Ok, after waiting for weeks for parts and taking the time to test everything I thought I would post what I came up with to solve the problem.
This is what I came up with for myself and may or may NOT work for you. If don’t understand the issues involved the please consult a qualified person to help you. Electricity is dangerous and can injure or even kill if handled improperly.
After studying the SolarEdge wiring diagrams I felt it was best to try and duplicate the same functions they do when using the Auto Transformer. The solution I came up with uses what I’m calling an Inverter Combiner Box. One big advantage to this design is I can just use the Main Breaker in the Sub Panel and don’t need to duplicate breakers being used in the Inverter Combiner Box.
Pic #1 shows what I feel is the very least you must do be safe running the Growatt with the AT. (does not protect against loss of neutral for reasons other than a breaker trip)
Pic #2 shows what I have been running now over a week without any issues. (so far…) I does still have a potential problem, as mentioned in an earlier post, that it could cycle the Main Contactor if for some reason the sensor was seeing 120v only part of the time. (not sure what could cause that to happen though...)
Let me know what you think
Sorry I don't have same fancy design software being use by
USUSUS
For those who are just reading this post and not the whole thread:
Growatt issues:
- Output is 240v only.
- Should be shut down if loss of neutral occurs.
- Dry contact does not work like we need it too.
- Has no direct way tell which source is being output.
Auto transformer:
- Needs 25A breaker (per SolarEdge)
- Needs breaker trip protection
- Should be shut off when running on Grid power
Several key metrics should be met.
- Neutral Bonding – Neutral should be bonded to the grounding conductor and in one place only and must be a permanent bond. We should not be switching it on and off using a contactor. (per NEC requirements)
- We need to avoid placing the Auto Transformer in Parallel with the Grid.
- Want to be able to have the Growatt switch to Grid/Utility as a backup to Solar/Battery system automatically.
- Want the system to cut all power to the Load if:
- The neutral is lost for any reason. (loss of 120v)
- One the breakers running to the Auto Transformer(s) trips.
Given the above constraints and following the same method that SolarEdge uses I ran a Neutral line from the Main Panel to my Sub Panel. My Neutral Bond is in my main panel so that will insure all Neutrals are tied to Ground regardless of which source is powering the Loads.
I tested the Growatt and AutoTransformer running off PV and Battery in this configuration to insure it didn’t affect anything. It did not. Everything functioned exactly the same with or without the Neutral wire coming from the Main Panel and no current could be detected on that wire. This is what should happen as the L1 & L2 coming from Main Panel are isolated from the Sub panel in PV/battery mode.
I then tested the Dry-Contact on the Growatt which I determined does not work as we need it too. It activates when the battery is low and then switches back once it transfers to Grid Power. The solution I came up with is to use a Current Sensor on the lines coming from the Main Panel to the Growatts. (I also discovered you can use 230V sensor placed between one leg of the output from the Main Panel and the other leg of the output from the Growatts.)
This solution uses shunt trip breakers, Auxilliary Contact Breakers, two (or more) Contactors, and Voltage and Current Sensors.
Shunt trip Breakers on the output from the Growatts – which trip if the AT Breakers trip.
Auxiliary contacts on the Breaker for the Auto Transformers – Which will trip the Breakers coming from the Growatts in the event of an overload or short circuit of the AT.
A Normally Closed Contactor for the Auto transformer which insures it stays on unless the system is running in ‘On Grid’ mode.
Current Sensor on the output Wires from the Main Panel which will activate the N.C Contactor on the AT, cutting the flow, when power is flowing from the Main Panel.
I then put a large Normally Open Contactor off the output of the entire system tied to a Voltage Sensor which will ensure Power only flows when a proper 120v is being detected.