Regenerative breaking on MMM
 

So, you'll notice none of the questions I ask are anything like anyone else's because, well, I'm a freak.

I am working on a diesel powered vehicle for a Biofuel race from Berkeley CA to Las Vegas NV. Basically, no matter what, we can start with 1 gallon of gasoline's worth of energy (battery charge, biodiesel, granola for the hippies on bikes.) All other energy needs to be collected AND processed during the trip from biomass. I want to try and make it on one gallon.

SO

I am working on the idea of a parallel hybrid system using an electric motor to get up to speed and a small diesel engine to generate electricity and power the vehicle at speeds fitting it's point of peak efficiency.

How would I generate power? Simply by applying a small amount of parasitic drag with the electric motor when the vehicle is running under diesel power until a desired battery level was reached (20% to 0% drag, depending on power levels.)

I'd probably be using 4ah leadacid for the battery source, which should accept a charge fairly readily.

How effective is the drag break at recollecting energy on the CC controllers, or is it simply a shunt that isn't useful for collecting power?

Thanks!

P.S. I just got my V3 in the mail this morning. That's for another robotic project, though.

The regenerative braking on the controllers is simply a done so as there is a place to put the energy created per Patrick. To keep things from over heating it goes into the batteries however as I understand it doesn't create a significant amount of energy.

So it uses the battery as a load, not really as a means to recover much energy. Maybe it would still be enough to make this usable. The idea is to simply avoid the complexity of a transmission and to have a hyper efficient power train once the diesel is at speed. 99% of the drive time would be at speed.

The braking is regenerative because it has to be -- can't dump that much energy anywhere but back into the battery. (The battery is used as a load, but using a battery as a load mean charging the battery...)

It is not, however, optimized.

Still gets fairly good efficiency up to about 35% braking power -- above that the conversion efficiency gets lower.

It would be easier (and probably more efficient) to use a nice brushed motor as a generator (dynamo) direct from the engine. Use this to charge your battery and run the electric drive system.

like an alternator???

You may want to consider looking into how regenerative braking is performed on trains and subways. Ya know that burst of heat you feel coming from a subway is from the motor being used as a generator and dumping it's load through huge resistor banks. Then there are some systems where the generated energy is dumped back into the grid.

There may be more documentation available out there on how this is done - and much easier with a brushed motor (as mentioned) - then with a BL one.

Could use a BL motor and use a 3-phase bridge rectifier, since that is somewhat how an alternator works...

No matter what, the energy you expend will be more you capture because of efficiency losses. But, if your biodiesel engine can be freed from the stop and go part (and the inefficiencies that entails), maybe it will overcome the inefficiency of the added electric motor drag.

So at, say, 50% breaking, efficiency of regeneration is lessened?

Meaning 20% breaking is within the "optimal range" what ever that percentage of regeneration is. I don't need high efficiency here. I just need simplicity.

I want the control loop to be simple (adjust numbers as needed):

If voltage > 12, run at 0% parasitic drag break.
If 12 > voltage > 11.5 , run at 10% parasitic drag break.
If voltage < 11.5 , run at 20% parasitic drag break.

The idea is to float around 3ah out of 4ah of charge capacity in the battery giving me enough of a buffer before I over charge if I use the MMM as the breaking mechanisms instead of relying (completely) on mechanical breaking.

Think the MMM can run for 20 hours straight, at 12 volts, doing next to nothing? ;-)

That's the idea.

nah, each point of the conversion has loss. Fuel to mechanical to electrical to battery to electrical to mechanical. I want to go from fuel to mechanical as efficiently as possibly with some waste to electrical to allow the mechanical to be as simple as possible. More simple than the average card with a 5 speed tranny.

use AIR flow to recharge the battery . also install a set of bicycle pedals where the gas and brake belong . or use virbration to charge the batterys. i saw a flashlight you had to shake to build up a charge. the shocks could do that.

I was just thinking about a way to get rid of the first conversion from 3 phase. If you can build an easy rectifier you are good. Braking with the MMM will be regenerative no matter what, so unless you are using a freewheel on the driveline you will get back a few percent. Using a MMM on the generator side would be a horrible idea IMO, the efficiency is not there for generator use.


What is the goal of the project? Maximum distance, minimum fuel expenditure over a specified distance?

If I were going to collect waste energy, it would be from the heat off of the cylinder.

That's a good idea and something I'll play with, but I am thinking the power I'll need for acceleration will be so trivial that it's not a very important that i make the perfect generator.

This is to make wacky shit and learn new stuff and promote bio fuels and hang out with cool people and get chicks... making it to Las Vegas is optional :intello:

Enter Bose (yes, the same Bose that does audio): http://auto.howstuffworks.com/car-suspension9.htm

The flashlight you shake is basically a piston-like motor. Instead of the rotor turning, it goes up and down. Either way, it induces a voltage in a coil, just not nearly as well as a rotary motor.

If it works as advertised that will be awesome. nice find.

Well damn is that is slicker than dog snot.

I wonder did Dr. Bose have a heavy hand in this himself or was this designed by other Bose engineers? The guy is a genius for sure!

I work on large mine size diesel-electric wheel loaders. The engine drives a large generator which supplies power to 4 wheel motors. These have a very complex control system too them. These use resistive braking instead of regenerative braking, same idea the energy is just used differently. wasted as heat through a bank of resistors instead of "topping" up the batteries.

We also have electric trolley buses that run off overhead lines. when they brake or travel down hill the motors turn into generators and pump electricity back into the grid.

Lemme get to my point. The way I know regenerative braking to work. You can't power the motor to move the vehicle at the same time as you're making it generate power. if that makes any sense.

With the wheel loader for example. you step on the throttle and power is supplied to the motors to move the vehicle. The moment the operator takes his foot off the throttle. Power is no longer being supplied and all 4 motors turn into generators, pushing power through the resistor bank and slowing the loader down.

If you were to use the drag brake as you suggest. When the batteries fall below ~80%, the drag brake engages and tops the batteries up.

The batteries being at 80% and then applying a 20% added load to the motor might slow the vehicle down to the point where the drag brake is doing nothing for the vehicle. Voltage gives you speed, as your motor slows it'll draw more amps from the battery. Further draining it, the cycle continues until your battery is dead. Sorry if its overly exaggerated

Have you thought about coupling a small 12v or even 24v alternator to the motor to keep the batteries topped up. To me this would seem like a smaller overall load then the drag brake. In this way you could still use the motor to generate power when traveling down hills or during braking applications. coupling the alternator to the motor (depending on the size of motor you are going to use) may or may not grossly affect the rotating mass of the motor.

In which case an idea just came to mind. An electo magnetic clutch (EMC to simplify) to activate/deactivate the alternator drive. Once you're up to speed the EMC could activate and the alternator would top your battery up as needed.

Or also if you wanted to try and collect the wasted heat energy from the exhaust or cylinder head. What about a thermocouple/thermopile to generate power? mind you it may be more involved than you would like

Ignore me if this makes no sense

Now why would you say that? The efficiency is pretty good actually, it's just not optimized for generation.... but neither is a 3 phase bridge rectifier either. Above about 35% braking the motor starts dissipating a bit of power as the phase currents get really high -- and that causes a loss of efficiency.

The main difference is that a bridge won't ever BOOST the voltage for the battery -- if the battery voltage is lower than the motor EMF voltage, the bridge won't do a thing. An active boost brake (like on the Monster) will boost the voltage higher to charge the battery.

Patrick

ok so my putting mechanical brakes on my buggy is causing a LOSS in run time cause the motor is not charging up the battery during braking? very interesting

Awesome info!

I figured this was a good way to go because this is how a lot of hybrids work, they use brushless motors as generators when the ICE is performing optimally. I don't imagine that this is something that would be the primary focus of CC since you aren't in the market of making hybrids, but I doubt the technology is that much different.

So, this set up is so easy. It's all very trivially simple.

For cyclists, there are "Flip-Flop" hubs that have a fixed gear on one side (like a track bike) and a coaster gear on the other (like a BMX bike.) Off of the fixed gear, I'd attach the motor so that, so long as the vehicle is moving, the shaft of the motor is moving. If the motor is under power, the vehicle goes. When the motor isn't under power, it spins idle OR can generate power.

On the coaster side, the diesel engine. Simple engine, clutch set up allows the engine to idle at a stop, and the engine continues to idle until the wheel is spinning at the engine's optimal speed. Then engages.

When the engine is engaged, the motor idles or charges.

One speed, two power plants, existing bike parts, and a very simple bit of logic.