DIY Hot Tub with Mobile/Online Control

About This Project

I made a DIY Hot Tub out of an old 100 liter IBC tank and I want to control all of it via the web. I had used in an earlier version WebIOPi for this, but now I've changed it all over to Cayenne.

The "whirlpool" (sadly currently without whirl) is equipped with a small filter pump and a heater. I've checked multiple methods of heating the 800 liters of water to temperatures of about 36-40 degrees Celsius. It was too expensive to keep this amount of water hot all the time. The electrical heater is only 2kW which could only heat 3 degrees per hour.

After some research, I was thinking about a Webasto Diesel car heater (5kW), which I can run on heating oil. These are cheap on Ebay.

After a few tests with about 100 liters of water, I was ready to get this into my whirlpool.

The water flow is pool > filter pump > heater > pool.

There are 3 temperature sensors:

• Water temperature

• Heater output temperature

• Air temperature

For electrical safety, I have no 220V at the pool. It's only on the controller box, which is about 3 meters away. The filter pump works with 12V AC from its own power supply and the Webasto heater works with 12V DC.

What's Connected

• Raspberry Pi B+

• 12V power supply with 17A current max

• Car 12V to 5V-USB step-down for the Raspberry Pi

• Heater

• Relay board with 2 relays

• Box for installation

• 3x DS18B20 temperature sensor in waterproof housing

Triggers & Alerts

To ensure that the heater is only on when the pump is on, I've created a trigger in Cayenne that says "if relay (heater) is on then relay (pump) is on", and another one that says "if relay (pump) is off, then then relay (heater) is off".

I also don't want the pool to be hotter than 40 degrees Celsius, so I've set up another trigger that says, "if water temperature is above 38 degrees Celsius, then turn off relay (heater)".

Scheduling

To save energy and conserve heat, I've set up a scheduled action in Cayenne to turn off the relay (pump) during the night time. For redundancy, I've also set up a scheduled action to turn off the heater at night time, just in case it's still on.

Dashboard Screenshots

Project Photos