Depends. Is the clutch engaged? If not, no motor spinny.

Is the motor's field getting power or does it still have a recirculating current keeping a field going? If not, spinning doesn't make electricity. If it's a series motor, regen is difficult to control so a lot of controllers don't do it. Check your controller to see if it can or not.

Permanent magnet motors either brushed or brushless are super easy to do regen with.

non-series field motors are also easy.

But since series motors have the field in series with the main windings, then as soon as those start to produce a voltage and thus current, the current in the field goes up too, creating a greater voltage across them, and this quickly repeats itself until the field is too strong, probably resulting in the very fast cessation of rotation of the motor.

 

While it depends on the motor, your son has discovered the concept of regenerative braking. In theory it is possible to recharge the batteries with a portion of this recovered energy.

However it depends on the motor type. AC motors and shunt DC motor can do regen braking without too much hassle. Series DC motors on the other hand are a challenge because if the motor is coasting, there is no magnetic field to use to generate current. There have been some experiments in regen braking of series DC motors, the most widely recognized being Otmar Home Power article on the subject here:

http://www.cafeelectric.com/curtis/regen/index.html

But even he admits it's a challenge.

BTW to answer the question, if the motor is in fact acting as a generator, then it functions as a brake, slowing the vehicle down. Kinetic energy is translated into electrical energy, which can be used to recharge the batteries.

But the amount of recoverable energe isn't too very large. So most folks who cannot do it easily simply forego regen. It's no problem with a series wound motor, because unless you take a special interest in the controller, it will free spin when coasting, not regen.

Hope this helps,

ga2500ev

 

And if I recall correctly, Ot gave up on the regen project for series DC.

Part of the problem here is that to get the best performance on a series DC motor for traction applications, our brush timing is advanced. This makes reversing the motor an issue (but not impossible) but makes regen braking very difficult because the brushes are advanced ahead of where they should be to make use of the power generation.

The field must be separately excited to handle regen, as Ot outlines in his article, and this becomes quite problematic, requiring a set of contactors to reconfigure the motor wiring.

Even then, at best, you're looking at about a 3-6% boost, give or take, from regen.

Regen is very nice, and in concept it should work very well, but in reality it doesn't provide as much of a gain as people tend to think.

 

A series or AC motor needs to be "jump started" to start acting as a generator. If there is no electricity going (and hence no magnetic field), it won't start generating. In contrast, a permanent magnet motor always has a magnetic field, so it can generate electricity any time it is spinning.

Fine point: Your motor will likely have a little bit of residual magnetism, so it'll actually produce a little bit of voltage.