# Solenoid control

Discussion in 'The Projects Forum' started by Xefro, Dec 29, 2014.

1. ### Xefro Thread Starter New Member

Dec 17, 2014
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Hey guys, I have a 12v negative triggered solenoid that I need to power.

When the solenoid receives the ground signal I need it to go to full voltage for 2 seconds and then drop down to 400hz 60% duty cycle until the ground signal is removed to avoid burning up the solenoid.

What would be the best way to accomplish this?

2. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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Does it have to be a PWM signal or could you just use a series resistor to reduce the current?

3. ### MikeML AAC Fanatic!

Oct 2, 2009
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1,066
Do you mean that you want to apply 12Vdc to the solenoid for the first two seconds, and then reduce the current through the solenoid to 60% of the initial current?

All you have is one input? What is it? A switch contact to ground?

4. ### Xefro Thread Starter New Member

Dec 17, 2014
5
0
Correct on both accounts.

5. ### MikeML AAC Fanatic!

Oct 2, 2009
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What is the DC resistance of the solenoid?

I'm guessing less than 10Ω?

Last edited: Dec 29, 2014

Dec 17, 2014
5
0

7. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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370
Where does the 2 seconds come from, is this just an arbitrary figure? e.g could it be 1 second or 0.5 second?

8. ### MikeML AAC Fanatic!

Oct 2, 2009
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Here is how I would do this:

The simulated "switch to ground" closes at 0.1s, and opens at 4.1s.

This shows a close up of the solenoid current during PWM. Note the freq, duty cycle, and average current... I used 6Ω as the solenoid resistance, so the current initially is 2A. 1.27/2 is 63% during PWM.

Last edited: Dec 29, 2014
9. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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370
If all you want is to ensure that the solenoid receives full power to fire initially and then reduced power to hold it in place without burning out; you could try fitting an 8 Ohm 10W resistor paralleled with a large >=10,000uF electrolytic capacitor, in series with the solenoid.

10. ### MikeML AAC Fanatic!

Oct 2, 2009
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It will take a huge capacitor, and then the current profile is still an RC time constant, where it spends very little time near the peak current. Also, R1 has to be a 10W resistor (also huge).

Jul 18, 2013
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This is presumably a AC solenoid? why can't you use a DC solenoid and avoid the burn out problems, an AC solenoid should normally never see a reduced voltage.
Max.

12. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
1,461
370
Yes, I believe I already said the resistor should be rated at 10W, which I would not consider "Huge", Nor would the capacitor be "Huge" due to its low voltage rating.

It's just a suggestion, something the OP could try if he just wants a simple solution rather than an electronics project.