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groningen avatar image
groningen asked

Easy way to find out if MPPT is throttling - would like to have a dump load activated

Dear All


I know this question (or parts of it) has been asked multiple times, but maybe some of you have a easier or updated way of controlling this.


The idea : During the day when the battery is full and I still have excess solar, I would like to trigger a dump load (boiler - +- 2000W).

The question : What would be the best way to go about this?

First I would need to have 'too much" solar i.e. (SOC is almost full) and the house load is maintained.

I have noticed that my MPPT's are then switching to Absorption / Float, so this is my first "clue" that I have excess solar. (I have read that some have indicated to check Modbus, but I have no clue how this works).


Also, I have two (parallel) MP-2 and a CerboGX so I assume I can use this to trigger a relay?


Side question : What would be the best option regarding relay? Solid state?


I am not to familiar with the VE-CAN / ModBus stuff so I was hoping to keep it simple. The other option I assume is Node-red, but I still have to learn this option and how it works.


I also assume a easier way would be to program it (not sure how) that if SOC is 95%, switch on the dump load, but I was hoping to have something a bit more intelligent.


Any information will be appreciated / You-tube or manual or ....



MPPT Controllers
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klim8skeptic avatar image klim8skeptic ♦ commented ·

@Groningen If your mppt has a relay you could use that to switch the contactor.

mppt-relay.png

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seb71 avatar image seb71 commented ·

Side question : What would be the best option regarding relay? Solid state?

For the boiler power wires, use a contactor.

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matt1309 avatar image
matt1309 answered ·

Hi @Groningen

A few ways to do this. If you're grid tied and don't have export limits/using ESS then it's easy you just see you're in absorption phase and can see exporting. And then if exporting > the load you'll turn on then turn on load. (I have this setup and I do the check in node red and if there is enough excess power i turn on the load using a shelly smart switch which is turn on via node red). I prefer to use a smart switch like shelly as I find it more flexible than just using the one relay built in, as i can have multiple loads using multi shelly smart switches etc, however whatever works best for you.


If you're not grid tied then then it's a bit more involved. As you mentioned MPPT throttling can be noted within modbus registers. I can't quite remember which register, maybe MPP operation mode 791

Here's the list of registers below.

https://www.victronenergy.com/upload/documents/CCGX-Modbus-TCP-register-list-3.00.xlsx

Pretty sure you can also access this information via MQTT (I'll paste dbus address/MQTT topic information in links below).

However what's probably easier though is doing the logic of "if there enough power do x" all in node red as then you dont need another system, you can just run it all on the gx device you have.

For example I think the solar charge node in node red give you access the MPP Operation mode. You could then check that and then turn on the load. In terms of working out if there's "enough" excess power I'm not too sure.

Personally i would probably just write something in node red like:

if MPP operation is in current limit then turn on load, wait a few seconds for MPPT to catch up, then check if lots of battery is being used. If it is then turn off load. and dont do this check again for a timeout interval say 5mins.



Some useful links:

Modbus info: GX Modbus-TCP Manual [Victron Energy]

DBUS paths useful for working out MQTT topcis: dbus · victronenergy/venus Wiki · GitHub

MQTT explained: GitHub - victronenergy/dbus-mqtt: Venus OS service mapping the D-Bus on Venus OS to MQTT


For node red details it's not really Victron specific so i dont know of any good pages in particular.

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groningen avatar image
groningen answered ·

Hi @matt1309


Super thank you for the quick response.


Yes I am grid-tied, but no feed-in allowed.

Also, our electrical supply is somewhat unstable as frequent power cuts happens on a daily basis.

But yes, I also think Node red would be the best option. I have updated my GX and loaded the Node-red file, I just have to sit and learn the coding options.


In the far far future, I would like to take into account the weather prediction to check if it should switch on or not or maybe "pre-heat" if it predicts cold weather the next day.


I guess the relay on the Cerbo GX will also work, that is if I struggle to get a Shelly. But I see what you are aiming for as you can trigger it as you think best (override - multiple loads with multiple Shelly's)





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matt1309 avatar image matt1309 commented ·

Hi @Groningen


That makes sense, I think node red is your best bet.

Node red isn't too bad once you've got the basics of programming understood (if statements being the main thing).

One thing to note is to add a little buffer when turning on and off the loads for MPPT to catchup. For example if you turn on the load it'll take awhile for MPPT to catch up, so some battery usage might be used, so if you wrote this in node red

if (PV < Loads){ //ie battery is being used

turn off load

}

Then the load would be instantly turned off after being turned on (then back on, and back off etc...)


You'll need to add some sort of delay or buffer. either with time or watts.

Happy to help with any node red specific queries once you get stuck in.


(Your forecasting plan can also be done in node red, get weather data via some external API and then turn on/off loads based on that).


When it comes to detailed questions around this stuff you may get better responses in modifications section of the forum rather than Questions and ANswer section


EDIT:

ChatGPT can be a game change when learning JavaScript for node red, if you are ever stuck with understanding something. Was super helpful when i was learning it.

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groningen avatar image
groningen answered ·

@matt1309


Thank you very much for the advice on Node-Red. I will definitely give you a shout if I get stuck on programming.


Also, I understand your "buffer" check. Something like a hysteresis effect on the equipment.


Also, I also think Chatgtp might be something to keep a eye on as it can be a useful tool.


Again, many thanks

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