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The relay “ON” state the BMS refers to is the energizing of the relay. As others have said, if you use the “NC” connections then this will be inverted.

The BMS supports up to 64 modules so over 250V DC - however I really don’t recommend that, it was designed for 48V usage.

Each module can only measure up to 4.4V - normal range for a lithium cell.

So I will need to make a hardware modification on the modules to support 6.5v?

What type of cells operate at 6.5v?

The diybms isn’t suitable for this voltage, the modules use attiny chips which are only rated to 5v max.

What the parameter is responsible for - Relay default? In my understanding, what state should the relay be in by default? I understand correctly that if I switch this parameter to on, then the logic output will be 1, if I turn it off, then 0? (Other parameters are disabled)

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A controller code version number somewhere on the web page.

@Fred7421 would you mind requesting this feature over on GITHUB ?

Correct. The “default” rule is the starting position of the relay when the BMS is powered up (after the code has started running). On=1=Energised, Off=0=Not Energised.

Wow. Maybe that’s the problem? I expect the output to change immediately after the setting is changed, and you say that only after a restart.
Or I misunderstood and this does not affect the level of the logical output?

You misunderstood, what I mean is when you first power on the controller the relays will be in an unknown state, after a few seconds the code will start and set the relays to the “default” state.

Once the code has then stabilised and read the modules it will run and process the rules, and then apply the relay state as the rules determine.

When changing the “Relay default” settings from off to on - should the state of the logic output to BMS change?

Yes, it should, as long as another rule is not over riding it. Perhaps this is a bug with the new rules code?

The last clarification. Should the change in the output be instant or only after a restart?

I would expect it to be instant. Since the last code change with the new relay rules in it, I think when the rules are saved, all the rules are reset but the default relay logic isn’t applied correctly.

Now I will describe how it actually works (Firmware HysteresisRules, All rules X):
Relay default - OFF -> On the corresponding output, logic 1
Relay default - ON -> On the corresponding output, logic 0

And all the rules work out in exactly the same style. Logically correct to do the opposite.

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Okay, my relay board is happy with the outputs of the PCF chip - it must internally invert as its using an optocoupler to drive the relay.

What external relay board are you using?

I am using standard aliexpress relays or relay via conventional power transistor. They all wait at the input for ON 1 and OFF 0