Modified automotive alternator

[sbkenn]

Hi All.  I am thinking of modifying a car alternator so:
Dismantle the rotor.
Replace shaft with non-ferrous.
Replace the coil with NdFeB tubular or multiple bar magnet(s).
Maybe, wind a lesser coil round the magnet ... can the NdFeB flux be boosted with a coil ?
Re-use magnetic commutator.
Build a regulator which boosts the flux when maximum output is needed, reduce (reverse bias) it to prevent battery overcharge ... or just dump excess power to a resistor/water heater
With an alternator capable of providing more power than the turbine, simply dump power to prevent over-speed.  Times that strong winds are
likely, are times when hot water is most useful anyway.

Comments please.

[Flux]

Basically magnet materials behave as a saturated air gap, the field to gain any extra flux will be the same as for air (not viable). It is more viable to reduce flux but even so you won't have enough space for a practical winding in addition to the magnets to give much control, a dump regulator is the way to go.

Don't expect much hot water from a modified car alternator, at least with direct drive.

Flux

[sbkenn]

I live on a boat.  The main alternator will be belt driven from a diesel engine.  I have 2, 110A 28V alternators, one of which which will be run at  >4000RPM.  Engine coolant is used to heat radiators in the cabins, 230V alternator will power a heater element in the coolant for more heat, and quicker warm-up for the engine.  For wind power, I have a 1.8m 3 bladed turbine ( I may add a 2nd turbine in front of the 1st) , which will belt drive the 2nd alt, at probably 1:3.  A minor complication of living on a boat in a tidal harbour is that the whole windy assembly will have to be balanced as the boat leans over substantially when aground.
Further power systems will be a small petrol engined, standby generator, again, belt driving a smaller automotive alt.  Another, this time, ex army 80A 24volt driven off one of my propulsion engines.  Yet another (yet to be acquired), will be driven off the 2nd prop' engine.  Quite a system to manage !
Can anyone suggest what the comparison is between the electromagnet in the regular alternators, and a PM using Neo' magnets of the same volume.
How about 1/2 the volume, with iron (and coil) making up the rest of the space.

Shane

[joestue]

Neodymium magnets are an air gap, with about 1 million amp turns per meter of magnet in the airspace. So they generate about 1T field at the surface of the magnet. It simply isn't possible to put that many amp turns through a copper coil.. by a factor of like 10. but the magnet is an air gap, which is why you can't practically increase or decrease the flux by wrapping coils around the magnet.

When combined with magnetic pole pieces, such as the stock alternator claw pole forging, you will have no problem saturating the core, and generating a lot of heat in it, but you won't practically increase the output of a vehicle alternator because its limited by core saturation. the only benefit is for low rpm, where they don't generate enough power to run the field coil.

[Flux]

I think that you may get some form of control if you keep the field coil and add neo magnets by turning down the claws and adding rectangular magnets to the claws. You certainly won't get any boosting but you may get bucking for control. The main problem may be heat, when cold you can push neo back along the recoil line quite a long way but above 60 deg  C you may start demagnetising it.

Flux

[sbkenn]

I had considered the de-mag scenario.  I think I will run with just  Neo for now, starting with approx half the coil space.  I will also buy some more of the 2.5kW alt's ... if there are any left, they were only £65.
Thanks