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  1. #301
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    Feb 2006
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    Quote Originally Posted by cjbfisher View Post
    I'm in the process of doing the impeller>filter bag mod, and was wondering if the length of the transition piece will have any effect on the performance?
    Not really - its actually better that it be a little longer because this helps to smooth out some turbulence.

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  3. #302
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    Aug 2008
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    Birkdale
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    Thanks Bob.

  4. #303
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    Oct 2017
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    Sydney
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    136

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    Quote Originally Posted by cjbfisher View Post
    I'm starting to mod the intake for my Carbatec 2hp dusty. I have a 16mm melamine faced MDF disc to replace the metal impeller cover and a 25mm mdf backing plate to make a total of 41mm with which to form the reverse BMH. These both have a hole machined to the id of the 6 inch DWV pipe. I then have a further 2 25mm mdf plates with holes machined to the od of the pipe so the pipe will slip in and fit to the reverse BMH.
    I have come to a standstill with regard to forming the reverse BMH. I don't have a lathe, or access to one, and a 38mm roundover bit is prohibitively expensive for what will possibly be a one time use.
    Has anyone got any other suggestions, or even a router bit that I could borrow/hire?
    @cjbfisher - If you have any photos of the unit you are making it would be good to see it, even in progress is fine. I am keen to make something similar and would like to see a photo of what you are making.

    Thanks!

  5. #304
    Join Date
    Jun 2020
    Location
    Melbourne
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    2

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    Quote Originally Posted by BobL View Post
    Next the power ratings.
    The name plate says 240V , 7.7A and 2HP (240 x 7.7 = 1848W or 2.46 HP)

    However, in stock DC configuration I find it only draws 5.0 A at 238 V.
    The naked impeller draws 5.2A at 238V,
    Whether the bags are attached makes no difference to the current draw.

    The actual power drawn is thus 5.0 x 238 = 1190 W or 1.59HP
    Compare that to my 3HP system which in stock format draws 9.4 A at 238 V or 2237 W or 2.98 HP

    It appears this 2 HP unit is not actually 2 HP but more like 1.6HP?

    I will do some air flow measurements WIGRTI.
    Hi Bob, what an informative thread this is!
    I haven't read the whole 303 posts (yet) but I couldn't find any clarification offered for the apparent inconsistency within the motor nameplate ratings.

    The simple answer is that it's an AC motor so the power factor (PF) has to be taken into account. The PF is the cosine of the phase angle between voltage and current; for a DC (= direct current) motor, PF = 1. Power = Volts x Amps x PF. For an AC motor at full load the PF is typically around 0.8 and for the motor quoted, it is (2 x 746)/(240 x 7.7) = 0.81
    At less than full load, the power factor will likely fall and could be as low as 0.2 at no load.
    Therefore, to determine the power being consumed by an AC motor it is best to use a power meter rather than measure just the current (unless you have a current vs power curve), or if you can measure the phase angle between volts and amps, you can calculate the PF.

    Apologies if this has already been explained elsewhere in the thread.
    Cheers

  6. #305
    Join Date
    Feb 2006
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    Perth
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    Quote Originally Posted by SROman View Post
    Hi Bob, what an informative thread this is!
    I haven't read the whole 303 posts (yet) but I couldn't find any clarification offered for the apparent inconsistency within the motor nameplate ratings.

    The simple answer is that it's an AC motor so the power factor (PF) has to be taken into account. The PF is the cosine of the phase angle between voltage and current; for a DC (= direct current) motor, PF = 1. Power = Volts x Amps x PF. For an AC motor at full load the PF is typically around 0.8 and for the motor quoted, it is (2 x 746)/(240 x 7.7) = 0.81
    At less than full load, the power factor will likely fall and could be as low as 0.2 at no load.
    Therefore, to determine the power being consumed by an AC motor it is best to use a power meter rather than measure just the current (unless you have a current vs power curve), or if you can measure the phase angle between volts and amps, you can calculate the PF.
    Thanks for that nice clear explanation - yes I eventually remembered this (had to drag it back from long lost memories).
    Some time after the start of this thread I made small dyno to test HP outputs of motors and used PF to calc motor efficiency.
    I have been meaning to go back and edit these issue but never got around to this.

    If its OK with you I might insert an edited version of your explanation back into the first post to save people needing to get to post #304 for an explanation.

  7. #306
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    Jun 2020
    Location
    Melbourne
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    Quote Originally Posted by BobL View Post
    I have been meaning to go back and edit these issue but never got around to this.

    If its OK with you I might insert an edited version of your explanation back into the first post to save people needing to get to post #304 for an explanation.
    Thanks Bob - yes that is perfectly okay. It's been a long time since that thread started!

  8. #307
    Join Date
    May 2010
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    Not far enough away from Melbourne
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    4,088

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    Quote Originally Posted by SROman View Post
    The simple answer is that it's an AC motor so the power factor (PF) has to be taken into account. The PF is the cosine of the phase angle between voltage and current; for a DC (= direct current) motor, PF = 1. Power = Volts x Amps x PF. For an AC motor at full load the PF is typically around 0.8 and for the motor quoted, it is (2 x 746)/(240 x 7.7) = 0.81
    At less than full load, the power factor will likely fall and could be as low as 0.2 at no load.
    Therefore, to determine the power being consumed by an AC motor it is best to use a power meter rather than measure just the current (unless you have a current vs power curve), or if you can measure the phase angle between volts and amps, you can calculate the PF.
    You have no idea how happy I am that you gave the SIMPLE answer.
    We should not judge people by their peak of excellence; but by the distance they have traveled from the point where they started.

    Henry Ward Beecher

  9. #308
    Join Date
    Nov 2016
    Location
    USA, Indiana, West Lafayette
    Posts
    188

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    Quote Originally Posted by doug3030 View Post
    You have no idea how happy I am that you gave the SIMPLE answer.
    You should see the complex one, although it's partly imaginary.
    Dave

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