Lower Battery Voltage than PM Motor Voltage

Discussion in 'General Electronics Chat' started by zezizou, Nov 17, 2014.

  1. zezizou

    Thread Starter New Member

    Sep 26, 2013
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    So I'm trying to connect a permanent magnet motor to a set of batteries that are rated at about 44V.
    The motor is rated at about 48V and has an input power rating of around 30kW.

    (Adding another battery is not possible for this design unfortunately and I am unable to pick other batteries due to sponsor constraints).

    I was curious, could one use a buck-boost DC/DC converter to bump up the battery voltage from 44-48 V?
    Is it possible to design a DC/DC converter with an output power close to that of the motor's input power (~30kW)?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Try running it at 44V. It will draw a little more current than at 48V, but the power input wont change much...
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You will be giving up about 15% of max power (if that). Is it possible to have a switch to change between series and parallel connections? Motors can be run well above their rated current for short bursts. Perfect for high torque to launch from a standing start.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The voltage determines the RPM, the current (torque) is determined from the load, a DC motor generates a voltage in opposition to the applied voltage, this is how the current is limited, when the generated voltage nears the applied voltage, (it can never equal it) the maximum rpm is reached (at that voltage).
    A PM motor is always a Shunt field motor in application.
    All you are going to achieve by using 48v is slightly more RPM.
    Max.
     
  5. zezizou

    Thread Starter New Member

    Sep 26, 2013
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    Apologies for my lack of knowledge... but does a permanent magnet AC motor behave like a shunt DC motor?
     
  6. zezizou

    Thread Starter New Member

    Sep 26, 2013
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    The motor says it's a PMAC; however, it says the voltage range is 48V to 450V... That's why I'm confused as to where the AC comes into play

    Also...I have a torque vs speed (RPM) chart yet it says "Performance typical of 104 Vdc/550 Arms operation."

    I've tried to search all I can about the motor besides that and unfortunately cannot find any more relevant data sheets.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes it is essentially the same except of course the wound shunt field can be varied, if the field is lost in in a wound field motor it runs away, and can possibly destruct if no load.
    If it has no brushes and has 3 stator connections/winding's and a P.M. rotor then it indicates it is PMAC motor.
    Max.
     
  8. zezizou

    Thread Starter New Member

    Sep 26, 2013
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    Thank you so much.

    For more knowledge would it be beneficial to study shunt DC motors then move on to PMAC? Mainly because they are very similar?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The DC brushed motor, both shunt or PM and series wound are fairly simple and common, and usually just need a DC supply, the PMAC and BLDC (brushless DC) generally require a drive that works in conjunction with some form of commutation device on the motor, see Hall effect sensors.
    Max.
     
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