Newbie with AC motor 2

[ultragotcha]

Hello to you all,

I'm from a mechanical background and I'm very new to the electric world. I'm planning on building a little contraption that shoots pet food accross the room (no kidding). I recently scavenged an electric motor from a food beater/blender. All it says on it is : 230V, 50Hz, 170W. It all works fine when I plug it. I live in Australia and everything here is 230V, so no worries there.

My question is: The motor spins way too fast at the moment, how can I slow it down ?

Thanks in advance for any help,
Cheers

 

[eemotor]

One way you could reduce the speed of your motor is to reduce the incoming frequency from your power source. However, I don't think that's cost effiecient for your application. In majority of motors such as the one you describe, speed is contolled by varying the voltage applied to the motor terminals. Something you can try is to place a resistor of an appropriate power rating in series with one of the terminals going to the motor. Another solution is to use a TRIAC. This way, you can control the voltage in both, positive and negative half cycles and by contolling the firing angle of the TRIAC, you can effectively vary the RMS voltage going to the motor terminals, thus varying speed. Yet another possible solution might be to use a transformer or a VARIAC to obtain a lower voltage.

 

[dpc]

If this is a one-only project, try scrounging a gearbox from something.

This motor sounds pretty big for what you want to do. If you had an old variable speed electric drill, it might do the trick.

 

[Marke]

Hello ultragotcha

I would expect that this motor is probably a universal motor. Check and see if it has brushes. If it does, then it can be controlled by varying the voltage applied to it. For a one off, this is probably best achieved by going to one of the Dick Smith or similar store and buying a motor speed controller kits. NOTE : These can not be used with induction motors unles they are a special high slip induction motor.
Varying the voltage will vary the torque and this in turn will cause the motor to run at a lower speed, depending on the load torque.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[jraef]

Only in Australia would they need a machine to shoot pet food across the room...

Is it a pet croc or something?

"Venditori de oleum-vipera non vigere excordis populi"

 

[ultragotcha]

Thanks a lot for all your replies.

Here is the motor in question:

http://members.westnet.com.au/ultragotcha/ACmotor.jpg

Will a triac work with this kind of motor?

I went to an electornics shop today and asked to see a triac. There were a few different models with different tolerances to amperage and max voltage. I'm gonna start reading some electronics basics in order to, hopefully, design a little circuit board with a triac and potentiometer to control the motor speed. I'll keep you posted on how it goes

 

[Dopler]

Looks like an induction motor, not universal type, Marke mention that, if you vary the incoming voltage the speed will not change, torque will be reduced.

Dpc mentioned about using a variable speed drill/screw driver, you can couple it to the equipment with the choke; some drills have a trigger with a rotating nut to maintain it working at desired speed.

 

[ScottyUK]

Hi dopler,

I'll politely diagree with you because I can see what I think are brush holders on the motor. The covers appera to be a blue colour. One is at the very bottom of the photograph immediately below the thin white lead coming out of the glass fibre sleeve, and the other is parly obscured by the black lead at the top left of the motor body.

If this is the case, Marke's comments regarding control of universal motors apply.

Ultragotcha,

A triac on its own will not help you. You need the rest of the circuit too. You can buy a mass-produced item made in China or wherever for less than you can buy the components for in the West. What are you planning to feed with this thing?





------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[Dopler]

ScottyUK you must be right, and apparently you can see the armature winding.

Don't worry, like you said, it’s a great education.

 

[bass1mj]

I don't know how high-tech you want the project or if it only for testing. Try a light dimmer to control the speed of the motor if it is only for testing

 

[eemotor]

You can try using a light dimmer. It may or may not work. Keep in mind that most light dimmers are not suitable to work with inductive loads, such as a motor. A light dimmer may be damaged by the voltage spikes created when current changes rapidly in a motor. Another cause for concern is the phase shift between the voltage and the current in an inductive load. You can build a modified light dimmer using a TRIAC and controlling electronics between the live and neutral wire. Check out

http://www.semiconductors.philips.com/acrobat/applicationnotes/FS013-014.pdf

for a sample circuit.
There is a way to get around some of the problems that inductive loads introduce to light dimmers. You can wire the light dimmer to your motor and add a resistive load in parallel with the motor. I would suggest a 500 ohm resistor rated for at least 120 Watts. If you'd rather not buy the resistor, you can use a 100 Watt light bulb in parallel with the motor instead of the resistor.

 

[TomG33]

Jraef,
It's not the Crocs you gotta worry about,.............

It's the Yabbies that Eat them.



Tom

 

[TomG33]

ultragotcha,
I would be following up the earlier sggestion of the variable speed Electric Drill.

not only do you get a variable speed but you also get a choice of a two speed gearbox. Somewhere between the two you should be able to find the optimum speed.

The best part is that all of the design and experimentation has already been done at someone elses expense.

170 Watts is a fairly small power rating so even the smallest Drills should be enough. The one I have is 500 Watts and it is not really all that big in the scale of Power drills.

Take a walk through the tool shop in "Bunnings", I am sure you will see something there

your mechanical background should be able to fashion some mounting arangement to your "Croc Feeder"


Tom