# how to slow down an electric motor

#### daveydo

Joined Nov 5, 2015
1
Power supply input: 100 to 240 volts, 50 to 60Hz, 1.5 Amps; Output: 15 volts, 4 Amps. Horsepower and torque: 0.5 HP, 40 in-lbs, 300RPM. Comes with a 9-foot US cord.
I have this motor on a device and it does have a thumb turn roller, what i call a rheostat device, that does control the speed, but at the onset of activation of it, at its slowest activation of the motor via the rheostat, the motor turns too fast. How can I slow it down?

#### wayneh

Joined Sep 9, 2010
16,114
What do you mean the output is 15v? Is there some sort of transformer in between the mains power and the motor? Is there also a rectifier?

Any possibility to use a gearbox?

#### Aleph(0)

Joined Mar 14, 2015
591
what i call a rheostat device
If motor induction type, control needs be inverter drive (like VFD). If motor brush and com type control can be rheostat which means variable resistor but way inefficient! Should use pwm or phase control! Slow as 300 rpm means gearmotor or sophisticated driver for dc motor.

but at the onset of activation of it, at its slowest activation of the motor via the rheostat, the motor turns too fast. How can I slow it down?
With poor designed phase controller start setting and av higher than lowest setting so plz try turning control back down just after motor start Also vfds and dc motor controllers are cheap to buy and easy to design and build so you're spoiled for choice of solutions to trouble

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#### TheButtonThief

Joined Feb 26, 2011
233
Motor speed control? Easy, PWM.

#### Techno Tronix

Joined Jan 10, 2015
139
If it's direct drive you can install a VFD (variable frequency drive control) - not real cheap. If belt driven, you can change the sheaves to slow down (increase driven sheave dia. or decrease driver diameter.

#### Dodgydave

Joined Jun 22, 2012
8,471
Can we have a picture of this motor and its controller, where's the 15v coming from?

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
If it's direct drive you can install a VFD (variable frequency drive control) - not real cheap.
Actually, VFDs are less expensive than you may think -- for instance, a unit applicable through 3 HP may be purchased new for Ca. $500 (USD) --- On the other hand, should the motor in question be of commutated construction, I concur with posts #3 and #4 in that a PWM based controller is the best solution where speed and torque regulation are required... best regards HP #### MaxHeadRoom Joined Jul 18, 2013 19,186 Actually, VFDs are less expensive than you may think -- for instance, a unit applicable through 3 HP may be purchased new for Ca.$500 (USD) --
HP
Or just over \$100.00 if you want to go Chinese, (Huanyang).
variable freq does not work well on 1ph induction motors, they tend to drop out of run on load at low rpm.
I suspect it is DC?
Max.

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
variable freq does not work well on 1ph induction motors, they tend to drop out of run on load at low rpm.
FWIW Shaded pole units seem to perform acceptably at low Freq/AV --- That said, I doubt the OP's 1/2 HP motor is of shaded pole construction

Best regards
HP

Joined Jul 18, 2013
19,186
FWIW Shaded pole units seem to perform acceptably at low Freq/AV ---
HP
Shaded pole motors are usually small/fractional motors, and in most cases are controlled with a simple phase angle (Triac) control, I don't recall ever seeing a VFD for one of these which I suspect would be un-economical to produce?.
Max.

#### Hypatia's Protege

Joined Mar 1, 2015
3,197
I don't recall ever seeing a VFD for one of these which I suspect would be un-economical to produce?.
No doubt -- I was citing results from my own experiments with DIY VFDs and 'skeleton-frame' shaded pole motors (think turntable and Tektronix 'boat anchor scope' fan motors)

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