[WCRiot]

Hey all. I know I am the new guy and that I am going to get a lot of crap for asking such an amateur question but I have to. I can't stop thinking about electric cars right now.

How does the Regenerative Braking work for the current hybrid cars?
How is the Regenerative Braking on hybrid cars different from the Regenerative Braking used by DIY EVers?
Has anyone placed a generator onto their braking system to act as additional charging for the batteries and help with braking?

The reason i ask this is: I think of those old school bicycle generators so that you have have a head light on your handlebars. Those generators obviously create drag and that is why they would not be used during normal operation but, what if there was a way to properly mount and activate the same style generator to your car? The drag would only be placed on the car when braking (which would reduce brake pad wear). I know it would not be a lot of voltage or current supplied for charging but would the engineering effort be worthwhile, maybe? But wouldn't every little extra help increase the distance that an Ev can travel?

thanks,
BIGman
Be gentle...

[david85]

I'm fairly new here as well, but I'll take a crack at your question.

Your example of using a generator to create "drag" to slow the vehicle down and recover energy at the same time, is basically how current hybrird work. Normally, kinetic energy is dissipated through heat in friction brakes, and there is also the normal wear and tear that comes with it.

Once the hybrid comes to a stop, there is now some extra electricity available to the electric motor in the powertrain of the car (in many cases the motor doubles as the generator), so that when the light turns green, it is re-used to help accellerate the car back up to speed.

This is usually called "launch assist", in that the extra power is only used when needed almost like a supercharger, but once the car is on the freeway, you are still getting driven by gasoline alone.

So for inner city driving, there is an improvement in range, and fuel economy, but in the case of parrallel hybrids, there us usually no difference in MPG under consistent speed conditions.

There are some examples of advanced pure electric vehicles (pancake motor in each wheel) that can do away with friction brakes alltogether, while offering some of the most advanced traction control systems ever seen. (all that with ONE moving part per wheel)

I don't know if anyone here is using regen, so can't comment on that.

[WCRiot]

So the current hybrids are using the electricity generated from the kinetic energy from the brakes? Can you explain this a little more? How exactly is this done?
Is there Piezoelectric material involved? is there a simple generator like i explained that is attached to the rotor when braking?

For this launch assist that you are referring to: Is the energy stored in a basic capacitor? This is probably a better idea than what i was referring to about using the brakes to actually charge the batteries.

I love all the technology that is in these hybrid and electric cars. I hope that the gasoline vehicles begin to advance more for better efficiency and emissions.

[houseoffubar]

WCRiot, The current parallel hybrid's (Prius, Insight) all use AC motors, and controllers. These are quite efficient, and simple to regenerate, by simply reversing the load to the motor. The motor then simply turns into a generator, sending power directly back to the batteries. For a better explanation, do a Wikipedia search http://en.wikipedia.org/wiki/Regenerative_braking
Most D.I.Y EV's are DC systems, for many good reasons. DC is substantially cheaper. It does not require an inverter to change the battery DC to use in the AC system. DC is very durable, and common to find. Many a DC vehicle has been built using forklifts, and golf kart's, ETC.
AC has it's advantages as well, it is more suited to use as direct drive, than DC, as it can spin to higher speeds in general due to it's lack of brushes, while having almost the same starting torque as a DC system.
For the most part it is the complexity, and expense that keeps D.I.Y.er's using DC. Hope that is some help. Eric

[david85]

Yep, and about capacitors, so far no full production hybrid or battery powered car has used them to recover braking energy, but there have been a few experiments. I remember a city bus that used a hyrdogen fuel cell, battery bank (nickel hydride), AND a bank of capacitors.

The fuel cell allowd fast refueling and longer range, the batteries provided high draw power for long hills, and the capaciters were used for the Regenerative Braking, since capaciters can accept a dump charge more efficiently than most batteries (slaming the brakes can cause a lot of powerflow).

Very complex, but I guess it proved the point.

These days, there are capaciters that are getting close to having enough reserve to double as the battery, while on the other hand, some batteries can be dump charged to deliver capaciter-like performance. I'm not a fan of fuel cells, but it seems that there is still some slow developement in the technology.

[eRubicon]

To answer your first question, you could use a car alternator (high output variety) attached to free shaft (assuming you have a dual shaft motor) to produce some drag for break assist and produce some power. Alternators spin relatively freely when not under load. A switch on your break pedal that would engage with very light pressure(like break light switch) could complete the circuit to "load" the alternator, thus creating drag and producing charge. In a EV with transmission, depending on the gear you're in, this could provide significant drag-breaking. The output voltage would be a hangup. Alternators are voltage regulated for 12 volt systems. The amps can be as high as 180 amps though. You could just use it to charge your 12 volt acc. batt. but this might not "load" the alternator enough for significant drag unless you had pretty high demand on that batt.(Electric power steering, etc.) Not sure about voltage capability of alternator itself. Might just need a change of regulator to allow higher voltage and you might be able to charge traction pack minimally.
Anybody got real experience with this? I've just been rolling it around in my head for a while.