# Does this circuit require a ground?

Hello, and good day.

So, let me give you some background info first. My friends commercial refrigerator's temperature sensor is busted, so the refrigerator is permanently "off". He circumvented this with a quick hack which required him to bypass output power to the input. This is great because his refrigerator works, but now it will never shut off, freezing everything. The solution was to use an Arduinio and a relay to alternate the flow of power (chosen because these are the parts at hand).

http://imgur.com/a/JAL2B

If you take a look at the image I made (it sucks, I know), you can see a crude deception of whats going on. But, before I go any further, I would like to make sure that you all understand that when the circuit is complete, i.e. the power flows from each side of the bypass, that everything is OKAY.

The relay allows me to interrupt that flow of power by sending voltage from the Arduinio. So, from what I stated above, when the circuit is complete (not interrupted) everything should work fine. Yet, what I don't know is what is going on with the electricity when the flow is interrupted. My hypothesis is that the relay would overheat, but I am not sure and thats why I am here.

To restate, when the flow of electricity is interrupted (stopping at the relay), how can I make a ground if one is necessary. Can you all give me some insight on whats going on?

Disclaimer:

Sorry, but I am bit of a newbie. If I left something out, or if I used the wrong terminology, then I apologize. If you have any questions, ask them, and I will get back to you as quickly as possible.

Your link does not produce an image - perhaps you could take a picture and enclose it?

regards

Allan

A relay is a switch, just like the switches that operates the lights in your house. They do not overheat when you turn the lights off, do they?

Suppose that the relay was not there. How would you get electricity to flow? Connect the two bare wires together, right? How would you get electricity to stop flowing? Disconnect the two bare wires, right? Well, that is all that the relay is doing. Some other part of the wiring to the two black boxes manages the complete circuit.

allanhurst: Your link does not produce an image - perhaps you could take a picture and enclose it?

regards

Allan

Funny. I saw the picture. Some nice naked girls. Too bad you couldn't see them.

You need to place the relay in a suitable enclosure so nobody can touch the high voltage.

The relay isolates the Arduino from the switched circuit. The module's Gnd must be connected to the Arduino Gnd, what you already did, that's perfectly sufficient.

You have to find a data sheet of the relay module, whether it supports the voltage and current drawn by the load (fridge).

I would NOT use an Arduino relay module to switch mains power for a fridge (wet grounded metal). Those relay modules are not made safe enough for that. It also seems you don't have the experience with mains power. Let an electrician handle this before you kill yourself or others. A thermostat robbed from an old fridge could be a better/safer solution. Or order a new thermostat from ebay for less than \$5 shipped to your door. Leo..

Wawa: I would NOT use an Arduino relay module to switch mains power for a fridge (wet grounded metal). Those relay modules are not made safe enough for that. It also seems you don't have the experience with mains power. Let an electrician handle this before you kill yourself or others. A thermostat robbed from an old fridge could be a better/safer solution. Or order a new thermostat from ebay for less than \$5 shipped to your door. Leo..

PaulS: A relay is a switch, just like the switches that operates the lights in your house. They do not overheat when you turn the lights off, do they?

Suppose that the relay was not there. How would you get electricity to flow? Connect the two bare wires together, right? How would you get electricity to stop flowing? Disconnect the two bare wires, right? Well, that is all that the relay is doing. Some other part of the wiring to the two black boxes manages the complete circuit.

DrDiettrich: The relay isolates the Arduino from the switched circuit. The module's Gnd must be connected to the Arduino Gnd, what you already did, that's perfectly sufficient.

You have to find a data sheet of the relay module, whether it supports the voltage and current drawn by the load (fridge).

So, it seems that I have some conflicting opinions here. From what I can gather, two people are saying I should be fine, and one person is shouting, "No!".

There are some measures on the relay, perhaps one of you all could make sense of it?

Also, if anybody knows of any sources that explain what these measure are, could you please share them.

This article here demonstrates a similar scenario where a 120v outlet is being controlled by the same relay and arduino.

http://www.circuitbasics.com/build-an-arduino-controlled-power-outlet/

The logic was that we could directly subsitute the power source, the appliances power via bypass with the outlets power (the three prong male connector is the power source). Yet, I noted in the picture that there was a ground and a negative (I think?), so in order to perform a substitution I would need to include the equivalent wires.

@Wawa

An electrician was brought in, and he had installed the bypass. He is ordering a part, and by the time it get in and installed, it may be several week later. The Arduino is just a quick hack to get something working in the meantime.

karafar: @Wawa

An electrician was brought in, and he had installed the bypass. He is ordering a part, and by the time it get in and installed, it may be several week later. The Arduino is just a quick hack to get something working in the meantime.

Can't you use a plug-in timer in the mean time (assuming this fridge has a common power lead). And set it for X minutes "on" per hour.

I did warn for those relay BOARDS. Some of them haven't got the track spacing between coil and contacts for mains power. I assumed 230volt, because you didn't post your mains voltage. Leo..

Wawa: Can't you use a plug-in timer in the mean time (assuming this fridge has a common power lead). And set it for X minutes "on" per hour.

This seems like the best solution. I will look into it.

Thanks you all!