Has anyone tried using a light dimmer switch on a synchronous motor to control the speed?
I use a 220 volt 3w 50 Hz motor which rotstes at 20 RPM ,(Ilive in the UK),and would like to be able to control the speed, would a light dimmer switch work?
Phil

being here in the U.S. , i'd say that i have never seen a light dimmer that could handle 220V - man i'd talk to an electrification

Hi Terry,
All our supply is 240 over here, our dimmer switches are built to the voltage so I'm not worried about them.
However, I dont have the knowledge to know if a synchronouis motor can be controlled by one or if it is controlled by the mains rating.
Phil.

The speed of a synchronous motor is regulated by the frequency of the A/C power source, not voltage. I suspect you will find it difficult to find a dimmer that regulates frequency.

~Bert

Bert has got it right. Get one in the RPM you desire. The only other (economical) choice is a DC or AC/DC motor.

Phillip
With a synchronous motor, the speed is regulated by the number of windings in the motor. That is the reason that the motor is called a synchronous motor.

If you use a lamp dimmer and hook it up to the dimmer, you will be cutting power to the motor in the form of lower voltage or current. That is the way that lamp dimmers work.

But if you hook up the dimmer to the motor, you will simply result in a motor that is still running the same speed, but it will start to get hotter and hotter, with less and less power until it finally just quits rotating.

Rather, use any AC/DC series wound motor that has brushes and the lamp dimmer will work just fine.

--
In contrast, if you have a DC permenant magnet motor, you can vary the voltage to the motor from 0 to its maximum rated motor voltage and the speed of the motor will track quite well and have not only a direct voltage vs speed relationship, but also a direct voltage vs power relationship.

In recent years, I have changed all of my rod building motors over to DC motors with appropriate speed control change mechanisms to get this nice linear speed change curve that works so well with this style motor.

Good luck
Roger

Thanks Roger,
Can you let me have any details on the type of motor and where I can find them?
Appreciate any help you can give.
The reason I'm looking to do this, is to have an all purpose wrapper/drier base rather than to swop between one and another for the different speeds.
There seems to be several opinions whether speed, (within reason say 4 to 20 rpm), makes much difference, but but getting a contollable set up, I'll have the best of both worlds.
Regards,
Phil.

Phillip, do I understand correctly that you wish to use the same motor for wrapping and drying?

If so I don't think that is wise. The little dryer motors are quite cheap and can even be scrounged from various items....clocks, microwave ovens, lawn sprinkler timers, barbeque rotisseries, etc. A DC motor and power supply with enough horsepower and RPM to make a wrapper is quite a good deal of money if you are buying new on the retail market. That is basically why none of the power wrapper use them. But as Roger has been telling many here, they are vastly superior (IMHO).

Besides, I dry at a few RPM but wrap at several hundred.

Russ in Hollywood, FL.

Russell is right on.

If you want to do drying - pick up a dc or ac timing motor. You can pick up small dc gear motors for less than $20 which will work just fine. Since these are very low current motors, you can easily pick up a dc voltage supply that will simply plug into the wall.
You can search the internet and or @#$%& sites as well as surplus stores for these motors. You can also, as Russell pointed out, pick up low rpm ac timing motors that will simply plug into the wall outlet and give you the necessary rpm directly.

Then, for a lathe, if you want a variable speed, you need an ac/dc series wound motor if you want to have a variable speed. A very common - readily available source is a common ac electric drill.
Or, if you want, you can use a common dc variable speed rechargable drill. You can use the ac drill directly and plug it into the wall, toggle the handle to get the speed that you want, or lock it to full speed and then use a common foot pedal rheostat or electronic speed control to give you the speed that you want. If you use a dc rechargable drill, you can use it as is, and use the batteries to supply the voltage. However, for long hours of turning, the batteries really don;t give you enough use time. So, then it makes sense to power the drill with a varabable voltage dc power supply - that is adjusted with a foot pedal. This leaves your hands free to take care of your turning tools.

Take care
Roger

Phillip,

The following information will save you a lot of time, money & frustration.

1. The RPM of Synchronous motors is determined by the Line frequency and can not be changed with any external device, such as a foot pedal or dimmer switch. There are Synchronous motors, like those used in ceiling fans, the RPM of which, can be changed in specific fixed RPM increments. But these type of motors are not suitable for rod wrapping or drying.

2. As previously mentioned, to achieve a variable speed motor control, you must use a D.C motor. For rod wrapping or drying purposes, this motor must be geared down via internal gears, or via external pulleys. To obtain a continuously variable speed control you must use a foot pedal rheostat or a dimmer switch. However, if a dimmer switch is used, it must not be plugged into the 115VAC wall outlet because the output voltage will be to much too high for the type of D.C. motors that you will need. What is required is a step down transformer, which will step down (reduce) the voltage to the same voltage level of the motor that is being used. The input to the dimmer switch, is then connected in series with one of the output wires of the transformer. The step down transformer can be a Wall transformer, which is often called a wall wart. Examples, of this type of device (although not the same output voltage levels), are those used for charging your cell phone of rechargeable screw driver.

CAUTION TO THOSE READING THIS POST: IF YOU USE A DIMMER SWITCH, IN ANY LOCATION OTHER THAN IN THE HOUSEHOLD WALL OUTLET, YOU WILL RISK GETTING ELECTROCUTED IF YOU DO NOT USE AN ISOLATION TRANSFORMER. (This comment specifically refers to the preceding paragraph).

Even if you use a geared down D.C. motor, you can not (in a practical sense) achieve both rod wrapping and rod drying, without additional speed reducing pulleys. The reason for this is as follows: Assume that you have an internally geared D.C. motor that runs at 20 RPM. If you reduced the input voltage, low enough to get 4 RPM, there is the high probability of burning out the motor or the foot pedal, because the motor works as follows:

All motors act as generators, so when the armature is rotating in the magnetic flux of the field windings , it generates a Reverse voltage, (called Counter ElectroMotive Force) which is in opposition the the applied voltage. The magnitude of this Reverse voltage is a function of the motor's RPM. At the motor's rated RPM, this Reverse voltage is almost equal to the applied voltage. For example: Applied voltage = 12 volts; Reverse voltage = 11.5 volts. Since these two voltages are opposing one another, the difference in voltage is: 12v - 11.5 volts = 0.5 volt. Therefore the current drawn by the motor is = (Voltage divided by the resistance of the armature). Assuming the resistance of the armature is 2 ohms, then the current drawn by the motor will be 0.5 volts divided by 2 ohms = 0.25 amp. at the motor's rated RPM and Voltage.

When you limit (reduce) the voltage to the motor via a foot pedal so that the motor RPM is lowered to 4 RPM, the the armature is rotating much slower in the magnetic flux of the field windings, so the Reverse voltage is drastically reduced (remember, this voltage is a function of RPM).
Let's assume that at 4 RPM, the Reverse voltage is 1 volt. The the difference in the applied voltage is: 12v - 1v = 11 volts. The current drawn under these conditions is therefore = 11 volts divided by 2 ohms = 5.5 amps. If the motor or the foot pedal is not rated for 5.5 amps, they will be burnt out!

The foregoing explanation is fictional, and was for purposes of explanation only. Actual values depend strictly on specific motors. This information was included for readers who have experienced foot pedal or motor burn-outs.

To reduce the RPM down to 4 RPM, and to over come the foregoing problem, it is necessary to shift the operating point, by means of additional pulley. This in essence, transfers the motors rating down from 20 RPM to 4 RPM. This means that a pulley is required for the 20 RPM motor's shaft and a 2nd pulley to the rod chuck/holder shaft.The diameter ratio of the two pulley should be 20 divided by 4 = 5:1 ---> In other words, the pulley on the rod chuck/holder shaft, should be 5 times the diameter of the pulley on the 20 RPM motor's shaft.

Phillip, The whole point of this post is that if you do not have sufficient knowledge of electric motors or have the ability to make pulley's and holders for shaft bearings, I would recommend that you forget trying to do rod wrapping and drying on one set-up.

Expert rod wrappers, like Tom Kirkman and Doc Ski, get perfect finishes by drying their rod manually by hand.


This post was meant to help you understand what you would be getting into should you choose to proceed.

Best Regards,

Rena, (My qualifications for this post is that I am a Graduate and Practicing Electrical Engineer)

Rena took the time to add a lot I didn't care to bother with. Bottom line, it would cost too much to do what you want.

I have a 110 volt DC permant magnet motor that is rated at 1000 RPM. It is not your typical motor and its intended use is as an elevator door operator. It will indeed run down to low RPM and even handle a stall condition for days on end. The retail price of the motor is well past the cost of most complete power wrappers. The power supply, comprised of a center tapped transformer, full wave bridge rectifier, and smoothing capacitors would add another couple hundred. Then you have a foot pedal and ideally you want the old resistive type and not the new triac based ones.

Point being for that for the whole nine yards plus my labor to make it.....well the price would be so absurdly high I'm too embrassed to mention. It is only because I have friends in the biz and get to scrounge a lot of electrical equipment that I own such a thing.

Russ in Hollywood, FL.

Russ and Rena,
Yes, you are right.
You are also right, that if you pay full retail price for items you may very well have a wrapper or dryer that will be very very expensive, using some of the components mentioned above.

However, don't underestimate the resourcefullness of the folks who practice this wonderful thing that we call rod building.

Sure you can spend several hundred dollars for motors, gears pulleys etc.

But, if you are resourceful, if you go to on line @#$%&, surplus stores, good will and salvation army stores; you can build very useful and functional products for very little money.
Yes, it will take some or a lot of your time, but if you have that to contribute, you can often build excellent products for very little money.

As Rena pointed out - DC motors work very well for things like drying, power wrapping and lathe work use. Just pick out the motor that has the necessary maximum rpm for your application and build or obtain a power supply to drive the motor.
Also, ac/dc series wound motors work very well for wrappers, especially, if you use a pulley system to slow down the nominal 5000 wide open speed of many of these motors.
Then, the common AC timing motors of 5-10 rpm commonly used in grills, timing motors and micro wave ovens work very very well for dryer motors.

I have also built many dryer motors using dc gearmotors of the correct speed, using a simple inexpensive plug in wall transformer to convert the current ac voltage to the necessary lower dc voltage required for the motor in question.

If need further information, just drop me an e-mail at

hflier@comcast.net and I will give you some updates.

Take care
Roger

Phew,
Thanks guys, never realized what I was getting into.
Think I'll stick with the standard motors and use 20 RPM for epoxying and drying from now on.
Thanks for all your input and obvious knowledge.
Phil.