parts of a regenerative braking system

Well, you CAN make an induction generator- but you have to have an excitation voltage present to make it work. In fact, if you take an ordinary induction motor and instead of having it drive a load, drive it FASTER than it "wants" to turn (ie, faster than its synchronous speed), it will in fact generate power and feed it back onto the supply grid. It just can't start from scratch, you have to put it on an AC grid to generate the induced currents in the armature before it can start generating. And, if you do this on a large scale as wind-power "farms" do, then you need to pay attention to things like power factor correction (relative phase between current and voltage) because induction motors and generators don't operate at unity power factor.

But yeah, I agree that saying "every motor will act as a generator" without caveat is incorrect. If you want to use, say, a variable-frequency drive AC motor as a regenerative brake, its got to have a "smart" controller to make everything work right. Not the least part of which is deciding when to start applying the friction brakes smoothly and seamlessly so the driver gets however much stopping force he wants without noticing a change from regenerative braking to friction braking.

Reply to
Steve
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A brushless motor is a stepping motor and requires some high- powered electronics to provide a rotating signal to the many leads of the motor. Not simple. And it won't act well at all as a generator. An automoble alternator will not act as a motor. Period.

The simplest way is to use a series-wound DC motor with separate field and armature feeds so that forward, reverse and braking can be performed easily. Field current is always one polarity and armature current is reversible. Overall current is varied using solid-state devices like a MOSFET and some interface components. Braking is achieved by either shorting the armature leads together or connecting them to the battery, while the field is fed current varied to achieve the amount of braking desired..

You need first to get a course in basic electricity, then think about this again. It's much more involved than you think. The fact that there are few setups like this out there speaks for itself.

Dan

Reply to
Dan_Thomas_nospam

Yeah, I should have added the caveats. I was meaning that any motor type likely to be used in an electric or hybrid car. And for the variable f motors I did mean that they needed the smart controller. In fact, in an earlier post my contention was that the controller for a good hybrid was a pretty fancy piece of high power electronics. Smart and able to switch high current at high frequencies.

Reply to
Don Stauffer in Minnesota

Right, the controller is really the hard part, and it's part of the reason why the electric car craze of the 1920s died.

Back then, they used DC motors either with a rheostat in the field coil or with taps on the field coil to adjust speed over a fairly narrow range. This is inefficient, and efficiency is everything when you are trying to run off a limited capacity battery.

These days with solid-state electronics it's a lot easier to make an efficient controller with a PWM circuit driving a big switching transistor driving the motor. But, because we have electronics, it's ALSO possible to go to more complex motor designs like the "brushless DC motors" which are really multipole AC motors with position sensors driven by a digital controller.

Needless to say, regenerative braking makes the control system a _lot_ more complicated, because it first needs to reconfigure everything so the motor is rewired as a generator (with most motor designs) and secondly it needs to regulate the power produced for effective and efficient battery charging without damaging the battery and at the same time make sure the generator sees a constant load so that the drag it produces does not vary.

--scott

Reply to
Scott Dorsey

A brushless DC motor is NOT a stepper motor. Two different animals entirely. Most brushless DC motors (as used in, for example, computer case fans) are actually very simple AC motors (either induction or hysteresis motors) with a small electronics package that turns the DC into an AC drive signal. A stepper motor is far more complex, and while it is technically a DC motor with no brushes, its a very unique sub-class.

Reply to
Steve

A potentiometer is a variable resistor, and it's simply impractical to use for direct control at the power levels you're talking about. You could get by with large diodes and relays if everything is DC; otherwise you'll need large MOSFETs or IGBTs, but you can get by with SCRs and Triacs.

Check

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a site that covers everything electronic, and look not only for regenerative breaking but also for variable frequency drives, or VFDs, and hard disk drive motors and controllers (they use regenerative breaking).

I'd seriously consider making my first prototype all-electric since regenerative braking alone is quite a project.

Reply to
rantonrave

Okay I guess I should take a short course on Electricity or maybe read even more books or websites.

But I guess I can't handle everything and I still have to leave the electrical/electronics part to the engineers since I'm already handling the mechanical part of the vehicle.

But just for experimenting and testing, I guess I'll just look for the right kind of motor and a good controller such as Curtis.... although Curtis Controllers seem to be too expensive.

I have a question... If there's a brushless DC motor then is there a brushless AC motor? Or are they just the same? I'm still confused here.

Reply to
lethaldriver

A brushless DC motor is secretly a multiphase AC motor in disguise.

Almost all AC motors are brushless. Most AC motors you see are induction motors, in which the changing magnetic field from the field coil induces current in a wire loop on the armature, which induces an opposite magnetic field in the armature, causing the armature to turn in the field of the field coil. No brushes required, but speed control is very limited.

--scott

Reply to
Scott Dorsey

So do brushless DC motors need inverters when powered by car batteries??

What motor do you recommend for an electric car/bike?

What kind of motor does Toyota use in their Prius? How about in golf carts?

Reply to
lethaldriver

guys, any inputs here?

Reply to
lethaldriver

They need an electronic control unit which is usually built into the motor itself, which turns each coil on and off at the appropriate time. It's not really an inverter per se.

For a bike, I might consider a permanent magnet motor with rare earth magnets, because they have a very high power to weight ratio and they occasionally turn up military surplus for cheap.

Dunno, I never took one apart.

Most use universal DC motors, with some sort of control system that adjusts the voltage on the field coil to vary the speed. This was an excellent design back in the seventies when control electronics were expensive. The efficiency is poor and there is no regenerative braking, but who cares? It's a golf cart. The worst that can happen is someone has to carry their own clubs.

--scott

Reply to
Scott Dorsey

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