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enter image description hereI'm trying to build a Van der Graaf generator with my little brother for a school project. The thing is we get a electric motor from and old blender and want to use that for power our generator, but the motor is too fast and make vibrate everything around.

I was wondering if there is a simple (and safe way) to reduce the speed, I read that the speed in this induction motors is regulated by the frequency, so the question is: is there a simple (and safe) circuit to lower the 60 Hz ( and 110 V) of the electric network, to say the half of that frequency? Or a third?

Thanks for your answers.

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  • \$\begingroup\$ Add a photo of the motor. I don't like the sound of you and little brother playing with 110 V motors. \$\endgroup\$ – Transistor Jul 11 '16 at 13:50
  • \$\begingroup\$ Haha. sorry is a huge photo, that is the motor i have \$\endgroup\$ – RolandDeschain Jul 11 '16 at 14:18
  • \$\begingroup\$ That's a brushed series-wound motor as I and Neil_UK suspected. \$\endgroup\$ – Transistor Jul 11 '16 at 14:28
  • \$\begingroup\$ I see. the circuit proposed in tinyurl.com/gro48w4 will work? \$\endgroup\$ – RolandDeschain Jul 11 '16 at 14:40
  • \$\begingroup\$ If the motor is designed for 110v AC, it will start to run slowly at 30 V. Universal motor is not polarity sensitive, you may use either AC or DC. Use a 30 v step down transformer, salvage it from old audio power amplifier. \$\endgroup\$ – soosai steven Jul 11 '16 at 14:53
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No, there isn't a simple or safe way to reduce the frequency of the supply.

I doubt that a small high speed blender would use an induction motor, it is much more likely to be a brushed series wound 'universal' motor. See if the armature is wound, if so, that's what it is.

These are usually controlled for speed using a phase angle controller, basically a heavier duty version of a lighting dimmer switch.

You have several options.

A Van de Graff uses very little power, almost all the energy is spent in roller and belt friction, a good mechanical construction should keep these losses reasonably low. Try to get a small DC motor, and run it from batteries.

If you must persist with mains, then put a mains filament lamp in series with the motor and see what you get, if you can't get hold of a phase angle controller rated for the power of the motor. This is perhaps the least dangerous way (note I don't say safest, it's only as safe as your competence with making sure mains connections are insulated) of messing with mains. Use more lamps in series or parallel, or different values to adjust the speed.

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  • \$\begingroup\$ HI, thanks for answer. i check using the lamp yesterday but then the motor doesn't move. I believe you are right the motor is a 'universal motor' . So, a thing like a lightdimmer switch will do the work? , can you show me some pics of what i should look for to buy \$\endgroup\$ – RolandDeschain Jul 11 '16 at 14:16
  • \$\begingroup\$ a circuit like tinyurl.com/gro48w4 could work? \$\endgroup\$ – RolandDeschain Jul 11 '16 at 14:24
  • \$\begingroup\$ @RolandDeschain: What size lamp did you use? Did the lamp light? \$\endgroup\$ – Transistor Jul 11 '16 at 14:28
  • \$\begingroup\$ yes, the lamp light fully, i use a small 40W bulb, and a 60W . The motor didn't move, just make a bit of noise . \$\endgroup\$ – RolandDeschain Jul 11 '16 at 14:31
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This motor is not an induction motor so controlling frequency is not the correct method. The motors in kitchen blenders, mixers and things like AC powered dremel tool and electric drills are "universal' motors. You can tell from the commutator and brushes which I can see from your photo.

You can safely control the speed of these motors with a speed controller designed for these universal motors, such as this one: http://www.harborfreight.com/router-speed-control-43060.html

Just make sure the speed controller has more than enough current capability to handle your motor. The 15 Amp rating on this example should be enough to handle your blender motor.

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  • \$\begingroup\$ Would he be safer running it from a low-voltage transformer or DC supply? \$\endgroup\$ – Transistor Jul 11 '16 at 17:06
  • \$\begingroup\$ Yes, safest would be to just use a low voltage motor and supply, like a 12V car motor (like a power window or windshield motor) and a variable bench supply but the line voltage speed controller would be safe enough if he insulates the wires well, used the ground connection to a metal enclosure, added a fuse for protection, etc. Would also be the most straightforward at this point. \$\endgroup\$ – Vince Patron Jul 11 '16 at 19:39

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