Mains interference capacitor?

[Autolycus]

The Kenwood Chefette blew its fuse today. Wretched thing is only 31 years old, too.

There is a 0.1uF capacitor across the mains input, which is now registering as a dead short on a multimeter, and I know this to be a Bad Thing. It is shunted by a 5.something megohm resistor.

I realise that I could send off 5 quid and as much again for postage to an on-line spares stockist, or I could fight the crowds to get to Maplins or the famous Bob Potts's shop tomorrow, but what the worst that would happen if I simply left it out?

[Frank Erskine]

Just a potential bit of interference to your radio.

[Frank Erskine]

That said, the filter does provide a bit of brush spark suppression too.

[Jim Gregory]

If you omit it, Kenwood will mainly cause RF interference to mains AM radios at home and in nearby surroundings. You may have already experienced this irritation during the period leading up to its failure. Renew it with a 1nF (0.1uF) 250VAC working (or 600Volt DC working) metallised polypro cap, in series with a 120ohm 1/2watt resistor. This is likely to be the switch on/off suppressor and not a motor spark suppressor. Try Maplins for bits. Jim

>

[Set Square]

Or get one of their all-in-one jobbies

for 2 quid.

[Andrew Gabriel]

No it isn't -- a snubber network wouldn't fail in the way the OP described.

[dave]

Isn't 1nF .001uF?

Maybe that capacitor is for power factor correction and does it's bit to save the Earths dwindling resources.

[Jim Gregory]

Mea culpa. Not a 1nF. 0.1uF = 100nF Jim

[meow2222]

As has been said, it should work ok but may interfere with radio, tv, other electronics, and the motor &/or switch may not last as long.

Nowadays youre supposed to use an X rated capacitor for putting across mains. These have some self healing ability, so have much better long term reliability than any old cap. Note that 250v caps will be totally unsuitable, the absolute minimum you can get away with on mains is

350v, and thats on filtered lines only. For use on a motor I'd pick either a 600v cap or a mains x rated one.

NT

[The Natural Philosopher]

A visit from John Prescott :-)

Oh and a bit of snow on the telly, and a fizz on the radio, when its running

When in doubt, rip it out.. Go fer it.

[The Natural Philosopher]

Not at 0.,1uF it isn;t.

Need several uF to do any good.

Provbaly use more resources makingte capacitor :=-)

[The Natural Philosopher]

400 VDC, or better 440V DC is the normal rating to put on 240VAC (about 415V peak) But you should make sure the capacitor is rarted for mains use.

Lots of scrap mains powered equipment will have suitable capacitors on em- actual size is not critical - and a pair of side cutters and a screwdriver down the council dump usually nets a few useful items.

[PC Paul]

Since all it does is reduce interference, have you actually tried running it with the cap removed?

There may be something more serious going on. Hope not.

[dave]

I know :-)

[Dave]

The link points to an all-in-one device and then goes on to describe it as a 100 uf resistor and a 0.1 micro farad capacitor.

Now I know what a 0.1 micro farad capacitor is, but what is a 100 uf resistor?

A quick google turned nothing up.

Dave

[Chip]

On Mon, 26 Dec 2005 22:17:56 +0000 (UTC),it is alleged that Dave spake thusly in uk.d-i-y:

The product description was written by the same clueless one who 'designed' their unusable website I think. Pity, Maplin used to be good ~10 years ago:(. From memory I believe it's actually a 100 ohm resistor.

[somebody]

Do one hundred lines of....

milli micro nano, milli micro nano, milli micro nano,

etc Someone

[somebody]

In message , somebody writes

Oops, just read it properly, 100uf *resistor*. Me Bad.

Me do 100 lines of....

me bad me bad me bad

:-( Someone

[meow2222]

Weaselreply: it would improve the pf a tiny little bit :)

NT

[meow2222]

0.1uF + 100R is the standard thing for switch arcing suppression, but not for motor suppression. Motors are more likely to use a cap directly across the motor terminals with no R, often but not always followed by ferret beads on the wires leading to the motor + cap. If you put a 100R+0.1uF across the motor it wont be very effective. A 10nF with no R would be better than that.

NT