Implementing Safety Shut-Off Relay In Project

Question

I am working on a project which I have poured lots of cash into that involves water, pressure and electronics in very close proximity of each other... Lately, I have been considering adding some fail-safe mechanism which will cut all power to the machine if any water is detected by some carefully placed water sensors. I am no electrical genius (really far from it) so I was curious if there was a way to create a toggle circuit which the brain(arduino) could trigger that would manipulate a relay cutting power to the device; ultimately requiring human intervention to reset.

I realize that this is most likely impossible/not ideal, and that some of you may suggest a secondary, battery-powered system to do the job.

Thanks

Answer 1

You can use an Latching relay and a momentary switch. So this would operate as follows, to get the system started you would have to press the momentary switch and hold it until the arduino latched the relay to the position where power is supplied to the machine. Once the system was running and water was detected by the sensor then the arduino would latch the relay into the position where power is no longer being supplied and it would take a human to come and press the momentary switch to start the system again

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

Do not implement safety systems in software. If you are relying on this circuit to prevent a dangerous situation, i.e. electrocution or fire, then you had best use something more reliable than a bit of Arduino code to assure your safety.

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Here is a (modified) example of something I once designed to protect a submersible pump. These pumps live under-water so it is important to detect if water is leaking into the electrical parts, which would be bad.

Notes:

• Relays rated for large currents (i.e. anything over a few amps) are not called "relays", they are called "contactors". Contactors are rated for full line voltage (230 VAC) and large currents (the Schneider CT series covers 16-100 A.)

• this system is self-resetting, i.e. the power will be cut off automatically in case of water being detected, and power restored automatically once the water leak is no longer detected. You can arrange a latching relay of some sort, in series with the contactor coil, if you desire a hand-reset latch.

• The Flygt MiniCAS II is the first example of a leakage alarm that came to mind. It is an industrial product and probably overkill for your needs. However, "water leakage alarm" is a good thing to search for.