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Discussion Starter · #1 ·
I know some stuff can be figured out from other crap, but I don't know what kinda crap I need, and I don't know what kinda stuff I can figure out! Worst off, I don't know what kinda shit I need to search for to figure out what the other stuff & crap is!

I guess that means that I'm looking for theory, or general wisdom. What I need to know right now is what the hell is generated? I know there will be more that I need, but just that for now.

Like, I know that the "drag" can be expressed in watts, it's like negative horsepower. A deceleration is a speed change, which is the exact same as acceleration.

How do you figure out the maximum and minimum voltage, from this?

If it was an infinite high voltage, then when a motor were switched to open circut (while rotating), it could *theoretically* reach any voltage, no matter how few amps. So it could spark between the terminals, in a "whisper-thin" arc with very little amperage, assuming VA=W, right?

That does not seem right!

Does anyone know of a good website/paper/tech bulletin/book that I should read?
 

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I'm not %100 on the theory but I can observe.

generator basics:
1. take a small dc PM motor, chuck it up to a variable speed drill, and connect a voltmeter (they are fairly high impedance). The voltage output WILL be proportional to speed/rpm.

2. add a resistor to the motor terminals, now you have current and a bit more load on the drill (torque input). the current is the voltage output at that rpm divided by both the load resistance and the internal resistance of the motor windings/etc. the voltage output drops a little because the motor windings and resistor act like a voltage divider.

3. put a lower value resistor on there, get more current, more torque on the drill, more voltage drop in the motor for a given rpm.

therefore: rpm~volts out (no load), torque in = current out (you have to actually apply a load to change the current at a given rpm).

same sort of thing happens when it is motoring. current = torque, volts ~ rpm. Power is a function of volts*amps or torque*rpm. Due to winding resistance/friction/etc electrical power != mechanical power. electrical power is less in a generator, and more in a motor.

4. replace the resistor with a battery(watch the polarity, should spin same direction as drill). It too has some resistance.

5. if you spin it with the drill so the no load motor voltage is the same as the battery voltage, no current will flow. The back emf from the motor is the same as the battery. If you spin it slower, the battery will discharge. if you spin it faster it will charge. the current is a function of the voltage difference and the total circuit resistance.

Apologies if that is all obvious. Anyway on to the "theory".

you are right that if you simply open the circuit mechanically, while current is flowing, you will get a voltage spike, it is a big inductor after all. DC motor controllers have a diode in parallel with the motor, and when the pwm cycle is off, the current continues to flow in the motor. But even without the extra diode, the mosfet/igbt also has a diode, so the voltage spike would go right up to pack voltage and then you get some current, but that is less efficient. And 3 phase controllers are silly with diodes. So not a problem.

I don't know exactly how to analyze a motor by looking at it, but the voltage output (or needed for input) is a function of the rpm, the number of turns, the resistance, the amount of flux the wires are traversing. turns and length are interchangeable (how much wire is passing through the magnetic field in the right orientation). you can think of the turns as being like putting batteries in series, kinda.

once you know the voltage, the current is the total voltage difference divided by the total resistance, i.e. superimposed.

Anyway thats my guess, you can probably google generator theory or something.

motors ARE generators.
 

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Here is a video of Mizlplix driving his car and using the regen function
to stop his car, most of the time he uses NO brakes. He has an adjustable
lever on the collum (pot) He is using a Curtis Controller.

http://ivanbennett.com/forum/index.php?topic=171.0

------------------------------------------------------------------
 

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one last note: so the main problem with dc motors is you can't control the field strength, and you have to be moving faster than the pack voltage would have motored you to. But sepex allows you to increase the field strength and thus the voltage output, and so it can do regen. If you have a gearbox you can also downshift, till you cant, regen current is not controlled, and brushed motors have opposite demands on brush timing vs generators. and series generators have other issues https://www.electrical4u.com/characteristic-of-series-wound-dc-generator/

induction motors can "simply" apply a frequency that is lower than the rotor rpm.

bldc/pmac have to rotate the field at the same rpm as the rotor but they shift the position of the field WRT the rotor field so it pulls the rotor for motoring, and gets "pulled" by it for regen.
 

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Discussion Starter · #5 · (Edited)
Hmmm...

That requires more information than I have, and I'm not that interested in knowing things like, "how many windings".

I was more interested in equations that require measurements that we (may?) have and I have no idea why. Like milliHenry's. I have only used those when making audio crossovers! (for a choke, like half a transformer, that kills high frequencies)

Now I plan to put my plans in pictures, and allow them to be evaluated. I may be half-nuts, but that means that half of my ideas will be good!

WOAH! Mizlplix's car is awesome!
 

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Discussion Starter · #7 ·
For that I would need a motor, and I don't have one yet. I gotta know some numbers! (IDK which numbers :p )

I would then need a variable mechanical power source, to turn the motor as if it were in a coasting car.

I would also need a variable electrical load, and somekinda variable electrical power source (to run something like the field in a sepex). The load would need enough capacity to handle the generated current at it's highest, or the voltage at it's highest. Pick one, or both, but not at the same time. Either could, theoretically, exceed the maximum or the brushes, slip rings, or commutator. So I need a way to measure them both, too!

I have plenty of DVOM's! Anybody got a motor to hack?
 
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