# Electric generator with diametrically magnetised magnet?

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#### J_Nichols

##### Member
I bought a diametrically magnetised magnet like this (http://www.first4magnets.com/circul...rically-magnetised-n42-neodymium-magnet-p3641) some time ago to build an electric generator.

I have been reading a little bit of information on the net and I think it is a good idea to ask here too this simple question. The questions are about some basic designing concepts:
1. The configuration of the coil and the magnet - Where to place the magnet in relation with the coil? How do I should wind the coil?
2. What parameter to check to get a desired voltage - More turns of coil means more voltage? What is the ratio turnsutput voltage?
This is the configuration I think will work:

#### chemelec

##### Well-Known Member
As well as More Turns, Probably Faster Rotation will also increase Output Voltage

#### gary350

##### Well-Known Member
I see a problem. The magnetic field has to change N, S, N, S, N, S, across the coil. If you have wire around PVC pipe and the magnet rotates inside the pipe the magnet field is rotating around the coil not across the coil. I have built several generators just for my own education purpose. The magnet field much change from N to S and back to N for it to generate. You can use 1 coil, 2 coils or a dozen coil connected in series or parallel to get either AC or pulsing DC output depending on how it is wired and built.

If for example the blue color is N and the pink color is S and magnet rotates inside a coil there is never a changing magnet field across the coil if the wire is wound in the same direction as the magnet rotation. The wire has to be wound 90 degrees to the magnet rotation. Magnet can also rotate in a U shape metal core with a coil on the metal core. You can spin the magnet in a metal donut with several coils inside the donut.

A picture is worth a 1000 words wish I could upload photo but my good computer crashed and I am using this antique laptop and i am still trying to figure out how this thing works.

You need an amp meter and volt meter connected to a test coil. The faster the magnet spins the higher the voltage goes up to a certain speed where more RPMs makes no difference. Read amps and volts on the meters to learn watts then do the math to determine wire size for a certain voltage amp coil.

A 500Hz generator is much smaller than a 60Hz generator for generators of the same watt rating. When you design and build a generator built it for a certain Hz. If you build a 60Hz 100 watt generator then run it at 400Hz the wire size will be too small extra for power it produces. At 400Hz it could be 250 watts that will be too much for a coil designed to be 100 watts.

#### J_Nichols

##### Member
I see a problem. The magnetic field has to change N, S, N, S, N, S, across the coil. If you have wire around PVC pipe and the magnet rotates inside the pipe the magnet field is rotating around the coil not across the coil. I have built several generators just for my own education purpose. The magnet field much change from N to S and back to N for it to generate. You can use 1 coil, 2 coils or a dozen coil connected in series or parallel to get either AC or pulsing DC output depending on how it is wired and built.

If for example the blue color is N and the pink color is S and magnet rotates inside a coil there is never a changing magnet field across the coil if the wire is wound in the same direction as the magnet rotation. The wire has to be wound 90 degrees to the magnet rotation. Magnet can also rotate in a U shape metal core with a coil on the metal core. You can spin the magnet in a metal donut with several coils inside the donut.

A picture is worth a 1000 words wish I could upload photo but my good computer crashed and I am using this antique laptop and i am still trying to figure out how this thing works.

You need an amp meter and volt meter connected to a test coil. The faster the magnet spins the higher the voltage goes up to a certain speed where more RPMs makes no difference. Read amps and volts on the meters to learn watts then do the math to determine wire size for a certain voltage amp coil.

A 500Hz generator is much smaller than a 60Hz generator for generators of the same watt rating. When you design and build a generator built it for a certain Hz. If you build a 60Hz 100 watt generator then run it at 400Hz the wire size will be too small extra for power it produces. At 400Hz it could be 250 watts that will be too much for a coil designed to be 100 watts.
Thanks for the explanation. I didn't know that a changing magnetic field moving in the same direction of the wound coil would produce no change.
I am reading a little bit more about what you have said and maybe I will ask latter more questions.

#### alec_t

##### Well-Known Member
Have a look at this for an explanation of how motion, field direction and current direction are related.

#### kinarfi

##### Well-Known Member
At first glance, this looks like it would produce DC voltage.
Using a PVC pipe would amount to large air gap, but if PVC tube is thin walled, OK

##### Well-Known Member

About 30 years ago I was involved with aircraft power generating systems, mostly DC Starter / Generator systems for turbine prop engines. Above is an image of the magnets we used on some of the product. If you look closely you will see some small chips on the poles which is why this one was a reject. The magnet sections provided Excitation to the generator portion. Been so long I forget which units these were even used in. The center ID diameter is about 1.825" and pole to pole the OD is about 3.500". Following the magnetizing process (they were all made stronger that required) they were tested and placed on a "knock down" stand where the magnetic field was reduced to a specification. This magnet is similar to what ClydeCrashKop posted.

Ron

#### J_Nichols

##### Member
At first glance, this looks like it would produce DC voltage.
Using a PVC pipe would amount to large air gap, but if PVC tube is thin walled, OK
View attachment 101248
Hello and sorry for the time to answer.
I haven been watching this youtube video (
)

and it seems the solution you have drawn in the bottom right. The problem with the video is there is a large air gap, but it can be solved using another kind of tube.

Is this the correct setup?

#### dr pepper

##### Well-Known Member
Hey ron is that a alnico magnet, one of those you need a keeper ring to prevent loosing magnetism with the magnet out of the gen?
Fitters nightmare, but you got a lot of power for the size.

##### Well-Known Member
Hey ron is that a alnico magnet, one of those you need a keeper ring to prevent loosing magnetism with the magnet out of the gen?
Fitters nightmare, but you got a lot of power for the size.
I am not sure what they were made from. I have a few and have had those things for close to 30 years or so. They are what I would call average strength as I haven't a clue anymore what the gauss ratings were. Later in my career I worked with some incredibly strong magnets used in special motors. Like most powerful magnets they were extremely brittle. Company badges used RFID and a magnetic strip and if one of those suckers got close the strip was history. Likewise if they got close to your wallet say goodbye to your credit cards. We had a room "The Magnet Room" dedicated to their mounting and use as well as unpacking. Been over 3 years since I retired now.

Ron

#### dr pepper

##### Well-Known Member
If I'm correct alnico's were 'charged' by an impulse from a magnetic winding, similar to how a neodymium is done, only there needs to be a 'keeper' around the magnet to maintain lines of force, removing the magnet from its keeper or silicon steel stator once assembled causes it to loose most of its magnetism, I think its summat to do with the opposing poles being on adjacent lugs of the magnet.
That explains why yours are only moderate strength, if they are alnico's.
Alnico like neodymium chips easily, they were popular from the 50's till about the 80s when neo's became cheaper.