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Bearleener 07-31-2008 12:20 PM

Do-it-yourself regenerative braking?
Often I just can't avoid hitting the brakes and coming to a stop. To make significant progress on my fuel economy I'd like to look into regenerative braking.

Regardless of energy storage method, how do you get the power from and to the pavement?
Mike's E-wheel at Is it too late? - MIMA Honda Insight Modified Integrated Motor Assist Tour De Sol is technically beautiful and seems to work well, but it's quite complicated.

It's hard to attach drive components to the sprung components (tires, wheels, driveshafts). Seems as if one needs to tap into the transmission or starter gear or something, where you can firmly attach the regenerative components to the engine. But on the engine side won't work if you're EOCing and braking.

How about a second alternator somehow connected to the regular alternator belt and charging an auxiliary deep-cycle battery? Don't know if the belt is up to the job, though, especially when using the energy. (I know, why not go completely electric?)

How about a compressed air bottle as the storage medium, powered by an air motor that is either open (regular driving), pumping into the bottle (braking) or being driven by the compressed air (accelerating). Basically, hook a small Craftsman air compressor to the alternator belt or something. Many trucks etc. use air starters (but they've got the pneumatics on board anyway for the air brakes). But again, both of the above systems can't charge (regenerate) when the engine is off.

The system starts charging when the brake light switch is on and starts discharging either when you press the gas, or, only as a "start rolling and bump start from a stop" assist when you press the gas and the engine is not running.

What ideas do you guys have?

Daox 07-31-2008 12:24 PM

I think any regenerative system is going to be quite complex.

MetroMPG 07-31-2008 12:43 PM

I think about this every time I have to press my brake pedal. :)

The challenge would be sizing the system electrically (and mechanically, as you point out with the belt concern) to be able to offer any meaningful braking resistance. I recently drove krousdb's Prius, and if I'm not mistaken, I was seeing 50-60 amps (@ 270+ volts) when using regen to its full extent. And that offered only "mild" deceleration.

I think the answer (to enable engine-off operation) might lie in tapping into the transaxle, perhaps via the 5th gear, as axmonster was considering using for EV assist:

John L. 07-31-2008 12:57 PM

Just an idea if you attach to the engine, don't forget you can probably put something on the flywheel in the same way the starter drives the flywheel. If you found the right motor drive you could even have your starter be your regenerator, but a standard starter motor would probably be useless for this. Some engines have a dust cover on the bellhousing though, and you might be able to put something there that meshes with the flywheel teeth.

MetroMPG 07-31-2008 01:02 PM

For regen during engine-off situations, even better (but more complicated) than the 5th gear method would be tapping into the input shaft so you could choose between 5 (or however many forward gears you have) generator speeds as you slow down.

larryrose11 07-31-2008 01:15 PM

I once worked on a bolt on HEV system in my old days @ DCX. It worked well, but wasn't hooked to the brakes at all, jut regen when you lifted from the pedal. Is could. but it would be complicated and costly to say the least.
Can you program?
How are you with CAN (Controller Area Networks)?
You could probably do it for about $5K on the cheap side.
The low cost option would be a small EV setup bolted on, and an interface / control box.
You could then just plug into the grid.
Did I mention I'm an HEV engineer?

EOD guy 11-05-2008 03:24 AM

I was actually just thinking about this, and JUST had the idea (after watching Obama get elected) so I haven't figured out ANY specifics yet, but bare with me for just a little bit. I was looking at windmill generators on eb@y, and because they are permanent magnet motors, they can be used as generators or motors, and although they only produce a measly 300 to 1000 watts when hooked up to a wind turbine, they are only spinning at roughly 600 rpm or so, at their fastest. They are capable of spinning at roughly 7,000 RPM, and creating up to 130v DC intermitantly (sp?) Now lets look at some batteries. *edited several days after posting* Capacitors. No batteries, JUST capacitors. It seems everyone is hung up on my mention of batteries. What if I were to use a couple enormous capacitors?

Alright, so far we have motors, generators, and batteries. Now, how to spin the generators. I was thinking something along the lines of a small tire, like from a go cart, or an ATV, and more or less a home brew landing gear system. If you stick a motorcycle sprocket on there from an old beat up dirt bike, and a motorcycle chain, especially if you gear it UP rather then down, you could put a linear actuator under your car, have it activate with the brake switch (the switch that turns your tail lights on) lowering your landing gear, which through a sprocket and chain, spin your generator(s) If you need more braking power, push your brakes in further. They still work after all. Now your generators are charging your batteries. If it doesn't slow you down enough, or create enough voltage, stick another generator in there. Or a bigger one. Or put smaller gears on the gens or a larger gear on your landing gear (I don't know why I like to call it a landing gear so much, but I think it would be fun to tell people about the landing gear on my tacoma). Now we get into wiring just a little bit. You would have two sets of wires, and two sets of some powerful diodes running from your gen/motors to your bats. In braking mode, you allow current to go from your generators to your batteries. In taking off mode, you allow current to go from your batteries to your motors. Q:wouldn't you need a giant switch to carry all that amperage? You're gonna burn your car down loser! A: No, we need a small switch to operate a solenoid. So when you decide to take off, you push a button, and you start moving. At about ten or 15 MPH, start giving your car a little gas, and retract your landing gear.
So, that's my theory. The major problems that I can see is ensuring your batteries stay charged, ensuring that your batteries stay healthy, and charging your batteries quick enough (can you tell I don't know a whole lot about batteries?). One possible answer to charging the bats qickley, would to possibly get some big, bad, capacitors, which are designed to charge, and discharge extremely fast. But I know even less about capacitors then I do about batteries. There are a lot of technical problems, but all in all, I think this can be done.
Now to figure out how to make my wife thinks she's seen a flying pig... (that's when I get to visit the playboy mantion!)

Blue Bomber Man 11-05-2008 03:40 AM

A generator and a motor are essentially the same thing being used in different modes. It is possible to design a motor that works as regenerative breaking (BluWaves wheel hub motors do this).

Working with capacitors is much easier than working with batteries from I understand so far (batteries, especially li-ion and li-poly, need complicated battery management systems). The limitation of the capacitor is your gravimetric and/or volumetric density compared to batteries, and the cost. However some are working on a battery pack that is a hybrid itself: both batteries and capacitors. The capicitors serve as a buffer to the battery: they can take the high regen charge and then feed the batteries at reasonable rate, and can provide higher power when needed for acceleration. I dont know how difficult it would be to interface capacitors with a battery back that would be effecient. I do recall seeing an electric car website that someone built maybe 5-8 years ago that had a hybrid pack though. I think it is easy enough to find info on.

EOD guy 11-05-2008 04:59 AM

I was just looking for giant capacitors on Eb@y and came across something that I think might be able to power a motor for long enough to make my idea useful... a 20 farad cap! It's for a sound system, but GADZOOKS!! That's a lot of bloody capacitance! Now I just wonder if it would move the car by powering the motors, or by detonating them with one massive arc of electricity... Thoughts, anyone?

groar 11-05-2008 10:27 AM


Originally Posted by EOD guy (Post 70935)
I was just looking for giant capacitors on Eb@y and came across something that I think might be able to power a motor for long enough to make my idea useful... a 20 farad cap! It's for a sound system, but GADZOOKS!! That's a lot of bloody capacitance! Now I just wonder if it would move the car by powering the motors, or by detonating them with one massive arc of electricity... Thoughts, anyone?

IIRC F = A.s / V
A car battery is 50Ah (180 kA.s) and 12V, ie 15 kF and you need a dozen batteries.
Your 20 F is a 1/750 of a battery for the same price :(
IIRC to run a car you need 200W/h so your 20 F is enough for 30 seconds.

!!! IANAL, nor a battery expert, so this may be as comparing apples and oranges...
As said by Blue Bomber Man, the capacitor is only a buffer between the batteries and the generator/motor.


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