Hello All - I am new to circuits and the community. I have a door project which requires an electromagnet. I am trying to accomplish the following:

Pwm vdc in:

1. Gain a bit of smoothing with a capacitor.

2. Protect the voltage source from spikes when the field collapses.

3. Near instant on while limiting inrush current, and create a "soft stop" leveraging the capacitor.

Am I on the right track with a circuit like this? Any guidance would be welcome.

 

Not really,
I don't think that Circuit will do anything useful.
If you will make a list of potential problems You are trying to avoid,
I'm sure we can come up with some viable solutions.

Is this a "Mag-Lock" ?, ( big rectangular Magnet mounted to the Door-Frame ) ,
or, a Solenoid-Actuated Striker-Mechanism ?

What will be providing Power ?

How much Current does it require ?

What is providing Control of the Power ?

Why do You think it needs a special control-Circuit ?
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What is the operating voltage source? And what does it need protection from??
Next, given that an electomagnet solenoid arrangement closes an air gap as it operates, and given that as the air gap closes the force increases, with the moving parts moving even faster as the attraction increases, how do you expect it to stop softly. Solenoids are seldom gentle, never without a lot of extra effort in the controls.All the questions that LQC asks in post #2 do matter a fair amount.
Really, if you want a gentle operation use a gear train and either a lever or a cam.And what is the control device? And how much energy will be stored in the magnetic field to be converted back into a voltage spike???
And we still do not know what sort of force and stroke this electromagnet is going to provide.
The simple way to avoid a spike is to slow the breaking of the circuit. Reducing the current from "max" to zero in 100 milliseconds instead of ten microseconds will make any spike 1000 times less. That may be worth the effort.

 

Thank you for the quick replies:

Voltage source is approximately 28vdc pwm from a control box output. The box cannot perform any sort of ramp or decay. Simply on/off 28vdc pwm 10a max

They are approximately 50w 27.5 vdc electrically operated permanent magnets (energizing negates the magnetic field).

The air gap/force is commentary is valid, and partially what I am trying to address - sound. Ramping the voltage from 28 to 0 presents a perceivable and desirably less harsh sound when re-engaging.

Ultimately looking for a simple circuit to allow release voltage to pass near instantly, and decay on power off to help with sound/spikes.

Thank you all.

 

"" (energizing negates the magnetic field). ""
Specialized Device,
manufacturer and part-number required for discussion.

This is starting to sound like a Fire-Door-Release setup,
if so, don't mess with it.

"" ......... a simple circuit to allow release voltage to pass near instantly, and decay on power off ........ ""
Controlling the Power to the Coil requires access to whatever Circuitry is Powering it.
This would be very cumbersome to attempt with any kind of "Passive" Circuit, ( GIANT Capacitor ).
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Fire doors are almost always traditional electromagnets so they fail open if power is lost - Not permanent electromagnets. That said - this has nothing to do with a fire door. Work holding is a typical application for electrically operated permanent magnets like these. My apologies for not more clearly articulating this.

They are Magnetool PEMR-150x250 magnets.

No hope for a relatively simple passive circuit then it seems?

 

Strange choice of device ...........
Magnetool provides no information other than general dimensions.

"" Ramping the voltage from 28 to 0 .............. less harsh sound when re-engaging ""

You gave no information on the Power-Supply, or how it is controlled.
If You want to leave the Power-Supply permanently "On",
and then control the actuation with an external Circuit,
that can be done fairly easily.
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Power from box is either on or off with button push.

Are there some circuit types you recommend I read about? You have any suggestions of your own? Thank you.

 

OK, so a rapid current RISE is fine. I have played with the opposite, an electrically powered door holder intended to stop grab-and-run thefts. at a small store. To provide a slower release you can provide a discharging capacitor that will allow a more gradual release. (no inductive spike this way) The main challenge will be charging that large capacitor. If a slower release because of current build up would be acceptable then the solution would be simple, just the LARGE capacitance across the coil.
Do you have the access ability to experiment with this project, or is it an "install and it must be perfect the first thing" sort of project? If the field-release/unlock time were stretched to one second that should reduce any noise.

Now about that "PWM" power from the control box: the only purpose of having Pulse Width Modulation is to be able to provide an equivalent of a variable amplitude. Thus physically at least, if the output REALLY IS actual PWM, then the challenge is all in the software, because PWM would indeed allow a ramping up and down of the current by reducing the duty cycle.