Hack SONOFF TH ELITE – 20A DRY Relay Contact – THR320D

When I bought the new SONOFF TH ELITE model to replace the old TH10/TH16 models, I had only one thought: to use the dry contact in my projects.

But unfortunately I was disappointed to notice that the SONOFF TH ELITE 20A power contact is a WET one, and the DRY one is 5-30V and 1 A, which in my case is unusable.

I used the old model to control the controller of an underfloor heating, but additionally I had to use contactors, to change the WET output to a DRY one!

Now, after being very disappointed with the new hardware, I decided to make the necessary changes myself to turn the WET contact into a DRY one and remove the additional contactors from the heating project!

Below are the images with the changes made. In practice, it was necessary to interrupt two wiring/circuit routes and to modify the way in which an electronic part (fuse) is connected to the circuit. That’s it, nothing more.

ToDo steps to follow to convert the WET contact to a DRY one for SONOFF TH ELITE, model THR320D in this images:

1. Back side of the printed wiring boards:

• the circuit is interrupted in the circled area A
• remove the electronic part, a fuse, from the location shown by arrows 1 and 2

2. The upper part of the printed wiring boards:

• the circuit is interrupted in the circled area B
• tinned the removed piece in a new configuration. One of the pins is extended and inserted into the same hole from where it was removed, arrow 2, and the other is directly attached to terminal 3, see arrow 3.

3. With the device unpowered (very important)

• check with a multimeter that
• * there is no continuity between terminals 1 and 2 (DRY Contact now)
• * there is no continuity (short-circuit) between terminals 3 and 4 (Power terminals now)
• * there is no continuity between arrow 2 and terminal 2 (old location for fuse)
• * have continuity between terminal 3 and the location indicated by arrow 2 on the back of the printed wiring boards.

4. With the device powered:

• Press the manual button and check with the measuring device that you have continuity between terminals 1 and 2
• Press the *OFF* manual button again and check that there is no continuity between terminals 1 and 2

Important:

This is a demonstration tutorial and does not cover any subsequent damage to this device. If you do not agree with this aspect, do not try to make these hardware changes!

Note:

To return to the WET contact mode, a single cable between the power supply and one of the relay pins (see image) is enough!

If SONOFF decides to bring a long-awaited improvement, it only has to eliminate the connection between the power supply and the relay output. It must also internally connect a terminal of the relay with the power supply through a short-circuit terminal!

In order to maintain compatibility with the already existing model, a 2P Terminal Short Circuit / Terminal Strip model can be used between the L-In and N terminals. Those who want to switch to the DRY Contact variant, Short Circuit / Terminal Strip can be removed from the inside, opening the case!

This is what I call a complete device, it’s a shame to put so much work and investment into such a useful but incomplete gadget for professional use!