I'm powering a solenoid from a battery, so I want to spend the minimum amount of power to get the job done. In this case the solenoid doesn't even have a return spring, so as soon as the armature has moved a couple of millimeters, the job is done. Can I measure the current draw or another electrical property to see when the armature has moved? I haven't been able to find a plot of how the current draw behaves in response to a step voltage.
As I understand it, the inductance of a solenoid's coil changes significantly as the armature moves. If it doesn't result in a clear change in the current draw as I feed it DC (or a falling voltage from a charged capacitor), would it be feasible to measure the momentary inductance by modulating the supply current with some AC signal?
If all this fails, I can certainly fall back to driving it with just a timed pulse and experimenting to see what the required time is.
Best Answer
The energy you need for the move of the solenoid core depend on several factors, such as:
As you see there are too many variables and these could be voltage and temperature dependent.
Thus a feedback is needed to signal that the move is accomplished. This could be a reed or Hall-switch or optical switch and could be quite an effort and maybe if you can define the maximum force needed it is simpler to have a driver circuit with fixed current profile. Since the initial force needed is highest(due to friction) an intelligent solenoid drive can be applied. You find more details here: http://www.ichaus.de/wp8_whitepaper_en .
This intelligent drive can also involve a microcontroller if needed.