Simple Fan Speed Controller

[richanton]

Here is my situation. I have a very small VFD(2hp) housed in a very large enclosure(standard Square D issue) next to a conference room. The enclosure has a muffin fan that is very loud. I want to reduce the speed of the cooling fan, since the drive enclosure is in an air conditioned room anyway. The fan is 120VAC and draws about 35 watts. I want to select a rheostat type controller that would allow me to drop the fan speed to the point where the noise is much less obtrusive.

I tried a controller I had laying around and it worked somewhat, but not very well. it only changes the speed by 15% or so. Is there a way to select a specific rating rheostat type controller that would be able to slow the fan down further, or is that more a function of the fan motor itself.

 

[OperaHouse]

31W is a big fan, I have one on my heat pump water heater. I have used a transformer to buck drop the voltage. That works a little better than a resistor at start and high slip. At high slip the operation can be a little unreliable.

 

[ScottyUK]

Some fan types are capable of operating with a crude phase angle controller. Typically external rotor types will be ok with this type of control. Does the fan have a type number or datasheet?

 

[richanton]

Here's a link to the fan I have, at least that's what they tell me, as the fan is hidden behind sheetmetal.

http://www.digikey.com/product-deta...2057686-VQ2-g-VQ6-40609412955-VQ15-1t1-VQ16-c

 

[smavo]

You could try a household light dimmer. I have used them before to slow down small motors.

 

[ScottyUK]

Capacitor motor, so keep away from phase angle control.

You can use a small autotransformer to reduce the voltage, or just replace it with a less powerful fan. You can almost certainly find one with the same diameter but reduced airflow, for example 5915PC-12T-B10-A00 has about half the airflow of the one you currently have and is the same frame size.

 

[richanton]

Replacing the fan may be the best option, but as I said, it's hidden, so I'll have to see if it can be easily accessed.

Thanks to all for the input.

 

[Skogsgurra]

Voltage control doesn't work very well unless you have a high-slip motor (the outrunners are high-slip and inside-out to be able to cool the rotor losses). So dimmer or transformer won't work very well. A fan with lower speed or a fan that can be voltage controlled is what you need.

I think that the air flow is generating most of the noise, so you can try to reduce it with a simple damper - preferably made from cloth/fabric bag that you put some cotton or other fibre into.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[MikeHalloran]

Just buy an interchangeable fan with a four-pole or six-pole motor. Using a fan that moves less air will reduce the heat transfer capacity of the box; you seem to be suggesting that's not an issue.

The two-pole fire siren muffin fans are usually bought by people looking for maximum airflow above all else. Said people don't have to sit next to the fans, ever.



Mike Halloran
Pembroke Pines, FL, USA

 

[jraef]

All that is fine, but understand that the fan was put in there for a REASON, to circulate air through the enclosure housing the VFD. If you slow it down, you reduce the air flow which means you INCREASE the heat in that box and you can potentially cook that VFD in its own juices in short order.

What people usually do in similar situations is to duct clean cool air into the box from a location where there is enough static pressure to ensure suitable air flow without a fan. So to accomplish that, you must calculate the minimum airflow required in that box for the worst case scenario of the VFD heat output. The safe bet if you do not know the heat rejection of the VFD is to assume 95% efficiency, meaning 5% of the kW going into the VFD will be rejected as heat into the box. Most are better than that, but none are better than 97% efficient (even the ones who claim 98% are usually spinning the truth). Once you know the heat rejection (including all OTHER devices in that box), you can get one of several on-line fan calculators to tell you how much airflow you will need at the ambient air temperature to maintain the maximum operating temperature of that drive (usually 40C) safely.

"Will work for (the memory of) salami"