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Thread: eAssist AC Induction Motor

              
   
   
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    Moderator Nuts & Volts's Avatar
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    eAssist AC Induction Motor

    I stumbled across this motor about a week ago. The OSU EcoCAR team has the engine out of the Malibu Hybrid Vehicle that they are using for the next build and I noticed it had the BAS (Belt Alternator Starter) motor on it. I didn't know much about it so I did a bit of research.

    The basics
    • AC Induction 8 pole Radial Flux Inrunner
    • Water/Glycol Cooled Stator
    • 15-18kW peak
    • 115Vdc Bus
    • 150Nm at 230Arms (in vehicle)
    • 30lbs
    • 4000RPM peak
    • 72 stator windings in wye, 56 aluminum rotor bars
    • 10 pole induction speed sensor


    I am hoping to get 50-60kW peak for 5-10sec from this motor. My limitations right now are understanding what speeds I achieve with a specific voltage. I understand how the frequency comes into play, but can't figure out if I can spin the motor above 4000RPM with less than 115Vdc...I will also check the bearings to determine that they are rated to higher speeds.

    I am looking at using either a Curtis 1238 Controller or a Sevcon Gen4 Size6 controller. I am concerned that the 300Hz of the Curtis will spin the motor quite a bit slower than the 500Hz of the Sevcon.

    Speed = 120*(freq/# of poles)
    Speed Curtis = 4500RPM
    Speed Sevcon = 7500RPM

    What factor does voltage plan thou? It appears that normally you keep the V/Hz ratio the same at all speeds, but this article states something about changing voltage to optimize efficiency. The sevcon has field weakening capabilities so that gives it the nod in my book even if it may take a bit of time and money to tune it. I think getting this motor up to 7-8k will make this a killer combo, because losses don't increase as much as a PM motor would with speed.

    Thoughts, or Questions? My motor may be here by the end of the week so I can add more data then.

    The best bit of information I found was from this video


    Possible Controllers
    http://www.sevcon.com/media/2104/gen4_web.pdf
    http://www.curtisinstruments.com/ind...torControllers

    Motor Sources
    http://www.tonkinonlineparts.com/p/_.../24261691.html
    http://www.gmpartseast.com/parts/gm-...generator.html

    Thanks to Tony Helms for actually getting me to want to look the motor over more closely Probably won't beat a Roadster motor, but I'll try haha
    Last edited by Nuts & Volts; 22 January 2013 at 1519.
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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    Thanks, very interesting. The narrator doesn't know much about induction motors. There are 72 teeth in the stator and 56 bars in the rotor. The number of poles is determined by the stator winding. It appears that the coil span would give about 8 poles. And 8 poles would be consistent with your synchronous speed-frequency calculation for the controllers. He also mentions 79 lb.ft. and 20 hp which yields 1330 RPM. Nice looking motor.

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    Moderator Nuts & Volts's Avatar
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    Quote Originally Posted by lugnut View Post
    Thanks, very interesting. The narrator doesn't know much about induction motors. There are 72 teeth in the stator and 56 bars in the rotor. The number of poles is determined by the stator winding. It appears that the coil span would give about 8 poles. And 8 poles would be consistent with your synchronous speed-frequency calculation for the controllers. He also mentions 79 lb.ft. and 20 hp which yields 1330 RPM. Nice looking motor.
    Yea I figured he was talking about teeth and bars, but didn't really know what to call them. The paper I linked states that the motor is an 8 pole machine.

    This is where I got the peak torque values from http://www.greencarcongress.com/2011...-20111215.html
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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    Senior Member ARC EV Racing's Avatar
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    Re: eAssist AC Induction Motor

    The 1238 has field weakening too, just in case that becomes the deciding factor.

    Sent from my AZ210A using Tapatalk 2

    www.arc-ev-engineering.co.uk

    ARCEVRacing on twitter

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    Moderator Nuts & Volts's Avatar
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    Quote Originally Posted by ARC EV Racing View Post
    The 1238 has field weakening too, just in case that becomes the deciding factor.

    Sent from my AZ210A using Tapatalk 2
    Thanks, I am putting together a comparision chart right now of the two controllers.

    Is there any difference between the 1238-7601 and the 1238R-7601? I am having trouble figuring that out...
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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    Senior Member ARC EV Racing's Avatar
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    Re: eAssist AC Induction Motor

    I think the 'R' tolerates the higher 96v nominal pack voltage (can be persuaded to work with 115v nominal though). Also it sounds faster

    www.arc-ev-engineering.co.uk

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    Re: eAssist AC Induction Motor

    The r is a newer Rev. I think its just a name change though. 7xxx series are all 120/130vdc Max depending on the literature you read . 6xxx are 108 Max.

  10. #8
    Moderator Nuts & Volts's Avatar
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    Quote Originally Posted by frodus View Post
    The r is a newer Rev. I think its just a name change though. 7xxx series are all 120/130vdc Max depending on the literature you read . 6xxx are 108 Max.
    Thanks Travis. The more I look at it I am liking the Curtis over the Sevcon. I have a spreadsheet that I will throw up comparing the models.

    Still trying to determine the Max speed thing.
    Does the field weakening allow the motor to spin faster than the 4500RPM that the Curtis frequency is limited to? That is before the BEMF limits RPM? From my understanding it seems that even with field weakening the Curtis controller will not be able to switch quick enough to spin the motor any faster regardless of the BEMF.

    IE a 150V, 300Hz and a 300V,300Hz control will only spin this motor to 4500RPM. Thou the base speed will be doubled on the 300V, which will still double power...
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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    Moderator Nuts & Volts's Avatar
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    Here is the chart I created to compare the controller options.

    Induction Controller Comparison.jpg

    I am leaning a little towards the Curtis because it has higher power capabilities and will probably be easier to set-up. May try to HV version depending on what the final price and specs look like.
    Whats under my tank may shock you!!! R6 Build, Blog/, [/URL] OSU Current webpage

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    Quote Originally Posted by Nuts & Volts View Post
    Still trying to determine the Max speed thing.
    Does the field weakening allow the motor to spin faster than the 4500RPM that the Curtis frequency is limited to? That is before the BEMF limits RPM? From my understanding it seems that even with field weakening the Curtis controller will not be able to switch quick enough to spin the motor any faster regardless of the BEMF.

    IE a 150V, 300Hz and a 300V,300Hz control will only spin this motor to 4500RPM. Thou the base speed will be doubled on the 300V, which will still double power...
    The maximum speed is set by the controller; the max frequency minus a few percent slip. The winding in the motor determines a volts per hertz ratio. The battery voltage determines the frequency at which this ratio can no longer be maintained (base frequency). At frequency above base, field is weakened and torque decreases. But the speed continues to follow the frequency. Eventually a frequency would be reached where there is insufficient torque to maintain speed but that is likely several times the controller limitation.

    In your example, doubling the voltage does not change the volts/hertz but doubles the base frequency and would double the maximum power if the V/f ratio was greater than 1:1.

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