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Banned. Registered Member #302
Joined: Fri Mar 10 2006, 05:22AM
Location: vancouver
Posts: 9
i recently decided to build a van de graaf generator and the motor i have is way to fast to use and i want to convert one of my mots to a variac any help whould be helpful
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
What voltage is the motor? If it is a 120v one you will need to many turns for it to be feasible to wind the secondary on a mot.
If it is a low voltage one, you have a chance, but it won't be a variac that you are making. You would remove the secondary (the thinner wire), and replace it with some medium sized wire. To get a variable voltage you need to put a tap (just loop the wire a few inches away from the core) every 10 turns or so. Then you conect the motor to one of the taps to get the right voltage.
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
Dimmers are normaly triac if i am not mistaken... and i dont think an inductive load would work that well (somethng about letting the smoke out of the dimmer switch?). Sounds like you need to get yourself a variac... I have two I got from hamfests - both rated at 7.5A / 120 (the ones that will go a bit over 120) and i paid $15 for one a $35 for the other. I also got a 50A one free from a friend who worked at a school and they used it for a stage light dimmer and i guess wanted to get rid of it for some reason.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
The speed control in power drills usually works with a triac, so I am sure there are ways to do this, even if it is not as simple as hoocking up the dimmer switch to the motor. Try to google for powerdrill schematics.
Registered Member #206
Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72
I was playing around with some simple phase control circruits some 3 years ago and I also tried to drive a vacuum cleaner motor and it didn't work at all. A "real" PWM control would be better.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The SCR firing circuits I developed for controlling voltage in my SSTCs will do motor speed control fine. I tested them with vacuum cleaner motors and they seemed to work no problem. Special lamp dimmers for low voltage halogen lamps with transformers also work. I used one of these to control the speed of the rotary gap motor (a vacuum cleaner motor again) on my old Tesla coil.
IME, it's just the cheap lamp dimmers that can't cope with motors. I tried a cheap one on my gap motor and it fried spectacularly :-@
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mot variac question
