Motor querey.

[Danmc069]

hi could u help me with this
a motor runs at 700rpm at 50hz what motor is suitable for this
a.2pole
b.4pole
c.8pole
d.12pole

 

[stef]

Hi mate,

it is p = 50Hz x 60 / 700 = 4 poles

 

[ghost]

I would have had to search my old text books to remind myself how to do that!
lol

 

[ghost]

Just googled it, here's a useful theory page for you

Motor Formulas

 

[stef]

Hmm, I wonder where the 120 constant comes from. I used 60 for one minute has 60 seconds so

p = 50 Hz * 60 seconds/min / 700 1/min = 4.2 poles

using the formula from the web page it would be p = 50 Hz * 120 / 700 = 8.5 poles

Now you made me confused

I got to find my smart book ...

 

[stef]

Hi mate,

found it in Brian Scaddan's C&G 2330/2356 book page 164:

n = f/p in the example he uses 50Hz (1 Hz = 1/sec) and two poles

-> n = 50 * 1/sec / 2 = 25 revs/sec * 60 = 1500 revs per minute

 

[Adam W]

Hi mate,

it is p = 50Hz x 60 / 700 = 4 poles

Is that '4 poles' or '4 pairs of poles', ie 8 poles?

 

[jpmiff]

Hi

In my experience a 2 pole motor runs approx 3000rpm. 4 pole motor runs approx 1400 rpm . 6 pole motor runs approx 1000rpm and a 8 pole runs at approx 700rpm

 

[stef]

Hi,

OK, mystery solved: p is the number of pole pairs which I over read
so, the web site you referred to is correct, this explains the 120 constant and therefore my 60 s/min is wrong (sorry!)

My excuse: it is the age ...