Interference Capacitor Substitution - Page 1
Forum section: electronics / beginners

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 01:36:19 pm
content: Hi,My vacuum cleaner died and it turns out that it was the mains cable with multiplehidden cracks. It was tricky to find it, because when I opened it I saw the following:I have already bypassed the capacitor and the vacuum cleaner works again.The cap had 4 wires. Two blue and two black. It was connected between live and neutral.Its a 0.2uF and two 2400pF XY.It says Y capacitor but the vacuum cleaner does not have a mains ground.The capacitor case was bolted on the metal motor chassis.Is it just a double capacitor in the same case for interference suppression ?Hard to find and expensive. Have you seen anything like that?Can I just replace it with separate X and Y capacitors ?Thanks.

author: wraper
author_rank: Unknown
timestamp: November 04, 2019, 01:40:18 pm
content: It's one 0.2uF X capacitor + 2.2n Y capacitors. If you cannot find it in one package, you can replace it with 3 separate capacitors. Earth connection is not required to use Y capacitors. They can be connected to chassis without earth connection.

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 01:45:05 pm
content: Perfect.Thank you very much for the diagram!What is the purpose of connecting the Y capacitors to the case, since its not earthed?I do not understand how that works.

author: wraper
author_rank: Unknown
timestamp: November 04, 2019, 01:52:36 pm
content: Quote from: hgg on November 04, 2019, 01:45:05 pmEven without ground connection it helps reducing interference.

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 02:05:11 pm
content: Yes, but where is the interference coupled?The motor chassis is floating.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 04, 2019, 02:56:44 pm
content: At RF the line / neutral are equivalent to ground. The separate ground wire is a safety device not a emi shielding requirement.

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 03:05:58 pm
content: Interesting.If this is the case, then can you just connect in series the two Y-Class capacitorsbetween L & N without connecting them to the motor chassis?Do you have any reference to read more about that?Thanks.

author: wraper
author_rank: Unknown
timestamp: November 04, 2019, 05:52:25 pm
content: You couple noise from chassis into L/N.

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 05:57:09 pm
content: So what is the purpose of the filter if you are injecting the motor noise into mains line?Isn't that what you are trying to avoid in the first place?

author: SeanB
author_rank: Super Contributor
timestamp: November 04, 2019, 06:36:24 pm
content: The capacitors couple the noise generating brushes to a faraday cage, formed by the motor metal. Thus the EMI is not going to be radiated from the long power wiring and cause interference. You can use 3 class Y capacitors in a triad, with them connected between line, neutral and the motor case, so that any RF noise will be attenuated, instead of radiating from the motor metal and the mains cord. You can use 3 10-47n class Y 275V capacitors there, typically a nice blue ceramic type, or a WIMA film type, your preference.Vacuum cleaner has lasted well, 40 years in operation, check the brushes are not worn and arcing, which could have sent off the old suppression unit, though they do die of old age, as they are paper film capacitors, yours looks like ERO made, but you do get new replacements for them.

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 06:54:33 pm
content: I see.What do you mean connecting them in a triad?Do you connect them like in the diagram above, but you replace the X with another Y ?"Vacuum cleaner has lasted well, 40 years in operation,"Indeed! When things were made to last.The brushes are fine and the suction of the vacuum cleaner is super strong.

author: hgg
author_rank: Frequent Contributor
timestamp: November 04, 2019, 07:38:17 pm
content: Maybe something like the following will be a close alternative to the Miele capacitor.

author: Zero999
author_rank: Super Contributor
timestamp: November 04, 2019, 09:50:27 pm
content: Yes, a capacitor between live neutral, live to earth and neutral to earth, will work.By the way, did the capacitor failure cause either the live or neutral conductors to become in electrical contact with the motor chassis? If so, that's bad and should never happen. Y capacitors should fail safely, gradually reducing their capacitance over time, never shorting or blowing up. In this case it's probably not quite as dangerous, since the motor will already be in a plastic enclosure with and gears or belts, connecting to external moving parts, being made of non-conducting materials such as plastic or rubber.

author: hgg
author_rank: Frequent Contributor
timestamp: November 05, 2019, 06:15:42 am
content: In this case we do not have an actual Earth connection, but the floating motor chassis, that's why I was baffled.No, the L N conductors never came in contact with each other. They were spaced apart insidethe capacitor with a very strong type of plastic. The capacitor probably failed open becauseI've never noticed anything while using the vacuum cleaner and the RCD or breakers never tripped.

author: Zero999
author_rank: Super Contributor
timestamp: November 05, 2019, 11:16:48 pm
content: Quote from: hgg on November 05, 2019, 06:15:42 amSorry, I meant to say chassis, not earth.I was talking about the live or neutral shorting to the chassis via the capacitor. In any case it won't trip the RCD if the motor chassis isn't earthed and it's inside a plastic enclosure, with no possibility of it coming in contact with an earthed object.

author: hgg
author_rank: Frequent Contributor
timestamp: November 06, 2019, 05:23:35 am
content: Yes, luckily nothing was shorted!