I was absolutely flabbergasted that multi-tap would be a solution in a modern high end appliance; For work I do a lot of DC/DC, and a bit of AC/DC DC/AC… and I was blindsided that AC/AC is so different. I’m in the EE generation where transistors are fast and amplifiers start at class D!
Scale-wise, this started as a one-off project adapting existing equipment for a research project - I needed to remotely activate the fans in an existing product as small part of a larger system. No need to make it productizable, purely research at this phase. I thought I’d be able to buy an off the shelf home automation solution (don’t reinvent the wheel when the wheel store has 2 day shipping), but I’ve been surprised how disappointing that search has been.
The difference in audio is overwhelming - driving it with the multitap transformer + relay array that it came with is effectively silent below 70% power, but using an SCR dimmer makes an annoying loud buzz at any power level. Or to put it in market pressure terms, I would have gladly paid 80$ more for a solution that didn’t add this noise… and I’m much less spendy than a typical home automation nerd.
I wound up just hacking in on the low voltage digital side instead. It isn’t as portable a solution and required a few hours of unexpected firmware work / reverse engineering, but it works good enough for the project requirements.
If I had more time on my hands and a good high-frequency hard switching solution I’d go ahead and productize it myself for those spendy home automation nerds.
I agree that ECM is the way to go when possible - the brushless fans in other parts of this project are beautiful. Not possible for this sort of retrofit.
@Bikkel - Interesting approach! It sounds really similar to a 3speed / 4 speed fan, which is essentially just turning the motor winding into a multi tap transformer… ish.