I've heard it's awful practice to conduct the spike to ground, but it would also appear recirculating it back to V+ isn't great, as that slows down closing of the solenoid.I'm not looking for a "well, it works dosen't it?" type solution. I'm looking to build a robust, effective setup.
I would place this across the coil as close to the terminals as possible!
You might look up actual data re "slows down closing of the solenoid". How slow is it?2-msec? 2-sec? As far as effective goes, probably 99% of the time [guesstimate], people just put the diode in reverse across the coil, so that should say something.
QuoteI would place this across the coil as close to the terminals as possible!Cheers for the device recommendation! I can't get close to the solenoid terminals unfortunately, these'll be a couple meters away.QuoteYou might look up actual data re "slows down closing of the solenoid". How slow is it?2-msec? 2-sec? As far as effective goes, probably 99% of the time [guesstimate], people just put the diode in reverse across the coil, so that should say something.1ms extra opening would be far, far to long in my application - that's why I'm concerned. I'm in the 1% unfortunately. I can't put the device across the coil (I should have mentioned that before!) but I can feed it back into the power supply that feeds the board before the regulators etc, as that ultimately is the same supply that feeds the external solenoids.I'm not sure if that, or conducting it to ground would be better...
Far, far too long! Check the movement speed of your solenoid. I suspect it's MANY msec longer than 1-msec. Mechanical devices tend to have a bit more inertia than electrons. Worse for bigger solenoids.
This induced voltage is called the fly back voltage. The flyback voltage is then clipped (Figure 2 Part G). This voltage level changes between manufactures and systems. The flyback voltage is adjusted for the injector design being used in the circuit. The flyback voltage is set for the electromagnetic coupling of the injector and the mechanical spring rate. The magnetic field around the injector winding is stored energy which is used to control the speed that the pintle is closing with. If the pintle is allowed to close too fast the pintle and seat will become pounded out and will begin to leak fuel. With a fast closing rate the pintle can also bounce causing extra fuel to be delivered to the engine. This extra fuel cannot be controlled accurately so the engineer must adjust the energy held within the flyback voltage to accurately control the closing rate of the injector.
This is done by using a zener diode across the PCM driver (transistor or MOSFET). See Figure 6.As the magnetic field falls back into the injector winding the energy is allowed to loop through the circuit. This allows the current to diminish at a set rate. The lower the voltage is set by the zener diode, the more energy is allowed to loop through the circuit. If a diode were used rather than a zener diode, this would let the most energy allowed loop through the circuit. A diode will allow the stored energy to loop until it reaches source voltage, in this case 12 volts. This would allow the injector the longest period of time to close. The higher the zener diode voltage, the shorter the period of time allowed for the injector to close. This is due to the energy looping through the circuit being cut off early by the voltage rating of the zener diode. If a 65 volt zener diode is used, the energy that is looping through the circuit is stopped at 65 volts which is 53 volts sooner than a diode, that allows the energy to continue to loop through the circuit until it reaches 12 volts. So the energy from a higher rated zener diode will shut off the energy looping through the circuit sooner which allows a faster pintle closing rate. Likewise, the energy from a lower rated zener diode will allow the energy to loop longer which will cause a slower pintle closing rate. This rate is set by the zener diode voltage which is matched to the injector design. The delay in closing voltage can be seen in Figure 2 Part H on page 27. Once the Pintle starts to fall through the magnetic
Also, there is so much electrical noise in an automotive environment that a bunch of EMI generated by injectorsis probably miniscule compared to everything else, especially spark plugs and ignition coils and alternators, as well as starter motors, air compressors, power steering pumps, on and on. Therefore, the manufacturers will have gone to great lengths to add protection cktry on their ECUs, on both the I/O pins, and the power and ground pins. I imagine an Arduino board would last about 3-msec in there.