Gallery, Projects and General > How do I??

High Voltage Switches

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John Hill:

The breaker that trips is only 10 amps (and is at the outlet) so hardly suprising, the main breaker for that circuit is 27 amps.  We do not have ring wiring in our house (in fact I dont know if it is even used in NZ).

Motor is 2 Chinese horsepower, capacitor start, capacitor run, dont know the RPM, maybe 1480.

I think the motor is capable of starting the lathe and any boosting by way of more start capacitance is not likely to gain anything as that breaker will still trip.  I could just short the 10 amp breaker (it is a discretionary installation) and it would likely be OK but I dont like to hear that Chinese motor struggling to get started under load as I have already had one fail and would rather nurse this one to old age if possible hence the clutch concept which will likely be no more complicated than a swinging mount for the motor and a lever control to slacken the belt when starting the higher gears.

I have to think twice regarding 3ph not requiring slip as the three phases set up a rotating magnetic field that is true  but current must still flow in the bars of the armature for the armature to have a magnetic field to interact with the stator field and I do not think there would be any voltage induced if the bars were not moving in relation to the rotating field.  This is what someone else says on the matter..

--- Quote ---In a three phase induction motor, the windings on the rotor are not connected to a power supply, which are basically short circuited. The squirrel cage winding, which is the most common type of rotor windings,

it looks like a running wheel used in cages for pet gerbils. When the motor is turned on the rotor is stationary, the rotor conductors experience a changing magnetic field sweeping by at the synchronous speed.  This result in current around the rotor windings, the level of this current depends on the impedance of the rotor windings.  This causes the motor action to be fulfilled, and the rotor experiences a torque and starts to turn.  The rotor can never rotate at the same speed because there would be no relative motion between the magnetic field and the rotor windings and no current could be induced.  This is one reason why induction motor has a high starting torque. 

--- End quote ---
  More at http://www.electricmotorsale.com/threephasemotors.html

Bluechip:
Hi Troops ..

Don't know where we are with this .. but there are breakers designed for use on inductive loads ie motory things ( and high inrush linear PSU's for that matter ) etc.

Different Curve

Here's one I grabbed at random, there are more..


http://www.aelgroup.co.uk/hb/hb040.htm

May be relevant, may not

Enjoy ...

Dave BC

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