Forums

Drive Solenoid with Push Pull

Started by Unknown April 14, 2013
I have an audio amp module that has a push/pull output. Can this be
used to drive a plunger type solenoid?

I am concerned that the current reversal at each half cycle would
cause the coil to alternate between N-S and S-N, thereby making the
plunger move twice per cycle, first in one direction and then in the
other.

If this is inadvisable, can I use a diode to recitfy the drive signal?

Art Brooks
abrooks@cjaudio.com wrote:

> I have an audio amp module that has a push/pull output. Can this be > used to drive a plunger type solenoid? > > I am concerned that the current reversal at each half cycle would > cause the coil to alternate between N-S and S-N, thereby making the > plunger move twice per cycle, first in one direction and then in the > other. > > If this is inadvisable, can I use a diode to recitfy the drive signal? > > Art Brooks
If you are using AC and it has a PM magnet, yes, it is going to move in two different directions in one cycle.. If you are truly using a solenoid, it should move in the same direction with both SIN and COS, where the base line, zero crossing, will allow it the move back to the starting point.. So thus, that will be 2 moves per cycle.. Is that what you wanted to know? P.S. AC solenoids are designed a little differently to help prevent this vibration, however, if you use a slow enough cycle it will still vibrate. Jamie
On Sun, 14 Apr 2013 11:24:58 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


> If you are truly using a solenoid, it should move in the same >direction with both SIN and COS, where the base line, zero crossing, >will allow it the move back to the starting point. So thus, that will >be 2 moves per cycle.. >
This is what I do not understand. If you have an air core coil and apply a bipolar signal, the magnetic field will reverse with each half cycle. How is a solenoid different? I would think the positive half of the duty cycle would force the plunger out and the negative would force it back in. Art Brooks
abrooks@cjaudio.com wrote:
> On Sun, 14 Apr 2013 11:24:58 -0400, Jamie > <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: > > >> If you are truly using a solenoid, it should move in the same >> direction with both SIN and COS, where the base line, zero crossing, >> will allow it the move back to the starting point. So thus, that will >> be 2 moves per cycle.. >> > > This is what I do not understand. If you have an air core coil and > apply a bipolar signal, the magnetic field will reverse with each half > cycle. > > How is a solenoid different? I would think the positive half of the > duty cycle would force the plunger out and the negative would force it > back in. >
https://en.wikipedia.org/wiki/Solenoid Quote "The force applied to the armature will always move the armature in a direction that increases the coil's inductance". Or think about a relay: It will pull in when you apply enough voltage. It will still pull in the same way if you reverse the polarity. Then there's all the AC contactors which are in essence also relays. Those need some lag in the armature, else they'll buzz, but both half-cycles pull them in the same direction. -- Regards, Joerg http://www.analogconsultants.com/
On Mon, 15 Apr 2013 09:23:44 +1000, the renowned abrooks@cjaudio.com
wrote:

>On Sun, 14 Apr 2013 11:24:58 -0400, Jamie ><jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: > > >> If you are truly using a solenoid, it should move in the same >>direction with both SIN and COS, where the base line, zero crossing, >>will allow it the move back to the starting point. So thus, that will >>be 2 moves per cycle.. >> > >This is what I do not understand. If you have an air core coil and >apply a bipolar signal, the magnetic field will reverse with each half >cycle. > >How is a solenoid different? I would think the positive half of the >duty cycle would force the plunger out and the negative would force it >back in. > >Art Brooks
Think of a bar magnet representing your coil and a piece of iron representing the plunger. The N side is attracted to the iron, but flip it over, and the S is also attracted. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
In article <mcemm8he9ah99cgp0pq813u91vaqtffce7@4ax.com>,
 <abrooks@cjaudio.com> wrote:

>This is what I do not understand. If you have an air core coil and >apply a bipolar signal, the magnetic field will reverse with each half >cycle. > >How is a solenoid different? I would think the positive half of the >duty cycle would force the plunger out and the negative would force it >back in.
Most of the solenoids I have seen, do not use a permanently magnetized plunger. They use a simple iron (I believe) plunger, which retains little or no magnetism from one half-cycle to the next. It's equally well attracted by either polarity of the magnetic field. By analogy... a soft iron nail will be "picked up" equally well by either the north or south pole of a oermanent magnet. As long as the nail isn't magnetized itself, neither pole of the permanent magnet will repel it. -- Dave Platt <dplatt@radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads!
On Sun, 14 Apr 2013 17:41:08 -0700, dplatt@radagast.org (Dave Platt)
wrote:

>In article <mcemm8he9ah99cgp0pq813u91vaqtffce7@4ax.com>, > <abrooks@cjaudio.com> wrote: > >>This is what I do not understand. If you have an air core coil and >>apply a bipolar signal, the magnetic field will reverse with each half >>cycle. >> >>How is a solenoid different? I would think the positive half of the >>duty cycle would force the plunger out and the negative would force it >>back in. > >Most of the solenoids I have seen, do not use a permanently magnetized >plunger. They use a simple iron (I believe) plunger, which retains >little or no magnetism from one half-cycle to the next. It's equally >well attracted by either polarity of the magnetic field. > >By analogy... a soft iron nail will be "picked up" equally well by >either the north or south pole of a oermanent magnet. As long as the >nail isn't magnetized itself, neither pole of the permanent magnet >will repel it.
Think energy. Hamilton's principle. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
abrooks@cjaudio.com wrote:

> On Sun, 14 Apr 2013 11:24:58 -0400, Jamie > <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: > > > >>If you are truly using a solenoid, it should move in the same >>direction with both SIN and COS, where the base line, zero crossing, >>will allow it the move back to the starting point. So thus, that will >>be 2 moves per cycle.. >> > > > This is what I do not understand. If you have an air core coil and > apply a bipolar signal, the magnetic field will reverse with each half > cycle. > > How is a solenoid different? I would think the positive half of the > duty cycle would force the plunger out and the negative would force it > back in. > > Art Brooks
The core of the solenoid isn't a magnet. But it'll attract to a magnet regardless of pole position. Just take a magnet and experiment on your fridge door, you'll notice it does not matter which pole you use. It'll stick to the door either way. Now do that with another magnet. You'll then get the effect you're thinking of and if the solenoid core was made with a magnetic it would vibrate. In short, you would then have a speaker! :) A solenoid is not quite like a AC relay coil. The coil in an AC relay has to be wound differently because it already has a core and it's fixed, but the field it generates would cause vibration if it wasn't for the way it was wound with the little ring on top. With solenoids, it tries to pull on the core to make it one with itself, regardless of pole position. When that happens, the core then has a pole and now is magnetic, but it abides by the pole that is currently being generated, so it'll always pull in. There may be a small magnetic hysteresis in the core and that will contribute a little to what noise you have with AC as the power source. Jamie
Spehro Pefhany wrote:
> On Mon, 15 Apr 2013 09:23:44 +1000, the renowned abrooks@cjaudio.com > wrote: > >> On Sun, 14 Apr 2013 11:24:58 -0400, Jamie >> <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote: >> >> >>> If you are truly using a solenoid, it should move in the same >>> direction with both SIN and COS, where the base line, zero crossing, >>> will allow it the move back to the starting point. So thus, that will >>> be 2 moves per cycle.. >>> >> This is what I do not understand. If you have an air core coil and >> apply a bipolar signal, the magnetic field will reverse with each half >> cycle. >> >> How is a solenoid different? I would think the positive half of the >> duty cycle would force the plunger out and the negative would force it >> back in. >> >> Art Brooks > > Think of a bar magnet representing your coil and a piece of iron > representing the plunger. > > The N side is attracted to the iron, but flip it over, and the S is > also attracted. >
Sounds like the Castro district in San Francisco :-) <duck and run> -- SCNR, Joerg http://www.analogconsultants.com/
On Sun, 14 Apr 2013 17:24:38 -0700, Joerg wrote:

> Or think about a relay: It will pull in when you apply enough voltage. > It will still pull in the same way if you reverse the polarity.
Don't bet on it. Lots of relays these days are polarized, and they don't always tell you, expecting you to notice the + and - labels. Then there are relays with built-in parallel diodes... -- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)