Capacitor type for triac switch circuit

[raldred]

Hi,
I've been reading a few posts on this forum about triac switching circuits.
I am using a circuit from electronics-lab (attached)
I'm after some help as to which type of capacitor to use (pulse,suppression etc), i'm hoping someone here can help

I have found this for example; would this be suitable:
https://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0148474

Thanks
--Rob

 

[FvM]

A specification like 275VAC usually refers to a "X2" capacitor, a family of devices dedicated for mains voltage parallel connection for
filtering and EMI supression purposes. They are mainly build as polypropylene (MKP) or polyester (MKT) metallized foil capacitors, available
from all major manufacturers. They are perfectly suited as triac snubber. The series resistor possibly allows the usage of a regular 630V
DC capacitor, that has less pulse current capability.

 

[betwixt]

That capacitor is ideal.

The only electrical requirement is that it is rated to withstand the incoming AC voltage but the type you found has the extra advantage of being 'fail safe' in case of a problem. It is still possible for it to go short circuit, in which case you get very high leakage through the circuit and probably the series resistor will smoke. X2 capacitors are rated to be connected directly across the mains lines so are designed to be safe under normal mains conditions.

Brian.

 

[karesz]

Hi,
I think these is a good one for your application !

K.

 

[raldred]

Thank you all for your replies, its very helpful stuff.
I only need a few of these and apparently RS will only sell them in packs of 20 which is a shame.

I've also been looking at a WIMA FKP1 1250Vdc/600Vac
Here's the datasheet: www.wima.com/DE/WIMA_FKP_1.pdf

or the WIMA MP3-X2:
www.wima.com/EN/WIMA_MP_3-X2.pdf

going off what i understand from your replies this also should be more than sufficient?
I can buy these in single units.

Thanks again.
--Rob

 

[karesz]

Hi Rob,
I think you can orrder from Newark/Quest & Future Electronics enetuelly too, check pls by https://octopart.com too...
K.

 

[betwixt]

I haven't checked but try looking at https://uk.farnell.com in Leeds, they are my usual supplier for components.

If possible, select on with "X2" rating - they are the ones designed to withstand AC mains directly across their wires.

Brian.

 

[raldred]

//edit/ new post because i've the capacitors now.
Thanks to all for help.