tas6 avatar image

Controlling a Dump load on AC2 Out using assistants depending on SOC AND charging level

Off Grid installation with 8.2 KW Fronius AC coupled on AC1 Out and 10000VA quattro

I have successfully set the relay assistant to switch on the AC2 Out relay when SOC is above 92% and off when SOC drops back to 91%

However when a cloud for example comes over and my PV drops significantly I want the AC2 relay to temporarily switch off again until it clears

I am thinking to use an additional relay assistant to switch AC2 off if batt voltage drops below 50.5 volts and on again when above 51 this i think would mean i only load AC2 when i am truly in surplus generation mode??

MultiPlus Quattro Inverter ChargerFroniusAssistants
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3 Answers
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mrhappy answered ·

One way is to use an external contactor with an NC connection, connect AC2 to its input and the dump load to its output, and drive the contactor with one of the relays in the quattro separately.

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Not sure what you mean by that, but having two assistant pairs controlling one function and have it work as an AND-logic is not possible in VEConigure AFAIK. Having simply two assistant pairs with different criteria would probably have them turning on and off individually. Imagine, in the situation @TAS6 posted, as an example the SOC is 80%, Assistant pair 1 is OFF, but sunshine comes in, the solar chargers start charging the batteries at high amperage and the voltage rises to over 51, the second assistant pair would turn ON and activate the dump load even though SOC is far below 92%.

If more than one assistant is controlling one specific function, an ON condition always override another assistants OFF condition. Because of this, external relays/contactors is one way to create an AND-type logic to get the functionality one is after.

That makes sense, because if you invert the logic it it will be OFF override.

I would think that if you just used voltage it would be a good indication that there is excess, as if you turn the load on and the voltage doesn't drop too much then the MPPTs have probably picked up the load vs battery. However I do CC/CV voltage charging of my LFP batteries but if you have bulk, absorption, float voltages that are diffrent this probably won't work and it would be best just to use SOC.

Nice. I think the tip from @pwfarnell below would probably work very well for @TAS6, i thought about the generator start-and-stop but disregarded it based on not understanding its capacity completely.

I am currently testing overflow-automation through node-red now. I set SOC, voltage, multiplus inverting as criterias as well as monitoring current flow. With that I can stop the dump load as soon as there is any current moving from the battery bank into the system.

What do you mean by "overflow-automation" I haven't heard of that before.

I also use NodeRed to control my loads, everything from Pool pump to hot water heater. I have installed 4x 1kw DC elements in my hot water heater and change how many stages I need based on PV. My system mostly just looks at Battery Power and SOC. I have CAN batteries so makes it easy.

I have also connected the Cerbo relay to the Aux input of the Multiplus to use the AC2-OUT for another hot water heater. Control the Relay via NodeRed too.

Overflow is my own term for dump I guess, battery fully charged and potential energy from PV...
Oh cool,

Also looking at MPP Mode is super useful at telling if there is more power available in case you haven't see it.

Yea that would be the completing bit of info, but unfortunately I have off-brand PV chargers. In the future maybe...
pwfarnell avatar image
pwfarnell answered ·

Would the method outlined in this post help because using the generator start assistant with the relay sense reversed means that the on conditions for the dump load are AND, i.e. you need to have both the voltage and SOC high to start the dump load. The off settings are then effectively OR, only one of the SOC or voltage needs to be low to stop the dump load. I have this programmed up for my Multiplus but have not yet loaded or tested it. The linked page shows power draw and SOC but you can also use battery voltage as a trigger.

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harold avatar image
harold answered ·

I think you can control it by the right order of the programmed assistants, for on and off!

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