Car ?'s

Here's a (probably dumb) question for any engineers out there:

Say you wanted to create a performance electric vehicle. Instead of using batteries couldn't you have a gasoline engine be the generator for the electric motor? Or would the gasoline engine + fuel end up weighing more than a battery negating any advantage? I suppose the question is how powerful of a gasoline engine would you need?

Again, this would be a performance oriented automobile and not something trying to be fuel efficient.

ShakyJake said:

Here's a (probably dumb) question for any engineers out there:

Say you wanted to create a performance electric vehicle. Instead of using batteries couldn't you have a gasoline engine be the generator for the electric motor? Or would the gasoline engine + fuel end up weighing more than a battery negating any advantage? I suppose the question is how powerful of a gasoline engine would you need?

Again, this would be a performance oriented automobile and not something trying to be fuel efficient.

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That's already done in hybrid vehicles. The engine charges the battery to extend running time.

Cad said:

Only the i3 does this that I know of, and its shitty. The problem is to have a generator that would make enough power for a performance vehicle, you’d end up with a relatively loud and obnoxious engine... why not just have the engine power the wheels? We are good at building those. You’d also end up with a battery anyway since you’d need some short-term storage for .. “high throttle events”. So you’d end up with both and both drivetrains would end up compromised. See: the i3, volt, etc.

Frenzied Wombat I don’t think any of the current hybrids use the motor to charge the battery besides the i3 REX. If I’m wrong feel free to point out the ones that do.

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I’m pretty sure all the combo motor/battery (hybrid) vehicles do this. I mean it makes logical sense, if you are using your motor rather than your battery (say hitting the gas hard on your Prius) it would make sense that some of that energy be used to charge the battery.

Cad said:

Ya I mean the gas engine is not connected to the wheels at all and just serves as an electrical generator. In the hybrids the electric motor does run in regen mode at low-load and charge the battery somewhat, but the gas engine is driving the wheels. I think what he’s referring to is where the engine ONLY charges the battery and the propulsion is fully electric. Sorry to seem like splitting hairs..

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If that's the case he's presenting, then It would be totally retarded to have a gas engine dedicated to charging the battery. At that point why bother having a battery at all, because you're going to get far better MPG on just direct combustion to the wheels rather than the reduced MPG you're going to get via energy loss when converting from gasoline to electric.

Best analogy of this setup I can think of is adding a whole-home electrical generator to your house that runs on natural gas, you were paying $200/month to TXU, and now you're all proud that your TXU bill is $0 but you have a $250 Atmos bill instead.

Cad said:

Well there’s a precedent for it though, Diesel locomotives and most ships have the engines not connected to the propellers at all. The electricity generated is used to power electric motors connected to the propellers.

I just don’t think it works in cars because you’d have such small spaces and people wouldn’t put up with the noise/vibration/etc.

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I'd be curious as to the reason that is done in boats/trains-- there must be some sort of safety or engineering reason, because you always lose some energy efficiency (typically in the form of heat) when converting from one energy type to another.

Frenzied Wombat said:

If that's the case he's presenting, then It would be totally retarded to have a gas engine dedicated to charging the battery. At that point why bother having a battery at all

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Doing a tiny bit of research it seems what I'm suggesting is called a "series hybrid" BUT without the battery. The gasoline engine, basically a generator, powers the electric motor directly. Again, don't care about fuel efficiency or range. Just pure, raw performance that an electric motor can deliver.

I brought this up because I watched the Netflix series "The Fastest Car". One of the vehicles was a home brew electric which was stuffed with batteries. So my thought was ditch the batteries and just use a gas engine to power the motor instead. I mean, I would assume that a gasoline generator could pump out more voltage than batteries..?

Cad said:

Only the i3 does this that I know of, and its shitty. The problem is to have a generator that would make enough power for a performance vehicle, you’d end up with a relatively loud and obnoxious engine... why not just have the engine power the wheels? We are good at building those. You’d also end up with a battery anyway since you’d need some short-term storage for .. “high throttle events”. So you’d end up with both and both drivetrains would end up compromised. See: the i3, volt, etc.

Frenzied Wombat I don’t think any of the current hybrids use the motor to charge the battery besides the i3 REX. If I’m wrong feel free to point out the ones that do.

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A normal "Hybrid" i.e. Prius = Small Battery + Small Electric Motor + Gas Motor. The Electric offsets and works "with" the gas - regenerative breaking and the gas motor charge the battery during breaking (reversing the electric motor spin is all regenerative breaking is.) and during stops or idle the gas charges the battery. - Both motors together can propel the car - the electronic alone cannot, yet the gas can.

Plug-In-Hybrid = Medium Size Battery + Mid Size Electronic Motor + Gas Motor. The electric motor can fully propel the car alone OR in conjunction with the gas motor. You must plug in to charge the battery.

Pure EV = Large Battery and Large Electric Motor. The Electronic Motor does all the work as does the battery and you must plug in to charge.

EV + "Range extender" - i.e. the BMW i3 = A normal and complete Pure EV with, what is essentially a gas generator that turns on to suppliment power drain / charge the battery - the gas motor has no direct locomotion capability- so if you run out of battery, the gas generator cannot propel your car... I have had a few people that have this, and the range extender is always causing issues and in the shop... I also do not know if you do run out of battery if you have gas/fill up the RE if it then can charge your battery and get you going again.

Cad said:

I think it's considerably more efficient since they can run the motors at peak RPM without concern for transmission/load/etc. The main failing of the gas engines in cars is that they suck shit efficiency at part load, so your 400hp motor making 40hp to sustain 60mph sucks. The 100hp motor sustaining 40hp is a lot more efficient.

In the ship/train they can just keep the motor running at peak efficiency wide open charging with no usability concerns.

Also for trains specifically having the startup torque to get the train moving, as I understand it, is a HUGE advantage of electrics.

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Wrong, actually. Petrol is much more efficient at cruise that electric. Electric is superiour in stop-and-go.

Cad said:

My 120mpge 675hp electric car disagrees with you, sir. I'll continue paying 2 cents per mile while you wonder if electric cars are more efficient.

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I'm not a scientist. Just quoting dozens and dozens who are.