What are these capacitors (ultra newb) - Page 1
Forum section: electronics / beginners

author: stojke
author_rank: Regular Contributor
timestamp: November 04, 2015, 12:06:26 pm
content: Hi guys, I would like to know what is the usage of these capacitors RIFA PME 271 Y?From what I learned they are Metallized Impregnated Paper capacitors and their usage is in "electromagnetic interference suppressor in all Y2 applications, line-to-earth". What does that mean? Can they be used as audio capacitors?They came from these boards, are they maybe audio amplifiers?Are these components worth keeping?

author: Gyro
author_rank: Super Contributor
timestamp: November 04, 2015, 12:47:44 pm
content: You've more or less answered your own question. Yes, the Rifa caps are metalized paper caps and are most commonly used for interference suppression (removing RF noise on the mains supply within equipment). Y caps are intended for connection between the supply and earth - they have a higher test voltage (several kV) due to the serious consequences of them failing short circuit. X rated caps are for connection across the mains (Live-neutral) for similar noise suppression purposed. Larger values of the Rifas actually sound quite rather good in loudspeaker crossovers (clearly yours are too low value though). NOTE: Old Rifa paper caps have a reputation for failing catastrophically due to moisture ingress - discard them if there is any sign of cracking, swelling or crazing of the resin. I also suggest that you don't try strapping them across the mains!With regard to the boards - They are probably most useful to you for practicing your surface mount soldering. try removing and replacing parts without damaging the PCB pads or components. There are however some useful parts that might be worth salvaging...- The LH0070 is a rather nice 10V voltage reference that is easy to wire up and might be useful in your lab.- The AD548s are precision FET Op-amps, a little old but still good performance.- The AD7547 is a Dual 12 bit parallel input Digital to Analogue converter. Hard to remove but being parallel input it would be easy to feed it with logic signals and observe the output without needing to worry about I2C or SPI protocols. It will be harder to remove, but you could always glue it on its back and use fine wire to connect to its pins on a proto board. It is probably using the LH0070 as its voltage reference.The datasheets for these parts are easy to find on the web. Download and study,Difficult to identify all of the parts - the 74HC... logic devices are too cheap to worry about, buy new instead. Those will be best used to practice your soldering.Hope this helps.P.S. The boards are not audio amplifiers - they're some kind of instrumentation (data acquisitopn) boards.

author: DmitryL
author_rank: Regular Contributor
timestamp: November 04, 2015, 12:55:27 pm
content: Quote from: stojke on November 04, 2015, 12:06:26 pmThese capacitors are quite infamous for developing cracks in their case, absorbing moisture and bursting open with a smoke if used as X-capacitors on mains

author: stojke
author_rank: Regular Contributor
timestamp: November 04, 2015, 02:12:46 pm
content: Wow, thanks for an amazing replyI understand now what do they do. Too bad these aren't audio equipment, kinda hoped they were due to analogue devices and such caps.Will keep them for practice as recommended