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Hacking an EQ-3 Model N

The EQ-3 Model N (2-language user manual) is a radiator thermostat which tries to be better than mechanical counterparts. To some extents it certainly is, it has a clock built in and allows to program temperature changes (7 changes for each day of the week). There are similar models with built in Bluetooth and other fancy stuff, too.

How the Model N Works Inside

Here are a few pictures from inside the device. After pulling out the dial wheel on the front (it's a snap requiring some force) and removal of 4 Torx screws found under the battery hatch it can be taken apart easily.

Take care of the display, it simply falls out when opening the housing. It can be seated back easily later, but only if it didn't break when it fell down to a concrete floor.

This is the Model N as it comes out of the box.

This is the Model N as it comes out of the box.

The same with housing removed.

The same with housing removed.

Looking from the side, one can see the valve actuator. The slightly hidden tin can is a simple DC motor, driving the gearbox right of it. The right end of the gearbox is to be mounted on the radiator valve.

Looking from the side, one can see the valve actuator. The slightly hidden tin can is a simple DC motor, driving the gearbox right of it. The right end of the gearbox is to be mounted on the radiator valve.

This is the circuitry board of the Model N. Noticeable dirt on this brand new device. For details, see the following description.

This is the circuitry board of the Model N. Noticeable dirt on this brand new device. For details, see the following description.

Goal of the Hack

One of the drawbacks of this model is the temperature sensor built right into the housing. As such it measures not general room temperature, but room temperature right next to the radiator, likely the warmest place in a room.

Everything electronic? Heck, then let's rip the sensor out and connect it back with a pair of long wires. This way, temperature can be measured anywhere. Sounds easy, right? With some soldering skill it is!

The Hack in Pictures

During the modification a lot of pictures were taken, so let these speak.

picture picture

How the Result Works

The modification turned out to work just fine. After confirming this the thermistor wasn't mounted in the room somewhere, but connected directly to the ISTA consumption counter of the radiator. And the Model N didn't like this, the valve fully opened and closed every few minutes. For whatever reason. Hard to say, because it's Closed Source, so reprogramming the microprocessor wasn't a realistic option.

This eventually led to development of the ISTAtrol, which uses the mechanical actuator of the Model N, but in combination with a DIY'd controller and Open Source firmware.

hacking_an_eq-3_model_n.1458596500.txt.gz ยท Last modified: 2018/05/27 16:10 (external edit)