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Controlling the Speed on a 240VAC Industrial Fan: Suggestions please


I have acquired an old "Airspeed" Industrial air circulator or fan, which stands on a pedestal. It still works, but at only one, fairly fast speed and in one fixed position. As a project, I am stripping it down and restoring it, while altering the overall look to something more in tune with a Steampunk aesthetic. As part of this I am adding a brass worm-drive which will enable me to alter the angle of the fan plus motor assembly on the pole to which it's attached. I would also like to be able to adjust the speed, either continuously, or using set points ( slow, medium, fast etc.). The motor appears to be single phase and connects directly to mains 240V AC supply. There are no electronics at all in the current construction - I would guess that the unit dates to the 1950s or 60s? Can any one suggest a safe and reasonably simple way to set up a speed control system?
All suggestions welcome, however banal - the more simply outlined the better. If you know of an electromechanical means of doing this, so much the better.
Regards and thanks

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jubin.babu32 years ago

I used SCR for speed control of fan,using atmel micro controller.But it only works on a particular fan, no other. What to do?

seandogue5 years ago
If you'd prefer an electromechanical method, I suppose you could always use a belt or chain drive and a traditional speed switch method like a derailleur or similar, and use a solenoid or continuous linear actuator to control the gear shift.
cutshopguy (author)  seandogue5 years ago
Thanks for that.
An electromechanical drive to select alternative speeds would be relatively simple to rig up, but what I need is some way to actually control the motor speed downstream from the switch setting selected. The only way I can conceive of at present is to use some form of rheostat, the "level"of which could be electromechanically selected. Any ideas?
At the point where you're mixing the visual of an electromechanical solution with speed control for fine tuning, I'd suggest the link I originally provided in my other post below.

The gear/belt switching would look cool, but for continuous control, only a "varidrive" (I think that's what they're called) would be suitable for an electromechanical solution...and very expensive (and still requires some form of variable supply or similar control signal to set the speed via the varidrive's interface), so that's why I suggested considering a phase control method below.

If you're interested...for info on varidrives (very cool btw) see http://www.usmotor.com/variablespeedbeltcases.html
For an electrical solution, then perhaps this link or a similar one (google ac motor control) *may help you
cutshopguy (author)  seandogue5 years ago
Thanks for the link - this looks really interesting and I shall read it diligently.
rickharris5 years ago
You can try running it though a commercial dimmer switch or an electronic speed control for an electric drill.

. Note electricity is dangerous to play with therefore this would be at your own risk.
cutshopguy (author)  rickharris5 years ago
Thanks for the response.
I've read somewhere that using an electronic lighting dimmer switch is not recommended because of safety issues?
An electronic dimmer is essentially what Iceng had provided. The only stipulation is it must be able to cope with the current.

HOWEVER as always playing with electricity is fraught with dangers. take care.
Yes, and the BT136 triac is only rate at 4 amps with a cooling heatsink. A
Lighting dimmers even if they can handle the power,
they used to be ( half-wave ) and that could burn up ( overheat ) a motor.
It is a cheep try if you have an oscillyscope and know what to look for
engineering wise.

A
iceng5 years ago
A simple Triac control.  Get Diac here.
It was not clear what kind of motor you were  refurbishing,
So I drew the top two contenders. Resistor values may need adjusting,
depending on motor type. Its drawn for five speed but can be three speed,
if you change the four 100K to two 200K.   A
triac-ac-motor-speed-control-circuit.png
cutshopguy (author)  iceng5 years ago
thanks very much for taking the time to respond so fully. The circuit looks pretty straightforward and I might build it to "Try it and see"

The motor is a 240VAC single phase unit, built under licence to GEC in the UK,by a company in Australia that appears to have gone out of business back in the 1950's. The data on the motor is:
A.C.Motor
Type B.S. 2505
Volts 220/240
Phase 1 C/S 50
H.P. 14 Amps 2.3 ( ?may be 23, partly effaced)
R.P.M. 1425
B.S. 170 Cont.
Insul. Class E
Might it be possible to adapt one of the old Singer sewing machine foot pedals to control the motor speed? That would be just a variable resistance wouldn't it?
Any suggestions would be much appreciated.
Something does not make reasonable sense,
I know you are reading the nameplate,

But the H.P. horespower can not be 14 that would draw 50 amps
The 2.3 amps at 220/240 VAC works out to a reasonable fractional H.P.

Yes a Singer would work if the resistance was around 400K ( unlikely )
but an eng could adjust C1, C2 R1 and R3 time constants.

The other difficulty would be the Foot Pedal is at highest resistance = lowest speed when the foot is off. That means at Power-On you must full step to start the fan.

A
And don't start them off on slow. I am always leery of voltage control of induction motors.
Good point !  Even a fan low speed load may not turn without a deep bar
rotor.  This a Steampunk aesthetic application.
We should design a near unity phase angle low speed release of a
lead weight on a string to pull the selector to the high speed setting :-)