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dirkw avatar image
dirkw asked

Cerbo GX: Periodic maintenance run at full load

Hello,

after there was unfortunately not "the" solution in the German-speaking area I try it again in the English-speaking area.


I am looking for a technical solution for an off-grid solar system with Cerbo GX, Multiplus 2 and MPPT RS to carry out the periodic maintenance run of the diesel generator in summer under full load.

In other words, the MPPT RS would have to be switched off automatically beforehand AND the SOC value must have dropped so far that the generator can run at full load for several hours.

Is there a technical solution for this with the Cerbo GX?

I have already found the maintenance run function, but it does not work under the conditions described above


I look forward to your creative ideas

cerbo gxGenerator
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2 Answers
Philipp Trenz avatar image
Philipp Trenz answered ·

Hi @DirkW,

I see two options here:

1. Do it half-automated

what I would do is, to configure the Auto start/stop not to a periodic run, but rather to start and stop at a certain SoC level. Then, you can shut the MPPT RS off and discharge the battery with your house loads until the generator kicks in.

The tricky parts are:

  • If your house loads vary, you cannot accurately determine when the generator will start
  • If your generator fails to start, it might empty the battery and as the MPPT is offline, it also won't be able to restart

For the first one, you could experiment with the quiet hour settings to move the generator start time a bit, e.g. in night hours. And for the second, if your at home and switch the MPPT manually, you of course will be able to switch it on again after the lights went dark.

2. Fully automated with Node-RED

Another path is to use Venus OS Large with Node-RED to build your own automation flow. It needs a bit of learning, but it's a very powerful tool as soon as you got the hang of it.

With a simple flow, you can switch your MPPT RS on and off based on certain conditions, for example:

  • Every Friday morning, turn off the MPPT to drain the battery over the day and night
  • Switch on the MPPT again when battery SoC is below 30%

Now, when you configure the Auto Start/Stop of your generator to start at a SoC of 35% and the generator fails to start, your MPPT can charge the battery again.

If you like, you could also automate the starting and stopping of the generator via Node-RED to add even more custom logic to it.





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dirkw avatar image
dirkw answered ·

Thanks for the good ideas and information.

I had already thought about connecting loads such as the hot water heater to discharge the batteries.

Once the system is in operation at the customer's premises and the new generator has been delivered, I will take a closer look at the subject.

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atebee avatar image atebee commented ·

I use Node Red to control a hot water heater (immersion element) via a Shelly relay and a contactor.

The whole generator start and load test would be fairly easy to automate this way.

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dirkw avatar image dirkw atebee commented ·

That's exactly the solution I had in mind with Shelly.
Do you control them with Mqtt?



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atebee avatar image atebee dirkw commented ·

I just use webhooks at the moment to set the relay state.

https://shelly.guide/webhooks-https-requests/

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