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Wiring Fundamentals: Pulsed Solenoids

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Pulsed Solenoids

03.10

00:00 - As mentioned in the electrical fundamentals section of the course, almost all the actuators we control in an EFI system are inductive to one degree or another.
00:08 One way we can take advantage of this inductance is with pulse width modulation.
00:13 Pulse width modulation is a method of providing a variable amount of power to an actuator.
00:18 Instead of only being able to have the actuator completely off or completely on, we can control it with more precision.
00:25 The way we pulse width modulate an actuator is to apply power to it and then remove it continually very quickly.
00:33 If we do this fast enough, the actuator will no longer be able to determine when it is powered and when it isn't, and we'll just see a lower level of power being supplied overall.
00:42 There are two main variables to consider when using pulse width modulation.
00:45 The first is the switching frequency.
00:47 This is how often we switch the power on and off to the device we're controlling.
00:52 We express this speed as a frequency or number of times per second.
00:56 A great example of pulse width modulation is a boost control solenoid.
01:01 It's typical to pulse width modulate these at a frequency of 20 hertz.
01:04 This means we're switching the power on and off to the device 20 times every second.
01:09 The second variable to consider when pulse width modulating an actuator is the duty cycle.
01:14 This is the ratio of time we spend applying power to an actuator versus the time we spend with the power disconnected.
01:21 If we look at our boost control solenoid example again, we're pulse width modulating a solenoid with a frequency of 20 hertz, or switching it 20 times per second.
01:31 This means every second is broken up into 20 50 millisecond time intervals.
01:36 If we look at just one of these 50 millisecond time intervals, we could choose to have the device powered for 25 milliseconds and then unpowered for the remaining 25 milliseconds.
01:46 This would be a duty cycle of 50% as half the solenoid's time is spent powered and the other half is spent unpowered.
01:54 If we then change the duty cycle to 10%, we would now power the solenoid for five milliseconds, and leave it unpowered for the remaining 45 milliseconds.
02:04 Wiring an actuator for pulse width modulation is usually no different than any other actuator.
02:09 We supply power to the actuator from our power supply circuit and use the ECU output channel as a low side switch to provide the ground connection.
02:17 However you need to ensure the ECU output channel the actuator is connected to is capable of pulse width modulation.
02:23 Your ECU documentation will have this information.
02:26 It's not unusual for multiple ECU output channels to support pulse width modulation but at different switching frequencies.
02:34 We've discussed a common example of switching a boost control solenoid at a frequency of 20 hertz.
02:39 But there are other actuators you may want to switch faster than this.
02:43 The actuator documentation will provide you with its optimum switching speed which you will need to ensure your ECU is capable of.
02:50 Most actuators we want to pulse width modulate are low current devices, and can be wired to the ECU output channel directly.