Trying to source strong (and cheap) electromagnets

Heya!

I'd like to use 16 electromagnets arranged in a 4x4 grid under a perfectly leveled glass plate to move around a steel ball on the surface of the plate. By turning the 16 magnets ON and OFF in different sequences the ball would roll around in different patterns.

I bought an 11 lbs holding electromagnet lift solenoid from Amazon and used a 1/2 inch E52100 steel ball for a first test. Unfortunately the magnet wasn't strong enough to move the ball even when the ball was just 1/2 inch off horizontally from the magnet.

Looking through different options on Amazon I found different types of electromagnets: a sucked electric lifting magnet electromagnet, a electric lifting magnet electromagnet, the holding electromagnet lift solenoid, etc. Are those basically all the same or are there some essential differences? If there are differences which one would be the best for my application? I also will increase the lifting force, of course.

Are there more suitable balls than the E52100 alloy that are somewhat affordable?

Thank you for your help in advance!

Erwin

Just make some. Its a wire around a metal core.

I bought an 11 lbs holding electromagnet lift solenoid from Amazon and used a 1/2 inch E52100 steel ball for a first test.

How did you power the electromagnet? A 1/2 inch steel ball should be no problem for a 11 lb electromagnet.

More to the point what current did you put through the electromagnet.

The inverse cube law of magnetic fields ensures that the force drops off very rapidly with distance.

You can always help matters by using a magnetised sphere.

was the ES52100 heat treated ? like a hard ball bearings ?

if so, what to you do to make it magnetic again ?

3/4 inch, about 50 cents each ? typical for ball bearning balls.

Note if the ball baring is stainless steel, then it won’t be very magnetic.

Your experiment "should" have worked.

I suspect your ball was stainless steel, which doesn't work very well with magnets.

You need to find an ordinary steel ball, I suggest.

Just to clarify...

Using the 11 lbs electromagnet worked "a bit", but simply not strong enough to create a magnetic field that bridges the gaps between the electromagnets. I am now getting a much stronger electromagnet, though...

According to different charts about steel alloys and their magnetic properties, the ES52100 steel ball is close to perfect and no, it is not stainless. It is ES52100...

As for driving the electromagnet I simply use a 12VDC power supply that gives the magnet as much current as it needs with no resistor in-between. At the end I'll use a standard DMX driver or Arduino + relays to run the electromagnets....

Cheers,

Erwin

As for driving the electromagnet I simply use a 12VDC power supply that gives the magnet as much current as it needs

That is not a very scientific way of looking at things. This assumes that your power supply is capable of providing "as much current as it needs" but without knowing how much current that is the you have no way of knowing if your poor performance is due to insufficient current capacity on the power supply.

A 60 amp power supply @ 12 VDC should be sufficient especially considering that the electromagnet has a spec sticker with "12 VDC / 0.33 A" on it, I guess :)

Why do we have to drag information out of you?

A current of 330mA and a voltage of 12V implies a resistance of 36 ohms. This is quite high and I am sure you could bet a much stronger magnet by passing more current through it.

1/2 inch is a very large gap - have the electromagnet much closer to the surface the balls are rolling on and it will fare much better (inverse-cube law).

The mechanical arrangement of the magnetic circuit is important - a wider core in the electro magnet may make all the difference.

I am somewhat confused, the force to roll a steel ball on a flat glass plate is very little.

Perhaps your electromagnets are too far apart - they need to be close together, again its that inverse-cube law you have be wary of.

Also you may find you can drive the electromaget hard to acquire the ball then back off to a lower current to hold it (and avoid overheating the electromagnet).

E52100 appears to be a grade of carbon steel so it will be ferromagnetic.

Mark,

The electromagnet is flush on the underside of the 1/8 inch glass plate, as close as it gets. As I wrote in my initial post, if the steel ball is off [u]horizontally[/u] more than 1/2 inch the electromagnet isn't able to pull it towards the magnet anymore.

As for increasing the current I am already giving the magnet all it wants from the 60A power supply. Would increasing the Voltage help?

Erwin

Would increasing the Voltage help?

Yes increasing the voltage would increase the current and it is the current that gives you the magnetic field.

Long shot - but rather than trying to use electromagnets - which have a permeable ferrous core (which as designed is mean to shunt the magnetic field closer to the device) - why not just use plain coils instead, with the steel ball acting as the core?

In a solenoid, the core is "pulled into" the middle/center of what is essentially an air-core coil. The same thing is done by a so-called coil gun (the projectile is "pulled along" by the air-core coils).

So - wind your own coils - I would get some heavy gauge wire (so you can dump a lot of current through it), and wind some coils of about a hundred or so turns (maybe "cable lace" the layers together) on a cardboard or wooden dowel close to the diameter of the steel ball.

Make one, and experiment with it using a fairly beefy power supply (something that can source a lot of amps - your current power supply may be sufficient; you'll have to measure your coil resistance and calculate the amperage drawn for the voltage its run at).

A ferromagnetic core will increase the field strength by increasing the magnetic permeability of the core (compared to an air core). Solenoids and rail guns use air cores because there's a fundamental requirement for the core to be hollow so that something can pass through it - since you don't have that requirement here, a ferromagnetic core would be better.