Chemically Regenerative Braking?

" snipped-for-privacy@yahoo.com" wrote in news: snipped-for-privacy@o13g2000cwo.googlegroups.com:

Doesn't this pretty much describe the battery operation in an electric or hybrid car? I can't imagine any other method that wouldn't be impossibly complex compared to a chemical battery. Maybe a regenerative fuel cell?

Don't make things any more complex than they need to be.

--Damon

Don't know much about fuel cells, but are they reversible, like a motor-generator?

A typical fuel cell takes hydrogen and combines it with oxygen from the air, producing water and electricity. Reversing the process is simple, it's called electrolysis. The problem is how do you store the hydrogen (the oxygen you can throw away because it's in the atmosphere already at about 20% concentration). Compressing hydrogen takes equipment that is too heavy and bulky and expensive to put in a typical car. There are other ways of storing hydrogen but they all have some type of overhead cost that makes them impractical.

A battery, as many drawbacks as it has, is still far better for recovering energy created by regenerative braking. Even a supercap or a flywheel would suffice if the amount of regenerative braking energy is limited.

we have reversible fuel cells available at

I recall something about using hydraulic accumulators. It would be much simpler.

Best, Dan.

The only method I know where regenerative breaking could be used in a non-electric propulsion vehicle is to use a flywheel. The engine spins up a flywheel which is then used in the drive train to power the wheels, through a suitable clutch system. During breaking the flywheel is spun up from the breaking effort. The engine will have to add the rest though.

Sure, that's a possibility. How about a ratcheting spring? There are ways. The actual usage determined more by about density, packaging, reliability and cost. A battery and electric motor are pretty useful.

Then regenerative braking on a fuel cell car should work.

An air motor/compressor and compressed air tank would also work. However, the problem with either this or the hydraulic accumulator is that the total amount of stored energy is limited by the volume and weight of the accumulator or pressurized air tank. Maybe enough to save energy from single traffic light stop and feed it back in to recover most of it when starting, however. That should help milage in an urban cycle.

Yes if you count energy store in a battery as "chemincal fuel".

If not, i don't think of any method. Theorically, you could break with a power generator and use electricity to electrolyze water, keeping hydrogen as a secondary fuel for the engine, but this would be costly and inefficient.

"Chemically-Regenerative Braking" sounds like marketing hype for battery recharging by the motor/generator. It's easy to do; a relay or two switch the armature from being fed by the power source to feeding the power source, and can be controlled by zero-throttle setting or light brake pressure. Hydraulic accumulators and compressing air have fatal flaws: very heavy, very inefficient. Both generate considerable heat, which comes right out of the energy being recovered. Diesel-electric locomotives have used dynamic braking for years. The motors become generators, and the electricity produced is run through heating grids in the roof of the machine and fans blow away the heat. They don't have batteries big enough to store the energy.

Dan

But the topic was not HEV.

Sure. That is exactly what was meant. Hybrid vehicles are some other animal.

Best, Dan.

There could be reversible fuel cells, certainly. The simplest chemical reversible situation is still the lead/lead sulfate/sulfuric acid storage battery.

Compress air.

Paul.... check your equations, there :-)

Compressing air is AT MOST 50% efficient. Old PV=NRT bites you in the butt- when you compress a gas the temperature of the gas increases. Unless you USE the compressed gas BEFORE it cools back down to ambient tempreature, you're throwing away over 1/2 the energy you put into the compressor as heat that leaks out of the gas storage reservoir.