# Fronius Galvo Error 302

My neighbour is having trouble with his Fronius Galvo. It is throwing STATE 302 (DC overcurrent) errors during the day, constantly disconnecting and then reconnecting. This started happening after he replaced his older panels (that were in a 11S configuration) with higher wattage panels in a 6S x 2P configuration.

Here’s a picture of the Galvo’s specs:

I see the IDC max is 19.8A and Isc pv is rated at 29.6A.

The panels are Canadian Solar CS3W 410W (polycrystalline, 144 half-cut cells):

I expect the operating current of a 2P configuration will be above 20A, but even with cloud edge effect it should not come close to 29.6A, so this has me a bit puzzled.

Does the Galvo throw state code 302 when it exceeds IDC max, or when it exceeds Isc pv?

Thanks!

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I don’t know about Fronius specifically, but for the MPPTs I know best, an overcurrent event occurs on the PV side. That’s means you’re exceeding the 19.8A operating current. Since you have two strings in parallel that can each make 10.5A, that’s likely the culprit. Since the Galvo has only one tracker, the options will be to either replace the Galvo with a model that has two trackers, or to put the modules in series (and maybe lose one or two).

Temperature coefficient is -0.28%/°C. VoC at 25°C is 47.6V, so at a somewhat random -7°C we’re talking max 10 modules in series (54.3V per module at this temperature).

So lose two modules, or replace the Fronius.

You could possibly gain a little room by limiting the max power in the Fronius configuration, but PV modules are constant-current devices, so while it may reduce the events, I doubt it will completely solve the problem.

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Surely the MPPT should be able to simply lift the voltage to drop the current to within its operating current range? There’s plenty of voltage headroom in this case.

Why do they even state a maximum PV short-circuit current of 29.6A when the practical limit is much lower?

The exact wording for state code 302 is: “Brief interruption of grid power feed operation due to overcurrent in the inverter. The inverter returns to the startup phase.”

I wonder if this has something to do with the fact that the inverter is 64% over panelled, even though both the panel voltages and currents are individually within specification. There’s no indication on the datasheet that there is a limit to over panelling the Galvo, but its sister model, the Primo, is limited to 50%. I would expect the electronics to be similar.

Perhaps it’s a case of the inverter not being able to raise the voltage fast enough in order to bring the current under control when the sun peeks out from behind a cloud? Does that sound plausible?

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In a way, that is exactly what it is doing. When it disconnects, the PV voltage goes up

I’m not sure, but I know the same is true for the Victron MPPT RS. The short circuit spec if also higher than the operating spec.

If I had to guess, it is because short-circuit is easy. The dissipation in the MOSFET is simply the current squared times Rds_on (resistance drain to source). But when it is operating, the MOSFET is constantly switching, so there is the additional dissipation caused by the propagation time (the time it takes the FET to switch on). So that is my guess. It has to limit to a lower operating level, or it will overheat.

That probably also explains why I heard recently that two other inverter brands magically increased their PV-side current with a firmware update. They probably discovered that there is some fat on the margins

Yes. It could be something like that too. The control loop can’t always adjust quickly enough.

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