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Topic: Need help: Using PWM on a solenoid for easy release. (Read 1 time) previous topic - next topic

Carcegen

I'm on a project where I'm injecting a thick liquid into a small applicator.  So the nozzle will not drip after the pre measured liquid flows past, I built a shut off "needle valve" right at the nozzle using a knitting needle (pointy end) attached to a hefty spring loaded solenoid positioned over it.  The device works great - send 12 volts to the solenoid and it lifts the needle up, allowing the fluid to be pushed out.  Remove power and the solenoid's backspring pushes the needle back into the nozzle hole eliminating any drips.  My problem is that the solenoid's back force spring slams the needle down into the nozzle hole so hard it actually gets stuck and will eventually deform the needle.  The needle is aluminum and the nozzle stainless steel.  I tried lighter backsprings but then the needle doesn't seat as firmly as I need.  So I thought = what if PWM could be used to power the solenoid to allow it to release more gently by doing a ramp down from 12 volts to zero (in say 100 ms).  Has anyone ever done this to give softer action on the release of a solenoid?  I have a free channel on my Arduino R3 motor driver board but wondered if it can handle a 1.3 amp hefty magnetic solenoid.  Even though that board uses an isolated power supply (12 volts in my case), I wonder if the back EMF from the coil could damage the boards?

If it is possible, are there some Arduino function sets that do a ramp up and down of a voltage for this type of purpose?

Thanks

arduinohabib

What is man's best friend? The breadboard!

ash901226

take the same precaution you would controlling a motor... use a flyback diode. and if you could just use a mosfet....
heres a good tutorial you can use
http://bildr.org/2011/03/high-power-control-with-arduino-and-tip120/
ok for the ramping up and ramping down the power....

my hint is to use for loop()
imagine how you would well increase the brightness of a LED.
ok for your application you would not increase the speed of the solenoid but actually your ramping up the solenoid power and making it pull the needle slowly ....

for the release imaging your fading the led brightness....
this in turn in your application will release the needle slowly....

arduinohabib

What is man's best friend? The breadboard!

ash901226

and make a RC circuit. and really make an analog output....

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