Opentherm Gateway Voltage levels

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Opentherm Gateway Voltage levels

Postby desatg » Wed Aug 23, 2017 11:13 am

is there a way to obtain adjustable voltage levels on the boiler side (X2)?
Now I measure a low voltage of about 5V and a hign voltage of about 17.5V (when the thermostat connected to X1 is transmitting).
I would like to adjust these values, namely:
_ low voltage should be set between 0V and 8V
_ high voltage should be set between 15V and 18V

Thank you
All the best
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Re: Opentherm Gateway Voltage levels

Postby hvxl » Sat Sep 23, 2017 9:58 am

I don't understand what you are trying to achieve. The voltages you reported already fall within the limits you specify.
But if you want to change the levels, you will have to use different values for D11 (low voltage level) and/or D10 (high voltage level).
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Re: Opentherm Gateway Voltage levels

Postby vfreak » Mon Jan 15, 2018 10:32 pm


Sorry for necroing, but I have very similar task to do:
I am planning to make gateway, with different voltage/current levels.
Why? Because I have an Immergas boiler with Immergas remote control.

I have a very strong "suspect" that Immergas uses same communication as Opentherm, but because they are not in the group, they modified just the communication levels.
Supply of my "suspect": In an Immergas remote description (it was in Czeh language) they wrote: "... based on Opentherm ..."
To prove, I will check with my brand new game oscilloscope DSO138 once I get from China via eBay and I put together.

With multimeter I know "standard" voltage is 25V and goes down when it is active.
Meanwhile standard current is 10mA and goes up when it is active.
...and I cannot switch the polarity of the 2 wires (written in Immergas documentation), so I can neglect D5-D6-D7-D8 graetz bridge.

So I am planning (after I realize some more fact) to modify
- D10, D11 - to tune the command voltage to boiler
- R2, R3 - (ratio) for current sensing of boiler answer
- I have to increase the 24V to min 28V to give 25V to the thermostat,
- I should change R7 to setup the "low" current and R11/R12 ratio to fine-tune the high current?
- R5, R6 not to fry (but sense) the thermostat voltage signals.

If Immergas inverted the signal levels, I have to invert back (eg.: OK1A pin1 to Vcc and pin2 to R8 for negating voltage to boiler).
If somebody could check these changes will be OK I would appreciate it (in theory now).

Meanwhile I do not really know how to be sure that commands are the same or not.
Maybe I build a "sensing only" first and see if everything works.

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