Page 2 of 2 FirstFirst 12
Results 16 to 20 of 20
  1. #16
    Join Date
    Aug 2012
    Location
    Greenmount, W.A.
    Age
    70
    Posts
    272

    Default

    ................. Did I read your reply right?
    the motor spec of 3.9amps is the FLA and does not include starting amps. It is the max amps at full load under running conditions.

    3.9 Amps is the maximum current drawn by the motor.
    It was not specified when this (condition) will occur.
    As the calculated full load current (for the specified wattage of the motor) is much less, I have assumed that the manufacturer of the motor is trying to say that this would be the starting current. Then again it could be the current drawn when the motor stalls. Either way, the conductors supplying the motor need to be of a suitable size.

  2. #17
    Join Date
    Jul 2006
    Location
    Athelstone, SA 5076
    Posts
    4,255

    Default

    Quote Originally Posted by A J in WA View Post
    ................. Did I read your reply right?
    the motor spec of 3.9amps is the FLA and does not include starting amps. It is the max amps at full load under running conditions.

    3.9 Amps is the maximum current drawn by the motor.
    It was not specified when this (condition) will occur.
    As the calculated full load current (for the specified wattage of the motor) is much less, I have assumed that the manufacturer of the motor is trying to say that this would be the starting current. Then again it could be the current drawn when the motor stalls. Either way, the conductors supplying the motor need to be of a suitable size.
    All motors are rated at full load...ie the rating stated is at full load running conditions.

    as start current times are brief the wiring only needs to handle full load current plus the normal fudge factor. start currents are generally accepted as being some where between 6-7 times full load current.

    Ie a 10amp motor at full load would be drawing 60-70amps on start up....thats a big cable size based on your theory.

    when in fact it will run on 2.5mm standard 15a amp cable quite comfortably. (assumes length of cable run is not excessive....ie a standard residence where switch board is in opposite side of house)

  3. #18
    Join Date
    Aug 2012
    Location
    Greenmount, W.A.
    Age
    70
    Posts
    272

    Default

    Re-reading post #1 the stated 3.9Amps is probably the stall current. If you multiply 3.9Amps by 240Volts you get 936VA which is about three times the rated output.

    Starting current will be as you say. This will produce an increased volt drop on the supply cable (during starting) which means low volts at the motor when starting. Probably not a problem in this case.

  4. #19
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    7,182

    Default

    Sorry to nit pic here but the rated current on a motor nameplate is not really the max current a motor can draw. Most motors can draw a lot more current that their rating if they are overloaded. eg my 3HP Table saw can draw up to 17A for about 5s before it trips the thermal overload.

    The rated current is usually the current that is drawn by the motor when performing its maximum recommended power output ie under its max recommended load.

    My motor testing shows that the current at maximum recommended power output usually coincides or is close to a motors peak power output.
    If a motor is pushed beyond this load most of the excess current drawn goes into heating the motor and produces very little "extra" and usually even "less" power
    Some quality motors can easily produce around 20% more power than their rating without serious overheating - I guess its the manufacturer just being conservative and maximising a motors lifetime

  5. #20
    Join Date
    Aug 2012
    Location
    Greenmount, W.A.
    Age
    70
    Posts
    272

    Default

    Good answer Bob. Real test with real results always beats theory!

Page 2 of 2 FirstFirst 12

Similar Threads

  1. motor driven cable strippers
    By jcatcmc in forum ELECTRICALS
    Replies: 1
    Last Post: 9th Aug 2020, 08:16 PM
  2. Cable disc brakes routing of cable.
    By gros21 in forum TRAILERS & OTHER FABRICATED STUFF
    Replies: 3
    Last Post: 14th May 2017, 06:41 PM
  3. Induction motor info
    By morrisman in forum METALWORK GENERAL
    Replies: 0
    Last Post: 15th Feb 2015, 08:17 PM
  4. Repulsion - Induction motor, single phase, 5HP
    By jhovel in forum METALWORK GENERAL
    Replies: 14
    Last Post: 26th Apr 2012, 01:25 AM
  5. Single phase induction motor wiring help needed
    By simonl in forum METALWORK GENERAL
    Replies: 9
    Last Post: 21st Apr 2012, 05:23 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •