How to make an electromagnet attract items at a distance?

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Old 04-27-17, 06:13 PM
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How to make an electromagnet attract items at a distance?

I’ve created an electromagnet using a steel rod, 7″ in length, 3/8″ in diameter, wrapping it with 36 AWG enameled copper wire (so there are a lot of wraps around the steel rod), all connected to a 9V battery. I’m trying to make the electromagnet pick up small staples/paperclips at a distance (up to an inch or two inches away from the objects), but my current electromagnet will only function if it touches the object. Which factor(s) of the electromagnet should I change: battery, steel rod diameter/length, wire gauge..? I'm at a loss here. Thanks very much in advance for help!
 
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Old 04-27-17, 06:21 PM
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Try a 12 volt car battery.
 
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Old 04-27-17, 06:29 PM
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If doing this is for educational or experimental purposes then do as Ray suggested. But if you're trying to make a tool then just buy it.
 
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Old 04-27-17, 07:17 PM
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maximize Amps times wire turns.
 
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Old 04-27-17, 07:51 PM
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Thanks for the responses, I appreciate it a lot. Yes, this is for experimental purposes and I will try buying a 12V battery tomorrow.
Another question, however. Is what I'm trying to do practical? Will a 12V battery realistically allow my electromagnet to attract small items from up to two-ish inches away?
 
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Old 04-27-17, 08:01 PM
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It's YOUR homework assignment. Experiment with it.
 
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Old 04-27-17, 08:05 PM
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When I was a kid I remember doing the same thing and using a model train transformer.
 
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Old 04-27-17, 10:26 PM
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When I was a kid I remember doing the same thing and using a model train transformer.
...Which puts out 12 volts...

Basically yes, upping the voltage will give you a greater field. Whether it gives you the result you want... Probably not. 24 volts (two 12V batteries in series) would have a better chance. Electromagnets are resistors. Their design limits the current flowing through them for any given voltage, and current is what actually creates the magnetic field. Increasing the wire gauge to 34 or 32 would decrease the coil resistance, allowing more current to flow, therefore creating stronger magnetic field at lower voltage.

Another thing affecting the field strength is your core material. Iron is ideal. Steel (especially hard steel used in hardware like all-thread and bolts) has much lower magnetic permeability than iron (it takes more energy to align the steel molecules).

You also want to make sure your coil is wound and layered as neatly as possible. Hand winding is about as sloppy as you can get with hair-thin wire, even if you are careful. You'll want to chuck the core into a drill and have someone hold it horizontally against a table at a low speed, while you carefully unspool the wire along the length.
 
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Old 04-28-17, 02:13 AM
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Back in the days of yore when I was but a bit of a lad we used telephone batteries* for these experiments. They were also called doorbell batteries. In phones that used a crank generator to notify centeral they powered the carbon microphones in the mouth piece. In doorbells well that's obvious. I doubt though you have ever seen one. They were 2" (yes two inches) in diameter and 6" (yes six inches) tall. Maybe three of those in series if they are still sold would give you enough "kick". We also used 6 volt lantern batteries which you can still buy and a couple of those either parallel or series might be something to try.

*Like the modern D cell battery telephone batteries were a single cell 1˝ volt battery just a heck of lot bigger with a lot more amps available.

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No I'm not really that old just old enough to be around after they stopped being commonly used but were still sold.
 
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Old 04-28-17, 04:55 AM
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A 12 volt car battery if you dead short the wire will get the wire red hot in seconds. You will need a resistance in circuit. I do this to magnetize screwdrivers.
 
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Old 04-28-17, 05:32 AM
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The electromagnet is a type of resistor, an inductive load. Hard to say if it will be enough of a load. That is what math or a smoke test is for.
 
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Old 04-28-17, 08:50 AM
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The strength of a magnetic field decreases roughly with the inverse cube of the distance from the magnet. What this means is that if you double the distance between the magnet and the paper clip, the strength of the magnetic field pulling on the paper clip is 1/8 what it would be at the original distance. We come to this number because the distance is 2 times, and the cube of 2 is 2 * 2 * 2 = 8, so 2x distance results in 1/8 force. A practical example:

If we start with a magnet that can pull 100 pounds at one inch, using our 1/8 rule above we can calculate magnetic force at various distances:

1/4" -> 6400 pounds
1/2" -> 800 pounds
1" -> 100 pounds
2" -> 12.5 pounds
4" -> 1.5 pounds
8" -> 0.2 pounds
16" -> 0.025 pounds (10 grams)

As we can see the strength of the magnet drops off very quickly over distance. This magnet that can lift up a full size truck at 1/4" can barely lift a few paper clips at 16". Think about what this means for your question on your experiment.
 
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Old 04-28-17, 03:04 PM
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Well, thanks for doing his homework for him, Ben
 
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Old 04-28-17, 05:24 PM
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Another question, however. Is what I'm trying to do practical? Will a 12V battery realistically allow my electromagnet to attract small items from up to two-ish inches away?
prolly not. but, before you give up, try 200 volts for 10 ms or so.
 
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Old 04-28-17, 09:20 PM
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Telecom guy the poster may think you're serious and not understand the humor of 10ms.
 
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Old 04-29-17, 06:40 AM
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Telecom guy the poster may think you're serious and not understand the humor of 10ms.
I do understand your point, but I am serious. Some of the most important solenoids in the world are rated for way less than one second operation time. I'm referring to the latches that control our largest substation circuit breakers. These are fed from either 125 or 220V dc and automatically de-energize the coil after movement occurs; which is usually around 10 to 20ms.

But, I have no idea if the OP can perform safely such a mission. There are various risks involved. So yes, beware and don't try without an informed parent involved.
 
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Old 04-29-17, 08:28 AM
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Thanks for that information, Telcom Guy. I was not familiar with those breakers.
 
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Old 04-29-17, 06:18 PM
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But, I have no idea if the OP can perform safely such a mission.
One could safely assume that if he doesn't understand even the basics of electromagnetism that he isn't capable of doing something like that. I don't know what would possess you to suggest such a thing to such an obvious noob.
 
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Old 04-29-17, 06:38 PM
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We are here to teach, Taz. We can't vet any of the OP's on this board. I've read lots of instructions here on what/how to use voltmeters.
 
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Old 04-30-17, 03:46 AM
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There's a huge difference between telling someone how to safely use a multimeter to accomplish something simple like checking that a circuit is dead before changing a receptacle and telling someone who doesn't even know the basics of an electromagnet that he should apply a ridiculous amount of voltage to it for a precise amount of time that he can't measure (FYI 10ms is about 15 times faster than human reaction time). You didn't even ask what the resistance/inductance of the coil was before you suggested it. That's not teaching, that's tantamount to assisted suicide.
 
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Old 04-30-17, 05:01 AM
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The OP hasn't returned. He is a student. This was a homework project. I think we have run the gamut on it. Suggest closing.
 
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Old 04-30-17, 05:28 AM
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Thread has been closed. Spectrum, if you have more questions PM a mod to reopen it.
 
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