Repair USB fan - Page 1
Forum section: electronics / testgear

author: Faringdon
author_rank: Super Contributor
timestamp: June 14, 2024, 10:56:58 pm
content: Hi,We have USB fan for solder smoke blowing away, and also for cooling mosfets.But it stopped working.I presume they are all DC motors.....do you know of a good website where we can get the right size one. ie, a good choice, i presume there are only a few standard size profiles, so that repair is easily facilitated.https://direct.asda.com/george/electricals/heating-cooling/fans/4-inch-usb-desk-fan-black/051274283,default,pd.html?istCompanyId=2698bd23-149e-43d1-940b-8cc94f7ea571&istFeedId=b60a77e7-a5df-4f2d-94a2-25f028ca9fb7&istItemId=rlrttlirr&istBid=t&cmpid=ppc-_-geor-_--_--_--_-dskwid-s92700068826815688_dc&utm_campaign=pla:_Fashion_-_Catch_All&utm_source=bing&utm_medium=cpc&gclid=0c03ea38448c12f59c7c8c54852acbdc&gclsrc=3p.ds&ds_rl=1238816&ds_rl=1255529&ds_rl=1254418&msclkid=0c03ea38448c12f59c7c8c54852acbdc&utm_term=4578710081597046&utm_content=pla%3A%20Fashion%20-%20Catch%20All

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 14, 2024, 11:42:14 pm
content: The ones I have are actually brushless DC motors (BLDC) with a tiny driver board in the hub. Because of this, I'd personally replace the entire fan.I tend to use cheap computer case fans myself. The three-pin ones are voltage-controlled (nominal 12V; usable range varies from 4V-12.5V to 8.5V-12V depending on fan make and model), and the 4-pin ones use 12V power and 20-30kHz open-collector PWM for speed control but default to full speed when there is no control signal. I've outlined the control schemein this post.One of my own hobby projects is a DIY soldering fume hood from a 60-liter transparent plastic tub with one large side cut out, and an activated carbon filter + hepa filter in what used to be the bottom, and fans mounted on the other side to pull air through the filters, using cheapish known-good PC case fans. Quietness is a big factor, the fume hood -like structure means not that much airflow/pressure is needed. Also the walls allow easy mounting of additional lights. Using two 120x120x25mm 12V PWM PC case fans andthis ATtiny85 based controllerI can use a 12V wall wart and adjust their RPM using a potentiometer I can put on a lead (somewhere accessible). Note that these fans have tachometers (two open-collector low pulses per rotation), and that controller varies the PWM duty cycle based on the RPM, and not just based on the potentiometer.The one cheap USB desktop fan (~100mm, or 4") I ever had (red metal one from Verkkokauppa.com) was horribly loud. It did move much more air than typical PC case fans, but it was so loud I couldn't really use it – but I'm a bit sensitive to high whines (high RPMs), which is why I prefer the larger fans whenever I can. (They move more air, because the area is larger, at much smaller RPMs.)

author: Faringdon
author_rank: Super Contributor
timestamp: June 15, 2024, 01:28:59 pm
content: Thanks, most of the youtube teardowns of the USB fans show it as being a little DC motor....and a common problem seems to be the brushes coming away from the spindle...that would make sense for us...because sometimes you shake it and it starts working for a bit.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 15, 2024, 03:45:00 pm
content: Quote from: Faringdon on June 15, 2024, 01:28:59 pmIt could be something likethis(clockwise rotation; 32mm diameter, 25mm length), or a similar common toy DC motor, likeAdafruit 711, connected across the USB 5V supply. These all have a 2mm shaft, but the RPM, overall dimensions, and current draw does vary.Here in Finland, for example theGembird NF-03costs less than 8€ in a local shop. The one I had was similar to that but custom-branded and red, and so noisy I couldn't tolerate it and gave it away.The brushes in these are actually just springy leafs of some metal. Based on a number of toys I destroyed as a child, I'd suspect a bad solder joint instead, or rather broken wiring near to soldering point (due to thin wires fatiqued by vibrations).Have you considered tearing down a broken one to see exactly what kind of a motor it has?