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Topic: Switching relay question (Read 361 times) previous topic - next topic

ChrisHigs

I plan to make my boiler controlled by my Arduino at some point with a web interface for it, probably running on my Pi.

For now I just want to be able to switch it on remotely with a relay and use the existing timer controls.

So I have a question about switching it using a relay. The relay will switch the 230V line to tell the boiler to switch on. The timer will also be doing this so if both are active, or only one, is it likely to cause problems or damage anything?

No, not really.
They are switches in series, and if the wattage is supported by both you are fine.

You should try not to switch the mains if possible: many boilers have a "Call for heat" zero potential contact available somewhere inside. This is the right place for a relay.
Otherwise for safety reasons you should use a relay and a power contactor, IMHO.

ChrisHigs

I'm 99% sure it switches the live. It's a pretty old boiler and all the action happens on the timer. It switches the boiler on, switches the valve for water/hearing and switched on the pump.

I've bought one of these: http://m.ebay.co.uk/itm/111613305832

I think if I want it to work the way I want I'd have to have the relay and timer switching in parallel so if either is on the boiler will be on, and off if both are off.

The placement of the relay/Contactor on this would depend on what the timer really switches on or off.
Ideally if the thermostat calls for heat your control circuit should open a draft of some sort, turn draft fan on and the pump to move the water.  If you want to control this remotely via Relay it would need to be after and in series of the thermostat unless you wanted a thermostat over ride setup. At this point you would need relay in Parallel of thermostat <<caution >> this setup if relay left on would let the boiler run constant. 
Sorry if I'm off base of understanding what you may be wanting to do with this.

ChrisHigs

#4
Mar 23, 2015, 12:09 am Last Edit: Mar 23, 2015, 12:10 am by ChrisHigs
Yup, that's what I want to do, at least for now (if I ever get around to making a timer/controller for it), have a remotely controlled override for the boiler.

I was hoping it would be feasible to have the relay in parallel with the current control unit, didn't know if both switched on would cause problems, damage the relay (like if it's off but the timer switches the power on so the terminals on the relay are live, even though it's off), or something.

terryking228

#5
Mar 30, 2015, 01:26 pm Last Edit: Mar 30, 2015, 01:27 pm by terryking228
I was hoping it would be feasible to have the relay in parallel with the current control unit, didn't know if both switched on would cause problems, damage the relay (like if it's off but the timer switches the power on so the terminals on the relay are live, even though it's off), or something.
Relay contacts in parallel with the existing boiler controls is not a problem as long as the relay you use can properly handle the voltage / current.

That configuration gives you a logical OR so the boiler would be on IF the existing timer OR your circuit is active.

The relay you have is similar to  THIS: and you could follow the links there to more info.


DISCLAIMER: Mentioned stuff from my own shop...
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

ChrisHigs

Excellent, just what I wanted to know. That's what I'll be trying to do, have the boiler on if the timer OR the relay has is switched.

Still need to work out the software to make it work now.

tkbyd

There is stuff relevant to what you are talking about at...

http://sheepdogsoftware.co.uk/sc2eh.htm

and, if you don't know about "the" diode for the relay...

http://www.arunet.co.uk/tkboyd/ec/ec1relay.htm

and for some notes on working with household voltages...

http://www.arunet.co.uk/tkboyd/ec/ec1mains1.htm

... but no test on Friday.

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