Drive Solenoid with Push Pull

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

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

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.

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

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

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

Sounds like the Castro district in San Francisco :-)

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...

Polarized relays are still boutique parts though, usually quite expensive.

Yeah, those would for sure tell you via the scent of molten plastic or the pop of a blowing fuse :-)

That's the reason for the + and - labels, otherwise it generally doesn't matter. ...Jim Thompson

Yup. They have permanent magnets built in. Just ran into that with the RF relays I used in the high-Z TIA we were discussing a couple of months ago.

Cheers

Phil Hobbs

Sounds like latching relays, we use them a lot at work..

Spring loaded PM's in the core of the DC coil. Simply select the polarity you need to set the static state of the relay.

AC units have an additional pin and diodes inside. they also have DC types with additional input, basically a unipolar verses a bipolar config.

As for the signal types, we do have some very small ones that are not very reliable. The magnet will let go under moderate low G-force and return to the off state. of course, there are multiple brands and I can't say that for all of them because I haven't used them all.

As for polarized (diode shunt) coils, we use those too but only for space savers. THe PCB mount types make it harder to route when space starts to get too tight at times. I find it some times easier to simply route a diode pad on the back side of the board under the relay, since I like using through hole tech for those kinds of components.

P.S.

Been looking at 3D printers lately. I've mentally collected a lot of different things I can do with it. We'll see how this plays out ;)

Jamie

Check out the Omron G6K series, latching and non-latching. They're all magnetically biased.

Cheers

Phil Hobbs

Brr. My son lives not far from there, in Coventry.

Cheers

Phil Hobbs

We have more exciting attractions around here, why check out relays when You can go to a cook out!

THis happen saturday in my town..

Jamie

We have an engineer that lives in Coventry.

P.S. I have never heard of any Hobbs in this area, he must live in stealth.. Jamie

Nah, he's a UConn student, or was until this week. He's transferring to UBC in the fall.

Cheers

Phil Hobbs