0
\$\begingroup\$

I am constructing a very basic miniature generator (25mm diameter), the rotor has 8 bar magnets, and there will be the same number of coils, wired appropriately, in the stator.

rotor/stator arrangement.

I understand that the magnitude of the induced current is much bigger with iron cores to the copper coils. However, I have only very basic materials. The cores will be short lengths of iron bar, similar dimension to the bar magnets, cut lengthwise to minimise the air-gap.

QUESTION 1: Can I wind the copper wire directly onto the iron bars? Would this cause some kind of interference?

QUESTION 2: The bar magnets are very powerful Neodymium type. If the air gap between rotor and iron cores of stator is minimal, I don't see what prevents the alternate "N/S" polarity of the magnets basically locking onto the iron cores and preventing it from rotating!

\$\endgroup\$
  • \$\begingroup\$ Not a great idea. But a layer of insulation (like Mylar tape) on the cores first will protect the wire's insulation from damage against sharp iron corners. \$\endgroup\$ – Brian Drummond Jan 11 '18 at 18:28
  • \$\begingroup\$ Good idea, thanks. The iron bar IS quite edged, so I will round of the edges and tape. \$\endgroup\$ – B Faulkner Jan 15 '18 at 17:22
1
\$\begingroup\$

Q1 that should be fine.

Q2 You will get this it is called cogging and is normal in this type of generator you need to apply enough force to overcome this.

You also need to give consideration to completing the magnetic circuit both in the rotor and stator. This allows the lines of magnetic force to easily propogate between each magnet in the rotor and each core in the stator. In its simplest form this would be an iron centre for the shaft which each magnet is attached to and an iron ring joining all the coil cores on the outside.

The magnetic force lines will propagating through the air. This gives you less magnetic field strength where it matters around the coils. A low efficiency generator can be made to work with this. If you look at a a good professionally produced generator it will optimise both the electrical and magnetic circuit.

\$\endgroup\$
  • \$\begingroup\$ RoyC - not clear about second potentially important comment on 'magnetic circuit'. Albeit possibly inefficient, will I not generate some level of AC with rotor magnets even WITHOUT iron centre, and without iron ring on stator? At present iron centres of stator coils are simple separate bits of iron bar not connected with each other. Assumed that rotor magnets on their own interacting with 'strengthened' coils would be enough? \$\endgroup\$ – B Faulkner Jan 15 '18 at 17:34
  • \$\begingroup\$ I agree in this case the magnetic force lines are propagating through the air. This gives you less magnetic field strength where it matters around the coils. A low efficiency generator can be made to work with this. If you look at a a good professionally produced generator it will optimise both the electrical and magnetic circuits. \$\endgroup\$ – RoyC Jan 15 '18 at 17:40
  • \$\begingroup\$ All good advice! Do I take it that if I DON'T have both an iron core to rotor and iron ring on stator, I basically won't have a 'magnetic circuit'? Very confused about where this circuit is going from/to. How does the iron core of the rotor improve the magnetic circuit for example? \$\endgroup\$ – B Faulkner Jan 16 '18 at 10:22
  • \$\begingroup\$ N pole of magnet to S pole. Imagine it as like an electrical conductor the air is a poor conductor iron is a good conductor. One of these is better than none both is better than one. \$\endgroup\$ – RoyC Jan 16 '18 at 10:27
  • \$\begingroup\$ I think I have grasped this 'magnetic circuit'! Assuming 'alternate pole' rotor magnets are attached to iron core, and there is an iron ring on the stator, I assume continuous magnetic circuit is as follows: e.g N to S of first magnet, then S to N through rotor core, then N to S of adjacent magnet, then S to N through associated iron bar of stator AND iron ring of stator, then N to S through next magnet etc. Is that correct? Final question - how does this more efficient MN. circuit improve induced current? Isn't this just a function of magnet strength, coil area + No. coils and rotor speed? \$\endgroup\$ – B Faulkner Jan 18 '18 at 10:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.