How do you build eddy current dynamometer?

Answer 1

This experiment can be highly dangerous!

1 First you need a DC electric power source. Depending on your application, a set of batteries (12 volts should work), a car generator or alternator or even a plug in battery charger might work. The greater the amount of power you want to measure the greater the amount of current. I like the car gen/alt idea since you can hook up pulleys and run them off your dynamometer, but you will still need a battery or a high powered ultracapacitor (I imagine that 50F or more for up to 15V might work on most set ups) in connection with the gen/alternator.

2 You will also need a chopper circuit to control and limit current to the stator. You can buy motor controllers that might work, as long as they are for a DC motor and are rated at the proper current for your system.

3 Frame for the whole assembly

4 Armature and stator. On low power applications an AC induction motor might work. If it is 3 phase just use 2 of the wires. If you want a more powerful dynamometer you will need a shaft with bearings, two thick iron disks with cooling vanes welded on them and four or more high powered electromagnets (more = more torque, less speed). Arange the electromagnets so that they are secured around the shaft by means of bearings with their poles parallel to the shaft. The more precise the better. Next secure the disks to the shaft itself so that the disks come in close contact with the poles of the electromagnets, one disk on each side, but not touching. You may have to make your own electromagnets with magnet wire and iron cylinders. Make sure that everything is secure and well balanced. Note that making your own system can be highly dangerous since it will have to create a lot of torque at very high RPM's. To see a real life eddy current brake look up pictures of the Telma Retarder. They have 8 electromagnets but are for very high torque and low RPM.

4 Make a motor mount for the motor on the frame and a way to connect it to the armature. This will have to be very precise.

5 You will need some way to measure torque. If you have designed it right the stator can spin on the armature. Connect a rod to the stator and then to a scale of some sort. Note that the scale will hove to be able to keep the stator from moving except for very small movements that are read on the scale as torque. The possition of the scale depends on the direction the engine rotates.

6 How it works. You start the motor and rev it up. The batteries or alternator, ect. supply electricity to the controller (that you control) which supplies current to the electromagnets in the stator. This causes current in the rotors which creat an opposing megnetic force. This in turn creates a torque load on the motor which is read by the scale. The more you turn up the controller the more torque you will have on the motor. The result is heat created in the rotors. You might be able to find a way to automate the system if you want.