Re: Cap. Discharge Res.
- From: "Arfa Daily" <arfa.daily@xxxxxxxxxxxx>
- Date: Fri, 30 Jun 2006 00:15:29 GMT
"M.Joshi" <M.Joshi.2a6kxf@xxxxxxxxxxxxx> wrote in message
news:M.Joshi.2a6kxf@xxxxxxxxxxxxxxxx
Having opened up the appliance, I discovered that there is an X2 0.1µF
275V interference suppression capacitor across the supply which has no
load present when the appliance is in idle mode. Hence, the capacitor
remains charged when the plug is removed.
I'm sure I have seen resistors across X2 capacitors in-circuit usually
in the Mega-Ohm range?
Looking at the Maplin metal film 2W resistors, they can handle 500V.
Well, I guess that one of them of say 1M, is probably not going to do any
harm. It will only result in a peak leakage current of around 360uA, and
negligible power dissipation ie heat in the resistor. It should discharge
the cap to a safe level in less than a tenth of a second, so much less time
than it would take you to get the plug out of the wall, and touch the pins.
Go for it, if that is your inclination. I think it would probably be safe
enough, provided you do a decent job of the soldering, and pay attention to
insulation and spacing issues.
Arfa
Arfa Daily Wrote:
"M.Joshi" M.Joshi.2a4q9b@xxxxxxxxxxxxx wrote in message
news:M.Joshi.2a4q9b@xxxxxxxxxxxxxxxx
Hi Arfa,
You are spot-on, I am referring to the capacitor across the
mains/supply (Usually termed X-type).
We have a kitchen appliance (Moulinex - I think) which has a motor
and
is connected by a switch which automatically disconnects when you
stop
using the machine.
I have found that if the plug is removed, you get a small
electric-shock if you accidently touch the live & neutral pins. I
tested this by plugging the appliance into the mains socket, then
removing the plug and shorting the two pins together. You can see
and
hear a small spark!
I am assuming that either the appliance has a faulty resistor
connected
across the supply capacitor or they failed to include one at
manufacture?
You might want to just open the thing up and have a look to see if
there is
a resistor across the cap, or that it's not a special CR combination in
an
encapsulated package, as they sometimes are. I think it likely you will
find
that there is no such resistor present, and the manufacturers felt it
safe
for it to be like that. It will have undergone stringent safety tests
at the
design and prototyping stages, and will have had to have shown
compliance
for safety regulations to have gained its CE approval. Moulinex may
well
self-certify of course, but it is more than they would dare do to
'fudge'
this.
If there is no resistor present, I wouldn't advocate adding one,
because as
another poster has suggested, this would quite possibly compromise
things
like fire safety. Bear in mind also, that any resistor across the
mains, has
got to be capable of withstanding at least the peak value of the UK
mains,
which is up around 360v worst case, so would realistically want to be
rated
to withstand 500v.
What you are encountering is by no means uncommon with this sort of
equipment, but does seem to be 'normal'. I would guess that the amount
of
energy stored in the relatively small value of the cap, is probably
considered harmless.
Arfa
--
M.Joshi
.
- References:
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