Easy motor question

Hey guys, I have a metric motor, and the nameplate shows an RPM of 2825, and the ratings are for 50 HZ. Although it doesn't exactly work out, I'm assuming that this must be a 2 pole motor. Using 120*50Hz / # of poles. 2 poles gives me 3000 RPM, and I would assume that the other 175 RPM are lost due to slip. Just wanted another opinion before I set this is stone. Thanks.

Russ

Yes standard 2 pole motor @ 50hz = approx 2800rpm and a 4 pole = approx 1400 rpm

Interesting...

I've never heard of a nominal 50Hz Motor being called a "Metric" Motor.

I don't see any corrolation other than that 50Hz users generally, but only generally, use the Metric-System.

Terry Woods said:

Interesting...

I've never heard of a nominal 50Hz Motor being called a "Metric" Motor.

I don't see any corrolation other than that 50Hz users generally, but only generally, use the Metric-System.

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Most of the motors I've used have metric bolt patterns if they are running base 50 hertz.

Perhaps that's what he means?

Maybe.

It probably refers to a metric sized motor (physical). We have had them in Ozz for as long as I can remember (1959).

When they first started coming to Ozz on machinery, the first thing we noticed is that they were very small and b****y (dare I say it after the ruckus in UK) hard to wind. The insulation I think was "H" - high temperature and that was absolutely right. The next thing was that all our BS/AF spanners did not fit and, at that stage, metric spanners were an arm and a leg!!!

Theoretically, synchronous speeds are 1500 RPM for 4 pole and 3000 RPM at 50 Hz. However, there is a considerable amount of slip. Some motors are worse than others. These days it appears that the slip speed is quoted and not the impossible to achieve synchronous speed. 2850 RPM is a very common realistic full load speed for a 2 pole 50 Hz squirrel cage motor.

I'm in full agreement with the earlier responses (except I have no idea what a metric wrench went for in Oz in 1959). It's a two pole motor, with a heck of a lot of slip. That's pretty common on the lower horsepower motors. The big boys run quite a bit closer to synchronous speed even fully loaded. Cheap to purchase and replace, but expensive (power wise) to operate.

I've never heard of a metric motor, either, but maybe shaft size, as well, is metric, not just the bolts.

Metric motor runs 50 RPS not 3000 RPM.

seppoalanen said:

Metric motor runs 50 RPS not 3000 RPM.

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I totally understood the thread until i got to this post ?

Whats 50rps ?

Anyways a standard 2 pole motor in the uk is yes 3000rpm nominal, i have seen some motors plates at down to 2730 rpm due to inefficiency and slip. Most though operate above 2900.

BobB said:

When they first started coming to Ozz on machinery, the first thing we noticed is that they were very small and b****y (dare I say it after the ruckus in UK) hard to wind. The insulation I think was "H" - high temperature and that was absolutely right. The next thing was that all our BS/AF spanners did not fit and, at that stage, metric spanners were an arm and a leg!!!

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Most of the standard motors here are wound Class F (180 degC) with a B rise on the AC side, its more normal to find a Class H (200-220 degC) wound motor on the DC side. Although if the motor is specially rated (S1,2,3 etc) then it may have been a special with H windings. Most good rewind firms here rewind with class H wire as there was very little cost difference to the Class F wire. Although the insulation (Normally Nomex 3 or 5 ply) is F rated.

As for winding the worst I have come across are those Low Center of Gravity motors fitted to woodwork machines here. Sometimes the Stator is 18" long with a 1.5" dia. rotor and wire of greater than 0.9mm

rps = Revolution / second = hertz

BOB B - Where is OZZ? And don't give me the Wizard answer of not in Kansas

OZzzz... = Australia

Well I should have guessed that from is profile

Just across the way from the Shaky Isles - New Zealand.

seppoalanen said:

Metric motor runs 50 RPS not 3000 RPM.

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50 revolution/sec = 60*50 rps= 3000 rpm

both are same know? I dont understand.