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Rheostat help

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springer

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#1
So I built an ugly welding positioned type thi g to help weld caps on the end of tubes. Problem is, the gear motor I bought is a little fast. I could do a bunch of swapping pulleys, but I dont have any spares and dont want to waste a bunch of money for no reason.

I know nothing about electrical stuff but have somehow figured out (I think) that I can use a rheostat. Cheap on amazon, problem is, I dont know which one to get. Watts, ohms, etc is all Greek to me.

Any help?

This is the gear motor I have: https://www.surpluscenter.com/Brands/SPG-Co/6-5-RPM-115-Volt-AC-Gearmotor-2051746-5-1770.axd

20181008_165831.jpg
 

whitmore

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#2
So I built an ugly welding positioner i... the gear motor I bought is a little fast.
I know nothing about electrical stuff but have somehow figured out (I think) that I can use a rheostat.
It isn't impossible, but the only way a rheostat can slow an AC motor (this is a shaded pole type) is by generating heat,
and even then, it requires the motor rotor to be designed magnetically soft. It isn't the rheostat that overheats, it's
the motor windings. A couple of drums and a bit of string is a better way to gear down (or even a footpedal
switch that just shuts the rotation off for your weld bead to catch up).

Fancier ways are available; a driven tire, bearing on a turntable, gives rotation periods that scale with the radius from turntable
pivot to the tire contact. No belts required (this is low speed, low power movement).
I can practically guarantee it'll be ugly enough for your satisfaction!
 

springer

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#3
I can practically guarantee it'll be ugly enough for your satisfaction!
Haha, I might have to tru that. Didn't even think about it. If a rheostat generates heat in the motor windings, def can't go that route. This motor has a short duty cycle and gets hot enough on its own. Thanks for the idea!!
 

benmychree

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#4
A device that varies cycles would do it, rheostats will not. I made a positioner with a DC motor and a speed control; one thing I had to do was to electrically isolate the motor' gearbox from the rest of the unit, because stray high frequency from the TIG caused the speed to go wild.
 

markba633csi

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#5
DC motors can be slowed, not AC ones usually (excepting brushless and 3 phase units). And rheostats are a poor choice anyhow. A Variac plus a rectifier and a DC motor is simple and workable, over a limited range of speed.
mark
 

Cooter Brown

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#6

RJSakowski

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#7
Universal motors, as are found in variable speed drills, are a type of ac motor where the speed can be varied. A rheostat can do the job but an electronic speed control does a better job.

Since 6.5 rpm is at the upper end of your range, you may want to rethink this. A separate gearbox fit with your choice of motor will give you greater flexibility. Cheap cordless screwdrivers generally have a fairly low rpm in order to develop enough torque. One of those coupled with a suitable gearbox could bring you into your desired speed range.
 

mksj

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Cadillac

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#9
Ive used devices like this for ac motors. I have to admit I know enough about electric to be dangerous. But haven’t burned up anything so I’m doing good.
CCA27A3F-D9D1-424D-B77C-A27B44A58858.png
 

tq60

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#10
Do NOT use reostat but instead just a light dimmer as they simply chop up the juice to lower net energy.

Motor type will determine if that works.

Most common a.c. powered motors are induction and dependent on frequency not voltage for speed so dimmer will not work.

A foot switch to tap the motor may work or locate old pneumatic drill and use it as motor maybe.

No electricity and variable speed via air pressure regulator.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 

BaronJ

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#11
Hi Springer,

Basically those shaded pole motors cannot be speed controlled, since the speed is locked to the incoming mains frequency.

I think the easiest way to slow your device down would be to do what you said, alter the gear ratio. Make the motor gear smaller and the larger gear bigger.
 

springer

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#12
Thanks for all the input. I think I'm going to add another contact wheel between the two. It will solve my belt tension issue as well. I'll mess with it this weekend and report back.

Thanks again.
 
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