Tiny motor needs lower voltages for lower speeds 1

[DRWeig]

Guys and gals,

Original control of a two-speed motor (1/20th HP) was from a transformer with 120V primary and a double-tapped secondary at 85V (for high speed) and 75V (for low speed).

Transformer is no longer available, what would be the downside of using resistors to drop the voltage instead?

Best to you,

Goober Dave

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[itsmoked]

You haven't stated what kind of motor...

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DRWeig]

It's a shaded pole type, single phase.

Best to you,

Goober Dave

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[itsmoked]

Resistors.. Shaded pole...

Resistors = no isolation
Resistors = power dissapation

If you don't need isolation there are 1.75A small Variac Transformers that are panel mounted. You could use two and set them appropriately or use one and just set it to 75 or 85V as needed.

1.75A Variac

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Have used triacs sucessfully for shaded pole motors. Windings are usually quite robust. But there may be an EMI problem.

Series capacitors do not produce EMI or dissipate heat. But tend to be somewhat expensive for reliable AC operation. Advantage: Can be installed without PCB. Just crimp then in series and tie them with nylon strips or whatever.



Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[DRWeig]

THanks for the tips.

I'll follow up after the experiments. Those little variacs may be the key.

Dave

Best to you,

Goober Dave

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[jraef]

Look for a "fan speed control" device. It's either a rheostat (old school) or a triac. Either way works fine for shaded pole motors. If it says "Electronic", it's a traic controller, if it doesn't and has a heat sink, it's a rheostat (dimmer).


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Compositepro]

Capacitors have traditionally been used for three-speed ceiling fan motors.

 

[zlatkodo]

Could be useful if it is about single-phase fan motor:
[URL unfurl="true"]http://winding.wixsite.com/design/single-post/2016/06/24/Multiple-Speed-SinglePhase-Fan-Motor[/url]

 

[Skogsgurra]

Yes, C-pro (4 Oct 16 04:35), but that capacitor is used to produce necessary phase shift - not voltage reduction.

A shaded pole motor produces the phase shift "inside" the motor (that's what the shaded/shorted pole does) so it can be very confusing to think single-phase cum capacitor and experiment with a shaded pole motor with a capacitor for voltage/speed adjustment..

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Compositepro]

Older fan motors were primarily shaded pole. Now many types are available but permanent split capacitor seems most common. With either type speed is controlled by reducing motor torque to get more slip. And that can be done a number of ways, including varying the voltage by a series impedance.

 

[DRWeig]

Thanks again to all! My client hasn't gotten back to me with actual measured amperes but the fan speed controller jraef mentioned may be the answer.



Best to you,

Goober Dave

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