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Hello all! After doing tons of reading on electric drivetrains and sizing of your electric motor for a specific application, I wanted to bring to light some hypotheses about how much power you really need.

Firstly, ICE engines aren't very consistent in how they produce power. If you look at a graph, you'll notice how they usually reach a peak then head down from there. Owners then use that peak figure for bragging rights, etc.

But herein lies the issue. That power is a peak! If you look at the average power throughout the Dyno run, you get a much lower number!

This is when I realized that even though most budget EVs are running under 100kw to the motor, that power is continuous and thus, has a lot more push than you would think for under 130HP!

And, when you build a motor for that much continuous power, you can get away with much higher peak numbers, for say, 0-60 times. This would only require 5-10 seconds of peak amperage.

This was the coolest thing I learned, that you can feed a motor rated for 48v 200a with 340v 1200a, but only for a short period of time (see: Duncan).

But this is just speculation. What do you guys think?
 

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Firstly, ICE engines aren't very consistent in how they produce power. If you look at a graph, you'll notice how they usually reach a peak then head down from there. Owners then use that peak figure for bragging rights, etc.

But herein lies the issue. That power is a peak! If you look at the average power throughout the Dyno run, you get a much lower number!
It's not just "for bragging rights" - that's what the engine will produce at the appropriate speed. The point of a transmission having more than one ratio is to allow the driver (or automatic transmission control) to choose the gear which puts the engine at the desired speed - fast enough to produce the desired power, but not faster than necessary. It doesn't matter than an engine can produce less than one-quarter of its peak output at 1500 rpm, because if the driver wants more than that the engine is not run at that low speed.

This is when I realized that even though most budget EVs are running under 100kw to the motor, that power is continuous and thus, has a lot more push than you would think for under 130HP!
A typical production EV with an AC motor and high (over 300 volts) battery voltage is designed to be able to produce the full rated power over a wide range of speed. A typical brushed DC motor (whether salvaged from something or very expensively purchased from an EV component supplier) has a power curve which is as peaky as a gasoline engine: peak power is only at some mid speed, with much less available at both lower speed (where power is proportional to the constant torque resulting from the current limit) and higher speeds (where power is limited by available voltage and the resulting decreasing ability to push current).

A lot of the perceived performance of EVs seems to result from the lack of a need to shift gears, and drivers' incompetence in shifting. Someone commented in a discussion in another forum that his Chevrolet Bolt accelerated "like a rocket", while in fact the Bolt (a fine and very capable vehicle) is no quicker from a standstill to highway speed than my ordinary gas-engine compact car; the difference is that to get the performance from the gas car one actually needs to move the shift lever and clutch twice.

Also, 130 hp was hot performance car stuff a few decades ago, so it should be more than enough for normal driving of a mid-sized car.

And, when you build a motor for that much continuous power, you can get away with much higher peak numbers, for say, 0-60 times. This would only require 5-10 seconds of peak amperage.
Yes, EV conversion performance (and Tesla's stupidly named higher-performance modes) depend heavily on thrashing everything (battery, controller, motor) with power levels (resulting in heating rates) that they can only stand for a few seconds.

There is a gasoline engine equivalent to this; for instance, the famous Buick Grand National (famed for impressive acceleration in its day) with its turbocharged engine and an air-to-water intercooler. During hard acceleration the water (actually coolant) would heat up so the high power could not be sustained, and the power had to be backed off for a while for the coolant to cool down before another hard run could be done... but that worked fine for sprinting up to highway speed or down a drag strip. Nothing new here...
 

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It's not just "for bragging rights" - that's what the engine will produce at the appropriate speed. The point of a transmission having more than one ratio is to allow the driver (or automatic transmission control) to choose the gear which puts the engine at the desired speed - fast enough to produce the desired power, but not faster than necessary. It doesn't matter than an engine can produce less than one-quarter of its peak output at 1500 rpm, because if the driver wants more than that the engine is not run at that low speed.

This is correct, but traditional transmissions cannot keep an engine at that peak point for very long. Even a dyno run in a single gear results in an "average" power level for that gear. Basically, a CVT is the closest you can get to delivering peak power throughout a speed range.


A typical production EV with an AC motor and high (over 300 volts) battery voltage is designed to be able to produce the full rated power over a wide range of speed. A typical brushed DC motor (whether salvaged from something or very expensively purchased from an EV component supplier) has a power curve which is as peaky as a gasoline engine: peak power is only at some mid speed, with much less available at both lower speed (where power is proportional to the constant torque resulting from the current limit) and higher speeds (where power is limited by available voltage and the resulting decreasing ability to push current.
This right here! I totally forgot how DC motors are very comparable to engines (mostly big block V8s in that regard) because of their immense starting torque which declines as soon as you rev 'em up. AC motors are what my ideas go best with because they aren't limited by brushes in terms of delivering power.


During hard acceleration the water (actually coolant) would heat up so the high power could not be sustained, and the power had to be backed off for a while for the coolant to cool down before another hard run could be done... but that worked fine for sprinting up to highway speed or down a drag strip. Nothing new here...

Perfect! One thing I've wondered is how "built" a motor has to be in order to sustain a particular amperage. If you can control the amount of heat building up in the motor, how high can you go before arcing will take it out?
 
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