Mains Relay

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.
--
Bill

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A triac would be a silent switch: http://uk.farnell.com/stmicroelectronics/bta41-600brg/triac-40a-600v-top-3/dp/1057288 (heatsink may be required)
Use the relay to switch the gate of the triac, which will take basically no current so less likely to rattle. You can also use a small optocoupled-triac to drive the gate of the big triac for a fully solid-state solution. http://uk.farnell.com/triac-output-optocouplers
Theo
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On Saturday, 17 December 2016 00:39:45 UTC, Theo wrote:

Buzzing is not sue to current flowing in the switch, it's down to relay design. Mounting it on bits of rubber would help - its box can also be rubber washer mounted.
NT
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Ofr if you don't want that just rectify the mains and have a capacitor across it and a different relay. There are lots of ways to do this in a less clunky way. Brian
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Feeding an AC coil with DC will mean current is limited by the resistance alone, and not by the coil impedance. This means the coil will run hotter, hot enough to burn out in some cases. (With small mains relays, the resistance is a significant portion of the impedance, but resistance becomes less significant as the relay coil size increases.)
The capacitor will also raise the RMS voltage from 240V up to 340V, and exactly double the coil power dissipation over the 240VDC case (which will already be higher than designed).
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Andrew Gabriel
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Had a quick look at RS and they list several suitable - this one is about a fiver:-
http://uk.rs-online.com/web/p/non-latching-relays/8287211/
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 12/17/2016 12:39 AM, Theo wrote:

Solid state relay, even easier?
http://www.ebay.co.uk/itm/SSR-40DA-SSR-Solid-State-Relay-Module-40A-Output-AC24-380V-Input-DC3-32V-Cover-/152011498715?hash=item23649764db:g:CZAAAOSwoudW4mvq
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As usual, they're a bit optimistic of the spec and the construction. I don't think I'd want to put 30A through one. Big Clive's teardown:
https://www.youtube.com/watch?v=DxEhxjvifyY

Theo
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On 17/12/16 00:08, Bill wrote:

I decent relay should not be obviously noisy. Try an Omron brand from RS/Farnell.
His immersion needs a relay capable of handling 13A resistive load AC at mains voltage with a 230-250VAC coil.
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On Sat, 17 Dec 2016 10:12:33 +0000, Tim Watts wrote:

The Omron mains coil relays (MY21) I have are silent, well apart from the click as they operate/release. B-)

Not sure that they are rated at 13A resistive though <wanders off to find one> nope 10A.
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Dave.
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On Saturday, 17 December 2016 10:12:38 UTC, Tim Watts wrote:

The immersion will draw much more than 13A when the element is cold.
NT
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     snipped-for-privacy@gmail.com writes:

No they don't. Nichrome resistance doesn't change anything like that of tungsten, and in any case, the temperature change is only a small fraction of that of a tungsten filament.
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Andrew Gabriel
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On Sunday, 18 December 2016 11:24:00 UTC, Andrew Gabriel wrote:

1.414x 13A = 18.38A, well above the 13A rms current. If mains voltage goes to the upper end of its permitted range, the current will be higher again. So the OP needs a 20A relay at least.
NT
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On 18/12/2016 12:42, snipped-for-privacy@gmail.com wrote:

Nonsense! Calculating the repetitive peak current is irrelevant. Relay current ratings are RMS values. An immersion heater is a very benign load - it's AC-21 service [1] with no significant inrush current. A 16 A relay of reputable manufacture should be fine, assuming any sensible number of switching events per day/hour.
[1] https://en.wikipedia.org/wiki/Utilization_categories
--
Andy

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Given very very few things draw constant current, I'd expect a relay rated at 13 amps to cope with a higher switch on load? Although I've never actually seen a relay rated at 13 amps. 15 would be more common.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Indeed so. 13A is a very British thing. Most other countries in Europe think about 15A - or even 16A.
--
from KT24 in Surrey, England

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On 18/12/2016 12:55, charles wrote:

And?
It's called Great Britain for a reason.
There is no such place as Great France or Great Germany.
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Adam

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On 18/12/2016 11:22, Andrew Gabriel wrote:

EICR on a rented property
Got a few odd readings.
I then asked "Do you want me to test the cannabis factory in in loft?
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Adam

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Mains relays are noisy, but does it have to be a mains relay? Could he just mot add a stage to his controller that could sink more current into a dc one fed from a another supply. Sounds like he is using the weedy switched supply in the controller to just switch a mains relay. That is always going to buzz.
Brian
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