Does a mains fan need a cap? - Page 1
Forum section: electronics / beginners

author: PinheadBE
author_rank: Regular Contributor
timestamp: June 04, 2025, 12:17:02 pm
content: Hi,I bought a Sunon fan, mains powered.It was delivered with a cap (see picture).What is this cap needed for (if needed)?Thanks

author: Refrigerator
author_rank: Super Contributor
timestamp: June 04, 2025, 12:48:54 pm
content: Normally AC motors need capacitors for starting, but they also have three wires for that capacitor connection.I've never had to connect a capacitor to any AC case fan.Too bad the datasheet doesn't mention any capacitor connections either.I'd wager a guess that you can connect it directly and it will work just fine.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: June 04, 2025, 01:12:10 pm
content: Is the capacitor connected to anything now?Perhaps if you connect it in series you can reduce the speed.Otherwise consider it as a surprise gift!!

author: picburner
author_rank: Frequent Contributor
timestamp: June 04, 2025, 01:21:57 pm
content: It is used to improve the EMC suppression as per attachment.

author: Zero999
author_rank: Super Contributor
timestamp: June 04, 2025, 01:24:32 pm
content: There shouldn't be any RFI from an AC fan with an induction motor.I was going to suggest it's for power factor correction, but 1.5µF would give an apparent power of nearly 25VA, yet the fan is only rated to 4.6W and the power factor won't be that bad.

author: picburner
author_rank: Frequent Contributor
timestamp: June 04, 2025, 01:34:28 pm
content: It's the only document I've found that explains the existence of that capacitor.Whether it's practically useful or not is another story.

author: wraper
author_rank: Unknown
timestamp: June 04, 2025, 01:51:05 pm
content: It uses BLDC motor. Just looking on it, presence of PCB gives a hint it's not a usual AC fan.

author: PinheadBE
author_rank: Regular Contributor
timestamp: June 04, 2025, 02:26:08 pm
content: Thanks to all for your answersTo answer some questions:- No, the cap isn't connect to anything. It was just delivered with the fan. I ordered 3 fans and got 3 caps- There is no PCB: this a cardbox I used just to take the picture- The fan is intended to cool down a MeanWell LRS-200-5 SMPS that will be encased. So it will be connected to an already big capacitive device, and my guess is that 1.5 µF will not make any difference. That SMPS is also already equipped with an EMI filter on its input and meets the EMC directives (see datasheet attached)- If it increases the apparent power to such a high level, I would rather not connect it. My mains counter does not count apparent powerYET, because it will be soon replaced by a "smart" one that does....I will try first without the cap and use an AM receiver to check for EMI. And connect the cap if needed.

author: golden_labels
author_rank: Super Contributor
timestamp: June 04, 2025, 03:41:39 pm
content: There has to be a PCB. Per datasheet (attachment) it’s a BLDC motor.And I can indeed see what looks like an edge of a blue PCB. Where the wires come into the motor, under the white gunk.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: June 04, 2025, 05:22:45 pm
content: The more I read the attached datasheets, the more confusing it gets.If the fan is indeed a BLDCdevice but it is fed from AC, then it must have a small SMPS which creates some EMI. Which caused it to not meet RFI compliance. The capacitor is an afterthought, to mitigate RFI by brute force.But, and this is a significant but, the datasheet mentions that it can be used at 50 or 60 Hz, but the RPM changes with frequency, the higher speed corresponding with the higher frequency. This behavior is consistent with an induction motor, not a BLDCmotor.So what is it?

author: Zero999
author_rank: Super Contributor
timestamp: June 04, 2025, 07:15:35 pm
content: Quote from: golden_labels on June 04, 2025, 03:41:39 pmI wouldn't take these Chinese data sheets too seriously.If it has an inverter, then why does it give different air flow speeds and pressures, for different frequencies?I call BS. It's just a plain old shaded pole motor.

author: Gyro
author_rank: Super Contributor
timestamp: June 04, 2025, 07:29:35 pm
content: I don't see any Class 'X' marking on that capacitor to indicate that it would be safeoffor across-the-line use. Also, what's going on with those double quotes?

author: wraper
author_rank: Unknown
timestamp: June 04, 2025, 08:39:38 pm
content: Quote from: Zero999 on June 04, 2025, 07:15:35 pmSunon is one of the largest if not the largest fan manufacturer, and it's Taiwanese. Used in many industrial and consumer devices from big brands. And I'd always use Sunon over say ebm-papst if possible because their fans usually are quieter per similar performance, better balanced, more efficient and last longer.

author: shapirus
author_rank: Super Contributor
timestamp: June 04, 2025, 08:41:52 pm
content: take it apart!

author: Zero999
author_rank: Super Contributor
timestamp: June 04, 2025, 08:49:15 pm
content: Quote from: wraper on June 04, 2025, 08:39:38 pmI don't care. Read the data sheet posted above. It's full of contradictions.

author: wraper
author_rank: Unknown
timestamp: June 04, 2025, 08:57:36 pm
content: Quote from: Zero999 on June 04, 2025, 08:49:15 pmMention at least one. BTW it looks like capacitor is supplied by TME, not Sunon.Quote from: Zero999 on June 04, 2025, 07:15:35 pmBecause there is no DC smoothing capacitor inside. Good luck finding shaded pole fan with 3000 RPM with power rating this low and motor this small. Shaded pole fan will have a huge motor surrounded by tiny blades. Also shaded pole motor will not have 3% RPM difference with 20% frequency difference.Example:https://media.distrelec.com/Web/Downloads/_t/ds/SF23092A_2092HBT.GN_eng_tds.pdf

author: SteveThackery
author_rank: Super Contributor
timestamp: June 04, 2025, 10:04:10 pm
content: Quote from: Zero999 on June 04, 2025, 08:49:15 pmI can't find any - could you point them out?I'm a bit puzzled about why it goes faster at 60Hz, but not 20% faster. Otherwise, I would guess it's an inverter driving a BLDC motor.

author: vidarr
author_rank: Frequent Contributor
timestamp: June 04, 2025, 10:15:17 pm
content: It is a DC fan running on AC.

author: golden_labels
author_rank: Super Contributor
timestamp: June 05, 2025, 12:49:14 am
content: Quote from: wraper on June 04, 2025, 08:57:36 pmNot only TME.Piekarz even explicitly lists it as a part of the offer, and so doesthis Italian store.And that last one may give us the best clue:QuoteIn other words: “we give you some capacitor, so nobody can tell we sold a non-compliant product.”From what I gathered, the capacitor is discontinued by Fabco. Perhaps somebody in the supply chain acquired a large quantity of unsold stock for pennies and throws them into boxes to feign compliance. The cap itself is a run capacitor, and IMO at 1.5 µF certainly doesn’t belong across 50 Hz rails in such a low power device.

author: wraper
author_rank: Unknown
timestamp: June 05, 2025, 12:58:59 am
content: Quote from: golden_labels on June 05, 2025, 12:49:14 amSome smaller companies simply resell parts they buy from TME. I know a local shop with like 80%+ of their stock consisting of stuff from TME. Confirmed by Piekarz and Italian store selling SR passives components which is TME house brand.

author: Zero999
author_rank: Super Contributor
timestamp: June 05, 2025, 08:45:21 am
content: Quote from: wraper on June 04, 2025, 08:57:36 pmIt talks about ensuring correct polarity, on an AC fan, which is nonsensical.1.5µF is one heck of a capacitor for EMI suppression on such a small motor.

author: wraper
author_rank: Unknown
timestamp: June 05, 2025, 09:52:38 am
content: Quote from: Zero999 on June 05, 2025, 08:45:21 amYou're talking not about a datasheet. TME adds a "quick start guide" of their own printed on A4 sheet that has nothing to do with manufacturer to a quite a bit of products. I have received them with multimeters, power supplies and other stuff I don't remember in particular.

author: floobydust
author_rank: Super Contributor
timestamp: June 05, 2025, 07:29:49 pm
content: My take on this is it's low voltage DC motor- induction motors that small are very difficult to make for the wire size and # turns. I don't see them that small, ever.Which means the capacitor is for the mains-dropper in the fan's power supply.

author: wraper
author_rank: Unknown
timestamp: June 05, 2025, 08:04:03 pm
content: Quote from: floobydust on June 05, 2025, 07:29:49 pmWrong, it's high voltage BLDC with no smoothing capacitor inside. How do you think dropper capacitor could possibly fit inside it?

author: floobydust
author_rank: Super Contributor
timestamp: June 05, 2025, 10:26:03 pm
content: I'm saying it's the external 1.5uF cap's purpose. I guess we'll see when OP fires it up.Edit: I missed that the cap is not part of the fan as-is, it seems to be an extra part tossed in. Very hard to make small HV windings.Bit more research I figured it out. OP's fan was discontinued end of 2022 and I could not find datasheets. The next-gen CF2062 version datasheet showsECN: 2023.09.15 MODIFY ELECTROMAGNETIC INTERFERENCEELECTROMAGNETIC INTERFERENCE X1 CAPACITOR 1.5uF/330V MIN. (OPTIONAL, ACROSS LINE AND NEUTRAL OF AC POWER INPUT LEADS)So I guess there's some issue with EMI and this is the fix which is a huge cap for X-duty.

author: wraper
author_rank: Unknown
timestamp: June 05, 2025, 10:35:48 pm
content: Quote from: floobydust on June 05, 2025, 10:26:03 pmExternal cap is supposed to be wired in parallel, not in series (according to that quick start guide from TME). Also it's a run capacitor which is a wrong part to be used like that, it's class D which is the worst and rated to last just 1000 hours. Not to say there is no mention of it in the actual datasheet, not that scribble from TME.

author: golden_labels
author_rank: Super Contributor
timestamp: June 05, 2025, 10:49:29 pm
content: To me the notes from sellers seem quite clear: the capacitor is irrelevant to fan’s operation.If we ignore above and, for the sake of this discussion, assume it is meant to be used as a run capacitor:(1)where does it go? Shouldn’t a run cap have at least one winding in series? The drawings don’t show it that way. Close to the begining of this thread somebody has already pointed to the obvious and I repeated that in my previous post: 1.5µFcapacitor directly across50 Hzrails, in a low power device?(1)As an individual part, the capacitor itself is a run cap.

author: floobydust
author_rank: Super Contributor
timestamp: June 05, 2025, 10:51:28 pm
content: Yeah I see it as kind of a bodge for some EMI problem they have. It's not a great idea across the line, inrush current for that cap can be quite high.