Speed Control for AC Motor

Thread Starter

fastbike

Joined Dec 29, 2020
120
I've searched the forums for a design and not found a definitive answer, so here goes.

I have 3 extraction fans in my house that have shaded pole single phase 230VAC motors of around 60W (One is larger at 100W)

I will be using a Finder slave dimmer (Finder part 15.11.8.230.0400) that accepts a 0-10v control signal to set the output via phase chopping.
It can do leading edge and trailing edge dimming so I'm assuming there is a mosfet based circuit inside.
My home automation system will be providing the 0-10v signal.

My understanding is that I need to set the output to be leading edge for an inductive load. (Although it does have two settings for leadind edge, see below)
I really only need about 3 speeds so I'm thinking of designing the control circuit to give the fan a period (say 3 seconds) at full power to ensure it starts, and then throttle back to the selected level. A bit of trial and error to observer performance and check the motor is not over heating etc.

Does this look like a plan or have I overlooked something ?

* The two leading edge modes are:
B2 - Dimmable compact fluorescent lamps (CFL), dimmable LED lamps (Leading edge)
B3 - 12/24 V halogen lamps with toroidal electromagnetic transformer, 12/24 V halogen lamps with “E” core electromagnetic transformer (Leading edge)
I assume I use mode B3.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Do you really require something that sophisticated for a simple shaded pole motor?
Is it not possible to use a simple Triac based unit?
Where is the 0-10v signal coming from?
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
Do you really require something that sophisticated for a simple shaded pole motor?
Is it not possible to use a simple Triac based unit?
Where is the 0-10v signal coming from?
I'm looking to use something off the shelf for the handling of the 230V, so it is safety and EMI certified.
The 0-10v signal is from my own designed and built controller box. Both dimmer and controller box are DIN rail mounted in the switchboard.

The operation is triggered by a signalling switch in the bathroom. Signals are sent from the switch to the controller via CAN Bus protocol. Other switches control lights in a similar manner (that control bus is powered by a separate 24V dc supply)


So back to my question, for the operation of the fan, at the 3 speeds, will the device that I've selected do the job without burning out the motor etc ?
 

Thread Starter

fastbike

Joined Dec 29, 2020
120
It's unlikely to burn the motor as they are designed to run inefficiently but the chopped waveform switching will generate EMI and harmonics with leading or lagging conduction angle control on a largely inductive load.
https://www.testandmeasurementtips....iable-speed-drive-to-change-a-fans-speed-faq/
Thanks, I will read that link. Given the relationship between (equivalent) voltage and torque, I will experiment with the fan on the workbench. There will be slightly more air resistance (load seen by the motor) given that when installed the smaller ones have a 600mm straight duct, and the larger on has loner ducting with a few bends.
 
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