Solenoid doesn't release quickly

Thread Starter

DBBCircuits

Joined Apr 22, 2015
7
I am trying to mechanize a harpsichord by using solenoids to activate the keys. I have purchased some cheap solenoids (60+!) but I find now that the release time is quite substantial - I mean like 1 to 1 and a half seconds. I hung the solenoid from a support, put some weight on the plunger, activated the solenoid and then deactivated it to allow gravity to pull it down. The plunger noticeably delays before falling. They are 12V solenoids and take about 0.5A. I have included a IN4001 diode in parallel with the solenoid and am testing them with a 12V power supply. I've read that a zener diode in series with the IN4001 can help it release quicker, but it seems like that will help decrease the time from, for example, 11msec down to 3msec. I'm far away from that! Is there something else going on here?
 

MaxHeadRoom

Joined Jul 18, 2013
19,747
Even with a BEMF diode that is unusually long unless they are Really large inductance.
Try one without the diode just to see if any appreciable difference or if the diode has any effect.
Can you post a pic of them?
Max.
 

dl324

Joined Mar 30, 2015
9,620
What are you using to switch the solenoids? If you can tolerate a higher back EMF, the field will collapse faster.
 

Thread Starter

DBBCircuits

Joined Apr 22, 2015
7
Solenoid.jpg Solenoid.jpg

Are you having difficulty with an 11 millisecond delay or a 1 second delay?
I'm not quite sure what response I need at the moment, but I know it needs to be a lot better than 1 sec.

Even with a BEMF diode that is unusually long unless they are Really large inductance.
Try one without the diode just to see if any appreciable difference or if the diode has any effect.
Can you post a pic of them?
Max.
No difference with or without diode.

See pic below.

Thanks for your help.

Doug
 

Thread Starter

DBBCircuits

Joined Apr 22, 2015
7
What are you using to switch the solenoids? If you can tolerate a higher back EMF, the field will collapse faster.
At the moment, I'm just switching the power supply on/off. I'm not planning on providing a higher voltage in my circuitry, but.......
 

dl324

Joined Mar 30, 2015
9,620
At the moment, I'm just switching the power supply on/off. I'm not planning on providing a higher voltage in my circuitry, but.......
If it's a decent power supply, it will have a fair size cap on the output. If that's the case, the delay you're seeing could be from the cap discharging. Try removing the lead from the solenoid.

If that's not fast enough, you could try putting springs on the plunger.
 

JohnInTX

Joined Jun 26, 2012
3,947
If it's a decent power supply, it will have a fair size cap on the output. If that's the case, the delay you're seeing could be from the cap discharging. Try removing the lead from the solenoid
+1 Turning off the supply won't do it. Here's an article about a zener in series with the BEMF diode, too.

Good luck.
 

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Kermit2

Joined Feb 5, 2010
4,163
One other item you need to check...
Does that plunger make physical contact with the metal of the solenoid anywhere? Does it touch at the back end when pulled in? Thin layer of rubber or some other soft non magnetic material which prevents surface to surface contact of the plunger will allow a much quicker loss of magnetism when you cut power.
Also you should drive the solenoid with raw rectified DC and leave out any capacitor. A cap acts like a battery and keeps current going when you cut the supply. The solenoid will hold without any filtered DC.
 

recklessrog

Joined May 23, 2013
985
As suggested by Kermit and Colin55, a small gap at the end of the plunger may be all you need, even just a small disc cut from a business card, or thin plastic glued to the end of the plunger should do the trick. I have some solenoids that were removed from an old gaming machine and these have what look like small fibre washer glued to the end of the plungers..
 

MaxHeadRoom

Joined Jul 18, 2013
19,747
As suggested it is beginning to sound like residual is keeping the armature retained for a second, this is how the magnetic latch unlatch types work, except on a stronger scale.
Just for the heck of it, reverse the polarity it normally operates at and see if any difference.
Max.
 

Thread Starter

DBBCircuits

Joined Apr 22, 2015
7
If it's a decent power supply, it will have a fair size cap on the output. If that's the case, the delay you're seeing could be from the cap discharging. Try removing the lead from the solenoid. If that's not fast enough, you could try putting springs on the plunger.
That's the ticket! Once I put a switch in the circuit, it released quickly. Now I'll have to figure out if it is quick enough, but at least it doesn't sit there for a second or so!! Thanks for the insight.


I didn't ask you what response you want. I want to know if you are talking about 11 MILLISECONDS.
Yes, I meant milliseconds but I was just using that as an example I found where the poster saved a few milliseconds by adding the zener as opposed to my situation where I wanted to save 1 second - I didn't think a zener would do that for me.

One other item you need to check...
Does that plunger make physical contact with the metal of the solenoid anywhere? Does it touch at the back end when pulled in? Thin layer of rubber or some other soft non magnetic material which prevents surface to surface contact of the plunger will allow a much quicker loss of magnetism when you cut power.
Yes, thanks to all who suggested a gap. I'll be doing that if only to reduce the noise of the clanking of the plunger against the stop.


Thanks to all for your great help!

Doug
 
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