question

It is already possible, you can switch on AC2 based on a lot of conditions, when using Lithium batteries it's really easy: just use battery voltage as a trigger. (or SOC if you prefer)

To expand on Boekels answer; This is possible and done through the Programmable Relay (Use ACOut2 relay) assistants functionality in VEconfigure.

You can test the functionality in VEconfigure by loading up the Fake Target dummy with full options before actually programming your Multi.

It would be great if you/someone could write up a more extensive description, step by step of what you do, and screenshots to help others in the future.

This documentation could definitely use some expansion and improvement:

https://www.victronenergy.com/live/assistants:start

Here's an example of using the generator start/stop assistant, dump load connected to AC-out 2:

'open relay to start generator' - this inverses the logic

'start generator on load': this is actually stopping the dump load (remember we inversed the logic), even when battery voltage is higher than the set 'dump' voltage:

'start generator when load higer than 5000 W' - let's say the dump load is 2000 W, if a lot of other loads are on, you might want to turn of the dump load to prevent overloading the inverter.

'stop generator when load is lower than 2000 W' - when other loads are lower, start the dump load

'Start generator when DC input voltage is lower than 56 volt' - this stops de dump load when battery voltage sags under 56 volts

'stop generator when DC input voltage is higher than 58 volt' - this starts the dump load when battery gets above 58 volt.


On systems with Li-ion batteries, I'd use switching based on voltage, although if you have a reliable SOC from a BMS this should also work.

On systems with Lead-Acid batteries, I'd use SOC as a trigger, but you can ad a secondary trigger on voltage also to prevent errors. (I don't work much with Lead Acid batteries anymore)

I have also been thinking about this (to run a water heater)...

Like most, my aim of the logic would be to only run the load when batteries are full & when there is enough PV power to support the load without draining the batteries.

If possible I would even like to avoid small 100% to 95% SOC cycles...

My thinking is that a reasonable way achieve this fairly easily would be with the following conditions (mainly with reference to BMV data);

TURN ON conditions;

If SOC is >98% AND if MPPT 'awake' (panels irradiated) AND both conditions maintained for >15 min then turn ON

TURN OFF conditions (that also kind of act as a basic PV available power check);

If there is a Battery Current DRAIN >1 Amp & maintained for >30 sec then turn OFF

OR if SOC is <95% OR if Voltage is <x V (just as a safety measure)

Using a large time condition (ie 15 or 30min) for the turn ON condition will avoid the load switching on & off consistently/frequently if the battery is full but there is not enough PV to support the load (without draining the battery).

As a result it should only be possible for the load to turn ON once 15 or 30 minutes and then 'check' if there is enough PV / charge current available to cover the load. Even in worst case PV conditions, such a short check (only as long as the turn OFF condition) will have a minimal effect on the battery SOC.

I believe that the BMV SOC is already available to use in the Multi (to use as a trigger/selection), but don't believe that BMV instant charge/discharge current is (yet) - this would probably be the main missing link...?

The small downside to this logic is that during the later stages of Absorption period the charge current would drop off (meaning significant unused PV power during this period of time), but the SOC condition will not yet be met until the battery is fully charged (basically after going into float).

To rectify this the SOC % used to turn ON could be lowered but then you could risk not fully charging the batteries in the same day... (if there is not enough power for the load & for charging simultaneously) Potentially the logic could be 'complicated' even further by adding a different/additional OFF condition that is only active for times when SOC is <95% (to ensure sufficient charge current is still flowing to the battery).

Any thoughts from anyone more deeply involved?

Does the 'basic' version seem reasonable to implement with only a few additional parameters provided to the Multi?

Regards, Mark.

Can the ACOut2 relay be driven high (and then low) with a Modbus TCP input to a CCGX from an external Modbus TCP Client? Would save me buying a relay for a system I'm working on.

Thanks,

Pat

It is great to hear that the relay hardware is already capable of this - and I will start to play around with assistants.

Here is the logic I would like for the AC2 relay:

+ If on shore power, open the relay and pass through the power.

+ If on generator power, once the battery has reached 90% charged open the relay and pass through the power.

+ If on inverter and charging via DC solar, engage the relay when the battery reaches 90% and disengage when it hits 80%.

And of course - there should be a way to manually override this automatic logic.

This would let all excess power very nicely flow into the hot water heater hooked up to AC2.

Any thoughts on how to implement this are appreciated.

My understanding from he above I could use the following to switch hot water system on and off

*)Use ACOut2 relay to start generator

*)’open relay to start generator' - this inverts the logic

(start generator = open relay to turn off ACOut2)

*)’start generator when load higher than 5000 W for 5 seconds’ -and

Open ACOut2 when load higher than 2400W for 10 seconds

Turn off hot water when load higher than 2400W for 10 seconds

'stop generator when load is lower than 1800 W' -

Close ACOut2 when load is lower than 1800W

Turn on the hot water when load is lower than 1800W for 10 seconds

*)’Start generator when DC input voltage is lower than 26.5 volt' -

Open ACOut2 when DC input voltage is lower 26.4

Turn off hot water when voltage is lower than 26.4 will have to experiment with this to get about the SOC I want especially with voltage sag.

*)’stop generator when DC input voltage is higher than 26.61 volt' -

Close ACOut2 when the DC voltage is above 26.61

Heat hot water when the voltage is above 26.61

*)When the generator is started must stay on for a least 10 seconds

When ACOut2 is Open and the hot water system is off must stay off for 5 minutes longer.

*)The generator is not stopped by AC input

I am not sure about this command, I assume it applies to the assistant as a whole, that is not effected by inverted logic with the start/stop, but will allow the assistant to run or remain in its current state even if AC input is active. That is I have shore power.

Would this logic work as water heater control with load diversion and with inverter overload protection?

TAB: Assistant Configuration

programmable relay (2) (size:186)

*) Use primary programmable relay.

*) Set relay off

*) when load higher than 2500 Watt for 10 seconds.

programmable relay (3) (size:47)

*) Use primary programmable relay.

*) Set relay on

*) when load lower than 2000 Watt for 10 seconds.

programmable relay (size:30)

*) Use primary programmable relay.

*) Set relay on

*) when SOChigher than 99%.

programmable relay (1) (size:33)

*) Use primary programmable relay.

*) Set relay off

*) when SOClower than 98%.

Total size of all assistants including the required

(hidden) system assistants is: 368