviceable otherwise.