Re: Buzzing relays? Anyone help?

["David" <clayt_d01@xxxxxxxxxxx>]

I've come across that with solid-state control in the past, it is a
tricky one. My t'penny worth..

Are your x10's in the same cupboard as the relays? - They may be
vibrating..

Current leakage from the x10 is the most probable cause of your buzz.
All silicon switches leak current, so your relays will work like a
speaker when not in the 'on' state. Ever listened to a dimmed light
bulb? they buzz slighty.
The leakage is at mains voltage, but at such a low current it is
almost negligible. Almost. Your singing relays seem to be sensitive
to it.

A single diode should not be used for mains control.
The 'back emf' produced by the coil when it switches off could
destroy the diode, and the half-wave ac it allows through when
working may cause overheating of the relay coil. Magnetic
polarisation of the core (due to applying dc current) could happen,
but is unlikely as other variants of this relay are made for dc.
Two diodes should be used in connected back-to-front with each other -
a diode '69' (ahem) - my pictures are worse. trust me;) The diodes
will protect each other from back-emf damage and allow full current
to flow.


Some ideas :)

Have you tried swapping the x10's with others you have? some may leak
less current than the ones you are using (less buzz).

Change relays - use a different model of relay. May not be as prone
to 'singing', especially a bigger, heavy duty type. My choice.

Move the board? does it need to be on that wall? or in the cupboard
at all? is the loft space suitable?

Do the relays -have- to be in the cupboard? They could be mounted
with the din rail depending on the switching arrangement of your c/h.

More relays - if your x10's are located away from the relays you
could use another relay (cheapest possible) to switch the relay in
the cupboard. That would kill the buzzing stone dead - current will
only flow when the smaller relay is on.

Making the installation 'float' on washers and grommets should work.
The trick is to not let your mounting screws come into contact with
the board the relays live on. Tap the board with your pliers to see
if there is anything at all on there that would vibrate and make
things worse.

Regards,

Dave


--- In ukha_d@xxxxxxx, mailinglists <mailinglists@v...> wrote:
> After a successful install of my automated hot water/central
heating
> controls (with many thanks to Neil Fuller for his donation of a
foot of
> DIN rail to securely mount the relays!), I've just noticed a small
but
> annoying problem.
>
> The relays buzz slightly when they are off. The installation is
> basically two big 240V relays connected into the CH/HW wiring, the
> relays have 240V coils that are switched by a pair of X10 appliance
> modules due to the distance between the server and the airing
cupboard.
>
> At a guess I'd say that the leakage current from the modules is
enough
> to make coils buzz. The problem is exacerbated by the relays being
on
> one side of a plasterboard partition wall, which seems to amplify
the
> buzz into the next room. Aside from the buzz everything else seems
to
> have worked just fine for the last few weeks.
>
> The $64K question is how to stop the buzz? Any ideas?
>
> Lee