OTGW print between eTwist and Elga burns out

[wimvandermaaten]

I bought an OTGW board with installed WiFi and firmware from Nodo shop.
I hung this between my eTwist thermostat and my Elga Ace heat pump.
But the PCB burned out at transistor 1.
Nodo shop put the print back in order, after which the GTWO was reattached with the greatest care. Although just before the OTGW Home page showed that discussions were taking place with the network, the printout has unfortunately burned out again. The thermostat connection still showed a small 25 Volts, but the meter on the boiler connection showed 0 Volts.
Can anyone give me a hint as to what we might be doing wrong?
Or are there any experiences with the eTwist thermostat that indicate it is unsuitable for a direct connection?
And... it would be great if the original designer of the whole thing could give a hint in the right direction!?
I'm waiting anxiously before we restore the print. The third time it should go right.
Kind regards,
Wim van der Maaten

[TheHogNL]

Did you read here? https://gathering.tweakers.net/forum/li ... es/2099846
Did you install it on the R-BUS interface instead of opentherm (so between the etwist gateway and the elga ace)?

[hvxl]

You asked the same question here. It would be best to keep the discussion in one place.

[hvxl]

May I assume the measurements you reported were done with the boiler and thermostat disconnected? In that case the voltages you found are normal. The OTGW consists of 2 electrically isolated parts: The main part with the processor and thermostat interface, and the boiler interface. The boiler interface part relies on the boiler to provide power. When no boiler is connected, it is not powered and so you will read 0 volts.

Transistor 1 is part of the boiler interface. So suspicion should fall on the Elga. The eTwist has no electrically connection to Q1. It cannot be causing that transistor to burn out.

The Opentherm specification defines a maximum voltage of 18V and a maximum current of 23mA. The BC558A can handle 30V and 100mA. So it would never burn out when connected to a (correctly working) Opentherm output. This makes me also suspect that you connected it to a different type of interface. One that is probably capable of delivering more than 100mA.

[wimvandermaaten]

May I assume the measurements you reported were done with the boiler and thermostat disconnected? In that case the voltages you found are normal. The OTGW consists of 2 electrically isolated parts: The main part with the processor and thermostat interface, and the boiler interface. The boiler interface part relies on the boiler to provide power. When no boiler is connected, it is not powered and so you will read 0 volts.

Transistor 1 is part of the boiler interface. So suspicion should fall on the Elga. The eTwist has no electrically connection to Q1. It cannot be causing that transistor to burn out.

The Opentherm specification defines a maximum voltage of 18V and a maximum current of 23mA. The BC558A can handle 30V and 100mA. So it would never burn out when connected to a (correctly working) Opentherm output. This makes me also suspect that you connected it to a different type of interface. One that is probably capable of delivering more than 100mA.

Thanks for your response.

The boiler interface was connected to the R-bus of the Elga.
Does the voltage and current of that R-bus exceed 30 V and 100 mA respectively?
I can't find anything about the specifications of the R-bus, but the R-bus of the Elga would automatically behave like an Opentherm output. Or is that not true?

[hvxl]

I can't find anything about the specifications of the R-bus, but the R-bus of the Elga would automatically behave like an Opentherm output. Or is that not true?

I don't think so. As far as I can tell, Remeha's R-bus is not compatible with Opentherm. Neither is AWB's E-bus. Only Atag's Z-bus is basically the same protocol.