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dyju711 asked

Controlling TriStar diversion controller over Modbus


I'm planning my off-grid system. The main issue I have is the AC coupled wind inverter which doesn't support frequency shifting.

In order to protect the batteries from overcharging my plan is to use Morningstar Tristar PWM in diversion mode.

Unfortunately it doesn't support communication with BYD's BMU. I hope it's possible to use Modbus communication and send to it charging parameters from the Venus OS (node-red).

It will allow TriStar to dynamically divert excess power and keep the batteries happy ;)

Do you think it's possible?

Thanks for your help ;)

Node-REDModbus TCPHydro and Wind Power
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Justin Cook avatar image Justin Cook ♦♦ commented ·

Hi @Dyju711, just FYI I have moved this question into the Modifications space to give you a better chance of input from others dealing with Node-Red and other off-manual installations. Cheers!

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dyju711 avatar image dyju711 Justin Cook ♦♦ commented ·

Hi Justin,

Thank you for that ;)

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1 Answer
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dyju711 answered ·

In MODBUS specification for TriStar there are few voltages options that can be modified but there is no information about current limit.

'EV_reg [57345][0xE000](V). Regulation voltage @ 25ºC. The battery will charge at 100% charge current until battery voltage reaches this setpoint. The controller will begin to taper input current so that this setpoint is maintained, but not exceeded.'

I'm not sure how Multiplus operates in off-grid mode when there is excess power from AC out and grid-tied inverter doesn't support frequency shift.

Can it still regulate voltage and current going to the batteries? In that case I would set fixed diversion voltage point in the TriStar in case batteries are fully charged and there is still power from the wind turbine.

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