Finding the Rated Speed for a Motor

I could only SWAG it with that little bit of info. If that confuses you go to www.acronyms.com .

You mean..without running the motor you have to find out it's rated speed????

Assuming an AC motor, if you have absolutely no data on the motor, the only way is to use a tachometer and measure it. Without the nameplate data you have no way of knowing the number of poles in the windings.

With all of the possible type of motors out there (AC induction, AC synchronous, DC series, DC shunt, brushless DC motor, stepping motor, reluctance, hysteresis and I'm sure I missed some types) you cannot tell a thing without experimentation or knowledgeable disassembly.

Any idea what will happen if you wire a two phase 3 amp stepping motor directly to 120VAC 60 hertz power line? All I can say is that it ain't pretty.

Just a clarification:

You have to run the motor with exactly the same power supply that the motor need. The only thing you have to run the test in a place where light is coming from a tube light. You can do it in workshop but the workshop light has to be from tube light. A single tube light in the workshop ensures that it has stroboscopic effect.

- MS

INDIA have 50 cycles. 50*60 = 3000.

(Note - in 11kv steps )

If its a normal line powered AC induction motor you likely only have a few primary speed ranges it would run at. For a 60 Hz system you would have around 3450 RPM, 1725 RPM and 1140 RPM. All three speeds are fairly easy to identify just by looking at the shaft spinning or at least I can easily tell them apart by looks any way.

If its another type of motor then you need to do the tachometer testing method.

...as MSAMAD stated, the "rated" speed of an AC-electric motor basically depends upon three things:

1) the number of field windings or poles

2) the frequency of the applied AC-voltage(s) (single or multi-phase?)

3) the designed percentage of "slip" (always less the 1:1)

...the "rated" load is usually specified as a torque value under load, hence the "slip" percentage. When there's no slip, there's no load. So, slip equates to load, and together they establish the motors "rated" speed under designed load.

Pointless exercise.

1. We have no idea what he meant by "motor"
2. He has no way of telling how it is designed even if we did.
   

LOL , you all keep saying how to determine speed from the number of poles. But as I said first, IF YOU HAVE NO NAMEPLATE, HOW ARE YOU GOING TO KNOW HOW MANY POLES YOU HAVE???

It's like calling your internet service provider to get help with a non-working internet connection and them telling you to go on-line and download a program! (This has happened to me more than once by the way).

The OP does not identify anything about the motor. There isn't even an identification if the motor(?) takes single phase, three phase, an exotic polyphase drive or even if this takes a DC supply. There's no mention of any starter circuitry or absence of a starter circuit or anything to go on other than it looks like a motor. Who knows, it may actually be a high resolution encoder and not even a motor. All of the suggestions so far tells me that people here think that the only kind of a motor that exists is an AC induction motor. We don't even know if this thing is bigger or smaller than a bread box.

Let's not forget that the load the motor will be trying to move can certainly have a speed effect. Can you say "locked rotor loading," sure you can. So even with an induction motor, the type of squirrel cage design will determine which NEMA class torque curve (figure 4) will be available to allow an attempted calculation of slip.

So I will state my point again. When one has something that looks like a motor but you don't know which kind of a motor then you know next to nothing. You must test the motor dynamically by running it or statically through disassembly.