X or Y rated caps

[Dave]

Hello, I can't see anything recent on this one but I'm sure it must have been aired before so sorry!. Recently acquired DAC90A with blown mains filter cap. Is a modern X or Y rated a must or will a 1000v polyester do just as well? If the general feeling is the former, where can I obtain them that won't cost an arm and a leg? I'm a bit fed up with a .50p component costing £5.oo p&p when reality says it should go out for about £1 p&p.
Moan over, this is the first time I have been back to the forum for a year or so and it's nice to see some of the regulars I remember being as invaluable as ever with their knowledge.
Cheers
Dave

[JoshWard]

RS have free postage and packing. Josh.

[paulsherwin]

A modern 1kV plastic film cap will be much more reliable than the original waxie, but X2 caps are a legal requirement for this sort of application now. They are *very* cheap - in fact, free - because you will find them inside every scrap switch mode PSU you come across - computer PSUs, old monitors and tellies, DVD players, practically anything. They are one of the parts that I always scavenge whenever I scrap something as they are very unlikely to be faulty and only take a second to desolder. 0.1uF is the commonest value but you will come across a range of different ones.

The value in the radio isn't critical and 0.1uF or 0.047uF will be fine.

Some big PSUs have quite high value X2 caps, up to 0.68uF sometimes. These can be used to build capacitive heater droppers and are more reliable and smaller than motor run caps.

Paul

[Kat Manton]

Hi,

It's worth mentioning the distinction between X and Y rated caps (I'd forgotten and had to look it up!)

Adapted from information found here:

Class X is for applications where failure could not lead to electric shock (connected between live and neutral).

Class X1 capacitors are intended to operate safely even in the presence of spikes on the mains supply of up to 4 kV, which are normally industrial supplies, but some standards call up class X1 capacitors if they are connected directly to the mains supply upstream of the equipment fuse, irrespective of the type of mains supply.

Class X2 capacitors are intended to operate safely even in the presence of spikes on the mains supply of up to 2.5 kV, which are normally residential, commercial and light industrial supplies.

X capacitors can be found from 0.001 uF to at least 10 uF and are only made in film.

Class Y capacitors are for applications where failure could lead to electric shock if the ground connection were lost. This includes those connected between live or neutral and ground, and aerial isolation capacitors.

Because Y capacitors shunt current to ground, leakage-current limitations limit their size to a maximum of about 4700 pF in many commercial and industrial applications and about 470 pF in medical applications. Larger ones are available however.

Y caps are available from 1000 pF to 0.1 uF and are made in both film and ceramic.

Regards, Kat

[MALC SCOTT]

Dave, pm me your address and i will send you a couple foc

[kalee20]

Originally Posted by Kat Manton

Y caps are available from 1000 pF to 0.1 uF and are made in both film and ceramic.

Ceramic Y capacitors should be used with care - they may have a significant temperature coefficient and lose a lot of their capacitance at temperatures above 70 deg C. Whereas film types (and paper types) are more stable.

This was imparted to me some years ago by (surprise!) a manufacturer using impregnated paper dielectric. The consequence is, as the capacitors are almost always used to form an RFI filter, equipment may fail to meet RFI limits at high temperatures. EMC tests usually take place in a coolish lab, with plenty of airflow, almost no clutter - exactly right to keep internal temperatures down.

So check the small print on the capacitor data sheet to be sure that things won't change in a warm industrial environment!

[howard]

Hello Dave,

I fitted 0.1uf 275v AC class X2 metallised paper safety capacitors to both my Bush DAC90As, directly onto the switch. They cost 63p from Maplins ..

http://www.maplin.co.uk/module.aspx?moduleno=98166

and are just the right size to fit onto the switch tags as can be seen in this pic of the chassis in my ivory DAC90A.

https://www.vintage-radio.net/forum/...3&d=1237821704

Howard

[Dave]

Many thanks chaps, I think I now have the full picture.
Regards
Dave

[BGmidsUK]

Good explanations, thanks. I'll keep a note of this thread for future reference


Brian