non PWM fan with PWM signal (3D Printing) - Page 1
Forum section: electronics / beginners

author: MyHeadHz
author_rank: Regular Contributor
timestamp: February 21, 2018, 06:13:36 pm
content: So I have a PWM signal that I want to use to control a fan that that doesn't have PWM support. The fan and supply are 12v and otherwise compatible.So I read around where people suggest using a small cap (16v 220uf or so) to smooth the signal to make it work. It's for a 3D printer, so once the print is started I would have to go through lots of menus to change it while printing. So, is there another way? I was thinking about setting the PWM to 255 (which is max, always 12v) and then just using a pot to have a manual control for it on the printer itself. Would that work?

author: ogden
author_rank: Super Contributor
timestamp: February 21, 2018, 06:30:38 pm
content: Quote from: MyHeadHz on February 21, 2018, 06:13:36 pmIt could work indeed, just control curve can change.QuoteExactly. Why don't you just buy proper fan which is supported by your 3D printer?

author: jasonbrent
author_rank: Regular Contributor
timestamp: February 22, 2018, 01:43:33 am
content: If you are referring to the 5015 blower fans, good luck. I went through 8 different brands before finding one that worked even reasonably well. And people who say theirs are working must be folk who cannot hear the PWM whine.The problem is there does not appear to be a proper 5015 sized PWM controlled fan on the market....A capacitor works, but you'll find that the range of control you have is decreased. For example, if 0 represented off, and 100 represented fully on, after adding the cap you may find that your working range is 15-60 with <15 being off, and >=60 being fully on.I think the real solution is to not use blower fans and come up with another reasonable fan that provides the cooling necessary.The answer of "buy proper fan which is supported by your 3d printer" is missing the mark.-j

author: ogden
author_rank: Super Contributor
timestamp: February 22, 2018, 06:33:05 am
content: Quote from: jasonbrent on February 22, 2018, 01:43:33 amRight. So answer "I think the real solution is to not use blower fans and come up with another reasonable fan" does not mean more or less the same

author: jasonbrent
author_rank: Regular Contributor
timestamp: February 22, 2018, 06:51:18 am
content: Quote from: ogden on February 22, 2018, 06:33:05 amYou miss the implied point of "this isn't a problem of a fan properly supported by a 3D printer".</shrug>-j

author: Ian.M
author_rank: Super Contributor
timestamp: February 22, 2018, 08:05:29 am
content: If its a PWMsignal, you'll need to use it to drive the gate of a MOSFET feeding a choke then a reservoir capacitor, with a Schotty catch diode from the opposite rail to the MOSFET drain so it acts as a PWM controlled buck converter to vary the fan supply voltage.If its a PWM controlledpower outputthe MOSFET and catch diode are probably already present so you'll just need the choke and capacitor. To select suitable parts you'll need to know the fan's full power load current and the PWM frequency.If the fan has tacho feedeback to the controller, it gets a bit more complex, as that means the buck circuit must be in the positive supply to retain the ground reference for the tacho signal, so it may need a level shifter between the PWM and the MOSFET.,

author: jasonbrent
author_rank: Regular Contributor
timestamp: February 22, 2018, 12:41:15 pm
content: Quote from: Ian.M on February 22, 2018, 08:05:29 amIan, good information. In many-to-most of these 3d printers, the fans are simple 2 wire hookups using arduino for sending a pwm signal to the pins (12 volt is more common than 24 volt).Some simple fans handle partial duty cycle voltages better than others. The common 3d printing slicers (takes an object model and converts it into "gcode" to drive the printer and accessories) include an option to kickstart fans by sending 100% duty cycle for a few moments to get them spinning before switching to partial duty cycle signals.A common modification for the Creality CR-10 (which is good bang for the buck fwiw) is to change the stock 40mm material cooling fan with a 3d printed "fang" to direct airflow to both sides of the material as it is printed using a 5015 blower fan.A quick hack that has been used is tossing a small cap across the fan leads to act as a simple noise filter to turn a partial duty cycle square into something closer to a constant voltage... the fans like that a little more.Mosfets for the outputs on these printer control boards only seem to be common on the bed heaters.-j