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T

tree d

Member
Not sure if most people realize that you shouldn't try to adjust AC voltage with a VARIAC.......If a fan says 115v: you should give it 115v. Variacs were not intended to run a load item like a fan at less than the intened voltage. They are for used for electrical testing and using foreign appliances that require different voltages.
DC devices can be safely run at lower that stated voltage......AC operates on a different principal and by running less voltage (variac) will burn your motor out quickly.
If I'm not mistaken, a 'speed controller' is microprocessor controled to slow the fan, but remain in phase so it doesn't burn out.
 
madpenguin

madpenguin

Member
pontiac said:
Theoretically a GFCI doesn't need ground
Click to expand...

Incorrect. The potential to ground has to be there otherwise you would have never have gotten shocked in the first place, and your GFCI certainly wouldn't have tripped.

pontiac said:
The GFCI thankfully detected that some current was was not returning to COLD (which was actually going through my body), and literally tripped in seconds.
Click to expand...

Yes, but going thru your body to where? at least 6 miliamp worth of current wasn't making it back on the grounded conductor (neutral), thus, it tripped, so it had to be going somewhere, which was an alternative path to ground.

So.... You were grounded somehow. Otherwise, your body would have been at the same voltage potential as the circuit. You wouldn't have felt it and the GFCI wouldn't have tripped.

If I had all pvc plumbing and I filled my bathtub up with water and jumped in, and then chucked a hair dryer in while plugged into a GFCI receptacle, I'm toast. Current doesn't just bleed off into nothingness so a GFCI actually does need a path to ground in order to operate. Whether it's the grounding conductor (ground wire) run with the branch circuit or whether it's you touching a metal water/gas pipe, the potential to ground still has to be there....
 
rasputin

rasputin

The Mad Monk
Veteran
Glad to hear everything worked out well, Pontiac. Electrical ain't nothing to funk with so good to know it was taken care of.

Learned a lesson, I'll be a staying away from fan speed controllers and instead opt for thermostats.
 
madpenguin

madpenguin

Member
Moldy Dreads said:
GFI and the speed controllers for fans suck in my experience..I don't use em anymore..
Click to expand...

Yea, they are susceptible to false tripping. So is any motor load really. Again, I pulled my GFCI from my washer outlet and replaced it with a standard receptacle for this reason.... :noway::noway::noway::noway::noway::noway:

I did however lay down several layers of roofing rubber underneath and around the washer and then put a carpet runner overtop. If I had kids, I wouldn't being doing crap like that.
 
P

Peat

Scary shit, Pontiac!
Glad you're ok! :yes:

FWIW, I dont trust fan controllers or GFCI. :confused:

...or society...:nanana:
 
pontiac

pontiac

Pass That S**t!
Veteran
madpenguin said:
Incorrect. The potential to ground has to be there otherwise you would have never have gotten shocked in the first place, and your GFCI certainly wouldn't have tripped.
Click to expand...

Whoops, meant to say grounding within the circuit isn't needed (ex. a toaster). Yea of course some form of ground connection is needed for the gfci to activate (me being the bridge in this case, like you said), otherwise there would be no imbalance between hot and cold for it to trip.
 
imnotcrazy

imnotcrazy

There is ALWAYS meaning to my madness ®
Veteran
A Variac is NOT the appropriate method to control inline fan speed. Yes, a variac does regulate output voltage but, varying a motor's voltage will only cause it to lose torque and Current will increase in an attempt to remain at full load speed. Any speed control you achieve by using a variac is only due to the motor not being able to properly drive the load IE: overloaded.

You NEED to use a solid-state (diac-triac) type of fan speed controller. These type of controls Do vary the voltage as well but in a completely different manner; which can be compared to you having the fan connected to a switch and you flip the switch on and off in rapid, equally timed succession. This allows the motor to "see" a lower applied RMS voltage while at the same time limiting current by removing the source voltage between cycles.

Now that that has been said:

Pontiac, was this the first time you had used this Variac? It's quite possible @ a low voltage the motor pulled excessive current causing a short circuit condition in the variac, regardless of fuse condition. The GFCI may have reacted to the Ground Fault faster than the Variac's fuse....
 
Che

Che

Active member
Veteran
Glad to hear you got it worked out Pontiac.

IMO KISS and use the right tool for the right job. I use a Canadian made "Can-Arm" fan speed control, and it was only $30. Works great and no risk of fire!
 
pontiac

pontiac

Pass That S**t!
Veteran
imnotcrazy said:
Pontiac, was this the first time you had used this Variac? It's quite possible @ a low voltage the motor pulled excessive current causing a short circuit condition in the variac, regardless of fuse condition. The GFCI may have reacted to the Ground Fault faster than the Variac's fuse....
Click to expand...

No, I've been using this Variac for quite a while now, as well as many other ICmag members; some for many years now.

This was definitely a defective Variac. If it was overload from the fan overdrawing current, the tiny 5 amp fuse would've fried in seconds.

Instead, I think a capacitor connection must've came lose and contacted the metal housing. That, along with the high probability of faulty internal grounding must've been the cause of the electric shock. If the chinese manufacturers didn't fuck up the internal grounding, any one of the inline circuit breakers, fuse, or GFCI would've instantly tripped. Instead, like madpenguin said, I became a bridge to ground when I touched the housing, and the GFCI tripped a lot quicker than any fuse/circuit breaker, ultimately saving my ass.

In conclusion, I'm just happy it's over with. I don't want to see that piece of crap again, and I'm hoping to get a full refund for it.
 
imnotcrazy

imnotcrazy

There is ALWAYS meaning to my madness ®
Veteran
FYI: A spinning motor when disconnected from a load becomes a generator....

And if the capacitor connection came lose, the motor would not start. The capacitor is what creates the spinning field. With the capacitor out of the circuit, the fan motor would only oscillate back and forth not make full rotations

Lastly, if as you say that the Variac was a "cheap, made in China" model, I wouldn't rely on the UL listing (if any is marked) is a legit one. Who knows if the (more than likely cheap) insulation they used for the Variac windings can even handle the kind of current they fused that particular unit for. Think, my fan pulls 0.7A @ 115Vac. Rated 87W reduce the Voltage by half the fan still requires 87W to drive the load. Like I said the speed reduction you see is due to loss of motor torque, therefore the fan spins slower. Just by reducing the voltage causes the first increase in current, but a motor will continue to pull more current trying to regain full speed as well as a loss in motor cooling by the fan running slower. The solid-state speed controls avoid these situations by removing the high current by completely removing the voltage supply every cycle (60Hz) the fan is still spinning and this time allows the motor windings to cool inbetween cycles moreson than the Variac type control.

It even states on the sides of the fans ( I have Fantechs) that they should be used with the KB Electronics Solid State units I provided the link for.

"Many of the cheaper variable transformers available today are made in China. There's nothing wrong with them, except that they generally have a fuse fitted - in series with the mains input. When set to a low voltage (say 20V or so), the input current is only a fraction of the output current, so it's very easy to overload them, burning windings and the brush. "

"Power delivered to non-temperature-controlled soldering irons can be varied, as can anything else within the variac's ratings. This includes BRUSH motors as used in power tools, vacuum cleaners and the like. While induction motors can also be used with a Variac, THIS IS NOT RECOMMENDED - it is easy to burn out the motor (and/or the Variac) if you don't know what you are doing." http://sound.westhost.com/articles/variac.htm

I can provide engineering refs for you to back my side if you'd like
 
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petemoss

petemoss

Active member
Aw shit! I've got the same variac. Not hooked up yet, just tested it briefly. Hope I have better luck with mine. Thanks for the warning, pontiac!
 
C

clide

Member
imnotcrazy said:
It even states on the sides of the fans ( I have Fantechs) that they should be used with the KB Electronics Solid State units I provided the link for.
Click to expand...

where is this link you refer to? im sure everyone would appreciate a safer way to slow down fans!
 
imnotcrazy

imnotcrazy

There is ALWAYS meaning to my madness ®
Veteran
The "Hum" Is caused by the Capacitor being "brought into and back out" of the circuit by the on-off cycling of the Diac-Triac control. The caps in these motors are designed to "Remove" themselves somewhat from the circuit via Impedance. You are hearing that hum similar to when you first turn on the fan w/ a switch because you are starting from a dead stop. The hum is the motor loading/unloading itself between Triac pulses.

Discobiscuit: Correct Variacs are good for Brush Type/Universal (AC/DC) Motors, Shaded Pole Motors NOT Induction Type Motors or Capacitor Start type motors.

The only TRUE way to properly Vary speed of an induction motor is via Frequency control, A motor's speed is directly proportional to the Frequency of voltage feeding it. But being the MFG of these fans specs the Solid State control I'd go that route..


EDIT: Wrote that first post twice, figures I forgot the link: http://www.kbelectronics.com/data_sheets/kbwc_data_sheet.pdf
 
S

stealthScrog

Member
well crap...I've heard good points from both sides, so that leaves me more confused. I think the only thing that will convince me one way of the other is to see a statement from a fan manufacturer (canfan, vortex, etc.) that recommends one or the other. Problem is, I can't find any statements. Hmmm...maybe I'll write them...
 
petemoss

petemoss

Active member
imnotcrazy said:
...

The only TRUE way to properly Vary speed of an induction motor is via Frequency control, A motor's speed is directly proportional to the Frequency of voltage feeding it. ... http://www.kbelectronics.com/data_sheets/kbwc_data_sheet.pdf
Click to expand...

I knew that...but forgot! Read about "variable frequency drives" many years ago and I mistakenly thought these variacs were the same. Thanks to imnotcrazy, we now know that variacs should not be used to speed control fans.
 
BesideHimself

BesideHimself

Member
Wow, glad everything turned out OK.

I dislike messin' with electricity - killed my grandpa, ever since I've been scared to death. Of death. Oh dear look who's stoned.
 
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