source for 25-30V AC Fan - Page 1
Forum section: electronics / projects

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 09, 2016, 06:43:49 pm
content: Does anyone know of a source for 25-30VAC fans? The original fan for my application has been discontinued by it's manufacturer. Specs were: 26VAC 50hz 10w 550mA / 26VAC 60hz 8W 450mA, 3-1/8" x 3-1/8" x 1-1/2"I'd like something of the approximate same size.Any suggestions? My google-fu isn't coming up with anything.Surplus/cheap would be ideal so I'm fine adding more discontinued items to my eBay search terms.Thanls!

author: Gyro
author_rank: Super Contributor
timestamp: December 10, 2016, 10:10:55 am
content: You might be as well looking for a DC fan and using a bridge rectifier. I'm not sure if you could get away without a smoothing capacitor or not (it might hum or have reduced power without one). The other alternative would be to fit a mains AC fan instead (depending on your application and any safety issues). For anything other than mains voltage, DC brushless fans dominate these days.Other than that, surplus probablyisyour only chance of finding one.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 10, 2016, 03:38:49 pm
content: Just use a decent quality 80mm 12V fan along with a rectifier and buck converter.

author: amyk
author_rank: Super Contributor
timestamp: December 10, 2016, 05:34:59 pm
content: 26VAC? Avionics?

author: SeanB
author_rank: Super Contributor
timestamp: December 10, 2016, 06:40:12 pm
content: Not avionics, no 400Hz rating. You probably will be better off with a 24VDC fan, a bridge rectifier and a step down converter from 36VDC to 24VDC, and use a ball bearing fan, good quality converter electrolytics and a small board to hold this lot. Otherwise a 48VDC fan and undervolt it, most will run on 36VDC with reduced air handling capacity.With a 24VDC fan you can even use a linear regulator to power it, you probably only have to dissipate 4W or so, and that can be done with a smallish heatsink, especially as you will have a convenient way to get airflow across it for better than convection cooling.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: December 10, 2016, 07:12:15 pm
content: Quote from: SeanB on December 10, 2016, 06:40:12 pmthank you EVERYONE for taking the time to reply. much appreciated. I will go with what you suggest. Cheers and Happy Holidays.

author: mariush
author_rank: Super Contributor
timestamp: December 10, 2016, 07:35:57 pm
content: Bridge rectifier > capacitor > linear regulator to 24v25v ac - > bridge rectifier - > DC voltage wiht peak equal to : 25v x 1.414 - 2 x 0.7v (voltage drop on diode inside bridge rectifier) = ~ 34v DC.Linear regulators need about 1-2v about the output voltage to output a stable voltage but after all you're going to use the output for a fan which will work with anything between 12v and 24v without worries. If the input voltage is smaller than what the regulator needs, most regulators would still work but just output slightly less voltage. You don't have to worry about minimum voltages, but you do need to worry about maximum voltages, as a 24v DC fan won't like more than around 28v DC.So anyway, you need to make sure you have at least around 26v DC , and that's where a capacitor comes in play... C = current / ([2 x mains frequency x ( Vdc peak - Vdc min) ]If we work with 0.5A of current and 24v (12 watts max) you have C = 0.5 / 100 * ( 34- 26) = 0.5 / 800 = 0.000625 Farads or 626uF. So go with maybe 680uF 50v or 820uF 50v and you're good to go. Don't go overboard as that means you'll only keep the minimum voltage much higher than required, and that means the difference down to 24v would have to be dissipated as heat by the linear regulator.Now you can just use a 7824 linear regulator or any other linear regulator that can work with input voltages higher than 30v or so.Ex of fixed 24v voltage regulatorsL7824CV works with up to 40v :http://uk.farnell.com/stmicroelectronics/l7824cv/ic-v-reg-24v-7824-to-220-3/dp/9756213L78S24CVhttp://uk.farnell.com/stmicroelectronics/l78s24cv/ic-v-reg-24v-78s24-to-220-3/dp/9756221MC7824CTG :http://uk.farnell.com/on-semiconductor/mc7824ctg/ic-v-reg-24v-7824-to-220-3/dp/9666257TS7824CZ:http://uk.farnell.com/taiwan-semiconductor/ts7824cz/ic-v-reg-24v-7824-to-220-3/dp/7174071and lots of adjustable linear regulators can accept up to 60v DC. They're equally simple to use, just have to use a couple of resistors to configure their output to 24v.

author: Zero999
author_rank: Super Contributor
timestamp: December 10, 2016, 11:55:35 pm
content: Another option is a 230VAC mains fan and a 24VAC mains transformer wired in reverse.

author: SeanB
author_rank: Super Contributor
timestamp: December 11, 2016, 06:28:14 am
content: Quote from: Hero999 on December 10, 2016, 11:55:35 pmIf you have 26VAC there likely is already a mains transformer there, so just use the taps on that to give 115VAC or 230VAC for a regular mains fan.