Electromagnet to actuate a permanent magnet

[ThaSatelliteGuy]

First, I realize that magnetism does not conform easily to simple, exact, equation-driven answers, but I only need a ball-park.

I have a design for something in my head, somewhat a kin to a human heart. It will need to pump air or liquid. Not much, and a little less pressure than a siphon or bloodpressure cuff. It will be of a similar design of a siphon bulb. My current plan is to mount the bulb, with a permanent magnet attached, then to use an electromagnet to 'squeeze' and then 'release' the bulb. The magnet is 1in by 1in sq, and claims to have a 80lb hold capacity. If flexing turns out to be a problem I can also use an array of smaller magnets along the surface.

My question is this:
What kind of electromagnet is best? How big? and what kind of electricity requirement to make this happen? I can overpower and compensate with distance or voltage, but it cannot be underpowered or sluggish. It only needs to move the mag about 1.5 in., but it must make decisive, quick pumps, and it needs to be able to get near 2 per second.

 

[israelkk]

1.5 inch is a huge distance for such a small electromagnet and any electromagnet at all. The claimed 80lb is in zero distance from the electromagnet pole. From 1.5 inch distance the force will be near zero. An electromagnet is best working with an iron not with a permanent magnet. Permanent magnet will create a force by its own and you will need something to push it back for next pumping cycle.

The electromagnet current, voltage, size and more, are a function of the design, distance, forces, cycle time etc,.

The correct way is to do static and dynamic analysis analytically or/and using FEA. You can do trial and error testings with off the shelf electromagnets but it may be time consuming, expensive and no guaranties.

 

[opster]

I'm currently working on two projects that deal with magnetism, and one of them invlolves pulling a piece of iron .75x.6x.1in from a distance around .3-.5inches. I have been able to generate a force of 2 to 4lbs, with a 1inch cube permanent magnet (NdFeB). The pulling force is varied (1 to 4lb) with a shunt (-a piece of iron that redirects the flux, thereby decreasing the flux that reaches the smaller piece of iron).

I looked at using an electromagnet at first but the size is too large. The device I'm working on needs to be around 1lb.

So for what your asking - force at 1.5inches - you're going to need an enormous electromagnet. If you want push and pull action then using a permanent magnet attached to the bulb,
with an electromagnet - from some distance - actuating the permanent magnet, .... then I would look at decreasing the 1.5inch distance. But the idea sounds interesting. Linear motors made like this require little maintenance, but unfortunately have short strokes.

 

[ThaSatelliteGuy]

Ok, since I made that post, I had a brainstorm come through...

using the bulb, I think, is about half stupid. I can accomplish it better I think, with a diaphram. It will give me more flexibility in my design as I will be able to increase diameter and therefore reduce required throw, and still move the same amount of air.

I am BTW only trying to move air... very little air at that. (At an extremely high estimate:5 cu in)

If you were able to generate a couple lbs at .5 inch, that would probably be enough. When you say 'enormous' electromagnet, just how big we talkin'? I have basically no size, weight limit. (other than smaller than a breadbox) If I can keep it around the size of a spindle of CD's that'd be fine.

Oh, and I need it to be basically silent. did the motor thing, too much noise.

 

[dgallup]

I think you need a moving coil transducer (like a loudspeaker voice coil) for the type of stroke you are looking for. The coil is suspended in the gap of the permanent magnet and can move relatively long distances.