Wilmac bandsaw restoration MKII

[Yorkie]

Nice to see you back on the forum Bob!

I very much doubt that you've caused this to happen  - I think it's coincidence that you've fallen victim to the 'RIFA cap syndrome'. What's happened in that it's gone short circuit ascross the mains - exactly what Class X caps aren't supposed to do. RIFA caps are legendary for going off with a bang without warning.  It's fitted across the main input and its only purpose is as a noise suppressor. If you remove it, the equipment (unless indeed there's a fault) should work without it, albeit it will cause interference to equipment such as radios & TVS. If the equipment doesn't you have a fault.

Class X suppressor caps go across the mains line and neutral, and Class Y go from line to earth and from neutral to earth. The way to remember which is which is 'X is a cross'.

They're used in all sorts of domestic equipment - electric drills and other power tools, vacuum cleaners, washing machines etc.  Hence, they're widely available.

You'll need a .047 uF one - you'll find them on e-bay - here for example, but you need to make sure you have the correct pin spacing:

http://www.ebay.co.uk/itm/5-X-EPCOS-B329...1381151488

Hope that helps a bit.

Good luck with it.

[Yorkie]

Ooops - don't know how that happened!

Tried to edit the post to add 'you'll need a .07uF one' and ended up with two posts for the price of one!

Must be a BOGOF deal on the forum today!

[Mark Hennessy]

Ooops - don't know how that happened!

Tried to edit the post to add 'you'll need a .07uF one' and ended up with two posts for the price of one!

Must be a BOGOF deal on the forum today!

No matter - I've hidden the first of the two

Always reassuring to hear of another Rifa incident - they never stop giving! I threw away a NOS batch last year, having kept them for some 20 years. Good riddance! X2 capacitors are not rare or expensive - although with such a safety-critical component I'd recommend avoiding eBay for fear of stumbling across a fake (that's not to make any specific accusations, of course!). Although perhaps more pricey or less convenient, go for CPC or Farnell or RS or Rapid Electronics. Better safe than sorry...

Cheers,

Mark

[Refugee]

It is not just Rifa capacitors that detonate in this way.
I have got two WIMA X-2 capacitors of similar construction to the Rifa type and although they are NOS they have still quietly split while laying in a drawer.

Here is a couple photos dated rather dubiously 9/11/2012.
   
   

I Have done some more photos to show how much worse they have got since 2012.
An NOS Rifa in the same drawer is just as bad.
My conclusion is that they count down to detonation from there date of manufacture with or without power applied and could do with an explode if used after date shown on them.

[robert the violinist]

Thanks for all the replies , so i need x2 type of the same rating (0.047 uf 250v) .Most appear to be 275v ? Do they have to be the same type i.e paper film or will other be a better replacement.
Bob
P.s you will have to talk in simple terms as i know basically nothing much about electronics, having joined this forum(which is very interesting non the less) for advice on a bandsaw restoration.
The thyristor i had lying around and as far as i know it has never been used and the capacitors had cracks in before i even applied any power to it.
For someone with not much experience of using a multimeter how do i test to see what the dc output of this thyristor is ??Where do i put the probes if there is nothing connected to it other than the mains supply cable.
It was bought with no instructions or info stickers on it other than its for a 1/4 hp shunt motor. and carries a 3 amp fuse.

[Alan Douglas]

Do they have to be the same type i.e paper film or will other be a better replacement.

They were made with paper or plastic film, depending on the manufacturer. The overall specification is that they will not catch fire when they fail

[Refugee]

The thyristor is a solid state switch and without power a resistance meter should show no connection from the two terminals and the case.
It is unlikely to be faulty anyway.

[Radio Fixer]

They are supposed to be self healing as well. I deliberately turned up to a KV on some and had a lovely crack. But they measured the same capacitance and had no leakage after.
Needless to say I chucked them.

Gary

[Alan Douglas]

The metalized electrode vaporizes around the fault. I once tried drilling a 1/4" hole through a mylar capacitor. After all the shorts cleared, it tested fine, if somewhat low in capacitance.

[Mark Hennessy]

Thanks for all the replies , so i need  x2 type   of the same rating  (0.047 uf 250v) .Most appear to be 275v ? Do they have to be the same type i.e paper film or will other be a better replacement.

If the replacement capacitor comes with a higher voltage rating, then that's absolutely fine.

Of course, the reverse might not be true

If the capacitor carries an "X2" rating, then it will be designed for continuous use across the 230V mains. Plastic film is a much better long-term bet than paper. And that's all you need to know about the capacitor

HTH,

Mark