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Discussion Starter · #1 ·
I installed a 2.6A gable fan against the gable vent in my garage (the smallest I could acquire at Home depot).

It works great, except that it blows so hard that a lot of the hot air can't make it out of the gable vent itself. So I went and purchased a fan speed controller from a local electronic supply company, to slow it down some:

KBWC-15K -----------------------
The KBWC-15K is a Distributor packaged Solid State AC Motor Speed Fan Control. It is designed for mounting in a 2" X 4" electrical wall box. It operates from 115 VAC, 50/60 Hz and has a maximum rating of 5.0 Amps @ 40°C. The KBWC-15K provides infinitely variable speed motor control for Shaded Pole, Permanent Split Capacitor and Universal (AC/DC) motors. The variable speed motor control contains an on/off line switch, a high gain RFI noise suppression filter, a minimum speed trimpot and a flame retardant ABS enclosure. Applications include range hoods, vibrators, humidifiers, fireplace blowers, fans, laminar flow hoods, heat tunnels and stirrers.
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There's a hum coming out of the motor now, and since I'd heard that light dimmers can burn out a fan motor, I disabled the electricity to the fan, in case I was accidentally given the wrong controller. Also, in looking through the fan manufacturer's documentation, it says not to use a solid state speed controller, which is exactly what this is, but it's description looks like it's meant for this particular application.

Could someone shed some light on this situation? Should I just let it run at full blast and remove this controller, rather than risk the motor?

Thanks,
--=Chuck
 

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I



1 - There's a hum coming out of the motor now,


2 - I'd heard that light dimmers can burn out a fan motor,


3 - Could someone shed some light on this situation? Should I just let it run at full blast and remove this controller, rather than risk the motor?

Thanks,
--=Chuck
1 - Quite normal,
it is a by-product of the electronic speed control method.
some motors and controlers do it more than others,
but all will do it to some extent.

2 - Only the wrong type of dimmers will burn out motors,
IE - using a light dimer instead of the proper motor speed controler.

3 - If it is the correct type of controler it will not burn out your motor,
it will just be a bit noisier.
 

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Discussion Starter · #4 ·
Sorry if it sounded like the motor wasn't working. Everything is working, there's just a significant hum. That, and the fan manual says not to use a "solid state speed controller".

Here's something that I was thinking ... I'd read that one of the reasons why a dimmer switch is inadequate for a motor, (and I didn't understand the detailed electrical description), was that when you move the rotary dial from off to on, you start off with the dimmest light setting, with a continual turning of the dial causing the light to get brighter. (Although I sort of understood it's only an issue if connected to a fan, and it's started at a speed so low that the fan cannot turn.)

And so alternatively, the reason given for why a controller like the one I have is ok, is that in twisting the dial from off to on, you start off at the highest setting, and a continual turn of the dial decreases the fan speed.

If that's the reason why this controller is fine, then here's the problem ... this fan has a thermostat on it. So it only comes on when temps reach ~100F. That, plus the fact that I would have this controller set to about half the fan speed, means that the fan would continually accept less than the maximum current. Since this fan will always be kicking on at at least half-speed, I don't know if it's an issue.

--=Chuck
 

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Discussion Starter · #6 ·
I asked the owner of the electrical supply company for something to regulate the speed of the fan, and this is what they gave me. Then, after installation I noticed the hum, and became suspicious about the solution.
--=cf
 

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Discussion Starter · #7 ·
I guess I'm also curious as to whether GAF (the makers of the fan) just decided to lump dimmer switches and electronic fan speed controls into the same category of banned controllers (both solid state speed controllers). Maybe like a CYA kind of thing, while in actuality the proper use of the latter is ok.

It sounds like the fan speed controller I have (http://www.kbelectronics.com/kbsearch/descriptions/popup_kbwc_15k.htm) is probably fine. Maybe the remaining issue I want to confirm is whether the fan can be turned on at half speed (when the thermostat triggers it), without any harm to the motor.

--=Chuck
 

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I'd remove the speed controller.

Then I would look at my air inlet vents for that garage. If you are not pulling enough fresh air in, that fan cannot eject the heated air.

In the worse case of a fairly tight garage, the fan would actually be overspeeding due to reduced air pressure in the fan vicinity.
 

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Discussion Starter · #9 ·
I called GAF today, and although they didn't address the "solid state" issue, the person I spoke with did say that the fan expects a certain amount of wind velocity, as it uses it to cool the motor. He claimed that by throttling it back, you would burn out the motor because our heat build-up.

I don't know if I buy that or not, because he suggested finding shallower fan blades to pull in less air. That sounds like the same thing to me as throttling back the current setup. You'd still risk overheating the motor due to reduced airflow, right?

This has mostly just been my experimentation with making an existing, workable solution better. I'm just going to remove the speed controller, and go back to how things were.
 

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I installed a 2.6A gable fan against the gable vent in my garage (the smallest I could acquire at Home depot).

It works great, except that it blows so hard that a lot of the hot air can't make it out of the gable vent itself.

Thanks,
--=Chuck
Two suggesttions -
1 - Instal some more vents to allow more air to be vented ?

2 - Change the blades on the fan, to ones with less pitch
so they move less air.
 
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