who knows about magnets?

[fehr]

I would like to know why people don't put coils on either side of a rotor containing rare earth magnets

 when building alternators.I would also like to know where the best place (cheapest) is to purchase

 magnets.

[DanB]

Its important to have steel or iron (preferably soft steel) everywhere in the magnetic circuit except where the coils exist.  So, in most cases well have iron on one side of the magnet, then a coil, and then either another magnet with iron behind it... or steel laminates.  The idea is to have the best possible magnetic circuit - this makes for a stronger field through the coil.  Voltage is directly related to the strength of the field.  We could have a plastic, or wooden magnetic rotor and put coils on either side like you suggest...and then perhaps some laminates behind those coils or something.  My guess is the output would be similar (perhaps a bit less) than if we just had one stator (one set of coils) existing in a much stronger field.  

Regarding where to buy magnets.  Our best deals for alternator builders are here:

http://www.wondermagnets.com/cgi-bin/edatcat/WMSstore.pl?user_action=list&category=Electricity%3
BRenewable_Energy

You can also check rareearthmagnets.com

check ebay!