lRemote DC voltage control question

Thread Starter

Fellow Traveller

Joined Oct 5, 2021

Brand new member here, I read the sticky posts and figured I would ask my simple variable DC voltage source question as I can't find a logical answer. I am trying to find a way to make or buy a wifi controlled DC voltage source or have some other remote method to control a DC voltage that takes a standard 12v DC input at fairly low current probably 400mA, so that I can lower the voltage of the 12v supply input down to as low as 6 or 7 volts in perhaps 1 volt increments.

I am trying to alter the speed (and noise) of 12v computer case fans that only have 3 wires (a red 12v positive DC input, a black ground DC wire and a tachometer signal output that I don't use) and when I use my variable output benchtop DC power supplies and rotate the potentiometer, the fan speed varies linearly from 3 volts up to 14v or so and so does the noise output so the fans aren't the issue, they work fine. I also tried using some wall-wart power adapters that were rated at 5v and 9v and I tried using a 12v supply with some 1N4001 diodes in series to drop the voltage down to 10.5 volts and that also worked fine, albeit at a fixed speed for each one.

So then I bought these variable DC PWM motor controllers based on the very cheap 1803BK chip and when I hook up my oscilloscope to the output, they do function to pulse-width-modulate the DC voltage down as I rotate the pot, but even when I put various size capacitors on the output, my case-fans won't vary in speed, so perhaps the 20KHz signal is too high or I need to use a large cap to filter the DC output and a small cap or two to filter the noisy output but either way, that variable speed option would only work to manually alter the speed if I put one of the controllers on each leg of the DC source feeding a fan or two and I'd have to walk to the basement and get on a step-ladder to adjust each one so hence I'd like a way to alter the DC voltage output of a 12 volt source by using my phone via wifi, or at least a semi-manual solution using a long piece of cable with a potentiometer on the end that I can run up into the back of a closet somewhere I can hide it.

Some history... I live in North Eastern Canada and installed a mini-split heat-pump in my basement last year and it worked fantastic all winter and summer for heating and cooling, i saved over $1200 on heating in the first year and my basement is dehumidified and much nicer. Last year I temporarily set up a couple 140mm computer case fans under the cold-air returns so they moved air from the main floor down to the basement so the air upstairs could get re-heated, and I also installed a timer on the blower motor of my forced-air oil-furnace so it runs in 15-minute intervals as I want to set it based on outside and inside temps (usually only run the furnace blower 15 minutes per hour except on coldest days). I have a wifi-enabled Google Nest thermostat on the main floor that controls the oil-furnace burner (only used when it gets REALLY cold) and I have a wifi enabled thermostat for my Lennox heat-pump in the basement (a new Mysa AC unit) and they work great so that I can control the heat-pump and furnace from anywhere in the world. What I would like to add is a way that I can speed up and slow down DC powered fans from my phone, or at least from upstairs in my house so we can have the least amount of noise and/or the most air movement depending on time/weather.

I haven't done much electronic engineering in probably 25 years and I have a pile of components so I could probably make a DAC (digital to analog converter) out of 7400 series logic chips and resistors and spend half a year of spare time making a board and soldering to get it working, I can even envision using a simple 555 timer in astable mode to do PWM control based on logic controls generated by an arduino or Pi which has a wifi interface that I can telnet to to alter the code, but I'd rather not have to learn to code those platforms yet... So there has to be a better way. ANY advice would be greatly appreciated and thanks for your patience reading all that.

I know that wifi-enabled potentiometers are a thing but then I need to use voltage-dividers and they are wasteful and limited in voltage range and current capacity. I know that I can probably use a couple of input voltages and a set of 4 or 5 wifi-controlled relays with normally-open and normally-closed contacts wired up so that when I enable one it adds voltage giving me 5v + 3v or something. But I can't think of a way that I can use an off the shelf or even a RaspberryPi or Arduino based system (which I dont have much experience with either) that can simply alter a 12 volt DC voltage source in a linear and controlled way. I saw that I can buy a cheap device like this that has a wifi module, but it seems way overkill to have a 4" LCD color display to adjust DC power and I dont need it to go to 60volts or that many amperes. This also looks like it might work for me, but again its way overkill and not WiFi but it looks cool

I also bought some very cheap thermostatic controlled DC relays, the model # is XH-W1209 but the short cable for the temp-probe and limited current rating of the small relay means I haven't bothered to program them to adjust the fan speed based on temperature difference between upstairs and down. I would also like to be able to quickly and conveniently adjust the fan speeds based on the amount of indirect feedback (verbal commotion that my wife and kid give me when they hear the fans running at too high of a speed), I already had to unplug one and put diodes on another but I need to get it working at a good volume (of air moved and volume of noise produced) before the cold season is here in a few weeks, ideally using an app or on a schedule so I can have it run higher when we are asleep or away, and quiet during the times we are at home with little ambient noise going on otherwise.

Thanks folks. And before anyone replies with "your question is really an HVAC question, go talk to an expert" or "you need a HVAC technician to balance your hot and cold air feeds, a fan is not gonna work" or "you should use a fan made for long-term use that is safe for heating systems", I get all of that, but I have no cold air ducting feeding my furnace, it picks up the warm air from the basement (heated by the wall mounted mini-split heat-pump), these fans will be pushing room temperature are and good computer case fans are rated for 50,000 hours and can push 70 cfm each and only produce 15dB of noise when running on reduced voltage. I even postulated about using 2 or 3 bathroom exhaust fans connected to a WiFi dimmer switch but they are noisier (even the expensive 1.5 or 2 sone models) and use way more electricity than computer DC fans do... The warm air coming out the furnace ducts on the main floor heats the house somewhat evenly but slowly and the ducts upstairs work much better when the cold air returns have fans pointing into the basement to help the cold air go back to get heated (heating a house like this has to be treated as a cycle, and even though very warm air in the basement rises, it isn't cycling enough to heat upstairs).

Coles notes version: I want to control a simple 12 volt DC fan supply voltage via WiFi or some smarter way than me running 50 feet of Cat5 cable to a potentiometer connected to a homemade PWM controller based on a 555 timer that I don't want to have to design, build and finish from scratch. This is almost 2022, someone certainly has controlled a simple DC voltage remotely before for cheap and easy?