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Old 08-15-2012, 04:32 PM   #1
guindilla
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Default Where to place an on/off switch - 5V circuit or 230V circuit?

Cheers,

I am designing a PID based on Arduino for an electric brewing system.

I will use the 5V circuit Arduino provides to trigger an SSR that will let high-voltage (230V as I'm in Europe) go through to a water heater resistance or water pump.

I want to put a switch to ensure that the heater or water pump can get disconnected, overriding the PID. I have a doubt about where to include this switch though.

I can put a 12V switch to cut the 5V Arduino circuit that will enable the SSR, thus ensuring that the SSR is off when the switch cuts the circuit.

Or I can put a 240V/15A switch after the SSR, so even if the Arduino activates the 5V circuit, the 230V circuit will be interrupted by the switch when required.

Bonus questions: I guess it should be OK and safe to use a 12V switch in my 5V circuit, as well as using a 240V 15A on my 230V to drive 13-14A of current. Is that right?

Thanks a lot.

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Old 08-15-2012, 04:50 PM   #2
audger
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as long as you just want to have a manual control to over-ride the arduino, you can put a switch in the low voltage line between the arduino and the SSR. this will let you swtich between "off" and "computer controled"...

this will not be a 'safety feature' though, and will not positively prevent current from going to the element (like if the SSR failed closed). it would only prevent the arduino from turning the element on. you could also put a switch on the 240v wires, which would positively cut power to the element for safety. or yes, you could do both.

if you just want to prevent or interrupt the arduino from triggering the heater, its best practice to switch the low voltage signal wire instead of the more dangerous 240v. in general, the fewer high voltage wires and switches you have to run, the fewer chances of an accident.

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Old 08-19-2012, 06:02 PM   #3
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Thanks for the answer. I think I'll use contactors eventually to control high amperage.

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