I can see it now
"When will the power come back on?"
"Quien Sabe? But it is said there is a lottery being started to guess the date--millions and millions of pesos being bet"
valhalla360 wrote:jharrell wrote:
Not sure what electric motors you are looking at but this is not my understanding. An induction motor such as on a typical electric pump will pull current based on load exceeding its rated hp if needed at any rpm (perhaps tripping a breaker or overheating). The locked rotor torque and pull up torque can be much higher than rated torque in order to bring the motor up to operating speed.
I guess one issue is the case of a set speed induction motor is how hp is rated between gas and electric, gas is peak, while the electric is operating hp. A 3/4 hp electric motor may have a peak of well over 2 hp from zero to operating speed.
When you get into variable speed electric motor such as those used in cars the power band is still far superior. For instance Tesla has peak hp at 8000 rpm but produces more than 80% of peak from 6000-13,000 rpm, a 7000 rpm range that is an rpm range greater than the entire operating range of many gas engines. Hence the need for only a single speed transmission:
I did a little checking and it looks like they limit torque at higher RPM to control thermal problems. The motor could keep up the torque but it would lower life expectancy. So the drop off after 6000 rpm is electronically applied. They could have added better cooling and kept the torque up...but the car is already overpowered.
A couple of notes:
- At zero RPM, it by definition, you don't have 2hp.
- The graph is misleading as they are comparing it to a drastically less powerful gas engine. I'm guessing they used a turbo engine as most torque curves are much more rounded and will result in a wider power HP band (they left the HP off the chart...presumably to help with the misleading).
They must reduce torque at high RPM in order to limit available HP at high RPM. (check the torque equation). If torque remained constant over the high RPM range, the HP would continue to increase and eventually the motor mechanical components would simply break! The motor would self destruct. This is typical for a variable frequency motor and drive application. The motor is built from components that will break eventually. Don't go beyond that point. Ask a top fuel dragster owner!!
jharrell wrote:
Not sure what electric motors you are looking at but this is not my understanding. An induction motor such as on a typical electric pump will pull current based on load exceeding its rated hp if needed at any rpm (perhaps tripping a breaker or overheating). The locked rotor torque and pull up torque can be much higher than rated torque in order to bring the motor up to operating speed.
I guess one issue is the case of a set speed induction motor is how hp is rated between gas and electric, gas is peak, while the electric is operating hp. A 3/4 hp electric motor may have a peak of well over 2 hp from zero to operating speed.
When you get into variable speed electric motor such as those used in cars the power band is still far superior. For instance Tesla has peak hp at 8000 rpm but produces more than 80% of peak from 6000-13,000 rpm, a 7000 rpm range that is an rpm range greater than the entire operating range of many gas engines. Hence the need for only a single speed transmission:
I did a little checking and it looks like they limit torque at higher RPM to control thermal problems. The motor could keep up the torque but it would lower life expectancy. So the drop off after 6000 rpm is electronically applied. They could have added better cooling and kept the torque up...but the car is already overpowered.
A couple of notes:
- At zero RPM, it by definition, you don't have 2hp.
- The graph is misleading as they are comparing it to a drastically less powerful gas engine. I'm guessing they used a turbo engine as most torque curves are much more rounded and will result in a wider power HP band (they left the HP off the chart...presumably to help with the misleading).
jharrell wrote:valhalla360 wrote:
Correction, the horsepower band for a gas motor is typically wider than an electric motor.
It has to do with the fact that typical electric motors can generate peak HP from 0 to max RPM...the result is the higher the RPM, the higher the HP (sometimes at the top there are some oddities in the torque but they typically are outside normal operating ranges). The result is a linear increase in available HP as RPM increases.
On the other hand, typical gas engines (and diesel) start with relatively low torque and the torque increases as the RPM increases ...but as you near peak RPM, the torque often starts to drop off. The result is the actual HP being generated (not the rating) for a similarly rated engine starts lower but builds more quickly before dropping off around the peak RPM...
This results in a range of ideal RPM where you can produce peak (really near peak) HP for a particular engine. For an electric, peak is generally only at the peak RPM.
Not sure what electric motors you are looking at but this is not my understanding. An induction motor such as on a typical electric pump will pull current based on load exceeding its rated hp if needed at any rpm (perhaps tripping a breaker or overheating). The locked rotor torque and pull up torque can be much higher than rated torque in order to bring the motor up to operating speed.
I guess one issue is the case of a set speed induction motor is how hp is rated between gas and electric, gas is peak, while the electric is operating hp. A 3/4 hp electric motor may have a peak of well over 2 hp from zero to operating speed.
When you get into variable speed electric motor such as those used in cars the power band is still far superior. For instance Tesla has peak hp at 8000 rpm but produces more than 80% of peak from 6000-13,000 rpm, a 7000 rpm range that is an rpm range greater than the entire operating range of many gas engines. Hence the need for only a single speed transmission:
Keep in mind that reving the engine from 6000 rpm to 13000 rpm is only increasing the vehicle speed by a factor of 2.17. The Cat in my Peterbilt makes 400 HP by 1100 rpm, reaches a peak of 500 hp by 1300 rpm and holds the power flat to 2100 rpm. So even a big slow turning diesel can double the speed of the vehicle while maintaining 80% of its peak HP.
