timpootle wrote:Your question has been answered - yes you can reverse a series wound motor using the appropriate contactors. What you can't do, to my knowledge, is use a series wound motor to give you regenerative braking. This involves reversing the field current but not the armature, or vice versa. As these windings are in series (hence the name) there is no tap-off in the internal wiring of a series wound motor to achieve this.
If anyone can tell me I am wrong I would very much like to hear how.
Reversing the voltage polarity to a series wound motor reverses the magnetic field of both the armature and stator (field coils), so the motor still runs in the same direction. This means you can even run them from an AC source and that's what they do in power tools where they are known as 'Universal' motors.
For a series motor to be reversable, you must have more than two terminals (ignoring some oddities like motors that reverse by moving the brushes). A series motor suitable for EV use, such as the ADC or Netgain will usually have four terminals, two for the armature and two for the stator.
Reversing the polarity of either the field or the armature will reverse the rotation, but if you want to be able to use regeneration, then you would reverse the armature, so that the residual magnetism in the stator iron will provide the excitation to start the motor generating.
What you would do is use the controller to short circuit the motor. The current would build up at a rate limited by the motor inductance and when the controller detects a preset limit it would unshort the motor. Then as the energy stored in the inductance is released it boosts the voltage above the battery voltage and so charging the battery. The duty cycle of the PWM is used to control the regen curent in much the same way that is done for drive.
The Zapi H2 controller amoungst others is suitable for regerative braking with series motors, but there are some limitations. Ideally the brushes should be set at neutral and that conflicts with forward drive requirements (too much brush arcing at higher voltages). Motors with interpoles that 'force' good commutation are available, but are physically bigger and more expensive. The Nelco motor in my Reliant Kitten that Evan still owns had interpoles, but the only other motor I know of off hand was the Kostov from Eastern Europe.
If you accept that all you are going to get is the equivilent of engine braking from an ICE, then most series motors will work up to about 96 volt, which is in any case the limit for readily available regen controllers.
In any case you have to be quite careful with regen. If someone crawled underneath your car and cut the rear brake lines, you might think they were trying to kill or injure you, but some people have felt happy to use regen on a front wheel drive car equivilent to machanical braking. You've also got the problem of the rate at which the batteries will accept regen current. You wouldn't want the braking to suddenly dissapear because the batteries were cool and at a fairly high state of charge. When GM built the EV1, they tied the regen into the ABS controller. The rear brakes were applied in proportion to regen and it would seamlessly shift between regenerative and friction braking.