Opentherm Smart Power

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Opentherm Smart Power

Postby marcgk » Sat Nov 07, 2015 3:17 pm

Hi,

Can anyone tell me how the Smart Power function works in the Opentherm protocol?
I build an opentherm gateway in the past, and I would like to update it so I can supply power to my ISense thermostat from the gateway.

Best regards,
Marc
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Re: Opentherm Smart Power

Postby D_Hailsham » Sun Nov 08, 2015 1:10 pm

Do you have the wired or wireless version of the iSense?

I found this in a copy of the Opentherm Newsletter which managed to escape onto the internet

Basically OpenTherm SmartPower consists of 3 power levels; low power (existing protocol specification), medium power and high power. The use of these power levels can best be described with an example.

A thermostat (master) with a large display and backlight function, is powered via OpenTherm by a boiler (slave). The display and especially the backlight of the thermostat demand more power in order to function. Only this demand is not constantly and depends of the use the thermostat. With OpenTherm SmartPower this problem is now solved. When the master needs more power (for the backlight), it will ask the slave to provide more power. The slave will then switch to a higher power level. When there is no longer a need for more power, again a request will go to slave to switch back to a lower power level. Which power level is being used, depends of the functionality.
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Re: Opentherm Smart Power

Postby marcgk » Mon Nov 09, 2015 8:28 pm

I have the wired version of the iSense.

But how is the slave providing this higher power level?
To increase power you need to increase the voltage or increase the current.
The slave talks to the master by changing the current level. So probably the slave uses higher current levels when in medium or high power level?
Normally idle current level is between 5-9 mA. So probably this level is increased?
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Re: Opentherm Smart Power

Postby ThinkPad » Tue Nov 10, 2015 8:41 am

What about the backlight on a Remeha iSense thermostat? I use it with my Agpo (Econpact 225c) boiler, which doesn't supply enough power it seems, because i have to put in batteries in the iSense to get the backlight to work.

Would it be possible to let the OTGW supply this needed amount of power?
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Re: Opentherm Smart Power

Postby Templar » Sun Nov 15, 2015 10:09 am

ThinkPad wrote:What about the backlight on a Remeha iSense thermostat? I use it with my Agpo (Econpact 225c) boiler, which doesn't supply enough power it seems, because i have to put in batteries in the iSense to get the backlight to work.

Would it be possible to let the OTGW supply this needed amount of power?


The OTGW supports the Smartpower feature. If the iSense does too, you're in.
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Re: Opentherm Smart Power

Postby hvxl » Mon Nov 16, 2015 1:58 pm

marcgk wrote:I build an opentherm gateway in the past, and I would like to update it so I can supply power to my ISense thermostat from the gateway.

Was it the Rev B gateway described here that you built? That one is able to supply the required power to the iSense. Just make sure you use firmware 4.0 or later.
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Re: Opentherm Smart Power

Postby ThinkPad » Mon Nov 16, 2015 2:22 pm

Templar wrote:
ThinkPad wrote:What about the backlight on a Remeha iSense thermostat? I use it with my Agpo (Econpact 225c) boiler, which doesn't supply enough power it seems, because i have to put in batteries in the iSense to get the backlight to work.

Would it be possible to let the OTGW supply this needed amount of power?


The OTGW supports the Smartpower feature. If the iSense does too, you're in.

So that means i can remove the batteries i now use, from the iSense and the OTGW will take care of supplying the current needed for the iSense' backlight? That would be nice :D
Will try tonight.
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Re: Opentherm Smart Power

Postby marcgk » Mon Nov 16, 2015 8:15 pm

The gateway I built is based on the same opentherm interface as in your design Schelte, but I used a different microcontroller (atmel). So I can't use your firmware.
My gateway is communicating with my iSense thermostat by Opentherm protocol, and communicating with my intergas boiler by both Opentherm and RS232. It's also powered by 24V from the boiler. The firmware for my gateway is written by myself.
I would like to update my own firmware with the Smartpower future, but I don't know how the smartpower function exactly works. I understood the opentherm hardware interface is the same, so it should be possible to add the function in firmware.
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Re: Opentherm Smart Power

Postby ThinkPad » Mon Nov 16, 2015 10:21 pm

ThinkPad wrote:So that means i can remove the batteries i now use, from the iSense and the OTGW will take care of supplying the current needed for the iSense' backlight? That would be nice :D
Will try tonight.

I just tried, and it works. The iSense backlight now works, thanks to the OTGW :mrgreen:
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Re: Opentherm Smart Power

Postby hvxl » Wed Nov 18, 2015 6:17 pm

marcgk wrote:I would like to update my own firmware with the Smartpower future, but I don't know how the smartpower function exactly works. I understood the opentherm hardware interface is the same, so it should be possible to add the function in firmware.

The "smart power support" implemented in my firmware is based on a few clues found on the internet, experimentation and logic reasoning. Not on official specifications. However, the experimentation was done with an iSense, so there's a good chance it will work for your situation.

The most important clue I found was on the Dutch version of Wikipedia, which mentions power values for each of the Smart Power levels. Comparing those to voltage and current values mentioned in the v2.2 spec suggested the following:
Low power: 40mW = 5V * 8mA (low voltage & low current)
Medium power: 136mW = 17V * 8mA (high voltage & low current)
High power: 306mW = 17V * 18mA (high voltage & high current)

So apparently for the increased power levels the line is kept high during the idle state in one or both directions. My first attempt was to simply raise the line during the idle state, but that didn't work. It turns out that the line is actually inverted. That was even easier to implement on the PIC. There is a bit that controls whether the output of the comparators is inverted or not. So I just had to set or clear that bit at the appropriate times. I don't know if it's just as easy on the atmel.

To enter high power state, the master simply inverts its line. The slave detects that and also inverts its line. To enter medium power state, the master inverts (or raises) its line for some amount of time (around 5 ms if I remember correctly). The slave should still invert its line in response to this, but the logic level from the master is not inverted in this mode.

The attentive reader will have noticed that this means that medium power mode is actually low voltage and high current (90mW), rather than high voltage and low current. That also makes more sense because it's much easier to utilize extra power from a raised current than from a raised voltage.

There's one more thing to consider: The iSense first indicates its desire to use Smart Power to the slave via HB0 in DataID 2. The slave must acknowledge this for the iSense to even attempt to use Smart Power. The iSense then switches to High Power mode and sends a Read-Data request of DataID 0 (status). The iSense will only continue to use Smart Power if the response is received correctly. So during experimentation you may have to frequently disconnect/reconnect the iSense. To be on the safe side, I also took care of returning support for OT version 3.0 in DataID 125, although the iSense doesn't seem to take that piece of information into consideration.

After the startup sequence has been completed successfully, the iSense will only ever use Medium Power mode. It switches between Medium and Low power mode in sync with the backlight.

For more details, please check the otgw firmware source code. That's what I would have to do too.
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