Too Many RPM Not Enough Torque...

At 36 slots the max technically possible pole pair winding for 3-phase is 4. But even though you will end up with half the current speed (at 1800rpm 60Hz you now must have 2 pairs or four poles) you won't get any torque gain, i.e your horse power will be about half and even little lower since the cooling efficiency will drop and you'll have to derate some. And still not counting the rewinding cost. The way to go if you need more torque is by gear or belt speed reduction. S.M.

And before somebody corrects me, 3 pairs or 6 poles is max and speed and power would be 2/3 of the current. Something wrong with that beer S.M.

Thank you, Simplemind, i like the name, like it simple

But you gave me the wrong answers, just kidding...I guess you are right, need at least 2 slots to make a coil, so a max of 18 of them...3 phases=6. 6what? I still do not get it all.

OK... To use those 18 coils as a stepper motor make no sense? Why? Is the rotor of a stepper motor wound? I do not remember. Never mind.

No problem i am just back to plan "A", the wounderfull AC/DC serie motor,with controlled CEMF.

Are you still following me?

Got ya. Corrected before you. (LOL)

Not stupid but intriguing, there really isn't much data on the web, but I found this...

http://www.pdhonline.org/courses/e176/e176content.pdf

Page 13 has the formula you seek, but exactly what type of motor do you have now? In particular is it a squirrel cage or wound rotor? I ask because I suspect that unless you have some way of rewinding the rotor you won't be able to change the number of poles and you'll be stuck at the design speed.

This book may answer more questions than you can ask....

http://www.amazon.com/gp/product/0131776916/ref=s9_simh_gw_p14_d2_i3?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=0300H44RGRZ76B7KKBBG&pf_rd_t=101&pf_rd_p=470938631&pf_rd_i=507846

As a last resort, you may find that running the output of the unmodified motor through a speed reduction (and therefore torque increasing) gearbox is cheaper than the time and effort you are going to expend otherwise, but it will be a great learning experience either way.

Hello RAMConsult, thank you also for your reply, Honestly i never tought so many people was welling to 'talk' about that tonight, it is great.

I undestand your point but i should clarified that i or should i said the motor physical size is limited to fit in a 6.5 in diameter sort of pipe. I am looking for a revolution of 30 RPM with controlled variation +/- 10. I already found a planetary gearbox 50:1.

The most important piece of information is that i have a lot of time and very little money, that is where the name come from PPP (patentage pour les pauvres,or poor boys enginneering, if you want) and as you mentionned a good electrothecnical experience.

Heu!! Yes Squirrel cage

Here's some 36 slot small motor I winded 6 pole years back just for the heck of it. It was single phase 3000 rpm 50Hz and worked occasionally on a VFD at up to 400Hz-8000 rpm (untill bearings died. Since I've no use for it nowdays never repaired it (actuall I didn't know I stil had it) I hope you can distinguish the windings every coil goes to one slot and then after two slots. And this at 3 layers.Every layer one slot off. So used 12 seperate coils 4 per phase connected in series on 1mm^2 wire and than painted with heat resistant black. Was it worth it? Propubly not If I had paid for materials, But the guy in the rewinding shop said he couldn't wind such a small motor and he prefered to give me the little copper I needed for free and not see it again S.M.

OK I surely whish to be able to stay in touch with you.

It is very interesting, and maybe i should wait to comment the pulley size...

I have to leave, come back tomorrow

Should've done the sums first!

As I see it, to get high enough torque out of this at lower RPM, you have 3 options:

1. Different motor
   
2. Gearbox
3. Fancy VF/VVVF drive

I suggest you research these to see which would be most cost-effective. Rewinding your motor is not an option.

Hello you too!

Thank you for your concern, but it is too late, I have got them all...

my best motor so far is a DC permanent mag from a thread mill, i also bought last fall 2 VFD to improve my Smithy, and as mentionned the 50:1 planetary gear reducer( Eurodrive, a beauty...).

Beside the physical restriction, and been an electrician (not an engineer) i prefer SCR or other semiconducteur over a different size pulley. Please take no offenses.

It is all about improving.

I think this might help you

sorry the letters are so small but if you are on windows use magnifier in accessories

Thank you very much

I have seen a lot of your comments on the forum, My hat off, for the time you take to share your knowledge.

One more time...

Which type of motor will produce the greater torque for same physical given diameter?

Serie...

DC motor!