Growatt SPF-5000-ES AT and N/G solutions

[??????]

Hey @timselectric - great thread, thanks for posting and knowledge sharing. I bench tested this with a 5000ES-US unit from SS and found an unfortunate shortcoming, at least with my implementation which seems pretty much identical to yours. If you're using a NC AT relay and going from off-grid back to on-grid, the time it takes for the two relays (ice cube and AT contactor) to actuate leaves the AT in a ground loop with the grid for a short period of time.

At least with my scenario, this short period of time is enough to run a significant amount of current through the AT (since it's grid balancing during the transition), causing OCPD trips. A word of warning to anybody else attempting this - connecting an AT in parallel to the grid could expose you to thousands of amps of balancing current. I was hoping this imbalance was going to be a few amps tops, but it's easily enough to trip the 15A breaker, and relying on a NC contactor to not weld itself shut while trying to interrupt this current is (imo) a serious safety concern. Appreciate your thoughts if you've got any.

Unrelated - I've got a neutral and voltage protection setup that seems to be working quite well for the AT (for not grid-balancing currents, heh) and I think might be useful to you if you're interested.

 

[timselectric]

thousands of amps of balancing current.

That's quite an exaggeration.
Most residential services are 100 and 200 amps. With the occasional 400 amp.
But I can definitely see it exceeding 15a. Depending on how many neighbors are tied together.
You would never be trying to balance the grid. Only the services connected to the same utility transformer.

There wasn't any delay in my setup. The transfer and AT connection happened simultaneously.

 

[timselectric]

I don't even recommend connecting grid to the system, anymore.
Just use a Chargeverter for the grid. And all of the issues disappear.

 

[??????]

There wasn't any delay in my setup. The transfer and AT connection happened simultaneously.

Thanks Tim - did you get a chance to measure your switching times and voltages with an oscilloscope while you had it running?

 

[timselectric]

Thanks Tim - did you get a chance to measure your switching times and voltages with an oscilloscope while you had it running?

No scope. Just a digital meter, and 5 senses.
I've never had any issues with my setup, that would require more sophisticated testing.