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Growatt 3000; Advice on using relay in series with inverters on/off switch for BMS discharge control.

apctjb

Solar Enthusiast
Joined
Jun 16, 2020
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I have a system with 2 Growatt 3000 (operating in parallel) and Chargery BMS with separate charge and discharge relays (external 250A DC contactors). With this configuration the BMS opens the discharge relay on discharge related faults, and the charge relay on charge related faults.

PROBLEM: because the Growatt 3000 is an all in one (inverter/charger) with only set of cables connecting the unit to the battery bank if the BMS opens the discharge relay , the inverter is totally disconnected from battery so no charging can occur. For example if the BMS senses a low voltage situation, the discharge relay opens, disconnecting the Growatt from the battery.

POSSIBLE SOLUTION: Install a small low current relay (controlled by the BMS discharge port), in series with the inverters on/off rocker switch and eliminate the discharge DC contactor . With this configuration if the BMS opens the discharge relay the inverter shuts down (same as turning off the rocker switch) but the Growatt 3000 remains connected to battery so charging can continue (Note: The on/off switch on the Growatt only controls the inverter, it does not turn off the MPPT or AC charging portion of the unit so even if turned off, charging can occur) . I would keep the 250A charging relay in series with the PV array for controlling overcharge.

No doubt others have tried this solution (it sucks to not be able to charge when the BMS opens the discharge port). Curious to hear how it worked and any words of advise.
 
1 line of my system shown below. Proposed solution; bypass the circled contactor and instead use relay in series with inverter toggle switch to turn off inverter portion of the Growatt All in One. Thoughts???1662132855044.png
 
set your growwatt shut down voltage higher so your BMS never shuts off on a regular (which isn't its purpose) All your settings can stop this
 
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