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Guptar
4th Mar 2018, 06:52
Talking about this elecrickery question which I was totally stumped with. Had to use the tactic, let't talk about this tomorrow.

An internal combustion engine's efficiency is the BSFC. How many pounds of fuel per hour per hp it makes. Engine A has a figure 1.0 while engine B achieves a 0.5. This makes engine B twice as efficient.

How do you measure electric motors?

Has the efficiency of electric motors improved over the last century?

Are they getting more efficient, as in for EV's to help improve EV range?

VP959
4th Mar 2018, 08:56
Talking about this elecrickery question which I was totally stumped with. Had to use the tactic, let't talk about this tomorrow.

An internal combustion engine's efficiency is the BSFC. How many pounds of fuel per hour per hp it makes. Engine A has a figure 1.0 while engine B achieves a 0.5. This makes engine B twice as efficient.

How do you measure electric motors?

Has the efficiency of electric motors improved over the last century?

Are they getting more efficient, as in for EV's to help improve EV range?

Both are measured the same way, essentially.

For an internal combustion engine efficiency is measured by the potential energy in the fuel used, versus the mechanical energy that it delivers to the load, which is usually anywhere between 25% and about 54%, depending on the type of engine. Big, slow turning, marine diesels can get up to about 54%, the very best car petrol/gasoline engine can get around 35% or so. Diesels are generally a bit more efficient than petrol/gasoline engines, with good diesel car engine maybe getting around 42 to 45% efficiency.

For an electric motor it's exactly the same, the ratio of electrical energy in to mechanical energy out. Electric motor efficiency varies from around 85% to over 90%, with the very best electric motors getting close to 95% efficient.

In practice all vehicle internal combustion engines have a pretty non-linear efficiency curve, with peak efficiency usually being around peak torque.

Electric motors tend to have a very much flatter efficiency curve, reaching maximum efficiency at a relatively low rpm and then staying pretty much flat until efficiency starts to drop off at high rpm due to increased eddy current losses.

PDR1
4th Mar 2018, 09:03
Essentially the same - if you wanted to do it in a dyno you'd measure power out for a given power in (or energy out for a given energy in). Efficiency is the latter over the former in both cases.

But it happens that with electric motors you don't need a dyno and can measure the losses quite easily in use, so you can do in-situ on-the-fly efficiency measurement based on a sum that is essentially:

Efficiency = (voltage in - voltage losses) * (current in - no-load current) / (source voltage * source current)

The principle is the same with both AC and DC motors, but the implementation is much more (mathematically) complex with AC motors.

But what you find is that the actual motor efficiencies are extremely high, so the scope for gains is very small. The limiting issue for range is what it always has been - the size and weight of the batteries. And that will need some new fundamental discoveries to do more than a bit of tinkering with.

PDR

WingNut60
4th Mar 2018, 13:38
My limited knowledge is putting me on shaky ground here, but as I understand it, the main areas for improvement are in overall circuit efficiency.
In particular with AC VS drives, where the motor may be very efficient but variable speed is achieved at the expense of efficiency, particularly at lower speeds.
There have been good improvements achieved with IGBT technology but still scope for further improvement.

Any sparkies out there who can elaborate?

VP959
4th Mar 2018, 15:14
All my home built EVs have used BLDC motors with power FET commutation, and the losses in the controller are generally pretty small. Up the frequency and switching losses dominate, reduce the frequency and IČR losses dominate in the FET Vdson. The key I've found is matching the motor Kv to the required application, so that the controller can work in the sweet spot where IČR losses are small and so are switching losses.

When moving up beyond the 5 to 20kW range I've been playing with, then changing to IGBTs , reducing the motor Kv and increasing the battery voltage makes a lot more sense. IGBTs have a fairly fixed on voltage drop at modest currents, that makes them poor when compared to FETs below around 100 VDC, but above that IGBTs really have an advantage.

The main issues that are gradually being overcome are the switching losses (need faster devices, with less hole storage) and bulk resistance reductions within the body of the IGBT. Even so, controller losses are now pretty small, and getting less with every new iteration of device.

Looked at as a system, battery IČR losses, controller losses and motor losses are broadly similar in magnitude now, with batteries getting better (lower internal resistance) and controllers getting better. Motors have a modest potential to improve, with the best being well over 90% efficient already.

WingNut60
4th Mar 2018, 16:26
Thanks VP.

I suspect that the original question (since it was looking at comparison with internal combustion) is probably aimed at electric motors in motor vehicles.

It's a bit hard to get any verifiable information about the systems in electric vehicles but I did see something saying that Tesla 90 systems get about 81% efficiency through the inverter / motor system. But I doubt that it's that high when driving at a steady but slow speed around town.
Probably still better than a gasoline or diesel engine though.

VP959
4th Mar 2018, 16:49
Steady, slow to medium speed is pretty efficient for an electric motor and controller. At low speed the commutation frequency in the controller is low, so the switching losses are low, the motor eddy current losses will be low, because of the low motor rpm, the motor and hence controller, current is low, so the overall IČR losses are low, so the car is probably at, or around, its most efficient.

The worst cases for an EV drive train are usually hard acceleration, where the current is high, so the battery, controller and motor IČR losses will be high, or sustained high speed, where the motor eddy current losses and the controller switching losses will be high.

ImageGear
4th Mar 2018, 17:15
I doubt that we will see any significant improvements in motor efficiency until we get rid of copper windings. Resistive (and therefore heat loss). Friction and other losses will continue to hamper any real innovation. The problem is that electricity is almost never delivered to the drive train in it's most efficient state often requiring batteries to operate most efficiently in one V/I mode with drive train motors best operating at different voltages.

Even 95% efficiency will not cut the mustard for future vehicle drive systems. The possibility of atomic and fusion drives remain some way off except in very limited applications.

IG1

VP959
4th Mar 2018, 17:48
I doubt that we will see any significant improvements in motor efficiency until we get rid of copper windings. Resistive (and therefore heat loss). Friction and other losses will continue to hamper any real innovation. The problem is that electricity is almost never delivered to the drive train in it's most efficient state often requiring batteries to operate most efficiently in one V/I mode with drive train motors best operating at different voltages.

Even 95% efficiency will not cut the mustard for future vehicle drive systems. The possibility of atomic and fusion drives remain some way off except in very limited applications.

IG1

I agree, but anything over 50% is a useful improvement over conventional car efficiency levels.

In pure drive train terms, just not having a gearbox and allowing the motor(s) to directly drive the wheels and provide both traction and regenerative braking is a significant efficiency improvement on it's own. Even in my pretty ancient technology Prius regenerative braking results in around an 8% overall efficiency improvement.

DType
4th Mar 2018, 19:35
But quoting 80/90% for electric vs 30-50% for ICEs rather assumes the electricity to charge the batteries is 100% green. And how about the losses from the electricity generator via the charger to the battery?

Denti
4th Mar 2018, 21:12
What about the losses from the oil well to the wheel of a car? Actually ICE car might reach 35% (or 40% for diesel) in an ideal point of their power diagram, however, average efficiency in normal driving is on average around the 16% mark. It is quite awful. Due to the high energy density in gasoline or diesel it doesn't matter much, it is easy enough to carry a rather large cache of energy around.

A litre of gasoline contains around 9.7 kWh of energy, the biggest car battery in a production BEV currently has roughly 100 kWh, which equates to 10,3 litre of gasoline. And it can reach up to over 500 km of range, of course depending on driving style and conditions. I believe the record with hypermiling was around the 1070 km mark. Now, that is not something anybody would do usually, driving around non stop at 40 km/h.

Of course the complete system does have losses, charging and discharging the battery, depending of course on charging speed, is roughly will result in roughly a 5% loss, transportation over the long range network will result in losses of around 2.5 to 7.5% depending on technique used (DC or AC networks, voltage used etc.). And yes, even if the full electricity would be generated using the same oil that is refined to power ICE cars, the whole system would be currently at least between 2,5 to 3 times more efficient than current ICE cars. If you mix in renewable energy it becomes less polluting of course. However, power to gas technology is available and could power ICE or more directly fuel cell cars. However, that technology is still extremely inefficient and does make even less sense than either BEVs or simply burning fossil fuels.

Of course there are different technologies for electric motors as well. Tesla used in their Model S and X an AC induction motor, the Model 3 has a more efficient 3-phase AC permanent magnet motor. Other car manufacturers have used permanent magnet motors all along. Apparently efficiency goes up from roughly around 95% to 98%. And that is pretty much through the whole speed range.

WingNut60
5th Mar 2018, 03:04
Be careful gentlemen, you're setting a dangerous precedent.
You may be bringing JB into disrepute.

11 posts in and no one has yet expressed a bellicose, belligerent or dogmatic stance on the subject.

Not even one rambling diatribe in sight (where are you K&C / Gertrude / Siti?).

And to my immense surprise, not one mention yet of either DT, Obama or even Elon.

megan
5th Mar 2018, 03:15
The minimum efficiency of electric motors is spelled out for those who live in EU land. Sorry about formatting.

EUR-Lex - 32009R0640 - EN - EUR-Lex (http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32009R0640)

IE3 Premium Efficiency
kW 2 pole 4 pole 6 pole (50/60 HZ)

0.75 80.7 / 77.0 82.5 / 85.5 78.9 / 82.5
1.1 82.7 / 84.0 84.1 / 86.5 81.0 / 87.5
1.5 84.2 / 85.5 85.3 / 86.5 82.5 / 88.5
2.2 85.9 / 86.5 86.7 / 89.5 84.3 / 89.5
3 87.1 / - 87.7 / - 85.6 / -
3.7 - / 88.5 - / 89.5 - / 89.5
4 88.1 / - 88.6 / - 86.8 / -
5.5 89.2 / 89.5 89.6 / 91.7 88.0 / 91.0
7.5 90.1 / 90.2 90.4 / 91.7 89.1 / 91.0
11 91.2 / 90.0 91.4 / 92.4 90.3 / 91.7
15 91.9 / 91.0 92.1 / 93.0 91.2 / 91.7
18.5 92.4 / 91.7 92.6 / 93.6 91.7 / 93.0
22 92.7 / 91.7 93.0 / 93.6 92.2 / 93.0
30 93.3 / 92.4 93.6 / 94.1 92.9 / 94.1
37 93.7 / 93.0 93.9 / 94.5 93.3 / 94.1
45 94.0 / 93.6 94.2 / 95.0 93.7 / 94.5
55 94.3 / 93.6 94.6 / 94.4 94.1 / 94.5
75 94.7 / 94.1 95.0 / 95.4 94.6 / 95.0
90 95.0 / 95.0 95.2 / 95.4 94.9 / 95.0
110 95.2 / 95.0 95.4 / 95.8 95.1 / 95.8
132 95.4 / - 95.6 / - 95.4 / -
150 - / 95.4 - / 96.2 - / 95.8
160 95.6 / - 95.8 / - 95.6 / -
185 - / 95.8 - / 96.2 - / 95.8
200 95.8 / - 96.0 / - 95.8 / -
220 95.8 / 95.8 96.0 / 96.2 95.8 / 95.8
250 95.8 / 95.8 96.0 / 96.2 95.8 / 95.8
300 95.8 / 95.8 96.0 / 96.2 95.8 / 95.8
330 95.8 / 95.8 96.0 / 96.2 95.8 / 95.8
375 95.8 / 95.8 96.0 / 96.2 95.8 / 95.8

james ozzie
5th Mar 2018, 07:33
Mr Denti touches on the subject of transmission and distribution losses on the electricity network. These can start to get significant if you have long transmission distances and multiple voltage transformations.

The power station alternator may generate at 11kV or 22kV; this will get stepped up to 132kV for exporting to the grid and maybe be further stepped up to 275kV for long transmission. The transformer are about 95-97% efficient and the transmission lines have quite low losses (a few percent, depending on loading).

Then there are multiple transformations at the distribution end (275kV to 132kV to 22kV to 400V)

So if you add those losses from "coal to kettle", the overall losses become significant in the total energy picture.

Denti
5th Mar 2018, 08:03
Indeed, losses can become an issue. Having calculated it for the german power system, which has its issues as the absolutely necessary north south DC long distance mainline isn't yet even out of its planning stages, the overall system coal to kettle in case of EVs is actually not that bad. We came up with around 2.7 to 3 times higher efficiency for a Tesla Model S compared to a same size/weight car from one of the german manufacturers with an ICE of similar power output. Which is not bad. It is different for smaller cars, especially if those have no active thermal battery management system like the Nissan Leaf for example.

Of course, the best possible solution would be distributed renewable power generation which basically eliminates long distance power transfer. But we are not there yet and for larger cities i doubt we will be there anytime soon.

VP959
5th Mar 2018, 08:15
Mr Denti touches on the subject of transmission and distribution losses on the electricity network. These can start to get significant if you have long transmission distances and multiple voltage transformations.

The power station alternator may generate at 11kV or 22kV; this will get stepped up to 132kV for exporting to the grid and maybe be further stepped up to 275kV for long transmission. The transformer are about 95-97% efficient and the transmission lines have quite low losses (a few percent, depending on loading).

Then there are multiple transformations at the distribution end (275kV to 132kV to 22kV to 400V)

So if you add those losses from "coal to kettle", the overall losses become significant in the total energy picture.

They do, but it's still just a bit more efficient overall (in terms of potential energy in the fuel to mechanical energy at the wheels) to charge an electric car than to run a petrol/gasoline car. The main reason (at least in the UK) is that the electricity grid generation and distribution system is pretty good overall, in efficiency terms.

Take a CCGT power station as an example. It can run at around 55% or better efficiency (the max is around 62%). Anything from a few percent to 30% of UK electricity is generated by renewable energy sources (hydro, wind, solar) at any time, which tends to push the fuel used to energy generated percentage up over 60% much of the time (check here if you want a breakdown of where our electrical energy comes from: Live monitoring of the UK electricity National Grid (http://gridwatch.co.uk/) ).

Total distribution grid losses in the UK from the power stations to the low voltage point of use in the home or workplace are less than 8% (see here: https://en.wikipedia.org/wiki/National_Grid_(Great_Britain)#Losses ), so although significant aren't enough to take the overall efficiency of charging electric vehicles from the grid below that of conventional vehicles using internal combustion engines.

There's also microgeneration to account for, which is missing from the above data. As an example, at least 50% of my own vehicle charge energy comes from my own solar array, probably a fair bit more in reality, as I export more energy to the grid than my car uses in a year, it's just not well synchronised all year around.

The bottom line is that, in the UK at least, electric vehicles are more efficient than internal combustion engined vehicles, even if only charged with grid generated electricity. There's also plenty of spare grid and generation capacity, provided electric cars are charged at the right times of the day. Peak usage in the UK is around 18:00, with so much spare generation capacity overnight that the 1/2 hour wholesale price may well go negative - suppliers are paid to use energy if they can sell it on.

Golf-Sierra
5th Mar 2018, 09:03
The minimum efficiency of electric motors is spelled out for those who live in EU land. Sorry about formatting.

EUR-Lex - 32009R0640 - EN - EUR-Lex (http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32009R0640)

IE3 Premium Efficiency
kW 2 pole 4 pole 6 pole (50/60 HZ)

0.75 80.7 / 77.0 82.5 / 85.5 78.9 / 82.5
1.1 82.7 / 84.0 84.1 / 86.5 81.0 / 87.5


This regulation would probably not apply to EV motors though it is a good indication of what the efficiencies might be like.

VP959
5th Mar 2018, 09:19
This regulation would probably not apply to EV motors though it is a good indication of what the efficiencies might be like.

No, generally that applies to industrial motors, that may not really need the higher efficiency that an EV needs. This is the combined motor and inverter efficiency plot for the Prius system, as an example:

https://cdn.greenoptimistic.com/wp-content/uploads/2015/02/ornl-motor-efficiency.gif

Note that in the "sweet spot" around slow to medium speed and load, the system runs at up to 92% efficient, but gets worse for the low speed, high torque case and also for the high speed case, pretty much irrespective of torque, pretty much as I suggested earlier in another post here.

cattletruck
5th Mar 2018, 13:07
That's a nice graph VP, would make for a very nice addition to the speedometer if a full width/length crosshair was added.

VP959
5th Mar 2018, 13:18
That's a nice graph VP, would make for a very nice addition to the speedometer if a full width/length crosshair was added.

It would indeed!

The compromise is that the Plug-in Prius optionally displays a horizontal bar graph on the HUD, that shows the energy use, which relates to efficiency reasonably well, with a red bit at the right that shows when you drop to the really inefficient (~80% zone) a brighter area to the right that shows when you're in the 80 to 85% zone and a pale green area when you are better than 85%. It also has a small negative area on the left that shows when the car is using regenerative braking, and how much charge is being recovered by the system.

This is pretty old technology now, though, so I would expect that the newer EVs, like the Tesla can probably do a bit better.

M.Mouse
5th Mar 2018, 13:49
Tesla have a variety of display options or rather a customisable graph.

You can choose to show energy useage over the past 5, 10 or 15 miles with the average power consumption in Wh/mile (Watthours/mile) with another number showing mileage available at the current average power consumption. I can look at a few other numbers and also see what range is in the battery expressed in official mileage numbers (calculated using one of the official test cycles), real mileage numbers or in % charge.

The interesting thing is that it makes you very aware of your energy use. Driving fairly quickly but steadily between my house and Crawley I use slightly more energy travelling to Crawley than in the opposite direction, presumably it is more uphill one way than the other.

Apart from the proliferation of speed cameras I now drive at as steady 70 mph or thereabouts because energy useage at higher speeds increases significantly.

An unintended spin off is that adhering the the motorway speed limit is a lot more relaxing than continually looking for unmarked Police cars or cameras!

From a standing start the car is quick and efficient from 0 - 30, 40, 50, 60 or 70 mph and the odd blisteringly quick acceleration seems to have little effect on overall energy used per mile.

KenV
5th Mar 2018, 18:48
While efficiency is measured as many people have noted in this thread, what REALLY matters is total system efficiency.

An internal combustion machine is an ENGINE, while the electric machine is a MOTOR. What is the significance?

An engine converts stored potential chemical energy of fuel into work. A motor converts electrical energy into work. But where does the electrical energy come from in the first place? It comes from an engine of some kind. Why is this important when comparing the energy efficiency of cars?

For a car with an internal combustion engine, all the conversions (and therefore all the losses) to accomplish work are done right there in the car. Everything is accounted for.

But for a car with an electric motor, some of the conversions (and therefore losses) are done OUTside the car. First, the electricity had to be generated. Assuming a fuel was burned to generate the electricity, there are some large unaccounted for losses. Then the electricity had to be moved over transmission lines to the car battery. More unaccounted for losses. Then the electricity had to be converted into potential chemical energy inside the battery. More unaccounted for losses. Then the chemical energy in the battery gets converted back into electricity. More unaccounted for losses. And finally you measure the losses in the conversion from electricity to work as previously described

So the answer as to how much more efficient is an electric car over an internal combustion engine car is not as simple as it seems. Even if we substitute solar power to generate the electricity, even a 100% efficient solar power plant produces nothing for half of each day (at night). The same with wind power. Much (most?) of the time a wind turbine is producing nothing.

On the other hand, are we really accounting for all the losses for an internal combustion engine car? For example, how much energy is lost drilling for the oil, transporting the oil, refining the oil, and transporting the refined fuel to the point of use by the car? In this thead we're only measuring that last step.

VP959
5th Mar 2018, 19:26
While efficiency is measured as many people have noted in this thread, what REALLY matters is total system efficiency.

An internal combustion machine is an ENGINE, while the electric machine is a MOTOR. What is the significance?

An engine converts stored potential chemical energy of fuel into work. A motor converts electrical energy into work. But where does the electrical energy come from in the first place? It comes from an engine of some kind. Why is this important when comparing the energy efficiency of cars?

For a car with an internal combustion engine, all the conversions (and therefore all the losses) to accomplish work are done right there in the car. Everything is accounted for.

But for a car with an electric motor, some of the conversions (and therefore losses) are done OUTside the car. First, the electricity had to be generated. Assuming a fuel was burned to generate the electricity, there are some large unaccounted for losses. Then the electricity had to be moved over transmission lines to the car battery. More unaccounted for losses. Then the electricity had to be converted into potential chemical energy inside the battery. More unaccounted for losses. Then the chemical energy in the battery gets converted back into electricity. More unaccounted for losses. And finally you measure the losses in the conversion from electricity to work as previously described

So the answer as to how much more efficient is an electric car over an internal combustion engine car is not as simple as it seems. Even if we substitute solar power to generate the electricity, even a 100% efficient solar power plant produces nothing for half of each day (at night). The same with wind power. Much (most?) of the time a wind turbine is producing nothing.

On the other hand, are we really accounting for all the losses for an internal combustion engine car? For example, how much energy is lost drilling for the oil, transporting the oil, refining the oil, and transporting the refined fuel to the point of use by the car? In this thead we're only measuring that last step.


I think we've had a good go earlier in this thread at trying to compare potential energy in the fuel to mechanical energy at the wheels, for both electric and conventional cars, taking into account grid generation efficiency and grid distribution losses. There's no doubt that when compared like this electric vehicles charged from the UK electricity grid are more efficient, even allowing for the losses.

What applied equally to both is the energy of exploration, extraction, transport and refining, but they should be pretty common factors in each case. The snag is that whilst conventional vehicles rely on highly refined fuels of three main types, petrol/gasoline, diesel oil, or liquefied petroleum gas for a small number, electric vehicles can use a very much wider range of primary fuels, from coal, through heavy oil, nuclear, gas (in the form of CCGT plants), hydroelectric generation, wind generation, tidal generation and solar generation, including small-scale microgeneration at the point of consumption.

Making a direct comparison of primary fuel potential energy, gets pretty complex, but overall there's no doubt at all that electric vehicles charged from the UK grid are overall more efficient at the moment. That may not apply in other countries, but here the comparison is pretty clear.