# B Power (in Watts) produced by gas vehicles (1 Viewer)

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#### scott22

Hi,
I am wondering how many watts would be produced if a gas-powered car was somehow rigged with a device so that in a parked position its drive wheel became an electric generator. If a person sat in this 130 HP car and stepped on the accelerator and maintained a reading of 30 mph on the speedometer (even though the car stays stationary for the experiment) how many watts could be generated?
Thanks,
Scott

#### mfb

Mentor
The speedometer registers the speed of the car. Even if you modify it to read "what would be the speed with the clutch fully engaged": The corresponding motor speed and power will depend on the gear and the load.

You can calculate the maximum you can get - how many Watts are 130 HP?

#### anorlunda

Mentor

Just using the units, 130 HP = 96 kw. But that is too optimistic.

I have seen proposals to use modified car alternators as AC generators to power a house. They targeted 7 kw as the rated power. That's enough to satisfy many houses.

#### trainman2001

Since the motors used in portable/emergency small generators are essentially the same internal combustion engines used in vehicles, the comparison should be equal. That said, purpose built generators have their prime mover and generator direct coupled, thereby eliminating all the parasitic losses from a clutch or torque converter, and transmission, drive line, final gearing, wheel bearings, brake gear drag, etc. All of this stuff sucks HP. Also, it was noted before, but bears repeating; without a load, there is no horsepower. If you're not concerned about efficiency, sure… go ahead, put you truck on a treadmill with a generator on it, and let er rip. But, the other missing piece is the control circuitry to ensure that you're generating a constant frequency (50 or 60hz depending on your nationality). You need load sensing governors to maintain a constant RPM to generate a constant frequency, or an electronic system to create an effective frequency regardless of input variability. Without this, the truck generator would be not only useless, but in some cases, destructive to frequency sensitive equipment.

#### zanick

What would be the point? Making electricity using small internal combustion engines isn't exactly good for the planet.
Ironically, that's the way we power electric cars today... most are "coal powered cars". ;) I guess you have to determine what your definition of "good" is. ;)

#### OmCheeto

Gold Member
Ironically, that's the way we power electric cars today... most are "coal powered cars". ;) I guess you have to determine what your definition of "good" is. ;)
Might depend on when and where you live.
Coal is losing ground overall, here in the states.

[Ref: US EIA Monthly Energy Review Table 7.2a]

ps. That reminds me. I signed up for 100% renewable energy awhile back. I should check and see how much it's costing me. They said it would only be a 5% increase.

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#### zanick

Not really.... i guess it semantics if it is coal or Natural gas, or wood... :) the point is, we are burning stuff to make electricity and it may or may not effect the environment in a measurable way.

true renewables we have access to (solar) is about .5% of the total.... add wind it goes to 4%.....and more for hydro... but in the end, most the electricity comes from fossil fuels.... and yes, it depends on where you live.

Might depend on when and where you live.
Coal is losing ground overall, here in the states.

View attachment 240141
[Ref: US EIA Monthly Energy Review Table 7.2a]

ps. That reminds me. I signed up for 100% renewable energy awhile back. I should check and see how much it's costing me. They said it would only be a 5% increase.

#### anorlunda

Mentor
Nearly 30 years ago, the airline magazine on a plane caught my eye. It talked about a startup company. The company had the idea to make an electronically enhanced motor that could act as the car starter motor, and as the car alternator, and as the backup generator for the owner's house, and to power a winch to pull the car out of a ditch. (It may have also sliced, diced, and made Julienne potatoes, but I don't remember that part.)

The point is that such a device would have been very attractive. It would have given the car manufacturer a competitive advantage. Therefore, the suggestion would have been carefully considered. But 30 years later it never appeared on the market (that I know about). My conclusion is that it must have proven to be more difficult to achieve and less attractive than first imagined.

Staff Emeritus
most are "coal powered cars"
Mine is nuclear powered. "Atomic batteries to power. Turbines to speed."

The primary advantage of electric cars is that electric motors are 2.5-3x more efficient than internal combustion engines.

#### mfb

Mentor
ps. That reminds me. I signed up for 100% renewable energy awhile back. I should check and see how much it's costing me. They said it would only be a 5% increase.
That doesn't mean much. It usually just means that company is buying more energy from producers of renewable energy and everyone else buys less of it because the production didn't change. The market price is the same anyway.

#### scott22

Hi,
I am wondering how many watts would be produced if a gas-powered car was somehow rigged with a device so that in a parked position its drive wheel became an electric generator. If a person sat in this 130 HP car and stepped on the accelerator and maintained a reading of 30 mph on the speedometer (even though the car stays stationary for the experiment) how many watts could be generated?
Thanks,
Scott
Would it be fair to say then that a vehicle with an electric-generating device attached to the drive wheel could produce 5kw, and that the engine would feel enough resistance to need about 10hp to produce it?

#### anorlunda

Mentor
That doesn't mean much. It usually just means that company is buying more energy from producers of renewable energy and everyone else buys less of it because the production didn't change. The market price is the same anyway.
That's very true. It is also practically impossible for consumers to verify the claims of those marketers. They can buy power from the market, and resell it as renewable without ever proving that the renewable content is higher. To verify their claims, you must be able to read their signed contracts with suppliers. Those contracts are sealed in the safes of their law firm, making them very hard to get to.

Of course that is fraud and against the law, but the prosecutor offices are staffed by lawyers not engineers. The lawyers suffer brain melt when they try to understand how the power markets work. Even if the prosecutors did master the ideas, that still leaves a jury.

The last time I checked (around 2004), the NY Public Service Commission responsible for enforcing all the regulations had 400 lawyers on staff and only one engineer.

#### sophiecentaur

Gold Member
What would be the point? Making electricity using small internal combustion engines isn't exactly good for the planet.
You can buy small 'petrol' generators that will give you a few kW; a much better prospect than trying to use the engine in a motor car. These are fine when there is no convenient mains supply available and you can buy larger diesel systems for off-grid use which will give you tens and tens of kW. The fact that people don't tend to use them when a mains suply is available is good evidence that they are just not efficient enough.
Things are different when there happens to be a cheaper, alternative fuel source, such as Methane gas etc. from an anaerobic digester.

#### OmCheeto

Gold Member
Would it be fair to say then that a vehicle with an electric-generating device attached to the drive wheel could produce 5kw, and that the engine would feel enough resistance to need about 10hp to produce it?
As far as "feelings"? Yes.
But the "feelings" of the gasoline might be hurt, as it would be feeling quite a bit more than that:

5kw = 5000 watts * 1 hp/746 watts = 6.7 hp (Close enough to 10 hp for government work. Hence my "Yes".)
Thermal efficiency of a gasoline powered car ≈ 20%
6.7 hp / 0.2 = 33.5 hp

Btw, I was thinking about this some more yesterday, and looked up the rated output of my alternator: 110 amps.
@ 14.4 volts, that yields about 1.6 kw.
Which, if I were just powering my house in the summertime, and not all my neighbors, would be more than adequate for my needs.
All I would need was DC to AC inverter.

Interestingly, in the winter, it might actually be cheaper for me to power my house with my truck!
That's because the missing 80% efficiency of a car engine is generally thrown away as waste heat.
Of course, lots of modifications would have to be made, both to the truck and my house, to get away with such a task.

Some of the rough numbers I'm working with:
130 hp truck
60 kwh/day winter (=2500 watts average continuous)
9.6 kwh/day summer (=400 watts average continuous)
15 gallon gas tank

hmmm....This should be interesting.

#### mfb

Mentor
That only works if you keep most of the heat of the truck in your house, but then you need a heat exchanger for the exhaust and a garage closely connected to the house, otherwise you accumulate all the nasty exhaust in your house or lose most of the heat.

#### OmCheeto

Gold Member
That only works if you keep most of the heat of the truck in your house, but then you need a heat exchanger for the exhaust and a garage closely connected to the house, otherwise you accumulate all the nasty exhaust in your house or lose most of the heat.
As I said;

Of course, lots of modifications would have to be made, both to the truck and my house, to get away with such a task.
I was guesstimating about $10,000 for the modifications, were I to do them myself. (Fat chance, at my age.) Guessing it would probably cost$100,000 were I to hire someone.

My financial thermal requirements for the last 12 months: $1152.73 Payback time for the$100k number: 87 years

Nope! I will wager all of my life's savings that I will not live to be 147.

ps. It's still a fun problem, to tinker with.
For instance, at idle, my truck generates 2.3 times as much thermal energy as I consume, in the winter, just keeping herself rolling around.
The thought of running outside starting and stopping her, every few hours, because it's either too hot, or too cold, well......
More engineering!

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