OK electrician types help me out please..

OK electrician types help me out please..

BigMatt-MadCustoms
BigMatt-MadCustoms

September 2nd, 2012, 12:12 pm #1

OK I need to spin a shaft at about 200 RPM will hooking a simple light dimmer to either one of these motors be OK to slow them down without burning them up..I won't be applying very much load to the shaft..

Thanks,
Matt

http://www.ebay.com/itm/1-100-HP-DAYTON ... 621wt_1129

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 500wt_1027
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GladMech
GladMech

September 2nd, 2012, 2:43 pm #2

I'm just an ME & licensed electrician, so I will defer to more detailed answers from real EEs.

These are both AC motors. I'm not sure about small split phase AC motors, but I know that on industrial squirrel cage AC motors, reducing the voltage will not affect the speed, the motor will just have no power and stall.

The only way to vary the speed on an AC motor is by varying the frequency (which typically is not cheap). Still, you might find a bargain on eBay or PLCcenter or similar - especially in this small a size. You are looking for a VFD, Variable Frequency Drive, adjustable-frequency drive, variable-speed drive, AC drive, micro drive, or inverter drive (all synonyms).

With the current interest in all things energy conservation related, the HVAC industry (Dayton) may have introduced small inexpensive VFDs for fan motors just like the ones you are looking for. Motor and drive need to be compatible.

Good hunting.
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Russ Kepler
Russ Kepler

September 2nd, 2012, 4:22 pm #3

OK I need to spin a shaft at about 200 RPM will hooking a simple light dimmer to either one of these motors be OK to slow them down without burning them up..I won't be applying very much load to the shaft..

Thanks,
Matt

http://www.ebay.com/itm/1-100-HP-DAYTON ... 621wt_1129

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 500wt_1027
Both of the motors you listed would not be appropriate for the form of speed control you suggested. "shaded pole" motors may be controled by frequency but the conroller is a lot more complex (maybe just rare) than a 3 phase variable frequency drive. For "dimmer' operation you would need a "universal" motor, basically an AC motor that uses brushes. Even then the speed regulation is kind of weak with a varying load.

Not knowing the application makes suggesting solutions difficult. I usually look for small 3 phase motors and VFD combinations if I have low speed with some torque requirements, if not a small PM DC motor and PWM control is the other solution I use.
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Maker Of Toys
Maker Of Toys

September 2nd, 2012, 4:55 pm #4

OK I need to spin a shaft at about 200 RPM will hooking a simple light dimmer to either one of these motors be OK to slow them down without burning them up..I won't be applying very much load to the shaft..

Thanks,
Matt

http://www.ebay.com/itm/1-100-HP-DAYTON ... 621wt_1129

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 500wt_1027
in powers that small, a substantial fraction of electric motors are shaded pole construction vs pure induction (which usually have a capacitor on them somewhere) The easiest way to tell is the capacitor, but if the RPM is not real close to a power-of-two fraction of line frequency, it's likely a shaded pole motor. (a binary fraction? 1/1 1/2 1/4 are the most common; sometimes you'll see 1/6 or 1/8 . . . those would be 3600rpm, 1800rpm, 1200rpm, 900rpm, etc.

To simplify, a motor that's rated between 3600 and about 3480rpm or 1800 to about 1740 rpm is probably induction, as is any motor that lists either capacitor start or capacitor start/capacitor run. You're unlikely to encounter a 1200rpm or 900 rpm induction motor in fractional horsepower applications.)

that said, the first motor is listed by grainger as shaded pole, and might work for you. The second one lists as permanent capacitor split phase, and won't be suitable.

Why is that important? because shaded pole motors behave differently when you cut back the voltage to them than a induction motor does. And that means that, while a light dimmer probably won't work (won't hurt the MOTOR. . . the dimmer might not be happy, though) you CAN vary the speed with a commonly available ceiling fan motor controller. You'll want the type with a knob rather than push buttons. Or you could use one of the speed controls sold for use with corded hand drills. Or just check that your dimmer can handle 'inductive loads' (which any motor is, capacitors notwithstanding)

now the real question is: will you get an honest 200 rpm out of a motor that's rated at 1550. . . and there, I think you're in trouble. Shaded pole motors don't speed-regulate well. As long as there's some non-time-varying load (a fan, or something with a similar sort of drag to it) you might succeed. if you're trying to drive a cam, crank or screw type mechanism, well, it won't hurt to experiment. . . .
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Bruce Bergman
Bruce Bergman

September 2nd, 2012, 11:19 pm #5

OK I need to spin a shaft at about 200 RPM will hooking a simple light dimmer to either one of these motors be OK to slow them down without burning them up..I won't be applying very much load to the shaft..

Thanks,
Matt

http://www.ebay.com/itm/1-100-HP-DAYTON ... 621wt_1129

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 500wt_1027
Getting a consistent low speed in the 200-RPM range will be difficult on a direct drive motor, they usually don't have a lot of power left when they get down that slow, and if it stalls you have a problem. If it stalls while unattended (nobody there to kill the power) that can turn into a Huge Problem.

First thing, if the speed doesn't have to be exact or precisely controlled, plan on going with some sort of a gear or belt drive to get the speed reduction you want. You might be able to use one of those induction motors at the 1800 RPM native with the reduction doing the work of dropping the speed.

If space and packaging are an issue, you can get Inline motor and gearbox combos where the shaft comes out parallel to the motor shaft, and they slide right into the same spaces.

If you need true variable speeds, the easiest way is a Variable Frequency Drive - an electronic power supply that puts out 3-Phase 240V to run a small 3-phase "Inverter Duty" rated motor - that part is important because basic motors can't handle the widely varying speeds and voltages the VFD puts out at the far ends of the speed spectrum.

VFD's are available in all sizes you might need (1/4 HP to 100 HP) where they'll take Single Phase 120VAC or 240VAC as input, very useful for running a regular 3-Phase motor where you can't get it from the local utility - but you have to read the spec sheets before ordering.

You can even do tricks like control it from a computer, or set automatic ramp-up and ramp-down speeds, and a maximum torque alarm and shutdown if something jams, instead of just Off and On.

The "Inverter Duty" motors will gladly run at the extreme high and low speeds a VFD can put out, where a cheap 3-phase motor will just let out the "Magic Smoke" and die. But read the instructions, they do have limits.

The other way is standard industrial gear, the 90V DC motor and a commercial speed control power supply - Grainger (Dayton) makes a ton of those too.
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BigMatt-MadCustoms
BigMatt-MadCustoms

September 3rd, 2012, 2:14 am #6

And wouldn't you know it my nephew had just what I needed in his barn...

DC motor and controller with gear reducer dropping the whole mess to about 180 rpm and it has a serious amount of torque..

Thanks to all for the replies

Matt
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