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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. |
