Hi,
I am new to the forum. I have two questions about electric drivetrain efficiency loss:
(1) FIRST SCENARIO:
Imagine a Wrightspeed drivetrain. A 300 KW battery pack sends electricity through wires to an inverter, which powers the 250 HP hub electric motor; but the motor also has a “Geared Traction Drive” -- see http://www.wrightspeed.com/technology/. Could we say that the electric motor operates at only .98 % efficiency, the inverter deducts another 2 %, and the hub-gearbox another 3 %?
In other words, what would be the “Battery to Wheel” energy loss? 5 %? 7 %? 10%?
*****************************************************************
Now imagine a much more “theoretical” scenario.
(2) SECOND SCENARIO:
A 300 KW battery pack sends electricity through wires to an inverter, which powers a 250 HP hub electric motor, which also has hub reduction gearing. But the year is 2020, and everything has been perfected even further: motors inverters, hub-motor gearing, etc. In such an ideal scenario, how much energy would be lost “Battery to Wheel”?
*****************************************************************
Engine-to-wheel energy loss in the world of ICE is a common topic, where lots of energy gets absorbed by transmissions. But it’s also a controversial topic. There is no “typical” figure for the percentage lost to a transmission and other components in a drivetrain, although some will cite 15 % for cars, and 30 % for trucks. Apparently in racing there is a "15 % inefficiency" rule, but a very detailed, well-written, well-informed, and insightful article suggests that the "15 % rule" is pure rubbish -- see http://www.superstreetonline.com/how-to/engine/modp-1005-drivetrain-power-loss/. Another webpage that is probably not to be trusted pegs the drivetrain loss as just 5.6 % -- see http://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.html \. A more empirical article that tested two cars, came up with figures for driveline inefficiency that varied from 17 % to almost 40 % -- see http://www.hotrod.com/how-to/transmission-drivetrain/ccrp-0311-drivetrain-power-loss/ . There's a really terrific thread in which some seemingly well-informed posters claim that modern car transmissions can lose as little as 10 %, while others who sound just as informed will say that 30 % is more nearly right -- see http://cr4.globalspec.com/thread/36270/Overall-efficiency-of-gasoline-powered-cars . And that's just cars. I wonder where the guesstimate of 30 % lost to the transmission for trucks came from?
In any case, what I am trying to determine is the same for an electric drivetrain. Between the surge of current provided by the the battery pack, and the final power output via the electric motors "at the wheel", how much energy do you think will be lost, due to various kinds of “inefficiencies”? Or what would be a reasonable rough-ball-park figure to work with? So far, the only thing that a friend has been able to find on the web is a Master's thesis written in 2011 -- see http://scholar.lib.vt.edu/theses/available/etd-05162011-220140/unrestricted/Gantt_LR_T_2011.pdf. So the question is a rather "new" one, if only because electric drivetrains are still rather new.
My motivation is the following. At present I am using a reasonably good web-calculator to try to figure on the different power requirements for a serial-hybrid electric bus-type vehicle driven at different speeds, altitudes, and ascending different kinds of slopes. There is a space where one needs to insert a percentage figure for “mechanical transmission inefficiency" -- see http://buggies.builtforfun.co.uk/Calculator/index.html :
So I would greatly appreciate it if those on this forum who are knowledgeable about “electric drive train efficiency loss”, might suggest a good percentage figure into insert in this part of the web-calculator. Even an informed guess would be better than my guess, which would be utterly arbitrary, because I am not an electrical or automotive engineer.
One caveat: I realize that on this forum there exists a long thread whose subtitle might be "To gearbox or not to gearbox?". I got the impression reading that thread that if a hub-motor's gearbox is well-designed, it can be very efficient, and the power loss will be minimal. See https://endless-sphere.com/forums/viewtopic.php?f=30&t=47930&start=30 . But I didn’t understand the half of it. My overall impression is that using a direct drive motor without a gearbox at low speeds kind of abuses the electric motor, if the electric motor is not large enough. So the choice seems to be between a smaller electric motor + gearbox, or a larger electric motor that has enough power and torque at slow speeds such that it won't get abused when used to direct drive. Tesla settled for the second alternative, the direct drive approach. I am guessing that Wrightspeed developed its two-speed "Geared Traction Drive" primarily because garbage trucks do so much starting and stopping, and are working primarily at such slow speeds. Apparently a gearbox is also important for some reason when there's a headwind, and when climbing hills. A direct-drive electric motor is not optimal when climbing hills, for reasons that I don't understand.
So for the present purposes let’s assume that a hub motor will have a gearbox, and that direct-dirve is not an option? In the two scenarios described above, what would the efficiency loss? What percentage for drivetrain inefficiency should I plug into the web-calculator at http://buggies.builtforfun.co.uk/Calculator/index.html, and why?
All best wishes,
Biotect
I am new to the forum. I have two questions about electric drivetrain efficiency loss:
(1) FIRST SCENARIO:
Imagine a Wrightspeed drivetrain. A 300 KW battery pack sends electricity through wires to an inverter, which powers the 250 HP hub electric motor; but the motor also has a “Geared Traction Drive” -- see http://www.wrightspeed.com/technology/. Could we say that the electric motor operates at only .98 % efficiency, the inverter deducts another 2 %, and the hub-gearbox another 3 %?
In other words, what would be the “Battery to Wheel” energy loss? 5 %? 7 %? 10%?
*****************************************************************
Now imagine a much more “theoretical” scenario.
(2) SECOND SCENARIO:
A 300 KW battery pack sends electricity through wires to an inverter, which powers a 250 HP hub electric motor, which also has hub reduction gearing. But the year is 2020, and everything has been perfected even further: motors inverters, hub-motor gearing, etc. In such an ideal scenario, how much energy would be lost “Battery to Wheel”?
*****************************************************************
Engine-to-wheel energy loss in the world of ICE is a common topic, where lots of energy gets absorbed by transmissions. But it’s also a controversial topic. There is no “typical” figure for the percentage lost to a transmission and other components in a drivetrain, although some will cite 15 % for cars, and 30 % for trucks. Apparently in racing there is a "15 % inefficiency" rule, but a very detailed, well-written, well-informed, and insightful article suggests that the "15 % rule" is pure rubbish -- see http://www.superstreetonline.com/how-to/engine/modp-1005-drivetrain-power-loss/. Another webpage that is probably not to be trusted pegs the drivetrain loss as just 5.6 % -- see http://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.html \. A more empirical article that tested two cars, came up with figures for driveline inefficiency that varied from 17 % to almost 40 % -- see http://www.hotrod.com/how-to/transmission-drivetrain/ccrp-0311-drivetrain-power-loss/ . There's a really terrific thread in which some seemingly well-informed posters claim that modern car transmissions can lose as little as 10 %, while others who sound just as informed will say that 30 % is more nearly right -- see http://cr4.globalspec.com/thread/36270/Overall-efficiency-of-gasoline-powered-cars . And that's just cars. I wonder where the guesstimate of 30 % lost to the transmission for trucks came from?
In any case, what I am trying to determine is the same for an electric drivetrain. Between the surge of current provided by the the battery pack, and the final power output via the electric motors "at the wheel", how much energy do you think will be lost, due to various kinds of “inefficiencies”? Or what would be a reasonable rough-ball-park figure to work with? So far, the only thing that a friend has been able to find on the web is a Master's thesis written in 2011 -- see http://scholar.lib.vt.edu/theses/available/etd-05162011-220140/unrestricted/Gantt_LR_T_2011.pdf. So the question is a rather "new" one, if only because electric drivetrains are still rather new.
My motivation is the following. At present I am using a reasonably good web-calculator to try to figure on the different power requirements for a serial-hybrid electric bus-type vehicle driven at different speeds, altitudes, and ascending different kinds of slopes. There is a space where one needs to insert a percentage figure for “mechanical transmission inefficiency" -- see http://buggies.builtforfun.co.uk/Calculator/index.html :
Mechanical Transmission Efficiency
Effy ???? %
The calculated power is the ideal mechanical power required at the wheels to drive the vehicle under the conditions you describe. The motor output power will need to be more than this - because some is lost in the mechanical transmission. If you specify a transmission efficiency (in %) a figure for motor output power will also be calculated.
So I would greatly appreciate it if those on this forum who are knowledgeable about “electric drive train efficiency loss”, might suggest a good percentage figure into insert in this part of the web-calculator. Even an informed guess would be better than my guess, which would be utterly arbitrary, because I am not an electrical or automotive engineer.
One caveat: I realize that on this forum there exists a long thread whose subtitle might be "To gearbox or not to gearbox?". I got the impression reading that thread that if a hub-motor's gearbox is well-designed, it can be very efficient, and the power loss will be minimal. See https://endless-sphere.com/forums/viewtopic.php?f=30&t=47930&start=30 . But I didn’t understand the half of it. My overall impression is that using a direct drive motor without a gearbox at low speeds kind of abuses the electric motor, if the electric motor is not large enough. So the choice seems to be between a smaller electric motor + gearbox, or a larger electric motor that has enough power and torque at slow speeds such that it won't get abused when used to direct drive. Tesla settled for the second alternative, the direct drive approach. I am guessing that Wrightspeed developed its two-speed "Geared Traction Drive" primarily because garbage trucks do so much starting and stopping, and are working primarily at such slow speeds. Apparently a gearbox is also important for some reason when there's a headwind, and when climbing hills. A direct-drive electric motor is not optimal when climbing hills, for reasons that I don't understand.
So for the present purposes let’s assume that a hub motor will have a gearbox, and that direct-dirve is not an option? In the two scenarios described above, what would the efficiency loss? What percentage for drivetrain inefficiency should I plug into the web-calculator at http://buggies.builtforfun.co.uk/Calculator/index.html, and why?
All best wishes,
Biotect