On our most recent IoT Podcast, Dan called into our IoT voicemail hotline with a question about controlling the speed of a small personal fan using a smart outlet. Dan wants a Wi-Fi outlet with dimming capabilities so he can increase or decrease the air flow with a digital assistant.
On the surface, this sounds reasonable and logical. After all, there are outlets and switches that can dim lights by limiting the flow of energy to the bulbs. But variable speed fans are not bulbs. In fact, you could burn out the fan or, in a worst-case situation, cause a fire by trying to use some type of dimming mechanism to control the speed of a fan. So in short: don’t do this!
Powering a motor, such as that in a fan, requires a lot of electricity up front in order to get the motor up to speed quickly. And most motors with variable speeds use some sort of variable frequency drive; something a dimmer control isn’t capable of doing. Put another way: Unlike limiting the flow of power to dim a bulb, for a fan, you need to convert power into some mechanical or moving action that will typically require wide-variances of power immediately. It’s simply not the same as a bulb.
All is not lost, however! We did find a few Wi-Fi-enabled pedestal fans available on Amazon. This one from Nash (shown above) is $95, for example, and a similar-looking option by Wasserstein is available for $60. Both work with Amazon Alexa and Google Assistant, so along with an app, you can bring up the breezes by voice as well.
To hear Dan’s question, along with our discussion in full, tune in to the IoT Podcast below:
There are three main types of dimmers — trailing edge, leading edge and sine wave. Light bulbs want trailing edge dimmers. Motors and power supplies (ELV halogen) want leading edge. Sinewave is more expensive but it can handle both motors and light bulbs. The waveform in some dimmer is even programmable and they can be adjusted to make all three waveforms.
I would like to see the industry stop making TRIAC based dimmer and move over to MOSFET based sine wave. That’s because you can dim an LED bulb down all of the way with a sine wave dimmer and you can’t do that with a trailing edge dimmer. That is kind of non-intuitive since you can dim an incandescent or halogen bulb down all the way with a TRIAC dimmer. The reason it does not work on LED bulbs is because LED bulbs have electronic power supplies inside of them which can not be fully dimmed on a trailing edge dimmer – you need sine wave to fully dim them.
I wish I could just turn the fan on with the smart plug, since the turn on mechanism of my fan is by pressing a button, once you turn off the smart plug to turn on again you need to press the fan button again. Any idea?
The following is from the perspective of a manufacturer. Our current products (only available in Europe) won’t be able to handle the currents indeed. We use a combination of a relay and IGBTs. The IGBTs can carry 5A continuous and 10A max: https://octopart.com/stgd5nb120szt4-stmicroelectronics-342647. You won’t find much better in a DPAC package. The relay can handle much higher currents continuously, up to 16A. If you just multiply 5 with 240V AC (Europe) this corresponds to 1200 W that it would be able to handle. In practice this is much lower for reactive devices due to drawing much more power at start-up or generating high currents when being stopped.
The advantage of using IGBTs is that you can tune in software when on the phase of a sine wave you will turn on or off a particular device. Rather than in hardware (in electronics with a triac) a chip sits in the loop. It measures the voltage and current and takes action when certain thresholds are passed or it does some more signal processing to calculate zero-crossings as accurately as possible. This information is then used to switch at a particular phase.
Our firmware is open-source, read more on https://github.com/crownstone/bluenet/blob/master/docs/DIMMER.md. If you have particular questions on how this is done, feel free to ask.