Electric car using a generator

Post by **KillerByte** » 13 Jun 2008, 07:52

We have electric cars that require recharging because they use batteries, this obviously limits their range.

We have new technology that makes engines more efficient and quieter.

Electric motors are powerful enough to propel a vehicle.

Generators are more economical because they aren't pushing/pulling the entire car.

Why not have a car that has a small generator that will run on less fuel than a normal engine, then have the electricity that is generated given to four electric motors (1 per wheel).

I34z1k · Post by **I34z1k** » 13 Jun 2008, 07:57

:\ Dude, you NEVER increase efficiency.

It's the same as using a generator to power an electric motor to turn a magnetron

Ike · Post by **Ike** » 13 Jun 2008, 08:01

easy, you lose energy when it's converted into electricity while internal combustion the energy is directly converted into motion.

Website · Post by **hamin_aus** » 13 Jun 2008, 08:04

KillerByte wrote:Why not have a car that has a small generator that will run on less fuel than a normal engine, then have the electricity that is generated given to four electric motors (1 per wheel).

Or even better...

Ike · Post by **Ike** » 13 Jun 2008, 08:08

po10cy · Post by **po10cy** » 13 Jun 2008, 08:30

why not have a car that is electrically powered, with a generator attached to the wheels so that when they turn they generate electricity to recharge the batteries? maybe have a tiny fuel tank just to power a generator to create a little bit of power for the batteries incase you run them flat. which shouldnt happen if the wheels generate more power than the car uses to move.

Ike · Post by **Ike** » 13 Jun 2008, 08:49

unless you live in a place called free fall hills that would never work... you will push your car 24/7

viceroy · Post by **viceroy** » 13 Jun 2008, 10:08

po10cy wrote:why not have a car that is electrically powered, with a generator attached to the wheels so that when they turn they generate electricity to recharge the batteries? maybe have a tiny fuel tank just to power a generator to create a little bit of power for the batteries incase you run them flat. which shouldnt happen if the wheels generate more power than the car uses to move.

Again, you're going to lose efficiency by attaching resistance to the wheels.

DarkStar · Post by **DarkStar** » 13 Jun 2008, 11:04

The only way the generator would be be useful, is if you ran out of batteries while on the road. Then, you would use the generator to give you enough charge to get you back home.

In the end, it's not really going to work. It would be more efficient if you had a normal petrol engine in the first place.

Samaya · Post by **Samaya** » 13 Jun 2008, 13:57

Generators are more economical because they aren't pushing/pulling the entire car.

You cant use a generator because the generator produces electricity by spinning a dynamo using a petrol/diesel motor. This Dynamo creates a certain amount of electricity depending on its RPM. The faster it spins the more power you get.

Imagine you are going up a hill, your electric motor driving your wheels need more current to keep the wheels turning at your required speed. Your generator will have to increase its RPM to increase the power output. So effectively you are still pushing/pulling the car with the generator.

Hex_Rated · Post by **Hex_Rated** » 13 Jun 2008, 14:19

His idea is right in that a generator running at a constant RPM would be more efficient than an engine thats varying it's power output. The problem comes in that batteries are the weakest link in the electric car. You need lots of them, too many for the idea to be viable (extra weight + small ICE + complexity etc). There is a commercial product using this solution and AFAIK it wasn't a complete flop. It had a small ICE generating power and feeding it to batteries.

Imagine you are going up a hill, your electric motor driving your wheels need more current to keep the wheels turning at your required speed. Your generator will have to increase its RPM to increase the power output. So effectively you are still pushing/pulling the car with the generator.

It's the buffering of the power that's the most expensive problem at the moment. If you have enough power left in the batteries, you can motor up the hill and then they charge while your on a flat or downhill.

I34z1k · Post by **I34z1k** » 13 Jun 2008, 14:28

po10cy wrote:why not have a car that is electrically powered, with a generator attached to the wheels so that when they turn they generate electricity to recharge the batteries? maybe have a tiny fuel tank just to power a generator to create a little bit of power for the batteries incase you run them flat. which shouldnt happen if the wheels generate more power than the car uses to move.

That's how many electric cars work, they use the breaks as dynamos...

Scavenger · Post by **Scavenger** » 17 Jun 2008, 19:43

Diesel-electric locomotives have run on this principle since the 50's. A diesel generator powers the electric traction motors, there is no physical link between the diesel engine and the wheels. 100% of the mainline Diesels in this country are diesel-electric. The reason for using electric motors is that they offer full torque right from standstill unlike a combustion engine. Its a bit of a waste in a car because they are so light and that torque isn't needed.

GreyWolf · Post by **GreyWolf** » 17 Jun 2008, 20:53

KB, let me explain why your idea d\won't work:

using internal combustion engine(ICE) to power generator: FAIL
ICE only have an efficiency of between 20% and 40% ( AT BEST!). that means that they only extract about 30%(AT BEST!) of the energy stored in the fossil fuel and convert it to usable power. the other 70% is lost to sound/heat/friction.

using ICE to turn generator: FAIL
cursory googling finds that generators used in hydroelectric dams are 95% efficient. so again you are losing energy to friction/sound/heat etc. and of course this is just at the generator, not to mention the energy you will lose of your generator is no directly connected to your ICE through a drive train.

using batteries to store energy from generator:: FAIL
car battery efficiency can drop to around 75% on load, losing energy to heat.

and finally we come to the electric motors, which currently are 95% efficient.

so lets now do some maths:
lets make an arbitrary unit for the energy stored in fossil fuel. lets call this a FFEU (fossil fuel energy unit).

lets assume that we are giving our car just enough fuel for 1FFEU

in the ICE we are losing 70%, so the energy coming out of the engine is 0.3FFEUs

then we lose 5% of the generator, so 0.95*0.3 = 0.285FFEUs

then we lose 25% of that at the battery -> 0.75*0.285 = 0.21375

and finally another 5% of that at the electric motors -> 0.95*0.21375 = 0.2030625FFEUs

so, you are going from 30% of energy harvested from petrol to only 20%. and thats why your idea doesn't work. too many links in the chain causing too much energy being lost to other things.

Hex_Rated · Post by **Hex_Rated** » 17 Jun 2008, 21:38

In theory it would improve consumption because you can run the engine at a constant RPM, providing the most efficient use of the energy. In practise it is too complex to be viable and adds loads more moving parts. The idea is not as useless as you would expect (see Jamin's DEI pic).

Another interesting fact is the majority of the efficiency loss from an internal combustion engine is not friction as you would expect but heat. I think the actual efficiency for an ICE is around 10%. A coal / oil power plant is closer to 30% efficiency which is why electric cars are slightly less damaging to the environment than ICE driven cars. But ATM electric cars still indirectly rely on fossil fuel for the majority of their energy.

Scavenger · Post by **Scavenger** » 17 Jun 2008, 23:02

You could always just resort to the buttered cat principle. The numbers add up.

Tolklein · Post by **Tolklein** » 18 Jun 2008, 07:27

Not sure how many cats you'd get to the km, so just get a hybrid.

Hex_Rated · Post by **Hex_Rated** » 18 Jun 2008, 14:27

Scavenger wrote:You could always just resort to the buttered cat principle. The numbers add up.

Perpetual motion machine?

Scavenger · Post by **Scavenger** » 18 Jun 2008, 18:53

Hex_Rated wrote:
Scavenger wrote:You could always just resort to the buttered cat principle. The numbers add up.
Perpetual motion machine?

Correct, that one with the buttered toast and the cat.

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