Electric Car Motor Slip Torque and Voltage

29 Мар 2014 | Author: | Комментарии к записи Electric Car Motor Slip Torque and Voltage отключены
BYD Electric Cars Electric Cars

Electric Car Motor: Slip, and Voltage

This is Part 2 of a interview with Eric about his AC-motored VW Passat

In this section, we talk

what is unique about an car motor (meaning one that was specifically to go into an electric Slip, voltage, and RPMs; the differences between AC and DC motor in electric cars; torque to number of poles in your car motor; high voltage

OEM Electric Car Motor (made for cars)

Lynne: I noticed you chose an electric car motor you know, came out of an electric car an old Ford Ranger EV, actually rather than some 3-phase AC motor, like say for an application. Was there a reason for

Eric: The motor I chose was in an electric vehicle and it is much and smaller than an equivalent AC motor. The electric car motor is cooled, which makes it smaller than air cooled which require heat

Industrial motors are also for continuous power, which it to be much larger than an car motor rated for intermittent which is better suited for an EV. The car motor is also sealed tight, and somewhat stubby, a industrial motor would stick out beyond the front and weigh 400 lbs.

Video of Eric’s car.

The AC Car Motor and Voltage


Why do you run your at 300v?

The 312VDC is required to a 220VAC (312V peak) wave. This is a common for a 3 phase AC motor. Most controllers are powered by 312VDC so this is why I am using such a voltage.

It sounds like a right voltage for an AC electric car which is such a different than the SWDC how many can you afford? approach. Is this

More batteries will get more torque from an AC car motor.

Most AC motors run RPM at 60hz 230v, so at 875 rpm, are at 30hz 115V. You can spin 1750rpm by running field so at 3500 (rpm) 60hz it will be spinning twice speed, but half the torque.

If you can supply 460v then you have full torque at

Slipping and Spinning: Not as Bad as it Sounds

the video, I see your car keeps on that’s what looks so about it. The DC electric cars seen will take off a rabbit, but when they get to cruising speed, there any more. Like a golf

Your car seemed to drive a lot a regular car.

Motor is related to slip. Slip is the between actual electric car speed and commanded motor For example a DC car at a stop can generate of torque because 100 volts produce 2000 rpm of slip.

you achieve 1900rpm, the torque is because now you can only produce of slip. With an AC electric car the slip is not limited by voltage, it is by frequency, which is basically So the motor can produce torque at high rpms.

The constant nature of the AC electric car motor it feasible to drive 0-75mph in one gear.

Slip. If the motor varies directly with speed, this sort of to the ability of the car to accelerate, then? So the SWDC, once you achieve or whatever is your approaching rpm at a given voltage, there’s not acceleration left. This the golf cart observation I guess. Thanks, I never got before, but I can see it’s a big drawback for a DC if you want it to act like a regular car like, for instance, accelerating to get something on the freeway.

With a DC conversion, there’s left to give as it approaches the top of its rpm

If you want fast acceleration, you to command the motor to spin than it currently is spinning. The slip means more the motor is producing.

Picture a car a big coil spring on the rear If you want to accelerate the car slowly, you push on the spring with force, and this would the spring slightly small of slip. If you want to accelerate you would command a large basically compressing the spring a

DC Motors spin a certain rpm per If 1 volt = 20 rpm, 2 volts =40 rpm, and 200v will =

AC motors will spin a rpm per cycle. If 1 cycle/second = 20rpm, 60 will = 1200rpm. The motor can command any frequency it wants to the and of course you need enough and current to produce torque.

. for a DC voltage will limit the max of the motor. Unless the motor has a wired field, this is

So the DC converters don’t throw to the motor because there’s no on the low-end torque — sort of all or nothing.

Your AC on the other hand, has rpm control to frequency; control the frequency, and you the rpm.

Correct. A DC controller vary the voltage to the motor. An AC will vary the voltage and to the motor.

Torque and Electric Car Poles

So what’s torque got to do it? Is that a constant, related to the of motor, and moved to the right or on the graph by the number of poles? never understood the poles bit well. More poles more low-end torque, high-end torque?

Is there a limit to the number of a motor can have?

Most AC car motors are 4 or 6 pole. The more the slower the motor will If both motors have the horsepower, the 6 pole motor have more torque and speed.

HP = speed * torque.

Voltage Safety

Are you a little careful with 300v folks are with 120v or (read: they get bitten A lot.), or were there precautions that you took that much voltage? On the note, I’ve always why there wasn’t some of GFI device that folks put between their battery and themselves so that if they heaven forbid — became the shortest path to electrons would stop

I have not tried this, but I think DC voltage will to ground, only AC voltage I suspect folks are getting with 120vac because chargers are not isolated from I know mine is not. I my battery pack into groups so the voltage within reach is somewhat limited. The (under the hood, where the gas was, spare tire and trunk area) make it a far to touch both ends of the pack.

There is 312v inside the controller, and I tried to make as finger safe as possible.

So AC is potentially more dangerous, You split your batteries up, I’ve heard is good for

It sounds like the controller is the risky part of the equation. How did you that finger safe, and precautions did you take while it?

I just enclosed everything in a box, and used finger devices such as the fuse It basically means you can’t any high voltage with fingers. I also retained the VFD housing.

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