My solution for a cheap air purifier - part 3
This part will describe the electronics for this 2nd air purifier.
I had a nice 24V fan lying around that would be perfect for this setup. It has a decent airflow but can also run very quiet at low speeds. It has a noticable airflow starting at around 6V and goes up to 24V full blast.
There is one problem, I don’t have a nice small 24V power supply. So as a fun little side project I decided to feed it off 5V supply and make a little boost circuit to drive it.
The circuit consists off an esp8266 that connects to my domotica MQTT server and allows you to remotely set the fan voltage, as secondary function it takes care of the control feedback loop for the boost converter.
It is currently designed so you can set the output between 7 and 30V. I will limit this when sending setpoint as it can push the input current easily over 3 amps with high spikes.
I constructed it from random parts I had lying around on my desk. So don’t put to much trust into the values, I just fiddled with it until it worked good enough (tm).
I still need to get a good diode for the schematic (as seen below), but my hack worked for now. I also used 4 20MOhm resistors to get my 5 MOhm, as that was what I had lying on my desk.
This is the test version:
A quick pcb:
And put together:
This will all fit together together with the particle sensors via node-red.
As always after finishing it some small issues popped up:
- I noticed on my Delta power supply that it spikes above 5Amps while pulling 3A average. It would actualy trigger the current limiter. I think I should add some input capacitors and inrush limiter. I forgot this, but easily to add.
- On full blast, the large amount of air pulled through makes a lot of unneeded noise. i will probably design another lid with bigger holes.