Electric motor vs. Gas engine

[Rex Schimmer]

One thing to remember about an electric motor is that its horse power rating is a function temperature, the motor is given a certain amount of voltage and amperage and when it reaches its rated temperature , while under load, that is its' horse power rating. Most electric motors can provide several times their power rating for a short time and if you can provide additional cooling they can run at an increased rating for extended periods of time. I have personally ran motors at 2.5 times their rated capacity simply by adding extra fans to cool it. An electric motor will generate as much power as you can feed it until it burns up or blows up. If you are running a generator (in reality just an electric motor in reverse) with an IC engine you typically need to have the drive engine 1.5-2 times the rating of the generator, this is due to the difference in torque curves of the two types of "motors".

Rex

[Rex Schimmer]

Standard electric motors are between 88-92% efficient based upon measuring the power out put/power input. Power in is amperes x voltage =Watts (746 watts = 1 hp) . Internal combustion engines are typically 30-40% efficient if you measure the efficiency on the amount of energy in the fuel/amount of energy produced at the out put shaft. If you add into the electric motor efficiency equation the efficiency of the electric generating system ( coal, natural gas, nuclear generation stations, etc) which are usually over 90% efficient then the electric generator-electric motor over all efficiency is around 80% which is still twice an IC engine.

Rex

[427dart]

Well I'll have to stick with the gas engine as I only have a 100 foot of extension cord available!

[Sparksalot]

"by Rex Schimmer » Sun Mar 13, 2016 4:51 pm

Standard electric motors are between 88-92% efficient based upon measuring the power out put/power input. Power in is amperes x voltage =Watts (746 watts = 1 hp) . Internal combustion engines are typically 30-40% efficient if you measure the efficiency on the amount of energy in the fuel/amount of energy produced at the out put shaft. If you add into the electric motor efficiency equation the efficiency of the electric generating system ( coal, natural gas, nuclear generation stations, etc) which are usually over 90% efficient then the electric generator-electric motor over all efficiency is around 80% which is still twice an IC engine.

Rex"

WHOA!!!

This is so far off on the efficiencies of generation let alone transmission of electric power to be in outer space. No thermal power generation method can possibly match the ideal defined by the Carnot Cycle. Imagine 90% under the Carnot Cycle. Do you have any idea?

Please offer an explained example of any electrical generating method which is in the 90% efficient range, even 80%. BTW, I'm an expert in the field so don't try BS by bluster such as above.

This is the kind of propaganda delivered by believers, those who want what can't be achieved. Thermodynamics has laws, learn them or be a believer, your choice.

[CharlieB53]

I can think of two other electrical generation methods with greater efficiency's than IC,, or coal/fuel fired.

Solar, uses NO heat. But current tech is not a very cost effective method, yet.

And Hydro-electric, again, NO heat, just dam up the river and use the difference in 'head' to drive a screw, or turbine linked to a generator.

And don't think for a second that hydro can't generate a LOT of power. Check out Grand Coulee, Bonneville, or most any of the other productive dams on the Columbia River.

But as a previous poster has already mention, our extension cords are nowhere near long enough to get to the grocery store.

[66Vette]

With electric cars, you have to bet on the come. Electric motors are far superior to the ICE when used in transportation for so many reasons. They have torque from zero RPM, they are far easier to manage and control (allowing regenerative braking and adaptive use of power), they are compact, lower maintenance, simpler, and cheaper. From an energy standpoint, their "fuel" (electricity) may not be more efficient than gas or diesel, but it is way easier to transport and can come from a variety of sources. Even if you derived your electricity from gas or diesel, you could burn that in places that are more tolerant to the pollution. (Millions of cars pumping out fumes in the LA basin is not what you want.)

You are already seeing them outperform ICE cars in some arenas of motorsports (shorter duration!). But the battery ain't there yet. Crack the code on batteries and the electric car will obsolete the ICE.

[Zmechanic]

I can think of two other electrical generation methods with greater efficiency's than IC,, or coal/fuel fired.

Solar, uses NO heat. But current tech is not a very cost effective method, yet.

And Hydro-electric, again, NO heat, just dam up the river and use the difference in 'head' to drive a screw, or turbine linked to a generator.

And don't think for a second that hydro can't generate a LOT of power. Check out Grand Coulee, Bonneville, or most any of the other productive dams on the Columbia River.

But as a previous poster has already mention, our extension cords are nowhere near long enough to get to the grocery store.

Solar PANELS are rarely over 30ish percent efficient, from a pure standpoint of converting the available solar energy in a given covered area to electrical energy. There are more exotic solar panels that are in the 40ish percent, but they are cost prohibitive for most things. Heliostats actually DO use heat. They focus a huge array of mirrors at a central tower to heat some type of medium (usually salts). Then they use that to boil water and power a steam turbine. Heliostats also allow power generation steadily throughout the day due to the stored heat.

[Rex Schimmer]

Sparksalot said: "
WHOA!!!

This is so far off on the efficiencies of generation let alone transmission of electric power to be in outer space. No thermal power generation method can possibly match the ideal defined by the Carnot Cycle. Imagine 90% under the Carnot Cycle. Do you have any idea?

Please offer an explained example of any electrical generating method which is in the 90% efficient range, even 80%. BTW, I'm an expert in the field so don't try BS by bluster such as above.

This is the kind of propaganda delivered by believers, those who want what can't be achieved. Thermodynamics has laws, learn them or be a believer, your choice.
Sparksalot


Sparksalot you definitely caught me here as my information is based upon the efficiency of the actual generator itself. I have done, at one time, quite a bit of work in power gen stations and my information from that experience is that the actual generator itself is over 90% efficient and this would be based upon the amount of power put into they generator shaft by typically a gas turbine. It converts that power to electric power at over 90% efficiency. I did infer incorrectly that the efficiency of the turbine and what ever was used to generate the steam was included in the overall efficiency, which is completely incorrect. I fully understand the laws of thermodynamics and the Carnot cycle. I probably took thermodynamics before you were born so please forgive an old "flange head" (that's short for mechanical engineer)for not being clear or correct.

Rex

[Rick360]

"by Rex Schimmer » Sun Mar 13, 2016 4:51 pm

Standard electric motors are between 88-92% efficient based upon measuring the power out put/power input. Power in is amperes x voltage =Watts (746 watts = 1 hp) . Internal combustion engines are typically 30-40% efficient if you measure the efficiency on the amount of energy in the fuel/amount of energy produced at the out put shaft. If you add into the electric motor efficiency equation the efficiency of the electric generating system ( coal, natural gas, nuclear generation stations, etc) which are usually over 90% efficient then the electric generator-electric motor over all efficiency is around 80% which is still twice an IC engine.

Rex"

WHOA!!!

This is so far off on the efficiencies of generation let alone transmission of electric power to be in outer space. No thermal power generation method can possibly match the ideal defined by the Carnot Cycle. Imagine 90% under the Carnot Cycle. Do you have any idea?

Please offer an explained example of any electrical generating method which is in the 90% efficient range, even 80%. BTW, I'm an expert in the field so don't try BS by bluster such as above.

This is the kind of propaganda delivered by believers, those who want what can't be achieved. Thermodynamics has laws, learn them or be a believer, your choice.

Yes, large modern coal fired power plants are in the range of 35-38% total efficiency. I work at one of the most efficient plants in the country and it is 38% total efficiency based on BTU input vs MW/Hrs output. That's at the plant not counting the transmission line losses to the end user/customer.

I can think of two other electrical generation methods with greater efficiency's than IC,, or coal/fuel fired.

Solar, uses NO heat. But current tech is not a very cost effective method, yet.

Current Solar Power is only about 15% efficient at converting the solar energy that hits a panel into electricity. In the lab I think they have some that are >20% but not commercially available yet.

Rick

[Brian P]

Random thoughts about "efficiency" on EVs ...

If you are hung up on using fossil fuel then it's possible that well-to-wheels might not be all that different from using a combustion engine in the car.

BUT.

Coal is on the way out. Ontario (Canada) no longer has any coal-fired generating plants. We are about 50% nuclear 25% hydroelectric ~5% renewables (mostly wind), and the rest is natural gas. A modern natural gas fired combined-cycle generating station (the natural gas is burned in a gas turbine, and the heat in the exhaust is used to generate steam for a steam turbine) can be near 60% efficient.

With renewables (solar and wind), the efficiency is secondary to the cost per kilowatt hour (i.e. a big but cheap unit may be more cost efficitive than a slightly smaller (i.e. more efficient) but expensive unit). Wind and solar power are pretty much in the ballpark on cost per kWh. Storage will be a problem when these start being a large portion of the supply - but we are a long way from having to worry about that. Problem with wind power is convincing the NIMBYs. Big problem in our area. In Denmark there is almost nowhere you can go in the whole country that is out of sight of all wind turbines. But they are generally accepted because people know what they mean ... the lights can stay on and they're not burning fossil fuels or nuclear to do it.

Electric cars aren't tied to a single fuel source. As your local grid sources transition from coal to something else, your electric cars automatically shift to greener power without you having to lift a finger. Can't do that with a combustion-engine vehicle.

Re powertrain efficiency ... At peak, a good Atkinson-cycle gasoline engine can approach 40% thermal efficiency and a diesel can slightly exceed that. BUT. This is only under ideal conditions. If you are driving under other conditions - or with the engine idling doing nothing! - the efficiency is nowhere near that and can be zero (idling). With an electric powertrain ... it is automatically doing nothing and using nothing when you are stopped.

Heat in the winter is an issue. Window defrosting in the winter is an issue. If the car is plugged in overnight, you can have the car do this for you ("pre-conditioning") before you even get up in the morning, and it's ready when you unplug to go to work. If it's not plugged in, then heating in winter kill the range.

Even in our climate, there are a decent number of Teslas on the road here (Toronto area). There are more of those C$100,000+ EVs on the road than all of the cheaper ones put together. The Nissan Leaf (which is a POS car!) is rare.

I am waiting for the Chevrolet Bolt and there is a pretty good chance that I will be buying one as my next daily driver vehicle.

[Schurkey]

I was one of the crew that built a fleet of "trolley buses" for a California-based bus fleet. This would have been mid-1990s. My memory is a bit foggy about them. They were very unusual for us. We had a trailer with a generator that we had to tow around when test-driving them.

The trolleys had two 600-volt motors in them, each larger than a beer keg. Part of my job was to route power cables, splice power cables, and install layer after layer of insulation on the cables. It was the first I'd ever heard of "cold-shrink" insulation. I'd worked with heat-shrink a bazillion times. The "safety training" we received for this specialized order of buses was that when exiting off of the bus, always jump from the lowest step to the floor with both feet so you don't become an unintentional ground path. They never said anything about entering the bus. The company was not real big on "safety". I also drilled holes in the "roof" to mount ceramic insulators into.

Two notes about the Trolleys:
1. Part of the electronics control package was an acceleration-limiter. Without it, they were concerned that "standees", the passengers who stand in the isle holding straps or the metal tubing of the luggage racks would be thrown to the floor if the driver stabbed the "gas pedal".

2. Once "my" company was finished with them, they were shipped to the fleet owner in California. This MIGHT have been San Mateo, but I don't remember for sure. We employees finally heard that the entire fleet sat in the parking-lot of the California transit company for something like two years while they dicked with the control package. I think the manufacturer of the motor controls went bankrupt during all this.

[Jagdpanzer]

Our ultra long stroke low-speed heavy fuel diesel ship propulsion engines have mechanical efficiencies of 50-51% in upper load range. With a good waste heat recovery system you can squeeze an additional 10-13% out of the exhaust and cooling for generating steam.

[Sparksalot]

"Sparksalot you definitely caught me here as my information is based upon the efficiency of the actual generator itself. I have done, at one time, quite a bit of work in power gen stations and my information from that experience is that the actual generator itself is over 90% efficient and this would be based upon the amount of power put into they generator shaft by typically a gas turbine. It converts that power to electric power at over 90% efficiency. I did infer incorrectly that the efficiency of the turbine and what ever was used to generate the steam was included in the overall efficiency, which is completely incorrect. I fully understand the laws of thermodynamics and the Carnot cycle. I probably took thermodynamics before you were born so please forgive an old "flange head" (that's short for mechanical engineer)for not being clear or correct.

Rex
Rex Schimmer New Member
New Member Posts: 13Joined: Mon Apr 06, 2015 2:33 pm"


Thanks for that clarification, yes, the electrical generator at a typical power plant is over 90%, the best are way over 90% efficient.

This is completely independent of course from whatever is making the shaft driving that generator turn. All energy conversions into rotational shaft power such as thermal from fuel fed internal combustion engines or external combustion steam cycles, nuclear or solar heat sources by steam cycles and even hydro power all have efficiencies associated with them which are well known and very carefully determined by both analytical and test methods. It also applies to all alternative energy generation such as solar photovoltaic and wind power. Nothing escapes very close scrutiny in power generation because the capital costs are very high, building the wrong plant is an economic disaster. The engineering challenge for way over a century has been to increase efficiencies to the highest level possible by innovations in design and construction.

I too am a "flange head" ME and a PE also. No idea when you did your undergraduate thermodynamics courses but I completed that work a bit over fifty years ago while drag racing so I may be older than you guessed. Nice to make your acquaintance sir.

[Sparksalot]

There is no hope for salesmen such as delivered here. Note that he cleverly stated "mechanical efficiency" when that is not at all what is being discussed in previous posts.

[Rex Schimmer]

Sparksalot,
Sounds like we are about the same vintage, I left school exactly 50 years ago and I probably took thermo around 1964-5.

Rex