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Can I lower the CFM of an inline fan through use of a speed control?

ThePizzaMan

ThePizzaMan

Active member
Veteran
OK, So I was given a 749 CFM in-line fan from a friend, and if I can...I would like to use it in my homebox XL which is 5X5X7.

I am aware that I will have to purchase a new carbon filter, but I want to be able to properly match the fan speed with the carbon scrubber.

So is this as simple as lowering the speed control to half way, and purchasing a carbon scrubber rated for max 400 cfm?

PLease help!


Thnx

ThePizzaMan
 
A

ak-51

When I first purchased a 6" in-line fan (sunleaves brand) I was told by the hydro-shop guy that I could rig up a contraption out of a dimmer switch and an extension cord to control the speed of the fan.

I felt fairly confident doing that since I had rigged up a few electrical things, CFL lights and pc fans and such. I picked up a dimmer switch and plastic junction box on the way home. Once I got home I plugged in the fan and MAN, that thing seemed pretty loud, I would definatly need the speed controller. So I rigged it up and plugged the thing in, strange thing was that it made a loud and noticeable humming noise as soon as it was turned on, much different than the noise it made without the speed controller on there. It just didn't seem right.

I did a little bit of research and a few people advised against their use, stating that they would put more wear on the fan, quicker. One person who claimed to be an electrician warned against using such devices on AC motors. His warning was something along the lines of "they're not made to go different speeds, DC motors would hack it, but AC is not made for such things". He also stated that such devices would be much more likely to lead to failures, and in some cases even possibly start fires. That was enough for me to read, there was probably some differing opinions but I didn't need to bet on anything that could wear down or destroy my lovely new $200+ investment. I just decided to run the fan at full speed, not really that big of deal.

I eventually rigged up some sound insulation, I initially put some 8" duct over the 6" duct on either side of the fan for about 2 or 3 feet. A while after that I wrapped some old t-shirts between the 6 and 8 inch duct, and draped some t-shirts over the fan. The sound is not that big of deal now. I would really recommend figuring out some sound proofing over bringing down the fan speed. The hydro-shop guy was also under the impression that the speed controller would not cut down the amount of used electricity since it only added resistance. I am not an electrician and I did not do enough research to defiantly say one way or another, but a few nay-sayers were enough to make me err on the side of caution.

Maybe you could rig up an adjustable air intake between the carbon scrubber and the fan? Just putting the 8" duct over the 6" duct was a major improvement for me, if you had a couple feet between the scrubber and the fan, and another couple after the fan to put said double-ducting then that would probably make a big difference in noise.
 
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V

V1AAA

Member
i have used an inline with the same cfm rating in my tent

i used it to cool the 600 in there.

to quieten it down i used some acustic ducting and its silent as a mouse now. my fan was placed outside the tent.

i used a carbon filter matched to the full potential of my fan

i use it on a speed controller as well.

if you get a filter matched to the max power of your fan you can always re-use it if you upgrade your set-up
 
K

kali

Member
I've had my 2 8inch fans hooked up to a dimmer for the last 4 years, I love the control and have not had any problems.
 
!!!

!!!

Now in technicolor
Veteran
In my experience, speed controllers make the fans louder than it would be running at full speed. Normally the motor isn't loud. What you're hearing is the air rushing out of the fan. Insulated ducts and a box built around the fan will help with noise.

As for wearing the motor out, they do in theory, but in practice, apparently it hasn't been an issue - at least that's what the guy at my hydro shop said. He has been selling speed controllers for years despite his warnings to customers that it may wear out the motor. No customer has had any complaints, according to him.
 
D

DopeRoper

My 150 CFM 4" Fantech fan was overkill in the cabinet I just built. I plugged it into a Speedster controller and set it at half speed and it works great. There's still plenty of airflow for cooling, and the noise level is way down.
 
P

PharmaCan

Active member
Veteran
Not all dimmer switches are created equal. If you take a dimmer designed for a 100 watt light bulb and hook it up to a 400 watt fan, you're going to have problems. Makes sure that the dimmer switch you buy meets or exceeds the expected load requirements and you should be okay. If you go to a place like Home dePot, the heavier duty dimmers are often near the ceiling fans. Or you can get a fan speed controller like xcrispi suggested.

PC
 
T

THC_Decapitator

I agree with !!! speed controllers do not work to quit your fan . In fact the motor is louder with a speed controller .Use insulated ducting
 
V

V1AAA

Member
damn you guys in the states are lucky

over here that would cost $80 minimum

xcrispi said:
Yep ,
I always buy a bigger blower than I actually need n slow em down .
This way if I ever upgrade or move up to a larger enviroment - there's a better chance I won't have to buy more gear / larger blowers . Here's a link to a very affordable plug n play fan speed controller , just dial the blower down till the filters able to do it's job effectivly .
Crispi
http://www.plantlightinghydroponics.com/hydrofarm-variable-speed-fan-control-p-2263.html
Click to expand...
 
Hawk

Hawk

Member
Kcar said:
There are two sorts of speed controllers for fans. The "dimmer" style from the hardware store won't work correctly(loud screeching sounds).

The type you need is the "Speedster" type or similar.
http://www.horticulturesource.com/product_info.php?products_id=1665
Click to expand...

That "Speedster" makes plenty of screeching sounds with my 6" 440cfm EcoPlus fan.

Those types of controllers use low frequency pulse width modulation to control the fan speed. They basically supply power in pulses. The fan motor is either on or off but it happens so fast it's not like the fan is herky-jerky or anything. The fan rpm is variable and "smooth" by doing this switching. However, it can cause the electric motor's commutator to vibrate. The commutator is the device that momentarily reverses the current inside the motor. All that on/off switching can make commutators really wale. Mine was especially bad at certain fan speeds.

The kind of speed controller that should not create commutator noise is a Variac. They change fan speed by changing the voltage sent to the fan.

Bulky and pricey but this is the only type of fan speed controller I'd invest in....

sc3m.jpg



$0.02
 
xcrispi

xcrispi

Member
Hawk said:
That "Speedster" makes plenty of screeching sounds with my 6" 440cfm EcoPlus fan.

Those types of controllers use low frequency pulse width modulation to control the fan speed. They basically supply power in pulses. The fan motor is either on or off but it happens so fast it's not like the fan is herky-jerky or anything. The fan rpm is variable and "smooth" by doing this switching. However, it can cause the electric motor's commutator to vibrate. The commutator is the device that momentarily reverses the current inside the motor. All that on/off switching can make commutators really wale. Mine was especially bad at certain fan speeds.

The kind of speed controller that should not create commutator noise is a Variac. They change fan speed by changing the voltage sent to the fan.

Bulky and pricey but this is the only type of fan speed controller I'd invest in....

sc3m.jpg



$0.02
Click to expand...

Props ,
I learned something today .
And those gizmos / Variac aren't all that expensive either by the way - I found em for $45.00 .
Crispi
 
hoosierdaddy

hoosierdaddy

Active member
ICMag Donor
Veteran
There are two basic sorts of controllers that can normally be used, motor slip and pulse modulation.
A cheap motor slip controller will allow the motor to push out the same torque but at a lower speed, which translates into excess heat and lower lifespan due to this excess heat. Both the motor and the controller can suffer from this excess heat, and running a controller of this type down to around 50% or less of the motor's original RPM can cause failure.

The pulse modulation unit like described by Hawk is a far more efficient unit. Most will call these VFD's for short (variable frequency drive). These units allow the motor to run slower and at a lesser torque by supplying the energy in pulses, which allows the motor to function at a reduced speed and rate as it did at full speed and rate. There is little to no excess heat created using this method, and as a result the equipment will mechanically last longer, and at a lesser cost of energy.
 
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