VARIAC

  • Thread starter Thread starter Donnie
  • Start date Start date
  • Watchers Watchers 5
Donnie

Donnie

Administrator
Staff member
Administrator
Forum Moderator
Joined
Aug 21, 2011
Messages
5,410
Points
738

Location
Madison, MS
Is anyone willing to look at this link from amazon and give me your opinion on these VARIACS or maybe you already know of a brand or type that is the better kind. I want to plug my dremel tool into it to SLOW the RPM down. I also want to use it on my Disk Sander to slow it down as it is way to fast as well. But, I do not want to loose the torque either. Expecially the Disk Sander, I want to slow it down, but I don't want it to loose its torque when I use it.

 
Those Variacs will adjust speed, both upward a downward. Nominal line voltage (110-120Volts in US) can be adjusted from near 0 volts to about 130-140 Volts with most Variac models
Any reduction of voltage applied to the Dermel will include a comparable reduction of POWER (Watts = Volts X Current), hence speed reduction. I haven't yet encountered any Dremel's that have built-in solid-state speed control, but if one is encountered you definitely do not want to plug it in to a Variac: lots if smoke likely to be generated.
I would say try the Variac but avoid turning the speed too low; that will slow it down, causing reduced torque as well. If a Dremel has any built-in speed reduction, I would avoid using the Variac, mainly due to torque reduction.
I have a Variac and an old Dremel that has a variable resistor speed control. I'll do som testing with them and see what kind of results I Get.
Happy Modelling.
Steven
 
So, my Variac puts out o to 150 VAC (10A, Max) with a 125V at the power outlet I plugged into.
With the Variac set to about 82%, it's output is 125V. If the receptacle voltage were to drop to 115V and the dial kept at 82%, the Variac output would be 115V.
With my original condition of 125V output, I plugged my Dremel into the Variac with a small abrasive wheel chucked in the Dremel jaws and tested its cutting on a scrap of brass tube (Dremel speed dial at fastest setting}, Then I turned the Variac dial to 100%, yielding 150V output to the Dremel and repeated the test cut. The abrasive wheel turned faster, with considerable more power.
With Variac back to 125
V outpur, I tried a few changes to the Dremel Speed Control setting. The built in Speed Setting Dial seems to cause a more of a reduction in torque compared to Speed Dial at 100% and reducing the Voltage Setting on the Variac. I believe this is due to the Dremel Speed Dial includes an increase in resistance to slow the motor and the increased resistance reduces available watts to the motor. The Variac Usesc a variable Viltage transformer whose only resistance is the copper wire of it windings.
I hope this all helps.
Steven
 
Steven,
this is a picture of my Dremel. I think overall, it is just too powerful for Ship Modeling. I probably need a cordless unit.

IMG_1526.JPG
 
What I am looking for is to slow the Dremel WAY down to let's say about 300 - 500 RPM
 
I'm sure a lower speed Dremel would probably solve your problem, but I'm not sure what the cost difference is between another Dremel vs a Variac. Another option to consider is to buy a small transformer to change 110VAC down to some lower value such as 24V, or 40V or ? Then, using the speed adjuster on your Dremel will put out a much lower range of Voltage, hense lower speed. Such a transformer could be set up with a switch to change between full line woltage and the reduced value, wothout unplugging/re-plugging. My personal preference would be to use the Variac, but I already have one. There are smaller size Variacs available that will output 0v to >120V. I'm not sure what the maximum current draw is for a Dremel tool, but I guess a 5 Amp variac is adequate and it would cost less than the bigger units that can output 10 or more amps.
 
I have been using for years a Dremel Model 221 type 2 variable speed control (it's a pedal). It is only for use with Dremel Models 232, 242, 245, 250, 260, 270,275, 280, and 732.

There are several of these units currently available on ebay. Well built. But now that I've shared this it's obvious that your Dremel tool is not one of those listed on the control. But maybe someone else can make use of this.
 
I found this 40VA transformer on Amazon for 14+$. Not sure if 40 VA is strong enough for your needs. All that you need to use it is a cord with a receptacle on one end. Strip the wire insulation at the other end and connect to the transformer. If you have an extra extension cord laying around, you could cut the plug off and use the remaining cord with its receptacle.
40 VA means Volts times Amps equals 40, therefore 120 V X .3333 A = 40VA . Volts X Current also equals Wattts, so the Watts power to your Dremel would be 40W.
Just food for thought; hopefully it will help you make the choice that best suits your needs.
Happy Modelling.
Steven
 
Dremel's use a brush type series wound motor. The speed vs torque curve for these types of motors shows that the torque is not consistent over the speed range of the motor. So no matter what type of variable voltage supply you use you will always have a sharp torque drop off below 500 Rpm. keep in mind that your dremel already has a variable voltage power supply built in and adding an external supply in line may damage the internal supply. I did take my Dernel and powered it off of my Variac. With the speed set to full speed on the Dremel it operated identical using the Variac. but when I tried to use both the Dremel overheated and the speed seemed to become inconstant.

Paxxon makes a rotary tool part number 115 that uses a brushless DC motor. This type of motor has the ability of producing higher torques at lower speeds and my give you the results you want. The Paxxon tool is only a few dollars more than the Variac on Amazon.

Keep in mind that all rotary tools are typically rated for a speed range of 500 to 30,000 RPM.

Jim Nunn
 
I forgot the disk sander. If the sander does not have a speed control then I would look for a electronic fan speed control.

such as this one - FAN CONTROL

Check the motors amp rating and select a control that has a equal to or higher than the motor. The electronic control or a variac his will not work on capacitor start motors. If the motor has hump on the motor shell it is most likely a capacitor start motor.

Jim Nunn
 
Donnie, I've been using a unit I built about 30 yrs ago, it's really simple. I purchased a dimmer switch, a plug socket, some household wire, and a plug. I assembled the unit together in a plexiglass box and to this day it still serves the purpose and it's very inexpensive. Hope it helps you out Mikeyt
 
I have built the same kind of box and use it extensively, more for woodburning irons and SIMPLE motor circuits that don't have any semiconductor components involved. I'm not sure if Donnie's Dremel has any semiconductors, or not. Most dimmers work by interrupting a portion of each half-cycle of the electricity so it is actually turning power on & off 120 times per second. Variacs have a smooth, sinewave output, assuming that the incoming electricity is not distorted.
My old (about 40 years old) Dremel uses a string of resistors in series with the switch to adjust power to the motor, and that Dremel works well with the dimmer and with the Variac.
Based in info from Jim, Donnie should contact Dremel if he wishes to try any of the suggested methods. No point in generating unwanted smoke.
 
Thanks, SAHaskell, I'm not an electrical engineer, but I guess I've been lucky, because I've never smoked anything with it in the last 30 yrs, again Thanks for the info SAHaskell
 
You must log in or register to reply here.
Back
Top