emonPi / Tx, Mk2 PV Router, with dual immersion elements

Newbie here.  There is a lot to take in. Going round in circles with information overload, so forgive me.

I ordered an emonPi, although now I am thinking I should have gone for the emonTX, as I see there is a sketch to preform the same function as the Mk2 PV Router (minus the output stage).

1.  Can the emonPi also run the Mk2 PV Router code?

2. It looks like you can use the emonTH to control the output stage (I saw it in one of Robin's videos), but there doesn't seem to be any info on that.  The Mk2 PV Router, appears to have a CT on the control output.  Is that necessary for normal operation, or is it just for calibration?

Here is my idea.  I have two heating elements in my tank. One at the top, and one near the bottom.  I want to use three temperatures sensors on the tank (which the emonTH can do), and then use either a double-throw relay or second triak to alternate between the heating elements.  The idea is, you start heating the top of the tank first, and then switch to the lower one, once you get to a set temperature.  I also want a GUI to show the temperature of the tank at the three points, and the option to set target temperatures for a time of day, even if it optionally means pulling power from the grid.



Robert Wall's picture

Re: emonPi / Tx, Mk2 PV Router, with dual immersion elements

1. I suspect it would be possible to run one of the Mk2 router sketches on the emonPi, and it looks as if you might be able to get an output via the RJ45 connector if you need it. However, I'm not aware that anyone has ever tried to do either of these things.

2. The CT on the controlled output is to measure the diverted power for indication purposes. (If you have a thermostat on the immersion heater, the triac state only indicates the power available for diversion, not the actual energy diverted since the 'stat will open when the max. temperature is reached. If you're using temperature sensors to override diversion at max. temperature, then that is no longer a problem.)

You will need a triac or a beefy transistor to drive your relay/contactor anyway, so why not use two output stages, one for each immersion element, which should be a lot more reliable?

But one thing is puzzling me, why do you want to use an emonTH to drive the output stage and run the control software on the emonPi? Are you planning to put the emonPi close to your consumer unit and use the radio to control the output switch via the emonTH, which is local to the immersion heaters?

LogicEthos's picture

Re: emonPi / Tx, Mk2 PV Router, with dual immersion elements

Ideally the output driver needs to be next to the immersion heaters. Three reasons for this. Firstly the power caballing feeding it is 2.5mm, and can't support two heaters simultaneously, without a major rewire.  So the switching needs to be done there.  Secondly, there is limited space around the consumer unit for more switchgear. Thirdly, the meters (including the generation meter) are on the other side of a wall, where I need to clip on my CT sensors, and so it's more practical to put the logic there, and transmit it.

Thanks for the info, that helps clear things up.


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