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candji
04-09-2010, 01:28 AM
Can somebody tell me what the 120 in motor rpm calculations is? rpm= 120xhz/#of poles

cool runings
04-09-2010, 01:36 AM
Can somebody tell me what the 120 in motor rpm calculations is? rpm= 120xhz/#of poles



rpm??

RPM = Revs Per Min

coolrunnings

.

candji
04-09-2010, 02:48 AM
yes,rev's per min

Magoo
04-09-2010, 03:06 AM
the synchronys speed factor for 3 phase motors.

Tayters
04-09-2010, 01:26 PM
Speed of rotation is:

Number of current reversals per minute / number of poles

For a 1 HZ cycle of a sine wave there will be 2 reversals, this will occur once a second. So to get it to minutes (remember we are after Revs per Minute) 2 x 60 = 120

Cheers,

Andy.

Quality
04-09-2010, 02:31 PM
Speed of rotation is:

Number of current reversals per minute / number of poles

For a 1 HZ cycle of a sine wave there will be 2 reversals, this will occur once a second. So to get it to minutes (remember we are after Revs per Minute) 2 x 60 = 120

Cheers,

Andy.

could not have put it better myself

I call it 1 and 2 but it does not explain frequency
its 2 cycles 50 times per sec but 25 times 1 and 2

nike123
04-09-2010, 05:24 PM
That number is constant in connection with seconds to minute conversion (as Tayters alredy explained).
If you using other formula with number of pairs of poles, that constant is 60 (seconds).
S = f60/p

where: S = rotor speed in rpm (revolutions per minute)
f = AC line frequency
n = number of pairs of poles

nike123
04-09-2010, 05:50 PM
the synchronys speed factor for 3 phase motors.

It is same for 1 phase motors! If we use revolutions per second, that constant(factor) is not used.

Yuri B.
04-09-2010, 08:17 PM
So, one who used "120" (60 sec multiplied by 2) was speaking about number of POLES in the formula,
if one prefers PAIRS of POLES, then just 60 would be used.