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Slowing a motor Answered

I have a 4 Watt mains powered motor that currently spins at 1.6-1.9RPM. I need to find some way of slowing it to maybe 1 revolution every 10 minutes. It's all sealed in a metal case and connected to the mains by a standard plug. I really need to find a way to do this without breaking it apart stuff as it may need a safety test later, I looked at dimmer switches as they essentially limit the voltage and are a max of 300w. Like this - http://www.jpgelectronics.com/products.asp?partno=350.109

I realise that they are made for lights but it's a similar principle and is only about £6. Would this work? Are there other options if I don't want to break into the motor housing or wiring?

Thanks.

Discussions

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Goodhart

8 years ago

The best way is to gear it down, but it is sounding like you are not really up for that either.   For instance, placing a very small sproket or gear on the shaft and a pretty large one for it to turn, will cut down the output speed (using the bigg gear now as output) but what ever the ratio of the gears are.   One can do this several times in sequence  to get it to the speed you wish.

Since this moter is not spinning "fast" as it is,  it shouldn't be too difficult to gear down to the speed you'd like 

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guyfrom7up

8 years ago

what type of motor is it? is it asynchronous?

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happysnail

8 years ago

It's fairly impenetrable and unscrewing it doesn't help as the other side of the screw just spins which is within the metal motor box. So I think that's a no.

Looks like this inside unfortunately:
http://i56.tinypic.com/14txwy1.jpg

Are there any other motors which would spin at a very very slow speed like this. It was a good option as it was cheep and came fully built and working rather than working from scratch with motors and parts, plus it needed to be mains powered but it's not ideal at that speed. Any other options generally, trying to avoid the complicated electronics side to it.

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happysnail

8 years ago

If it helps it's one of these: http://www.maplin.co.uk/mains-powered-mirror-ball-motor-9882

This is really an art project that became surprisingly technical so I have no idea what i'm doing to be honest. I take it there's no way of varying the frequency easily from the mains, how much is a little speed change? Any change is better than nothing.

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steveastroukhappysnail

Reply 8 years ago

Like Verence says, you'll lose RPM AND torque, which you probably can't accept.

Try this little lot from Maplin....

http://www.maplin.co.uk/search?criteria=gears

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verencehappysnail

Reply 8 years ago

Those light dimmers are normally only usable with resistive load (i.e. light bulbs). They may or may not work with inductive load (i.e. motors). But the motor will most probably not work well when 'dimmed'.

You would loose torque, if you dim the input voltage and if it runs at all, it may run not very smoothly.

Use a kind of gearbox - cogwheels, belt drive. That way, you will gain torque.

If it is safely possible, you can try and open the motor to see, if there is already a kind of gearbox inside that can be maybe modified for a different speed.

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steveastrouk

8 years ago

Although you CAN adjust the speed a little, you ain't going to get 10:1 change out of a variable voltage controller. These motors rely on mains FREQUENCY to set their speed really - its a bit of a fix to pretend that varying the voltage works.

The BEST way to do this is undoubtedly to add some gearing, either with, well, gears, or simple belts.

Steve