Untangling the Electronics in a PC Fan Air Purifier
Building a Corsi-Rosenthal box using PC fans isn’t hard, but many people are intimidated by the electronic components. Fear no more! Read this and you should be able to source and put together the electronics for any PC fan air purifier you want to build.
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At its core, an air purifier is made up of a
1) Frame
2) Filters
3) Fans
4) Electronics
The original Corsi-Rosenthal box uses filters and duct tape to make the frame, and a single fan that plugs into the wall. Nothing complex there!
The electronics in a PC fan Corsi-Rosenthal box aren’t complicated either, but there are choices as to the type of adapters or connectors used. These choices have all been explained in threads on Twitter, but who can find them? Let’s dig in.
At its simplest, all you are doing is connecting the PC fans to a power source. It is just a matter of choosing the proper cabling and connecting devices and power supply.
Let’s talk connectors!
Fans have a 3 / 4 pin connector, also called a PWM connector. That connector plugs into either 1) a cable coming off another fan 2) a fan splitter cable or 3) a fan hub. The fan cable, splitter cable or fan hub then plugs into either an adapter which plugs into a power supply, or directly into the power supply.
Below is a picture of a 3 / 4 pin PWM fan connector that you will find on each fan. Note the ridges that form a channel. When plugging this into an adapter or hub, this channel forces you to plug in the connector in the correct orientation.
This is a power supply connector, sometimes called a barrel connector. This round connector can come in different sizes, but you will want 5.5x2.1mm.
How do you plug a 3 / 4 pin PWM connector into a round power supply connector? With an adapter that has a 3 / 4 pin PWM connector on one end and a 5.5x2.1 power supply connector on the other end.
If you are only connecting one fan to a power supply, that is it!
PC purifiers, though, may have anywhere from 2 to 10 fans. If you are connecting 2, 3, 4 or even 5 fans, instead of the single fan adapter pictured above, you can buy a fan splitter cable. You can buy one that has 3 / 4 pin PWM connections on each end and then use an adapter to connect to a power supply — or you can buy a fan splitter cable that has the 5.5x2.1 power supply barrel connector already, pictured below. Plug each fan into the splitter cable and plug the barrel adapter into the power supply. You are done!
Instead of a fan splitter cable, you can use a PC fan hub. Simply plug each fan into the hub and plug the hub into an adapter cable which plugs into the power supply. Since this requires two components instead of one as in the prior example, this is likely more costly.
You want to connect more than 5 fans? There are multiple ways to do that. You could buy a fan hub that handles, say, 10 fans, plug the fans into it and use an adapter to connect it to the power supply. You will want one that uses a 4-pin male molex connector. The adapter will be 4 pin female molex to 5.5x2.1 power supply barrel connector.
Or, you could connect one fan hub to another fan hub and connect the fans to the hubs. PC fans are low power, so doing this should not cause problems.
Or, instead of connecting two hubs, you could connect a 4-fan splitter cable to a fan hub, allowing you to have 8 fans.
These components are all lightweight. Depending upon your purifier design you might want to tape them so cables are supported or do not end up in a fan. For my Topo Chico Box purifier, which has fans only on the top, I simply let the cables hang down.
Not every connector has to have a fan attached. It is perfectly fine to have a 4-fan splitter cable with only 2 fans connected. They run fine. A fan hub, similarly, doesn’t have to be full.
There is one more approach. Some people think this is simpler than the above approaches. If you buy Arctic fans that are designated PST (PWM Sharing Technology), your fans can be daisy chained together. Instead of buying a fan splitter cable or a fan hub, one fan plugs into another which plugs into the next. The last fan, then, needs to be plugged into an adapter to connect to the power supply, just like in our one fan example. PST fans are usually more expensive than non-PST fans, and the added expense is roughly what a splitter cable would cost. On US Amazon right now, a 5 pack of Arctic P14 PST fans is $40.99 vs $33.99 for non-PST.
Power Supply
The power supply needs to match the voltage of the fans and have enough amperage. Each fan draws approximately 0.1–0.15 amps (A), so if you are using less than 10 fans, a 2 A power supply should suffice. For a purifier you intend to plug in to the wall, get a 12-volt, 2 amp power supply (pictured many times above). I recommend you get a power supply that is UL approved, for safety reasons.
A 12-volt purifier can also run off a 5v USB port or USB battery pack if you buy a 5v to 12v upconverter, pictured below.
Some PC fans are 5 volts. For builds using 5v fans, buy either a 3 / 4 pin PWM to USB adapter, or a male 5.5x2.1 to USB adapter, and use a USB plug as your power supply.
On/Off switch
If you don’t intend your unit to run 24/7, you should consider adding an on/off switch. This switch connects to the power supply and, to me, is nicer than plugging and unplugging the power supply. The switches are inexpensive. I recommend the switch have UL component certification, as the linked switch does.
Conclusion
That’s all there is to it. You are now a PC fan electronics wizard. Links to all the items pictured are listed below. No go forth and build PC fan air purifiers — you can do it! If you want an example, you can see build information for my Topo Chico Box air purifier HERE, or HERE for several builds done by others.
Additional Commentary
3 / 4 Pin PWM connectors
There is a difference in capability between a 3 pin and a 4 pin PWM cable. Three pin cables do not have fan speed control, while 4 pin PWM cables do. This is irrelevant to building purifiers since 1) both have the same form factor, so fit in the same adapters, and 2) you want the fans to run at full speed for maximum air flow; since they are quiet, there is no reason to ever slow down the speed.
Electronics for fans which have LED lighting
LED fan lighting is cool but adds electronic complications. Lighting is 5v, will require additional cabling and adapters, and a device to control the lights. I have not done any builds with lights, due to the additional cost and complications. HERE is a build using fans with LED lights, for those interested.
Link to components (I do not receive affiliate commissions):
Fan Splitter cables:
4 fans: https://www.amazon.com/dp/B0BRHGVPQH?
2 or 3 fans: https://www.amazon.com/Power-Supply-4-Pin-Adapter-Splitter/dp/B01MAU7QD4
5 fans (have not used personally): https://www.amazon.com/GINTOOYUN-Splitter-Adapter-Extension-Security/dp/B09M81T6D4/
Fan Hubs and Adapters:
5 Fan hub: https://www.amazon.com/gp/product/B07M5P7VHG/
3 /4 pin PWM to 5.5x2.1 adapter: https://www.amazon.com/gp/product/B085S3Q7VH/
Above adapter is used for connecting PST fans to power supply or 5 fan hub to power supply
10 fan hub with 4 pin molex connector (have not used personally): https://www.amazon.com/Fancasee-Splitter-Internal-Motherboard-Extension/dp/B089KC3S5P/
4 pin molex (female) to 5.5x2.1 barrel jack to use with the 10 fan hub (also not used personally): https://www.amazon.com/RLECS-Female-Supply-5-5x2-1mm-Adapter/dp/B0823RFMHY/
Power:
Power Supply (12v, 2A, UL Listed): https://www.amazon.com/gp/product/B00GUT7FQ2
On/Off Switch with 5.5x2.1mm connector, UL Listed: https://www.amazon.com/dp/B07CB8TC39?psc=1
5v to 12v upconverter: https://www.amazon.com/dp/B07T6487LW
USB Adapter Cables for 5v applications (have not used personally):
5.5x2.1 to USB: https://www.amazon.com/Power-Yeworth-Connector-Charging-Adapter/dp/B07Q5PHHFK/
3 /4 pin pwm to USB: https://www.amazon.com/3-Pin-Sleeved-Adapter-Connector-USB-3Pin/dp/B07JW73KVR/
