How to convert 2-speed fan to variable speed and/or slow down the speed

[michael123123]

My under cabinet fan convector has a 2-speed fan, but I find the low speed setting still too noisy.

I'm capable of a bit of soldering and the like, so I was thinking about converting it to a variable speed, or keeping it as 2-speed and somehow reducing the speed of each setting.

I have attached a wiring guide for reference and would welcome any suggestions on how to go about this.

 

[Alec_t]

Whether or not you would be able to control speed as you want depends a lot on the type of fan motor. Is it a shade-pole type, or series wound, or tapped windings, or .... ?
Can you post a well-focussed pic of the motor and any of its ratings?

 

[michael123123]

Whether or not you would be able to control speed as you want depends a lot on the type of fan motor. Is it a shade-pole type, or series wound, or tapped windings, or .... ?
Can you post a well-focussed pic of the motor and any of its ratings?

Thanks for your reply, please find attached a photo of the front of the motor where the 3 wires connect, a rear view of the motor and a picture of the only other label/markings that I can see. The label reads:

Made by Ebmpapst
QLZ06/2400A79-3025L-1677 aes
240V AC 50Hz
25W I.CI.B
55411.20420
1200050
FA 2510016996

Edit: Found a spec sheet on rs-online for QLZ 06 series tangential blowers: https://docs.rs-online.com/7cd8/A700000006666868.pdf

 

[Alec_t]

That motor is a shaded-pole type. A suitably-rated fan speed-controller, widely available online or in store at a modest price, should do the job. But bear in mind reducing the speed will also reduce the fan's cooling ability.

 

[SUNRAY]

The following is what I have written elsewhere, bear in mind it was written specifically to address the origional forums comments:

Having worked in the controls industry since 2002 and dabbled with motors for a long time before that

I will say the only correct way that I’ve found to control shaded pole motor speed is by varying the frequency of the supply. Ignore the other person who said there are no single phase Variable Speed Drives, I’ve fitted dozens of them for small central heating pumps at 50W up to several KW.

The thing about shaded pole motors is they require their design power to work properly and reducing the speed by reducing the voltage has 2 distinct effects:

1/ the available torgue drops off very very rapidly to the point a 10% reduction of speed may easily remove it’s ability to start under any sort of load, including bathroom fans. Therefore it will require full voltage to start correctly.

2/ Running at the incorrect speed for the supply frequency will result in crazy back EMF levels and WILL result in higher current, to the point the motor WILL be running at a hotter, and very likely excessive, temperature with the resultant early failure. A number of times I’ve measured supply currents in excess of 5 time,s and even 10 times, the design current.

Resistive or triac dimmers MAY appear to do the job but caveat emptor.

I once demonstrated the effect with an extractor fan, slightly bigger than the average domestic bathroom fan and a resistor, as the series resistance went up, so did the motor current... affecting the power factor. This was a system installed by a rival company with several relays to add more resistors in parallel to progressively increase speed as the humidity increased. The fan ran 24/7 but repeatedly failed in well under a year (and fan supplier/manufacturer were refusing to keep honouring their 7 year warranty) whereas an identical fan elsewhere in the building ran at full speed 24/7 with no issues for years (as long as it was regularly cleaned). We replaced the botch with a VSD and gave a total 3 year guarantee, I believe we didn't get called in to honour it.

 

[michael123123]

Thanks for the replies, I've done some more reading now that I know what sort of motor I've got.

If I understand, the "correct" way is to vary the input frequency, but VSDs seem to be a bit more expensive than what I'm looking to spend. A look on rs-online yields these sorts of results.

Varying the voltage, with all its disadvantages, looks to be a bit more practical and also appears to offer the option of smart control via a Shelly dimmer. Then I'd be able to do something like blast it at full power when it's really cold in the morning and I'm still in bed, then throttle down to a quieter speed when I get up and start using the downstairs.

I would, however, need to ask advice on how to correctly wire the Shelly to the motor...