On 12/17/2016 2:54 PM, Adrian Brentnall wrote:
On 17/12/2016 14:15, newshound wrote:
On 12/17/2016 1:10 PM, Andrew Gabriel wrote:
In article ,
Bill writes:
Son's house is wired so he can, via his iPhone and home wifi, control
his central heating etc. etc. from the train.
Not sure what system, but it has a controller for the heating and a
separate controller for the immersion.
The heating is OK, but he didn't read the spec and the immersion
took so
much current that the controller died.
He has now, with some drawings from me, wired in a 30A rated relay with
230v ac coil. I bought him a box to mount it in, but it apparently
isn't
decorative enough for his walk-in airing cupboard, so as a very
temporary measure he has wired it all up al fresco via the old
immersion
isolator switch.
He reports that it all works well except for the buzzing from the relay
coil, which is bound to get louder when it's mounted in a box on the
wall.

I have said I'll ask around to see if anyone knows whether all this
type
of relay is noisy, or whether anyone knows how to select a silent type.

This really needs a contactor rather than a plain relay, and
contactors can hum (so it might be that's what you already have).
As someone suggested, mounting it on some sort of soft rubber
mounts (and using loose flex wiring to the contactor) will help
prevent coupling to vibration to a sound board. Trying a different
mounting orientation might also reduce noise.

Standard 40 Amp solid state relay, available with low voltage or mains
switching. Been using them for years to control immersion heaters at my
mate's brewery. May need a small heatsink, depending on how and where
they are mounted. RS/Farnell for conservatives, eBay for cheapskates
like me.

Do you find that the ebay ones are reliable?
There's a heck of a price difference between the ones from HongKong and
the ones from RS - £3 vs £40 (need 40A (probably) to switch 7kw load @
240v.

I'm currently using a mains-driven contactor, that comes on with a
satisfying 'clunk' (and, sometimes, a whine/whistle) - but, if it (or
the ssr) were to fail 'closed' then that might get interesting rather
quickly... as it's feeding a resistive heater in a medium-sized glass kiln.

What's the failure mode of the ssr's - in your experience?
Thanks
Adrian

I used RS originally and, I think, had one fail after a couple of years.
Did a rebuild with eBay ones (not necessarily the cheapest), one channel
is currently down (there is redundancy) but I havn't confirmed if it is
the relay or some other fault.

I hadn't worried about protection. The whole system is powered dowm
before draining. Overheating caused by one failed channel would be
picked up by the brewer's manual check on water temperature. (This is a
hot liquor tank, for anyone interested). I suspect a single heater (3
kW) would not be able to get the tank to boiling point, but if it did
there is about eight feet of water to boil off before exposing elements!