Electromagnet FAQ

What are some typical applications for electromagnets?

Can electromagnets be used to repel as well as attract?

What is the polarity of your round electromagnets?

How far away from the electromagnet can I hold attracted material?

What is the strength of the field over distance?

What is the practical effective field distance?

Can the field distance or force at distance be improved?

Does ambient temperature affect the performance of electromagnets?

Can the holding force of the electromagnet be adjusted?

Is an electromagnet that is rated for 24 vdc stronger than a unit that is rated for 12 vdc?

Can I attract any metal with an electromagnet?

How are your holding forces calculated?

Does the thickness of material attracted effect holding forces?

Do the magnets have residual Magnetism?

What is the Quick Release option?

Can I use a battery to power the electromagnet?

Do you sell power supplies?

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What are some typical applications for electromagnets?
Our clients vary in use from simple gate latches to hi-tech robotic articulating arm applications. Some of our most common applications include X-Ray bed fixed positioning, security door applications, automatic fire door applications, dentist chairs, automatic farm feeders, remote animal trapping, medical diagnostic equipment, motorcycle cruise controls, packaging equipment, electric brakes, simple solenoids, bus swing arm holders and cordless construction equipment.

Can electromagnets be used to repel as well as attract?
As they are sold, minimal to no repel can be achieved as they are designed to attract. What is needed to repel is a coil around an iron core with no outer shell. This configuration places a north pole at one end of the iron core and a south pole at the opposite end. The electromagnets as they are sold have a south pole and north pole on the same end. One pole is on the outside ring or shell and the other pole is located on the center post or core.

What is the polarity of your round electromagnets?
Since the units as supplied online have both poles on the same plane, it depends on which lead you connect the + or - power source to. Reversing the positive and negative feeds will switch the poles. One pole is on the outer ring and the opposite pole is at the center post. As standardly supplied, they are not good for repulsion as you will need an opposite poled electromagnet. Many of our standard units can be configured in this way, but forces are greatly diminished. Call for more assistance with repulsion applications.

How far away from the electromagnet can I hold attracted material?
The electromagnet achieves its maximum holding force when in direct contact with the attracted surface. You can review the gausses to distance PDF which will give you a better understanding of how distance from the electromagnet decreases the magnetic forces. Round Magnet Gauses Distance (PDF - 133KB) Rectangle Magnet Gauses Distance (PDF 85KB)

What is the strength of the field over distance?
Magnetic field in the air is reduced exponentially over distance.

What is the practical effective field distance?
Typically with all round electromagnets, one unit of distance requires about four units in diameter of the said electromagnet. As an example our 4 inch magnet has a usable field about 1 inch from the electromagnet where our 2 inch dia. electromagnet has about .5" and our 1.0 inch dia. electromagnet has a field up to about .25". At that point the field is usable, but may be fairly weak when using the units at their rated voltage.

Can the field distance or force at distance be improved?
The distance does not change much based on the fact that the physical makeup of the electromagnets determines the field. You can improve the field strength by doubling the rated voltage in a short burst and then reducing it to the continuous rated voltage for the holding portion of your application. It is a high voltage hit and hold circuit.

Does ambient temperature affect the performance of electromagnets?
Yes. As the ambient temperature raises so does the resistance of the coil reducing the ampere turns which in turn decreases holding force. Likewise, low temperatures lower the resistance of the coil decreasing the resistance which in turn increases the ampere turns thus increasing the holding force. Typically, normal operating temperatures will not produce significant performance changes. Extreme conditions hot or cold will affect the performance accordingly.

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Can the holding force of the electromagnet be adjusted?
Think of your applied voltage as a gas pedal. As you increase the applied voltage to the electromagnet the holding forces increase. So if you have an electromagnet that is rated for 24 vdc, and you only apply 6 vdc the holding forces will be significantly less than when the voltage is at the rated voltage, 24 vdc, of the unit. Likewise, you can apply 36 vdc to the 24 vdc rated unit and achieve in some cases, greater holding force than the rated holding force. The risk with overdriving the unit is that the coil may burn out as the internal coil temperature rises above the intended design parameters.

Is an electromagnet that is rated for 24 vdc stronger than a unit that is rated for 12 vdc?
No. The coils are designed to achieve a specific holding force at the rated voltage. For example, a EM100 with a 24 vdc rating will hold 25 lbs if the applied voltage of 24 vdc is applied to the unit. Likewise, an EM100 with a 12 vdc rating will hold 25 lbs if the applied voltage of 12 vdc is applied to the unit. The different voltage ratings provide engineers with design flexibility enabling them to match the electromagnet to their power supply.

Can I attract any metal with an electromagnet?
No. Electromagnets and permanent magnets alike attract metals with iron contents. The higher the iron content the greater the attraction. The lower the iron content the lower the attraction. Electromagnets and permanent magnets for example will not attract metals such as, aluminum, brass or gold to name a few.

How are your holding forces calculated?
Our electromagnet holding force ratings are based on an electromagnets attraction to a .250" thick piece of 1215 CRS or 1010 steel plate that covers the full diameter face of the electromagnet. The actual rating is based on suspended weight from that plate and is essentially a drop test. The rating given is the weight at which the magnet will not drop its weight thereby its maximum holding force. This test assumes only directly suspended loads and does not take in to consideration any sheer forces.

Does the thickness of material attracted effect holding forces?
Yes the effectiveness of an electromagnet is greatly affected by the material it is attracted to and the thickness thereto. If you have less than .250" thick material you may begin to see losses in holding forces particularly with our larger units as the magnetic saturation point in the attracted material is reached more quickly due to their stronger magnetic fields. Smaller diameter units may be less affected by thinner materials however; all are tested and rated based on their attraction to .250" 1215 CRS or 1010 plate steel.

Do the magnets have residual Magnetism?
In our DC rated units NO. Since we use low carbon steel our electromagnets hold very little effective residue magnetism after the units are switched off. In our AC rated units YES some. Since units marked AC have an in-line bridge rectifier which converts the input AC wave to DC through a network of alternating diodes the rectifier in effect does trap some minimal residual in the electromagnet.

What is the Quick Release option?
Our quick release models introduce an air gap at the center post of the electromagnet. This .003-.005" gap allows for quicker release of work hold material in applications that require faster release response. Please note that this option does decrease the holding forces from that of the non quick release model. Each unit has its own holding force for review online.

Can I use a battery to power the electromagnet?
While the answer is yes however, we do not provide engineering services to determine the battery required to power the unit you require. We will gladly provide you with the power consumption specifications for the unit in question and the rest will be up to you.

Do you sell power supplies?
No. Not currently but we plan to offer some soon. for now visit: http://www.powersupplydirect.com