How do BLDC Motor fans achieve high efficiency?

Discussion in 'General Electronics Chat' started by RamaD, Sep 2, 2018.

  1. RamaD

    Thread Starter Senior Member

    Dec 4, 2009
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    46
    BLDC Motor fans draw considerably lower power vs the normal AC fans, when I have checked their data.
    For about 220 CMM, BLDC fans draw 28W, vs 78W by the older fans (split phase, please correct me if I'm wrong) fo a slightly higher airflow.
    Can someone please explain how this efficiency is achieved?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    15,885
    4,659
    For one, a BLDC uses a permanent magnet field so this is a reduction in any current required, a AC induction motor, particularly a 1ph version is not a particularly efficient motor in the production of field.
    Also BLDC operates synchronously.
    Max.
     
    Last edited: Sep 2, 2018
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  3. RamaD

    Thread Starter Senior Member

    Dec 4, 2009
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    Will that be that inefficient?
    Meaning,
    bldc 28w gives 220 CMM. 7.86 CMM/W.

    Normal AC fans, 78w gives 235 CMM. 3 CMM/W.

    Even if we assume the BLDC is 100% efficient, then the AC fans (induction or split phase) are only 3/7.86=38% efficient. Suspect that it can't be that bad. I have always thought motors are pretty efficient above the 75% mark. Where am I going wrong?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    15,885
    4,659
    AC induction motors represent a transformer with a shorted secondary at the point of switch on, this decreases as the slip frequency decreases, a Shaded pole fan motor is even worse than a 1ph PSC motor as far as efficiency.
    Max.
     
  5. oz93666

    Senior Member

    Sep 7, 2010
    152
    32
    from search ...."Efficiency. (See also Energy savings) Full load induction motor efficiency varies from about 85% to 97%,"

    Where do you get these figures from for air flow ?? Are they accurate?

    If they are accurate , maybe the fan and not the motor is where the difference lies , brushless can run at a wide range of speeds perhaps allowing greater efficiency in moving air .... A manufacturer who has taken the care to use brushless ,will probably take care in designing the right prop and speed to match .
     
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  6. RamaD

    Thread Starter Senior Member

    Dec 4, 2009
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    That was my first doubt too. Searched so many fans.
    I am giving below a sample, which is not exactly the figures given by me earlier (Cant remember the exact ones), but are similar.

    https://www.amazon.com/Westinghouse...8&qid=1535957653&sr=8-2&keywords=CEILING+FANS

    61 W, 3588.69 CFM, 97 CMM.

    https://aeratronfans.com/ae3-specification/

    50 in. (1260mm)
    18.5W, 5765 CFM, 156 CMM.

    A third of power, and one and a half times airflow. That is why I am confused.
     
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