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PDM Installation & Configuration: Step 1: List System Components & Determine Power Draw

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Step 1: List System Components & Determine Power Draw


00:00 - In this worked example we're going to go through the power management system setup process for our SR86 endurance race car.
00:07 Now this is a Toyota GT86 that's become a dedicated race car for the South Island Endurance Race Series in New Zealand here.
00:16 It's fitted with a turbocharged SR20VE engine and really makes quite a lot of power and is a pretty impressive machine.
00:24 There's some really great electronics fitted to it so it's an excellent use case for a worked example to go through how we've configured the power management system in this vehicle and give you an idea about how this is set up in a race application.
00:38 Now the first part of this process is going to be to list our system components and determine their current draws.
00:44 So if we pop over to my laptop, I've got a bit of a spreadsheet open here which is listing our main electrical current draws that are going to be supplied by our PMUs.
00:55 So starting off at the top here, we've got our ignition coils.
00:58 Now our ignition coils, there's one coil per cylinder in this, we're running IGN1A smart coils, they're a really powerful grunty inductive ignition coil, well proven to applications over 1000 horsepower which we are nowhere near because this is an endurance race vehicle so we're definitely going to have enough spark energy for our application.
01:18 They do draw quite a bit of current though so I've got a steady state current limit, sorry steady state current draw, not a current limit, we'll be discussing current limits in a later section of this worked example.
01:32 But a steady state current draw list there of about 10A so we'll go through how I've come up with that figure.
01:37 Now ignition coils are not a fixed current draw device, they're not something that you turn on and then they're just constantly drawing current.
01:45 Ignition coils have what's known as a dwell period, so that is the period where you actually apply voltage across the primary winding in the coil.
01:54 Now it's a coil so current won't immediately start to flow, it will build up over that time because it's basically a pure inductor.
02:04 When you shut that current off, the magnetic field that's grown collapses through the secondary winding, generates a really massive voltage and that's where we get our spark from.
02:14 What this means is that that coil is not sitting there constantly drawing current and there's going to be sort of a different current draw depending on the engine speed.
02:23 So I'm going to size our approximated steady state current or in the worst case scenario, well not the worst case scenario but in the most extreme scenario, because we need to build the overall system to handle the engine when it's at its highest engine speed, outputting the most power under the most load, it's got to be rock solid reliable there, particularly for an endurance race car.
02:44 Now we've gone through the procedure for calculating approximated coil current draw in our wiring fundamentals course but we'll run through it just again quickly if we pop back over to my laptop again, I'm just going to bring up the calculator and we're going to use that to do just a bit of quick maths here.
03:00 So maximum engine speed we're anticipating is going to be 8000 RPM.
03:05 We're actually going to be a little bit underneath that when the engine is being run in an endurance race but once again we're sizing everything for the most extreme scenario and the engine will be tuned all the way out to 8000 RPM.
03:16 So if we're running at 8000 revolutions per minute, I can divide that by 60 and that's going to get us to 133 revolutions per second.
03:25 Now for each crankshaft revolution, there's only half a complete engine cycle so that means there's two crankshaft revolutions for a complete engine cycle so I can divide that by 2 to get us to 66.6 complete engine cycles per second and for a complete engine cycle we're going to have 4 ignition events so I can multiply that by 4 to get us to 266.6 ignition events per second on our engine here.
03:58 I'm going to round that a little bit, we'll just call it 250 and I can then take 1 second, divide that by 250, so if we take 1 and divide that by 250, we get 4 milliseconds.
04:15 So that means there is 4 milliseconds per ignition event on our engine when it's at its maximum engine speed.
04:23 Coincidentally, 4 milliseconds is around about how long we dwell an IGN1A coil for at standard battery voltage of around about 13.8 volts.
04:32 That's going to get that coil up from passing zero current up to maximum of around about 10A, so there's good data on IGN1As that you can look up on the internet and dwelling them for 4 seconds, you're going to get up to around about 10A of primary current draw.
04:47 So if I'm swelling it for 4 seconds, and there's 4 seconds per ignition event, that's kind of like I always have a coil switched on, so that's how I've come up with my steady state current draw here of 10A, sizing it for that absolute worst case scenario.
05:03 Down to our next line, we've got our injectors.
05:06 So the injectors fitted to this engine, there's actually 2 injectors per cylinder and they are an ID around about 1000cc injector, a high impedance injector.
05:17 So we can expect around about 1A of current draw per injector when it's switched on so we can call that 2A per cylinder.
05:25 So once again it's a similar math equation.
05:30 The, we're not going to call it the dwell time but the period of time that you switch the injectors on for is obviously not as constant as with coils because the amount of time that you switch them on for is going to be totally determined by the required air/fuel ratio and the operating point of the engine.
05:46 So we've got a little bit more of an approximation here but just sort of knowing these injectors and how much current they're going to draw in a pretty high demand situation, we've given that a steady state current draw of around about 5A.
06:00 We've got an awful lot of sensors fitted to this engine and included in that are lambda sensors, so we've actually got 5 lambda sensors fitted to this 4 cylinder engine.
06:09 That might seem a little strange but there's 1 lambda sensor per exhaust runner, so that's pre turbo, those are there for individual cylinder trimming, you can make sure everything's running nice and evenly.
06:22 Pretty important to make sure every cylinder is running as evenly as possible because when you're running an engine this close to the limit, any variance there really needs to be picked up on early and those 4 individual sensors in each exhaust runner are going to allow us to, will definitely give us an inkling of what's going on there.
06:40 We've then got 1 more lambda sensor that is in the exhaust collector and that one is used for the overall feedback for the modification of the fuel equation in the ECU.
06:48 Now lambda sensors can draw quite a bit of current when the heaters are on which is why for our 5 lambda sensors there we've given a steady state current draw of around about 10A.
07:00 We also have exhaust gas temperature probes in every exhaust runner.
07:05 So they are K type thermocouples, special high heat rated housings and they're coming back to a Haltech TCA8 thermocouple interface module so to read the temperature output from a thermocouple, you have to have a particular module just because of the way that the thermocouples work.
07:23 They take the tiny voltage generated by the thermocouples in response to a difference in heat and convert that into a larger voltage that can be read by our ECU.
07:33 Now this Haltech TCA8 is just a pure electronics module, it's not going to have any massive load so we've called that a steady state current draw of about 1A.
07:42 We're obviously going to need an ECU to control everything and run our engine and we've got a MoTeC M150 fitted to this vehicle so very high end ECU and it is also quite a high end application so really good unit.
07:55 Now ECUs generally speak don't actually draw a massive amount of current themselves because they primarily act as low side switches.
08:05 So they will take the current, so if we think about an injector, it will be provided 12V, in this instance by our PMU.
08:13 The other side of that injector comes into the ECU and when the ECU wants to turn the injector on, it provides it a path to ground.
08:20 So that's actually a current draw through the injector, it's not a current draw through the ECU.
08:28 That being said, in this instance, we've given our ECU an approximated steady state current draw of around about 10A which is quite high.
08:38 The reason for that is our ECU is running an electronic throttle body via an H bridge.
08:42 Now electronic throttle bodies can draw quite a lot of current when they're moving around so that's the reason we've got a 10A steady state current draw on our ECU there.
08:52 We've got a dash logger, MoTeC C125 so this is used for driver information, shift lights, we do a little bit of logging through it as well and we actually also use it as a CAN bus access point and use it as a gateway ECU to convert CAN bus traffic between different devices that don't natively want to communicate to one another.
09:14 Not a massive draw on those, I would suspect probably the back light in the LED is the largest draw on that, it's not actually doing any power switching so we've got a 2A limit on that.
09:26 Ecumaster 4x2 keypad in this vehicle as well as a CAN switchboard mounted on the steering wheel which reads the buttons and knobs on the steering wheel.
09:36 Once again, pure electronic devices, no massive current draws there so we've got a 1A draw on those.
09:43 The vehicle is fitted with a Hollinger sequential gearbox and I'm just going to make a quick change here because I've noticed that this says MME shift actuator where it's actually not, it's a Hollinger shift actuator.
09:55 So that is a actuator that is built onto the back of the gearbox that is supplied with air pressure and when you command it to, it will rack the gearbox through the gears, so this is going to let us have paddle shifting on the gearbox.
10:11 So we're going to need an air supply source for that to have air pressure in the vehicle, which we do have a compressor on our list here, we'll get to that a little bit later.
10:18 But this shift actuator itself, does have a current draw, so those solenoids are relatively powerful in the grand scheme of solenoids, so we've given them a power draw there of around about 1A.
10:33 Which is quite grunty so they're going to take that compressed air supply, switch it where it needs to go to have that actuator shift the gearbox through the gears for us.
10:42 We're running an SR20VET engine here so Nissan, as far as I'm aware never did a turbo engine of their variable valve timing SR20 motor but it is a path that people have run down and found it to be very successful and capable of making really good power quite reliably so we've gone that path as well, that does mean we have a variable valve timing solenoid that we need to apply power to as well so we've given that a current draw of around about 2 amps.
11:13 Once again that's not going to be a steady state current draw, it'll be drawing more and less current depending on whether it's changing the valve timing or holding it in a set position.
11:22 So we've based that current draw just on some experience and general knowledge around how that system works.
11:29 Now this is a turbocharged engine so we're going to need to control that boost.
11:33 So one of the actuators we've got on the engine here is a mac 3 port boost control solenoid.
11:39 We've got a current draw listed for that of around about 1A, once again, not going to be a steady state current draw, only going to be in effect when the boost is actively being controlled.
11:52 Little bit of experience around those valves, how much resistance they have in their actual switching solenoid coil and just looking at their current draw profiles from other projects over time, we've got a current draw there of around about 1A so not a massive draw on that one.
12:06 Getting down into some of the bigger draws on the system now.
12:10 So SR20 engine fitted to a GT86, it's got the SR20 alternator fitted to the engine so that means it's not a computer controlled alternator in this case like the vehicle would have originally had.
12:26 So we've got good data on that that we know its field is going to draw around about 5A of current, this is the alternator field rotor winding current which is obviously going to be only when the engine is not running.
12:40 When the engine is running, the alternator will be self supplying that current to the rotor.
12:45 Now I've written myself a note here, around about a 5A current limit but we're going to set, sorry 5A current draw but we're going to set a 15A current limit because of the wire size that is run to that alternator field.
13:00 So this is based on the alternator, the OEM wiring that was run to that alternator and it was measured somewhere between a 14 and a 16 gauge wire so we can put a current limit on that of 15A and know that that wire could pass that current all day long without a problem and if we get to that limit, we know there's an issue so we can shut that down.
13:20 We've got our starter solenoid as well because we want to have computer controlled operation of the starter motor.
13:27 Starter motor solenoids can draw quite a lot of current in the steady state mode when they're sort of holding the motor contacters together and keeping the pinion engaged with the ring gear.
13:40 They can draw quite a lot of current but they have pretty excessive in rush currents as well when they're actually moving that pinion gear into place and the contacters in the starter motor into place as well.
13:51 So we've got a steady state current draw there of around about 15A, pretty beefy in rush current expected on that one of about 50A.
14:00 Cooling is obviously going to be a really large concern for an endurance race car so we've tried to give ourself as much flexibility down the line around tuning the cooling system to cope with different situations, different tracks, different environmental conditions when we're out racing so for that reason we've gone with an electric water pump on this vehicle.
14:20 It's a Davies Craig EWP150.
14:22 Able to get some good factory documentation from Davies Craig on that one so I can actually bring that up here.
14:29 This is just a screenshot from their website but we can see they do give us a maximum current draw of 10A at 13V.
14:37 So we've got our expected current draw here of 10A, probably actually be slightly lower than that because we'll be running a slightly higher system voltage but that's the factory documentation so that's the point we're going to put that at.
14:51 When we first turn that on and that pump is spinning up to speed, we'll probably have a pretty decent in rush current, quite a grunty motor on those so we've called that in rush current, if we were to just turn it on from dead stop to dead start, of about 50A.
15:07 We're actually going to end up PWM controlling that motor to give us variable coolant flow speed but we'll get into that when we're designing our control functions a little bit later on.
15:16 Fuel system, so when we were talking about our injectors up here, we had 2 injectors per cylinder, each one being around about 1000cc delivery.
15:27 That's a lot of fuel, that's a lot of fuel for a 4 cylinder engine.
15:31 The reason for that is that we're going to be running E85.
15:35 So E85, far more knock resistant but also less energy dense so you need to inject more of it to get the same amount of energy, to get the same amount of power but you can run more advanced ignition and timing, more boost and have that engine run nice and safely without encountering detonation which is obviously what we want.
15:53 Lots of power and a nice reliable motor.
15:56 So we've got a pretty grunty fuel system setup in this vehicle.
16:00 We've got a DeatschWerks DW2000 lift pump, so that is in the tank running to a surge tank.
16:10 Now surge tanks in race vehicles, pretty unanimously used because we don't want any fuel slosh issues drawing fuel away from our main pressure supply fuel pumps so we're going to have that DW2000 supplying our surge tank there from the main fuel tank, keeping it nice and topped up and full.
16:29 And then we've got 2 DW300s inside that surge tank there which are going to be supplying the fuel rail.
16:36 Now each DW300, if you read the DeatschWerks documentation, they say is rated to 1000 horsepower plus.
16:43 I'd take that with a little bit of a grain of salt, they're definitely a super grunty fuel pump, I wouldn't be running 1000 horsepower engine on a single one of them.
16:55 In fact in this instance, we're not even going to be anywhere near 1000 horsepower, we're still going to run 2 of them because redundancy is key, particularly in our endurance race car application here.
17:07 So we've got 2 DW300s.
17:09 So I've got the factory documentation for those as well.
17:12 So this is our DW200 and for our supplying the surge tank operation, there's not going to be a lot of pressure demand on our system.
17:22 So I'm expecting this fuel pump to be running around about the 9A range down here.
17:27 Obviously the more pressure you require your fuel pump to build, the more current it's going to draw because it's going to be under more load, going to be using more power at the same voltage so it has to be drawing more current.
17:42 So I'm expecting that to be operating at around about our 9A range here.
17:46 I'd expect an in rush current of that of around about 27A, 3 times our steady state, fuel pumps have pretty impressive in rush currents but not the same as things like electric cooling fans for example.
18:04 We've got our DW300s here, so they are going to be supplying pressure, fuel pressure for this engine is going to be around about 43.5 psi, that's differential, across the injector.
18:18 So I'm expecting a current draw of between 12 and 12.5 amps here in this range.
18:26 So we expect a current draw there of 12A for each of those with an in rush of 36, once again just 3 times that 12A draw there.
18:35 Back to our cooling system.
18:38 So the key thing is as flexible and tunable as possible, we're absolutely running computer controlled thermofans on the vehicle.
18:44 Davies Craig 12 inch thermofans, used these on plenty of vehicles in the past, they're pretty well proven, nice and reliable.
18:52 So I've got the documentation for those here as well and maximum current draw, they spec it at 12V, we'd be running once again a slightly higher system voltage than this, 9A is the figure that we're going to put on those.
19:06 I've got a 45A in rush current draw on that so that's 5 times that 9A.
19:11 Radiator cooling fans are particularly notorious for really large in rush currents when they're spinning up to speed.
19:19 Absolutely the case when running them with conventional relays and fuses that they will pop a standard fuse on their in rush event.
19:28 You have to run much larger wires to them than you'd ideally like to and run a much larger fuse to get around that problem.
19:35 PMU's going to absolutely solve that for us so that's really great.
19:39 We've got 2 of them in there, so 9A each with an in rush current of 45A each.
19:46 Now I mentioned we've got a pneumatically operated sequential gear shifting system on this vehicle that's going to get us our paddles on the steering wheel controlling that shift actuator on the gearbox.
19:58 We've got to supply that system with compressed air so to do that we've gone to MME and we have spec'd out one of their air compressor and accumulator systems.
20:08 Now air compressors also are a pretty decent current draw so we're going to have to be a wee bit careful around this system in particular.
20:17 I've got the factory documentation just up here.
20:22 And if I scroll down we'll get some specs on it.
20:26 So should be able to get, yep got some current draw information here.
20:31 Now we're going to be running the system between 7 and 9 bars.
20:37 So that's quite a bit of pressure and we're going to have that be controlled by our MoTeC ECU as to when it is going to turn that air compressor on and off, it'll have a pressure sensor on the accumulator running back to our ECU.
20:52 When it gets, pressure will build up to above a certain level, it will turn the compressor off, it's going to have to fall back down quite a bit below that level to turn the compressor back on so we've got good hysteresis in there.
21:02 That does mean when our compressor turns back on, there's going to be quite a lot of pressure already in the system.
21:10 That's going to be a really large load for that compressor when we first turn it on so I'm expecting a really, pretty high in rush current event to happen in that situation so I've got those specifications there so if we were turning it on with a system pressure, say it was at 7 bar, we'd expect a current draw of around about 20 amps there.
21:33 Now I've just looked down this list and I've seen the maximum current draw we'd ever expect to see is 23A so that's actually the one I've specced here for our steady state current draw for that compressor.
21:45 Once again, just about designing the entire system to handle with the most extreme scenario, so we know it's going to handle anything that's just a little bit easier than that and then it's also going to be rock solid reliable when everything's out on the track up to temp and working really hard.
21:59 So 23A current draw there, estimate that to 25, multiply it by 4 and we've got an in rush current there of 100A so that's a really decent in rush current.
22:12 That's going to inform a lot about the wire size that we're actually going to run to our air compressor there, I'm going to be aiming for probably 12 gauge wiring of that one.
22:22 Going to be some really thick wires, likely using a Deutsch DTP connector to make sure we've got that current handling limit.
22:30 Air compressors, once again really notorious for having large in rush currents.
22:35 So we're going to have to make sure our system is capable of handling that nice and reliably.
22:40 Now I've added up all of our current draws here and we've run into a little bit of an issue.
22:46 So in the vehicle we've specced an Ecumaster PMU16.
22:51 We do have enough outputs, some of these things will actually get ganged up onto the same output so on pure output numbers wise, 16, we do have enough to run the entire system but if we add up our expected current draws, we're at 148A.
23:08 Now the maximum specified current draw for the PMU16 is 150A, that's far too close for my liking.
23:15 I really wouldn't run a system that close to the limit.
23:17 Now obviously a lot of these draws aren't going to be on all the time and we have specified everything for that most extreme scenario but that's still just too close to the limit, particularly because while PMUs are expensive, the price of fixing this problem with an additional PMU is going to be far far less than the price of going to the track and having the system fail and not being able to race.
23:46 So we are going to fix this problem with a little bit of a sledgehammer approach, in that we're actually going to put 2 PMUs into the vehicle.
23:53 Its also going to be great to show you the process of fitting 2 PMUs to the vehicle and how we're going to configure all that to work really nicely.
24:01 So that's going to give us some considerations around the design of our control functions, where inputs are hooked up to, making sure the CAN bus system can all communicate nice and reliably and how we're actually going to divide these loads up to keep them as evenly separated on our PMUs as possible.
24:18 So that should give you a good idea of the process to go through when specifying, listing out the electrical loads that are in your vehicle and determining their current draw so this is just a really early planning step, we're starting to generate our list that we're going to work from here to make sure that nothing is going to be missed and we've already spotted that one problem that we were too close to the limit of having a single PMU in the vehicle so we're going to have to have two.
24:43 So planning stages like this are absolutely something that you can perform before you have done almost any other work on the vehicle.
24:51 And all this planning upfront, although it can seem a little bit dry and tedious, is going to save you so much time and money on the back end, that I really thoroughly suggest that you get into it, even maybe going through a couple of theory practice examples for vehicles that you would love to build in the future, just to get some experience around doing it.

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