I have a hot tube heater but my pump doesn't reach the psi needed to trigger the pressure sensor. So, I'm going to bypass it with and arduino nano, DS18B20 temp sensor, and a relay. The pressure senior must have been limiting the current because when I shorted the leads the wire heated up. The specs of a general pressure is 120V 1A. So I need some ideas on how to Dissipate 120 W safely. Also the heat sits about 2 feet above water in a metal box with limited room. Any ideas will be helpful, thank you.

 

I have a hot tube heater but my pump doesn't reach the psi needed to trigger the pressure sensor. So, I'm going to bypass it with and arduino nano, DS18B20 temp sensor, and a relay. The pressure senior must have been limiting the current because when I shorted the leads the wire heated up. The specs of a general pressure is 120V 1A. So I need some ideas on how to Dissipate 120 W safely. Also the heat sits about 2 feet above water in a metal box with limited room. Any ideas will be helpful, thank you.

I'm struggling to picture your arrangement and wiring. Could you sketch out a diagram? What are you heating?

 

I'm experiment with Aquaponics and winter is coming, so I heating my above ground pond It is about 10'x3'x3' being pumped by a small pool pump. The heat sensor in can't be adjusted to the temp I need so I'm putting a new one that I can control.

 

I suggest adjusting the pressure switch. There is nothing here that an aduino can benefit, and you really don't want to get that little thing involved with a safety system. That 5500 watt heater could cause huge problems if it ever runs dry!! Also, it looks like your circuit is running the contactor coil on 220 volts while parts are labeled 120 volts. I see problems there.

 

I have a hot tube heater but my pump doesn't reach the psi needed to trigger the pressure sensor. So, I'm going to bypass it with and arduino nano, DS18B20 temp sensor, and a relay. The pressure senior must have been limiting the current because when I shorted the leads the wire heated up. The specs of a general pressure is 120V 1A. So I need some ideas on how to Dissipate 120 W safely. Also the heat sits about 2 feet above water in a metal box with limited room. Any ideas will be helpful, thank you.

In life if you are debugging a real device, someting does not work for a reason.
if you bypass a defect, it can cause more faults.

Which is why we need a circuit and if possible picture.

 

If the heater is above the water level then it has a very real possibility of not being full of water, and if the heater is switched on without being filled with water the heater element will quickly overheat and burn out. That is why there us a pressure switch to assure that the heater will be full of water before it switches on. So the solution is to have a pump with enough flow capacity to fill the heater and provide an adequate flow. Also, probably at two feet above the water level the pump is unable to produce adequate flow. It might possibly work if the heater and pump were much closer to the water level, AND if the system were full of water already.
So your very first requirement is to have enough flow through the whole loop, which it seems like your pump is not able to produce that much flow, OR, it may not be primed at all.
Your problem is undoubtedly in the fluid part of the system, not in the electrical part.

 

Thank you'll for your inputs. I'll reconfigure the plumbing to see if it will work but I still need a way to set my own temperature. Fish wouldn't be able to survive a hot tub temperature. That was the main purpose of adding the arduino, secondary is for data collection but this would be later after everything is working properly. Any ideas of where in the circuit to add it safely.

 

To control the temperature safely, for the fish, at least, there are thermostats made for exactly that purpose. Some of them are marketed as being for controlling the temperature of stock tanks, so that the water for cattle does not freeze. That would be a good choice because those devices are made for outside use and are heavy duty construction. They would also be safe electrically since they are designed for use by both humans and cattle. You would probably wire such a thermostat into the loop that controls the power relay.
The arduino temperature monitor system should be totally independent from the control system. I recommend two temperature sensors, one for the pond temperature and another to record the discharge water temperature of the circulation system. Then you would know what times it started heating and how long it ran. You could also have that Arduino control an alarm to warn if the temperature became too cold or too hot, before any damage was done.