13-05-2015, 09:50 AM
A schematic would be helpful, but personally, I would replace the isolation capacitors.
Class X capacitors are rated to be used between phase and neutral, and are designed not to fail catastrophically (should a spark occur thanks to an imperfection in the dielectric, the heat generated should cause the dielectric to swell up and self-heal). Of course, don't mention "Rifa"
Class Y capacitors are rated to sit between phase and "earth", or neutral and "earth". Of course, for a Class 2 device, "earth" is not Protective Earth, but it would be the chassis of the instrument - which might or not be accessible to the end user, depending on the design. Failure of these can cause electric shock, so they need to fail O/C.
Class Y capacitors tend to be low in value because otherwise they would cause excess leakage. 4n7 is entirely typical.
Just to add to the confusion, sometimes you come across capacitors that are double-rated (class X and Y). Most class X capacitors are X2, but X1 and X3 exist - possibly others. Likewise for Y. The differences are related to the pulse handling ability IIRC.
So, class Y is appropriate for the isolation capacitors.
For the spark suppression capacitor, it has to be rated to handle the AC mains. However, you could argue that worst-case, should the cap will fail short the motor will simply run continuously - perhaps not the end of the world? But honestly, mains-rated caps aren't that much more expensive, so chancing it doesn't really make sense. Alternatively, you could just leave it alone, as it's not a safety-critical part and it's not obviously faulty? Ultimately, it's a bit of a judgement call, but the motor winding will limit the available energy, so I can't think of an obvious safety problem here.
Needless to say, don't risk buying mains-rated caps on eBay! Counterfeit components is a big problem in the industry, and for safety-critical parts, it's worth buying from Farnell/RS. Even those guys occasionally get caught out, but at least you've exercised "due diligence", should the worst happen.
Class X capacitors are rated to be used between phase and neutral, and are designed not to fail catastrophically (should a spark occur thanks to an imperfection in the dielectric, the heat generated should cause the dielectric to swell up and self-heal). Of course, don't mention "Rifa"
Class Y capacitors are rated to sit between phase and "earth", or neutral and "earth". Of course, for a Class 2 device, "earth" is not Protective Earth, but it would be the chassis of the instrument - which might or not be accessible to the end user, depending on the design. Failure of these can cause electric shock, so they need to fail O/C.
Class Y capacitors tend to be low in value because otherwise they would cause excess leakage. 4n7 is entirely typical.
Just to add to the confusion, sometimes you come across capacitors that are double-rated (class X and Y). Most class X capacitors are X2, but X1 and X3 exist - possibly others. Likewise for Y. The differences are related to the pulse handling ability IIRC.
So, class Y is appropriate for the isolation capacitors.
For the spark suppression capacitor, it has to be rated to handle the AC mains. However, you could argue that worst-case, should the cap will fail short the motor will simply run continuously - perhaps not the end of the world? But honestly, mains-rated caps aren't that much more expensive, so chancing it doesn't really make sense. Alternatively, you could just leave it alone, as it's not a safety-critical part and it's not obviously faulty? Ultimately, it's a bit of a judgement call, but the motor winding will limit the available energy, so I can't think of an obvious safety problem here.
Needless to say, don't risk buying mains-rated caps on eBay! Counterfeit components is a big problem in the industry, and for safety-critical parts, it's worth buying from Farnell/RS. Even those guys occasionally get caught out, but at least you've exercised "due diligence", should the worst happen.
