Connecting 120mm AC fan directly to mains? - Page 1
Forum section: electronics / beginners

author: ksoviero
author_rank: Contributor
timestamp: January 30, 2021, 06:35:51 pm
content: While I have some experience with DC and BLDC fans/motors, I've never worked with AC fans before. Let's use this fan as an example:https://www.digikey.com/en/products/detail/sunon-fans/SP100A-1123XST-GN/1021235The fan says it's rated for 115VAC @ ~0.25A. Now, if I were to just connect the leads directly to the mains (in the US), what would stop it from turning into a small ball of molten copper? Does it have it's own impedance that causes it to only draw ~0.25A, or are you expected to provide the impedance externally?Thanks!

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 30, 2021, 06:42:49 pm
content: Don’t worry.If the nameplate indicates 115 VAC, you have absolutely no concern.The only minor concern would be if it is rated fo 60 Hz, and you plug it at 50 Hz.But I can’t recall anywhere in the world which is 115VAC @50 Hz.

author: Zero999
author_rank: Super Contributor
timestamp: January 30, 2021, 06:45:52 pm
content: What makes you think it's any different, just because the voltage is higher? It will work fine, drawing 0.25A from 115VAC. Insulate all the connections and connect the chassis to earth and it will be fine.

author: bdunham7
author_rank: Super Contributor
timestamp: January 30, 2021, 07:06:52 pm
content: Quote from: ksoviero on January 30, 2021, 06:35:51 pm"Impedance protected" refers to the fan itself, it has sufficient internal impedance at 60Hz 120VAC to prevent it from melting even if it malfunctions or the fan blade is obstructed. You can use it without providing a separate fuse for it.

author: Renate
author_rank: Super Contributor
timestamp: January 30, 2021, 07:16:31 pm
content: I use a 12 V 1 A BLDC to feed the furnace to my bathroom.12 Watts is a lot of blow.Your fan is over twice as big.Is that what you were expecting?

author: wizard69
author_rank: Super Contributor
timestamp: February 01, 2021, 12:27:51 am
content: If the fan is rated for 120 VAC then it can be connected directly to 120VAC. You have to do so in a way compliant with UL and NEC regulations but that isn't difficult.As for impedance, if a fan is impedance protected it means the unit is wired such that it can never draw excessive current and melt down. However(this is extremely important); not all 120 VAC fans are impedance protected. Fans that are not impedance protected will need external overload protection to prevent fires. Often this is simply a fuse. So it is very important to understand what sort of fan you have as supplemental protection will be required for fans NOT impedance protected.Quote from: ksoviero on January 30, 2021, 06:35:51 pm

author: tooki
author_rank: Super Contributor
timestamp: February 01, 2021, 04:57:24 pm
content: Quote from: schmitt trigger on January 30, 2021, 06:42:49 pmLots of Caribbean countries, plus a few others, are in the 120V "family" of voltages (110-127V in thewiki article), but at 50Hz. (Japan's 100V is also at 50Hz in half of the country.)As such, 120V AC fans (including the one OP linked to) are generally 50/60Hz.

author: TimFox
author_rank: Super Contributor
timestamp: February 01, 2021, 05:53:42 pm
content: And, many AC motors will turn slower at 50 Hz than at 60 Hz.

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2021, 06:55:18 pm
content: Quote from: ksoviero on January 30, 2021, 06:35:51 pmThe same thing that stops a 120V lightbulb from exploding when you screw it into a socket delivering 120V, it's designed to operate on the voltage that is stamped on the label. If you're curious about details of the motor design that determine the voltage it requires we can go into that, but if all you want is to make it work, just wire it up to the voltage it is rated to use and it will do what it's supposed to do. Externally a 120VAC muffin fan looks very much like a 12VDC fan but internally the motor is completely different. Small AC powered fans typically use a shaded pole induction motor.