Neodymium magnets

[Etownlax]

Where do you guys get all of your magnets? Better yet where do you get them "cheaply"?

I'm building a wind turbine sometime but I need to know where to buy decent sized magnets without having a huge bill.

Any idea's would be awesome.
-Randy

[Bob Boyce]

http://forcefieldmagnets.com/catalog/

[Etownlax]

Thanks for the fast reply... I'll look into getting some here...

-Randy

[Chris]

another good source that I use is http://engconcepts.net

[Etownlax]

Thanks for another source.

I have another question when it comes to magnets and magnetic coils...

How do you know how many coils to use and how many magnets to use?

I'm planning on a 3 phase alternator but I don't know how many magnets I need if I use 9 coils. I've seen some use 6 magnets(I think.lol) and others use 12. So how many magnets do I really need for a good alternator?

Any ideas are great.

-Randy

[Bob Boyce]

The number of magnets and coils is largely determined by the diameter of the rotor and stator. For efficiency, you want close to the same number of coils vs magnets. Having more than one magnet transecting a coil at once causes efficiency losses.

There is one thing to remember however. Use an odd number of magnets vs coils. If you use 9 coils for example, use 7 or 8 magnets, not 9. When you use the same, or multiples of the same number of magnets vs coils, the rotor will exhibit a very noticed cogging effect under load. This translates into stronger vibrational stresses that may cause premature failure. By using a differing number of magnets, the cogging of each coil is slightly offset from one another, so they do not create an accumilative effect that work together to create rotor impulses. This is a design flaw I see in many plans for homebrew wind generators.

When determining the number of coils, remember to rectify the output of each seperately. The offset magnet approach produces impulses that are out of phase with other coils, so combining multiple coils into a single rectifier is not as efficient. It will also rotate smoother at lower RPM with more numerous smaller diameter coils/magnets than with fewer larger coils/magnets

Bob

[Etownlax]

[Etownlax]

So basicly I need to rectify every coil(so for me a total of 9 rectifiers).

So can should I use a full-wave bridge rectifier like this...


And do I have the (+) and (-) right?

Thanks for the great help...

-Randy

[Bob Boyce]

As far as the bridge rectifier diagram, yes, it is laid out correctly. As far as the + and - (polarity) being correct, that depends on the rectifiers. Over the years, I have seen rectifiers with the band at the cathode instead of the anode, but most have the anode banded. As long as you use 4 of the same, and check to be sure they are anode banded, then your polarity is correct.

Bob

[Bob Boyce]

Oh, one more thing. Depending on the power level you intend to produce, diode cased rectifiers may not be able to dissipate enough heat. You may want to go with stud mounted rectifiers, and drill/tap holes into a pair of larger heat sinks for mounting the rectifiers into. Use one heat sink for a bank of case anode rectifiers (+), and another bank for case cathode rectifiers (-). Real simple to wire, as each coil lead connects to one rectifier on each bank. The + and - are taken from each of the heat sinks themselves. Just mount them on insulated standoffs to where they can be cooled by airflow.

Bob

[Etownlax]

[Etownlax]

A quick question...
If I have 3 coils that are rectified seperatly and are all making 5 volts can I wire them in series to make 15 volts?

-Randy

[nebbian]

[Bob Boyce]

[Etownlax]