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3 phase motor

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Gregory

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I have a 3 phase motor with no plate or manufacturer name .
The motor is delta .
How can I tell the HP rating and speed of this motor.
I do not have 3 phase power supply.
 

tcmtech

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Rough guess based on findings similar motors is about as good as you will get.

The problem is one frame size of motor can be made to be multiple speeds and power ratings so there is no way to know for certain until a few variables are filled in first.
 

tcmtech

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Manufacturer, Frame size, RPM, current draw at no load, a reference to other motors that match those values.
 

dr pepper

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The Hp is a tricky one, physical size gives an estimate, but thats only with 300% or so.
And if you know what to look for you can tell the speed by looking at the windings, a 2 pole on 50hz runs at 2880 rpm and a 4 pole 1440.
 

MaxHeadRoom78

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HP is dependant to some degree on size of stator for a given pole count, to determine that without running it is to examine the stator winding configuration.
What is the supposed Voltage?
Max.
 

dknguyen

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Is there a formula to work out HP of the motor.
Not really. It's kind of like asking someone to tell you the the horsepower of a car engine just by looking at it. It's not that simple. It'd would be far simpler and faster to decide how hot you are willing to let it run and then turn it up slowly until it reaches that temperature and measure the power.
 

gary350

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You can ohm the wires to determine which wire go to each of the windings. There are 6 windings in a motor.

How many wires does your motor have?

Some 3 phase have 9 wires some have 12 wire.

What is the frame size and physical size of your motor?

Look at WW Granger online match your motor up with a new motor frame. Physical size & shaft diameter will tell you what you have.

American motors are 240/480 vac 60 HZ. Canada is 50 HZ.

There are some 550 and 600 vac motors.

Coal mine motors are 5000 vac.

You can start & run your 3 phase motor on single phase with a capacitor. Once you get it started check idle current that will tell you the HP check idle current for other motors. Capacitor needs to be 60 MFD per HP use only a motor START capacitor with a push button N.O. switch to put cap across L2 and L3 for 3/4 of second until motor starts. Voltage across L1 and L2. Check current across L1 or L2 when motor is running with out the capacitor.

Capacitor size is not critical. If you can find a motor on WW granger with your frame size and shaft diameter that will be very close.

Example. Assume you think your motor is 5 hp because shaft diameter is same as a Granger motor. Cap needs to be 60 x 5 = 300 mfd. If you try 300 and motor will not start then try 400 and 500 and more if needed to get the motor to start. Remove cap at once when motor comes up to full RPM. Now that motor is running use an amp clamp to read idle current on L1. Check motor RPM too. Compare, motor shaft diameter, voltage, amps, RPM to new motor specs.

Checking idle current is more accurate than full load current because most motors can deal with short over loads like 20% for a short time like 5 seconds before the correct circuit breaker trips and turns the motor off. 3 phase motor tags show, idle current and full load current on both voltage 240/480. You say you have no tag so if your idle current is 12 amps on 240 volts and you find a new motor specs that say the same thing with same shaft diameter and same RPM it should be the same HP as your unknown motor.

There is another way to start a 3 phase motor. Connect a single phase motor shaft to the 3 phase motor shaft with, a shaft coupling or V belt pully also called shives. Start the single phase motor when it comes up to full RPM turn on the 3 phase motor and turn off the single phase motor. 3 phase motor will run good with voltage on L1 and L2 only. 3 phase motor RPM can be, 1725, 1400, 1200, 1100, 1000, 900 so check it with an RPM gauge. Low RPM motors are used for hydraulic pumps it keeps the pump from sucking vacuum bubble in the oil.

You can also start a 3 phase motor with a rope. Wrap a 1/8" diameter rope around the motor shaft 15 times with the motor bolted to a work bench pull hard. If you can get the armature up to about 600 to 800 Rpm it will start when you turn on the voltage.

What voltage and HZ do you have in Australia. Home voltage in USA is 240 that is the only choice we have at home in single phase unless you have a step up transformer or industrial variac.
 
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dr pepper

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The coils are grouped in opposite pairs, usually in sets of 3, so a 2 pole motor would have 3 pairs of coils one for each phase, a 4 pole 4 groups of 3, probably not something easily recognized unless you have some experience.
 

gary350

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There are 6 windings total.

There is also Delta & Star wound motors.

Low voltage coils are wired in parallel.

High voltage coils are wired in series.

Drawing says 440 volts but in USA there is no such voltage anymore only 240 & 480 but the power company can set a transformer special just for a company that has old 440 motors. Transformers have multi taps voltage can be set to just about anything you need by changing primary taps and secondary taps also. Our factory taps were set at, 481, 481, 482 volts for 3 phase. These are still not the drawings I would like to paste here.





240 volt wiring connect coils in parallel.

480 volt wiring connect coils in series.
 
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dr pepper

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Oops.
My last post wasnt clear (might still not be),
A 2 pole motor, each 'pole' has a north and a south coil, so a 2 pole 3 phase motor has 2 windings per phase = 6 coils.
A 4 pole motor, again each 'pole' has north & south, but there are 4 windings per phase so 12 coils.
An electrical rotation (mains cycle) for a 2 pole is one mechanical rotation (360 degrees), a 4 pole requires 2 electrical rotations per mechanical rotation, 6 pole 3, 8 pole 4, this is how you get diffo speeds, very like a Bldc motor.
There are usually 3 winding connections brought out to the terminal block on little motors, bigger ones that startup star/delta or dual voltage 6 wires. the individual poles being terminated internally. There are 2 speed motors & some Us ones that have loads of connections.
I served my time winding motors.
 
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dr pepper

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Looks like an Asea motor, hard to say the kw, cant really see how big it is.
Should say on the rating plate what the voltages are for star/delta, it could be that its meant for 440/660 instead of 220/440.
 

tcmtech

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Seeing what it's attached to would be useful.

If you know what it did reverse engineering things to come up with the likely HP required to do it isn't that hard.
 

dr pepper

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If its 1 hp or more I wouldnt advise you try and run it off single phase, esp if the load has a high start torque, unless you run it off a inverter drive or a rotary converter.
 

tcmtech

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