Speed controller or Variac?

Slim Pickens

Slim Pickens

I Blue my mind.
I have a 6" Vortex fan and a speed controller.It bothers me a bit that when operating the fan through the speed controller I notice a distinct hum.The hum seems more pronounced as the speed is dialed down to slower cfm's.Maybe it's because at higher speed,the noise of the fan covers most of the hum.

Anyway,I have heard mention of Variacs over the last few years,and wonder if that might be a safer solution?My problem is that I am unsure of what to buy,as there are different configurations.I see some that are 500w which would be more than adequate for a fan drawing 72 watts,but on the other hand they are only rated to 6amps or so,and the fan specs say 6.68 amps. Here is a link to some of the Variac offerings on Ebay,if anyone cares to look.

https://www.ebay.com/sch/i.html?_fr...2.A0.H1.Xvariac.TRS1&_nkw=variac&_sacat=92074

I am at a loss as to what to consider...if anything.
 
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I'm not an electrician, but a 72 watt fan that draws 6.68 amps doesn't make sense. Are you sure it's not 0.668 amps?

My old 1k HPSs drew 9.4 amps...

Any sparkies in the house?
 
Wouldn't that do the same thing to the fan? Since it's the fan humming I doubt it would change anything but I'm also not an electrician and never stayed at a Holiday inn express.

I have the same fan I believe and have tried a fan rheostat made for the inlines and a rheostat I use on my routers. Both left that hum so I went back to wide open.
 
Annaba said:
Keep in mind the blower an filter should be matched...too big a blower an you're not gettin proper filtration, too small a blower an the filter could put unnecessary strain on the blower, an less than adequate circulation...same goes with alterin the speed. :2c:
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Just tryin to keep the racket down and the cabinet from imploding from all the air trying to get pulled out. :)

Dandaweedman said:
Wouldn't that do the same thing to the fan? Since it's the fan humming I doubt it would change anything but I'm also not an electrician and never stayed at a Holiday inn express.

I have the same fan I believe and have tried a fan rheostat made for the inlines and a rheostat I use on my routers. Both left that hum so I went back to wide open.
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That is the reason I was looking at a Variac.Supposedly no hum.

Bush Dr said:
Sparky is up and about now but I think he's taking Wesson to the vets, so doubtless he'll chime in when he's back at the keyboard
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:)

180 said:
I'm not an electrician, but a 72 watt fan that draws 6.68 amps doesn't make sense. Are you sure it's not 0.668 amps?

My old 1k HPSs drew 9.4 amps...

Any sparkies in the house?
Click to expand...

This is the exactly what caught me off guard 180,but it says 6.68 amps in the listing specs.Maybe I had another senior moment,as that sure sounds off.I don't do enough of this to even raise to the level of dunce.Hence the questions.
 
Ok.So,I should have checked the manufacturer instead of relying on a listing's specs..Specially when it sounded so off to begin with.

180 was right,it is .68 amps.

Don't I feel stoopid.:salut:

Selecting a Variac should be a bunch easier based on the correct info.

I don't know much about 'lectrics.Could I just buy one of the small Variacs as this would be only for the fan?Maybe a 500w 1amp unit? (or thereabouts?)

I messaged the ebay seller to inform them of their error,and save some other poor schmuck some embarrassment. lol
 
Ah, good, I wondered.

Slim, how big is your cabinet, and what kind of light(s) are you running? A 6" Vortex is big enough to cool a 1k lamp. If you're running less wattage, you might get by with a 4" fan. Of course, if you can get a speed controller that satisfies you, that will also work.
 
Slim Pickens said:
Just tryin to keep the racket down and the cabinet from imploding from all the air trying to get pulled out. :).
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Sounds like you need a bigger intake if you're sucking it flat. (I remember her :prop:)

I would build a 16" x16" intake box that would hold a AC air filter to keep down the lint and dust flowing through. It would allow better air circulation and also combat mold.
 
180 said:
Ah, good, I wondered.

Slim, how big is your cabinet, and what kind of light(s) are you running? A 6" Vortex is big enough to cool a 1k lamp. If you're running less wattage, you might get by with a 4" fan. Of course, if you can get a speed controller that satisfies you, that will also work.
Click to expand...

180..I'm going to build a 4'x4' cab with a 600w (Although I like the idea of a 6'x6' that Tevye has).I will be doing some autos for a trial and may run a T5 in it for those.We'll see.I was going to run a 4" fan,but then I got a hair-brained idea.Not going to say what that idea is cause it is...hair-brained. :) If I can determine what size variac to buy,I think I'll do that.Maybe that hum would not harm anything,but I'd feel better if I could resolve it.

Staind said:
Sounds like you need a bigger intake if you're sucking it flat. (I remember her :prop:)

I would build a 16" x16" intake box that would hold a AC air filter to keep down the lint and dust flowing through. It would allow better air circulation and also combat mold.
Click to expand...

Right on Staind.I'll not build a box,but I will do a rudimentary frame for a filter.

Rudimentary.It'a a way of life for some of us.Lol
 
A Variac is a variable transformer, while a motor controller is typically a variable frequency drive.

I would use a VFD for a motor, as low voltage can burn a motor up.
 
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Graywolf said:
A Variac is a variable transformer, while a motor controller is typically a variable frequency drive.

I would use a VFD for a motor, as low voltage can burn a motor up.
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I didn't know that.

Not sure what to do then.I don't want to have to worry about my fan burnin up,and the hum from the fan running with a speed controller concerns me as well.

I'm getting a headache. :confused:
 
I probably shouldn't stress it..or mayhaps I could increase the size of the cabinet instead.I've actually been thinking about that possibility.

Or I could secure a smaller squirrel cage fan...or I could simply do outdoor.

I need a hobby.Maybe worryin about fan size is it? :D
 
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Annaba said:
You said in your first post your current equipment only makes the noise you're tryin eliminate with the dimmer connected...an hums louder the more it's turned down...so jus eliminate the dimmer altogether...again, your blower an filter should be matched, so if you're havin pressure issues, address that, an not the speed of the blower. You want negative pressure on the area you're usin it in. I use 6" filter/blower combos on a 4' x 6' closet, an a 2' x 6' closets, an both are optimal, IMO. There are many ways the actual airflow can be altered...the size of your intake vent, every bend in your ductin...the cleanliness of you filter an outer wrap...all these things effect how much air is actually bein circulated, but I would strongly recommend keepin your blower an filter matched, an leavin your blower on full power.

If you're experiencin too much negative pressure, simply enlarge the size of your intake vent.
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Good point on leaving the motor at full speed!

Air flow is easily controlled by throttling the intake. Unlike throttling the discharge, throttling the intake reduces motor load, because there is less air density.
 
I had looked at a squirrel cage fan years ago,but there was a disclaimer the manufacturer included that stated something to the effect of "do not restrict airflow".That has always stuck in my mind,and is why I was reluctant to do that.Now,if that wouldn't negatively effect the fan,that would be acceptable to me.Might not effect the noise of the fan...but I guess I can try it and see.

Thanks.
 
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