converting series wound dc motor to pma

[arklan]

i hope this is the right section.

i have a motor from an electric car that i killed the windings on the rotor (spirited driving).
motor is an ADC K91-4003
its a series wound motor so it has windings on the rotor, so my plan is to chuck the rotor on the lathe and turn the rotor down enough to make room for magnets and then put it back in.
not sure how to show pictures but the "stator" has 4 coils so im assuming i need 6 magnets on the rotor.
ill put them on a slight angle to try avoid a bit of the cogging.
the motor was pulling 45kw when going up hills and scooting around so im hoping to get at least 5kw from this as an alternator at around 200rpm (wishful thinking?)

is this viable or am i off my rocker? have i got anything wrong or am i on the right track?
thanks

[SparWeb]

Not sure, myself.
I've heard about the ADC motors, of course, in terms of their performance as traction motors for EV's.  Got some datasheets...
Not sure what would happen if you change half of it... if the rest can still do something.
What can you say about the wiring in the stator?  How many teeth, what do the coils look like, gauge of wire, etc.
There are some basic electrical parameters (poles, coils, connection groups, etc.) that you need to know about before you start otherwise you'll get "lots of nothing".

Just for starters, the field polarity on the DC motor's rotor is flipped many times per rotation.  Just count the bars on the commutator....  Now consider the number of brushes on it... so that means how many poles...?

[mab]

hmm.. I'm not a expert on motor conversions, but I have my doubts.

I assume it's wired like the old series wound car starter motors with 4 commutator brushes? 1 pair of brushes series connected with 2 stator coils?

my 1st thought is that the stator windings of these motors is designed to handle the full current of the motor with minimal voltage drop (on d.c.) so perhaps will not have enough turns to give you a good voltage as an alternator? - but that does depend on what voltage the motor was designed to run on and what voltage you are hoping for.

2nd thought is that as the stator is intended for d.c. the stator magnetic path will not be made from laminated iron to control eddy currents - that would be an issue if used as an alternator i think.

6 magnet poles, N-S-N-S-N-S ? I guess that would give you a 2phase (quadrature) output at 3 cycles per rev. That would give you ~100Hz at 200rpm.

[joestue]

You would have better luck rewinding the rotor, and removing the shoes and coils from the stator and adding your magnets there.

If the shoes of the rotor are integral to the lamination stamping then you have a chance of what you propose, but i would make a new rotor rather than destroy the old one. There is no need for expensive neodymium magnets, you can probably fit 6, 2x1x6" ferrite magnets in there for 30$

[arklan]

what do you mean by shoes?

[Warpspeed]

Fork lift motors in various sizes are another example of this type of series wound dc motor.
The difficulty will be that these will have a very low relative number of turns on both the armature and the stator.
They are essentially designed to be a low voltage, high current high rpm motor.

If the fixed stator poles (shoes) are replaced with permanent magnets, that would produce a dc generator, but the dc output voltage produced would be extremely low, unless the rpm were kept inconveniently high.  Rewinding the rotor for higher voltage is not going to be practical, and neither would a gearbox or switching power supply to increase the dc output voltage.

At least starting out with a conventional 220v three phase induction motor, the existing windings might be usable, at say one fifth the voltage at about one fifth the original rated rpm. Star connection or a six pole motor would further improve the volts per rpm.

There has already been a lot of work done by some pretty smart people on that type of conversion, and it would be pretty difficult to come up with something completely new or revolutionary along similar lines.