RE: Electronics help needed, resistor keeps failing...

["Keith Doxey" <ukha@xxxxxxxxxxx>]

I would agree with Jon that the resistor power rating is too low.

V2/R = 240*240/47000 = 1.225W so you need a 2W resistor.

You also need to ensure that the resistor doesnt get too warm as there is a
possible fire risk as well.

Best to use a "flameproof" resistor so that if it does fail it
does so in a
controlled manner.

Keith


> So I guess either the resistor value is too small or the power rating
> is insufficient.
>
> > I have recently fitted a AWM2 micromodule to control and indicate
the
> > status of my heating.
> >
> > Information here:
> >
> >
> http://www.automatedhome.co.uk/modules.php?name=News&file=article&sid=1652
> >
> > http://tinyurl.com/pg9u4
> >
> > I had a problem where a neon light was showing as lit all the
time
> > even when the module was lit, I found something about it on the
> > clipsal site:
> >
> > --
> > 30N-COLOUR A 250V - neon indicator (OTHER COLOURS)
> >
> > Note: Inductive loads occasionally cause neons to glow in OFF
> > position. To prevent this, place a 47k., 0.5W 240V resistor
across the
> > terminals.
> > --
> >
> > I bought a resistor from maplin and once fitted it did indeed
solve
> > the problem.
> >
> > However, the resistor fails after about a month, it's done this
twice
> > now, any ideas why this is happening?