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Practical Wiring - Professional Motorsport: Power Supply Design

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Power Supply Design

10.04

00:00 - The way we design the power supply system for our professional motorsport wiring harness does not vary in a substantial way from how we approached the task at the modified street car or club day track car level.
00:11 In fact, elements of it can often be simpler as a dedicated race car will often be completely stripped of other wiring, meaning we're no longer have to worry about interfacing to any existing electronics or harnesses in the vehicle.
00:23 Depending on the application, our power supply system may need to be capable of more advanced functions such as automatic fault finding and resetting, fault reporting and speed control of electric motors.
00:35 Our first design step is to look at our list of components and determine what needs to receive power from the 12 volt system of the vehicle.
00:42 For the EFI system this will typically be the ECU, fuel injectors, ingition coils, cooling fan and fuel pump.
00:50 Often we will have other electronic devices like an electric water pump, idle speed control solenoid, electronic throttle modules, logger, and dash displayers that also require power from the vehicle's 12 volt system.
01:03 Look at each device on your component list in detail, reviewing any documentation to determine if it will require a 12 volt supply.
01:11 Our next design step is then to run through the list of components that require 12 volt power and group them by when they require that power.
01:19 A common grouping is to have two power supply stages that are controlled by the driver of the vehicle.
01:26 The first of which, commonly called main power, contains the electronics which we might want powered up while the engine is not running.
01:33 This will include ECUs, dashes, loggers, and any other devices that we might need to communicate with in the pits when the engine is not running.
01:41 The second group we create contains the devices that need to be powered on in order for us to actually start the engine.
01:47 Commonly this is called enable power and will usually include the fuel injectors and ignition coils but may include other devices such as O2 sensor heater elements and pneumatic control solenoids.
01:59 Typically by this stage the remaining components on our list will require their power supply to be independent of other components.
02:06 Such items often include the fuel pump and cooling fans, water pump, and electronic throttle modules.
02:13 These components will usually have their power supply controlled by an ECU in the vehicle as their operation may be more complicated than simply on or off.
02:22 We might want to vary the speed of a fuel pump and a water pump in different driving conditions for example.
02:27 We'll discuss these more advanced control strategies in the actuator design section of the course.
02:32 I've mentioned electronic throttle modules in this section as their use is very common at the motorsport level and they have some particular power requirements that we need to satisfy for safety regulations.
02:43 An electronic throttle will be controlled by an electronic throttle control module.
02:47 Which may be external to or built into an ECU.
02:51 This module will have a separate power supply which needs to be controlled by the ECU so that that power supply to the electronic throttle system can be removed in an emergency situation.
03:02 All eletronic throttles have a spring within them that will default them to a closed position if their power supply is removed.
03:09 As a specific example, the Link Fury ECU which has an in built electronic throttle control module, has a separate pin which supplies power to that internal module and this must be powered from its own relay, the swtiching of which is controlled by the ECU.
03:26 With the decisions about when the components of the system receive power finalised, we now need to decide how that power will be supplied.
03:34 In a motorsport application, this will be done one of two ways.
03:38 Either using solid state relays and resettable circuit breakers for protection, or a dedicated power distribution module which bundles the switching and protection elements into one unit.
03:49 Deciding between these two options can be a little bit tricky and will usually come down to budget.
03:54 Solid state relays and circuit breakers are the cheaper option and if the power supply system does not require any complex control logic, can be a good choice.
04:02 If our power supply system is to use solid state relays as circuit breakers, the design process does not differ greatly from that described in the wiring fundamentals course.
04:11 We determine how many relays we need from the number of elements in the system that need to be powered independent of one another, and then number of circuit breakers we need by then dividing the relay outputs down into more well defined circuits.
04:24 There are two reasons we choose to use solid state relays over standard relays in a motorsport application.
04:30 The first is that their switching is performed electronically and is more reliable than the mechanical switching within a standard relay when subjected to the strong vibrations present in most race cars.
04:41 The second is that their electronic switching is much faster than a mechanical relay.
04:45 And this allows us to use a pulse width modulated input signal to deliver a varying amount of power to the connector device.
04:52 An example of this would be pulse width modulating the power supply to a fuel pump to reduce the load it places on the electrical system when its full flow is not required.
05:03 We replace traditional fuses with resettable circuit breakers as they can typically be mounted within easy reach of the driver, allowing the driver to quickly reset any that have been triggered, retrying the circuit in the case of an intermittent fault.
05:17 This may allow a disabled vehicle to get back to the pits or even continue racing if the fault is not dangerous or crippling.
05:23 Often the circuit breakers used are taken from aeronautics applications as they are engineered to be very reliable.
05:30 There are also circuit breakers available in a form factor which are a drop in replacement for a standard automotive blade fuse.
05:37 These can be a good option as they allow traditional automotive fuse holders to still be used.
05:43 If the budget allows for it, I would always recommend using a power distribution module or PDU for the power supply system.
05:50 They simplify the wiring and give much more diagnostic feedback as to the state of the power supply system at any time.
05:57 We'll have a brief look at PDUs and their benefits now but the configuration and setup of a PDU will be coverered in its own course at a later date as it can be a very complex task which we couldn't do justice to here.
06:11 You can think of a PDU as a collection of relays and circuit breakers combined into one enclosure.
06:17 The PDU will have a single, typically quite large power supply input pin or threaded stud.
06:24 It will then have one or more connectors containing its switch input and power output pins.
06:30 We wire our low current switches either driver or ECU control, to the PDU's input pins.
06:36 The PDU output pins are then wired to the parts of the EFI system that require 12 volt power.
06:42 When we configure the PDU we program the combination of inputs required to switch an output pin on.
06:49 And the maximum current that each output pin can supply.
06:53 If the current on any output pin exceeds this limit, the PDU will break the connection stopping the supply of current on that pin.
07:01 The PDU can then be programmed to retry the output pin multiple times and if the current limit is still being exceeded it will break the connection permanently.
07:10 It can then be programmed to send an error signal to the dash or display, alerting the driver to the fault.
07:16 PDUs are often capable of much more advanced functions however and their setup is a very in depth process.
07:23 Approaching the complexity of configuring the EFI control ECU at times.
07:28 As the PDU is a programmable unit, they add a lot of flexibility to our power supply system.
07:35 If the PDU has enough output pins, we can wire each of the components of the EFI system which require power to its own output.
07:42 Along with a control panel within easy reach of the driver and a selection of ECU outputs to the PDU input pins.
07:49 This decouples the decisions about when and how parts of our EFI system are to be powered, from the physical construction of the wiring harness.
07:59 The situation improves even further when we integrate network communications between the PDU and other parts of the EFI system.
08:06 We can then use signals sent along the network to control the power supply to the EFI system and this drastically reduces the number of individual wires that we require in our harness.
08:17 It also adds further flexibility to the system which can help us cater for future modifications.
08:23 Whether we use relays and circuit breakers or a PDU to distribute power to the EFI system, we need to follow the same steps outlined in the wiring fundamentals course in regards to sizing the wires and the circuit breakers or programmed current limits.
08:38 We use ohms law and the power equation to determine the current draw of our system components and then size the wires and the protecion system limits from this information.
08:49 In the motorsport world however there is another factor we frequently run up against which we need to plan for when we're sizing our wires.
08:56 And this is the size of wire that our connector pins can accept.
09:00 Often we will be using Souriau or Autosport circular connectors which are densely packed with pins of a single size.
09:09 These pins are manufactured to accept a narrow range of wire sizes and we can get into a situation where we want to pass a wire through a connector that is too large to fit inside a pin and then be crimped.
09:21 In this situation the solution is to run two smaller gauge wires in place of the single larger one.
09:27 This will take up two pin locations in the connector but it's often a tidier solution than using a second connector which could accept the larger size of wire.
09:37 Commonly the pin size in a connector will have a larger influence on our wire sizing than the current draw of the connected device.
09:45 As long as we ensure that we are always meeting the minimum power supply requirements.