Slowing an electric motor down

[Lykle]

Hi Guys,

I am in the process of finishing a vibratory tumbler. The problem is that the 220V electric motor I have is running at 3000 rpm and I would like it to be 1500 rpm.
Yes I know, I started out with the wrong motor but it was all I had.

Now, how do I slow it down? It is a cheap motor from a cheap car buffer machine. It will certainly have to be a cheap solution, so I can't go the controller route. All I can think of is a big resistor, but will this work? 

Looking forward to your suggestions.

Lykle

[John Rudd]

Sounds like it might be a brushed motor?

If it is then a simple speed controller ( like a light dimmer  ) would do the job......

Else go the mechanical route using a 2:1 belt drive reduction or gear system....

Details of the motor would help though..

[Lykle]

A light dimmer! Great, yes, why didn't I think of that.

I think it is a brush motor, no idea. It has no specs on it at all. I have a dimmer, I will try it.
Thanks you, John.

[David Jupp]

Make sure dimmer can handle the power - most domestic dimmers are only rated for a light bulb or two - you may overload and damage it.

If the motor is an induction motor (no brushes) then the dimmer (or resistor) will not work.

[Lykle]

Well, I tried it and the motor ran slow for about 30 to 40 seconds.
And then it jumped back to normal speed.

So it looks like the dimmer idea works, but the dimmer is too low powered, right?
It is an electronic one, so I am thinking it has an overload protection and it kicks in when it speeds up to full speed again. Sounds logical, don't you think?

I guess that if it is not a brushed motor, it would not slow start, right? I had a look at the motor and I don't see any screws for fixing the carbon brushes, but I still think it is a brushed motor with the brushes hidden in the cooling fan.

OK, so now I will try a bigger capacity dimmer. I used a 300 watts one and I think I might have a 1000 watts one.
 

[John Rudd]

Well, I tried it and the motor ran slow for about 30 to 40 seconds.
And then it jumped back to normal speed.


OK, so now I will try a bigger capacity dimmer. I used a 300 watts one and I think I might have a 1000 watts one.

Sounds like you blew the scr or triac...( its gone short circuit which is why the motor runs at full chat)

You need to use a dimmer with a bigger wattage rating or you could repair the broken one by changing the the scr or triac for one with a larger current capacity.....

[Darren]

Bear in mind the triac will get hot ... a good heat sink will help it live longer ...

[Lykle]

HI,

No nothing is blown, because when I switch it off and on again, it will again run slowly for a while and then speed up again.
I am using a remote control dimmer switch thingie and I am sure it has protection built in.
Unfortunately I don't have the 1000 watt version. That is just a switch.

I will have a look around, see what I can find.

[Darren]

Sounds like the triac is getting hot and shutting down?

[Lykle]

This is interesting.
This is where the motor came from: Kinzo 8E925EP car buffer.
Specs claim it is only 110 Watts.

So my 300 Watt dimmer should handle it easy. hmm.

[jiihoo]

Hi Lykle,

A motor is a more difficult load for the dimmer than an incandescent lamp. You should have a "fan speed controller" or "universal dimmer" which both are meant to control motors. I higher rated light dimmer would probably work, though, but no guarantees...

If you don't need variable speed and could use belts and pulleys in your vibratory tumbler design, consider the pulleys and belt approach suggested by John earlier. Some old threads that might interest you if you decide to go this route:
http://madmodder.net/index.php?topic=1903.0
http://madmodder.net/index.php?topic=1374.20
And at least Chronos has the belt material http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Plastic_Transmission_Belt_46.html

Is 3000 RPM too much for a vibratory tumbler? Many of the small-to-medium sized vibratory tumblers seem to use 3000 RPM. I can definitely see why the speed control would be nice as you'd get to test different speeds and see what effect it has, though...

Cheers,

Jari

P.S. Can we have a build thread of your project, please  .

[David Jupp]

Difficult to know without seeing the motor.

May be slow to start because of reduced power via dimmer - eventually it can pick up enough speed and run at normal speed, I could believe that if it was an induction motor.

If you can't find brushes, maybe it isn't a brush motor...

[John Hill]

I expect this tumbler will be left to run 24 hours a day?  If so I suggest not trying to slow the motor as that will likely cause it to run hotter than intended (if for no other reason than its fan will be running slow).

My suggestion is use a belt and pulley to slow it down which will also give you increased torque to turn your tumbler.

[Lykle]

Hi all,

Well, I went through my old electric bin again and found a motor and controller for a juicer. Now the juicer runs at 6000 rpm or so, but I wired the controller to my motor and it slowed it down nicely. Not enough yet, but I can replace the 100K variable resistor for a 200K and it might just work.

The reason I think I need to slow it down is that when the system starts up, there is a sweet spot where it vibrates nicely in harmony, it feels in sync.  Then the motor goes faster and I loose it again and the whole system rattles hard.

But I think I need to run it as it is for a while with material in it. Just to see what will happen with it. But finding the right abrasive material is a totally different challenge!

I have not been able to find anybody who has the abrasive material here in Cyprus and to order a 25kg bag from mainland Europe is going to take a lot of dosh, that I don't have.

So I was thinking of just using sand? The main purpose is the deburr and clean up stainless steel parts for my Danger Toys. Just sand with a little bit of water and some polishing compound.
Any better solutions or ideas?

Build thread? I can start a thread and post a few pics but most of the construction is done and glued in. So it won't be a build thread, more of a debug thread. I will dive into the workshop now and shoot a few pics.

Lykle