# Electromagnetic braking

• I
I'm working on a project and came across electromagnetic braking recently and I'm really curious to know if it's really feasible. The project in brief is a vehicle on a monorail at speeds of +600km/hr needs to be stopped. The monorail is made of an alloy of aluminium.
I have no background in electromagnetics, I wanted to know how I could go about calculating the heat it would generate, and how much power it would need if the size of the magnets was known?

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Grinkle
Gold Member
I don't have any experience with these systems, so the below is off the top of my head, fwiw. I am certain there are folks here with a lot more knowledge than I have about these systems.

if it's really feasible
That depends on the design targets, like braking distance, allowed weight of the braking system etc. Certainly one can take kinetic energy in a moving body and convert it to electrical energy - so in that general sense it is feasible.

Google to get an idea of how real world EM brakes work - they certainly exist. The basic idea is that you couple the moving thing you want to apply the braking force to with a magnet that is caused to rotate in an electric field by the momentum of the moving thing. As the magnet moves, it experiences resistance to the motion and this drags on the thing that you are wanting to brake, slowing it down.

You end up with electrical current that needs to be disposed of. If you send this current through a resistor to dissipate the energy, you get heat. You can get an idea of how much heat (to a first order) just by doing an energy balance - all of the kinetic energy of the moving thing needs to be turned into heat at the end of the day. If you can do something else with the current like charge a battery or send it into a power grid then maybe there is not so much heat to worry about.

Regarding power needs, the system is taking energy from the moving object, so just like brakes in a car, they wouldn't require a lot of external power to perform the braking per se. There would need to be some mechanism for engaging the moving train to the magnet, like there needs to be some mechanism for making auto brake pads grip the disk of a wheel. The cars brake pads don't use external power to slow down the car, and an EM brake does not use external power to slow down whatever it is braking, either. The EM brake is a generator, and the power it is draining away from the moving thing needs to be dissipated. If this doesn't make intuitive sense to you, then find a tiny generator in a toy or wherever you can find one, and turn it manually - it will be hard to turn. This resistance to turning is what does the braking.

ZapperZ
Staff Emeritus
I'm working on a project and came across electromagnetic braking recently and I'm really curious to know if it's really feasible. The project in brief is a vehicle on a monorail at speeds of +600km/hr needs to be stopped. The monorail is made of an alloy of aluminium.
I have no background in electromagnetics, I wanted to know how I could go about calculating the heat it would generate, and how much power it would need if the size of the magnets was known?
This is very vague. What type of resources are you given within the parameters of the problem? This will tell us (and you) if it is "feasible".

If I'm told that money is no object, and I can suck all the electrical power that I need, then this is feasible. But if I'm given only what I can purchase for \$100, and the household electrical supply, then that's a different matter entirely.

Zz.

jrmichler
Mentor
Try first searching eddy current brake, then eddy current brake calculation. Eddy current brakes use a magnetic field to generate eddy currents in a conductor. The conductor is moving relative to the magnetic field.

Electromagnetic brakes use an electromagnet to actuate a mechanical brake.