small ac motors

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Old 09-08-00, 12:52 PM
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I have a 110V revolving light. It revolves about 1/sec. I want to reduce the frequency so that it will revolve 1/2 sec or less. Is there some simple cheap way I can cut 60HZ down to 30HZ to make this happen?
TIA
 
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Old 09-08-00, 02:13 PM
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You really didn't provide enough info to do you a lot of good pertaining to advice. But I will try using what I know considering what you said.

If you have a DC servo motor then you can monkey with the voltage. changing the frequency would not make a noticable change in your revolutions of the motor.

So if you have a DC servo motor ok monkey with the voltage possibly using a reostat or such.

If you are using a normal a/c motor. The rpm is indinative to the manufacturers design. You usually will find a motor rpm to be mechanical speed or fan speed with little control for variation of speed without risking damage to the motor or creating a hazard due to a heat build up.

Most motors used on a sign or toy that has a slow revolution or slow wave is done by mechanical means, using a gear reduction type transmission. It is a little box that receives a mechanical speed as input and a slow rotation or reciprocating motion on the output. A lot of the times you can find the gear reduction type equipment at sign companies, electronics companies, or toy manufacturers. The gear reduction seems to be you most likely method of accoplishing what you want.

Hope this helps

Good luck

Wg
 
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Old 09-09-00, 06:11 AM
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Opps- It is a small AC 110V motor (3 Watts) with a gear reduction built into the unit. The unit is clamped together and although not sealed it could be detrimental to open it. Because of some simple tests I ran I am pretty sure that it is 'synchronous' to 60 HZ. e.g. lowering voltage did not effect the speed, applying load to make it stall causes it to reverse, it rotates either cc or ccw depending (I assume) on where it stopped when power was removed.

Although I have not been able to find a schematic of the motor or the winding type, I assume the only way to slow it down without changing gears (which is not worth it) is to reduce the frequency. So I was wondering if I could put a diode in series with the 110v hot lead, then filtering that back to (or close to)a sine wave (which would be 30 HZ vs 60) referenced to the ground lead, then boost it back up to 110 or so (probably does not need to be 110 exactly) with a junked transformer. Then ala, instead of rotating 1 per sec. it would rotate 1 per 2 sec.

I am using this as a rotating 'beacon' in a copula at a Florida Island State Park Marina that I volunteer at. Actually looks pretty neat, but would be better if it were slower. So needless to say it has to be cheap. Maybe I need to contact the coast gaurd to see if they have any junk beacons that I can work with.

TIA

TomA

ps this is pretty lengthy, hope not too.
 
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Old 09-09-00, 07:55 AM
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Boy are we having fun now. You are taking me to an area I feel a bit weak in. Electronics. I haven't dealt with electronics design in about thirty years. Good adviser huh?

So what I say now you need to confirm with an electronics expert before committing you motor's safety.

The way that I understand is if you install a diode you just made the circuit direct current. Now you can mess with the frequency, whether you lower the voltage with a transformer and step it back up or not. There is a device that you called a cycler which can reintroduce the hertz at the speed that you desire. 50 hertz or 60 hertz.

I do not see playing with the electricity's frequencey changing the motor speed in a controlled manner. Your motor is still AC and is still designed to be feed with 60 cycle 120 volt. Changing to 50 cycle should only make a minute change in the motor speed. Almost unnoticable.

I suggest trying to find a used dc servo motor to replace you original motor and then using a reostat sized to carry the load to control the speed.

If you go to a hoby shop and get lucky then you might be able to trade your gear reduction motor with one that is slower or with a variable speed dc servo motor.

Good luck

Wg
 
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