Amp-turns

Discussion in 'General Electronics Chat' started by shortbus, Nov 27, 2011.

  1. shortbus

    Thread Starter AAC Fanatic!

    Sep 30, 2009
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    In reading and researching for a project I've seen the term 'amp-turns' as used in motor windings and electro-magnets. Is it possible to use a large gage single wire to achieve a certain 'amp-turn' value? Or does it work like in transformers, that a number of smaller wires must be used to give an 'amp-turn' value?

    Can't seem to find a definitive answer for this.
     
  2. crutschow

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    Mar 14, 2008
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    An ampere-turn, as the name implies, is simply one ampere going through one coil turn. It is independent of the wire size or the coil diameter. Thus, for example, two amperes flowing through 100 turns would be 200 ampere-turns.
     
  3. Adjuster

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    Dec 26, 2010
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    If a certain number if ampere turns are required, it may be convenient to use a large number of turns so that less current will be required. On the other hand, this will imply a larger driving voltage due to the effect of higher resistance (and higher inductance if this involves AC).

    Sometimes however a very small number of turns will be desirable in an electromagnet, precisely because a lower resistance will allow operation at a relatively high current but at low voltage. This is the situation for instance with the relays sometimes used to sense the output from thermocouples detecting the presence of a pilot flame in gas burning appliances.
     
  4. thatoneguy

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    Feb 19, 2009
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    When stepping down very high voltage trannsmission lines, say 15kV to 480V @15k amps(hypothetical) , both sides would be rated for the same amp-turns (15k), and the tansformer would be called a 15000 amp turn transformer. Those voltages aren't switched outside your house, though.

    Voltages and ranges vary widely, with multiple steps between high voltage and 480V at various substations for neighborhoods. The amp-turn rating of the transformer is the peak power that can be drawn (before "brownout"). The more amp turns a transformer is, the bigger it is, and the higher the price (much, much higher).
     
  5. shortbus

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    Thanks guys for your answers. What I am contemplating is rewinding a three phase motor to run on 120V DC. with an inverter drive. So when stepping down the voltage I will need to increase the amperage to the winding.

    I've seen pictures of motor stators wound with a single large gage wire for each turn of the coil. How do the get away with doing this when it takes "X" number of ampere-turns to make the magnetic flux?
     
  6. strantor

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    Oct 3, 2010
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    I bookmarked this a few months ago. good info about getting motors rewound for lower voltages, in order to up the power. no so much about physically rewinding them, but the theory there might be helpful.
     
  7. shortbus

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    Strantor - I missed that thread. The guy, Coulomb, on that site is a wealth of knowledge about motors and controllers. One thread on another forum talked about splitting the windings to run them in parallel, took a 230V and ran it at 115V successfully.

    Got a bunch of 200A IGBT half bridge modules($20 each plus shipping). Looking for a 10HP motor cheap. Going to burn them up or make it work. :)
     
  8. crutschow

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    I believe you are looking at the stator rotor of an induction motor where the current is induced in the stator form the field windings. In that case you have a low number of low resistance turns but a large induced amperage to get the required "X" ampere-turns (which depends upon the slip speed). Squirrel-cage induction motors, for example, have large copper bus bars (in the shape of a squirrel-cage of course) for the rotor winding.

    Edit: The first sentence should read "I believe you are looking at the rotor of an induction motor where the current is induced in the rotor form the stator field windings
     
    Last edited: Nov 28, 2011
  9. shortbus

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    crutschow, not quite sure what your saying here:) The stator of an induction motor is the 'field', so where is the current from the field windings come into it?

    The really big squirrel-cage motors do sometimes use copper or brass for the bars but most motors use aluminum for the bars.

    In going back into some OLD books I have (1900-1920) I found my answer. A turn is one side of a coil embedded in the stator. No matter how many conductors are used. Since a coil is basically a loop of wire(s) in the stator core, each loop makes two turns in a coil. So it would be 2 times the number of amps in the conductor. They are also called the active leg of the coil.
     
  10. crutschow

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    I meant to say the stator field induces a current in the rotor windings.:p
     
  11. thatoneguy

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    Off topic, but how many "Turns" is a squirrel cage rotor, since they are all connected at each end. One?
     
  12. shortbus

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    Not crutschow, but each 'bar is considered a 'turn'. They are called "shorted turns".

    A bit of trivia, Tesla's original induction motors used wound rotors. thy looked similar to a DC motor, with no commutator. The start of the coil was connected to the finish.

    Another thing I never considered, is that a induction motor is thought of as a 'rotating transformer'. The primary is the stator and the secondary is the rotor.
     
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