Tesla Power Wall 2, Solax Hybrid Inverter, Solax Batteries

[scholar2k3]

Hello, I'm seeking assistance to prevent backfeeding between my Solax batteries and Tesla Powerwall 2. Despite utilising time-based controls in the Tesla app, the systems continue to charge each other. Both systems are connected to the same consumer unit via individual RCBOs. I want to limit charging to solar power only. Any guidance would be greatly appreciated.

 

[Chewbacca]

What happens if you charge both up at the same time? Do you have just a battery bank, or solar as well?

 

[arwooldridge]

Hello, I'm seeking assistance to prevent backfeeding between my Solax batteries and Tesla Powerwall 2. Despite utilising time-based controls in the Tesla app, the systems continue to charge each other. Both systems are connected to the same consumer unit via individual RCBOs. I want to limit charging to solar power only. Any guidance would be greatly appreciated.

Unfortunately two independent battery systems will exhibit this behavior, Normally they should be the same make and configured as master slave, however that does not help you now they are installed. Did not the installer advise you about this? Its just possible you could use homeassistant to control one or both to prevent this. One possible way would be to get homeassistant to switch alternatively between the two so only one can discharge at a time eg one in backup mode and one in normal self use mode, then alternate that every half hour or so. or preferably based on charge capacity, that would of course limit the discharge and charge capacity to just one of the batteries but would still utilize the full total battery capacity. As a short term workaround you could of course do the switchover manually albeit somewhat tediously. ie just switch one off at a time then switch over to the other when that battery has sufficient capacity.

 

[michael8554]

If no timers are set each battery should supply the house load minus solar production rather than charge.

Again, no timers, if battery One/ inverter One is "empty" then it should charge from solar.

But if battery Two/inverter Two is not "empty", inverter Two may sense inverter Two charging as a house load and start discharging ?

This happens when both inverters are set to charge at the same times ?

 

[arwooldridge]

If you are using CT's on one of the systems eg Solax,, there might be a workaround by fooling one system into thinking there is no grid current ( import or export) up to a certain threshold value which is higher than that of the other system's threshold. A simplistic solution might be two paralleled back to back diodes in series with the CT output. this would depend on the scaling of the CT's the Solax would then only take control once the Tesla battery lost control ( eg if too much Solar power or battery full) you could use 1N4001 diodes or maybe Shottky diodes if you needed a lower threshold. On the Solax the load resistor (burden resistor) for the CT is in the inverter unit so external diodes will block any voltage up to about 600mV for 1N4001 or 300mV for the schottky diodes. If that fails another possible solution would be to declare the CT's as different scaling eg if your CT's are 100 amp, declare them as 200Amp. this would of course affect any reports of import/ export power in your app. but the threshold solution would be preferrable as a first try.