SW 4024

Re: SW 4024

The Trace SW inverters were grid tie from the beginning. At least from around
1993 or so.

The GTI was WAY later, like, 1999 or 2000 and I understand that
they actually did sell back even without the GTI attached
which was basically just an inductor to reduce current distortion.

That whole GTI thing was a big farce and they were forced into having
to use it because of the way the SW works and some folks at the competition
didn't like it.

boB

Re: SW 4024

Depends on how old the unit is, somewhere there is tread that I looks up when the software was changed to prevent grid power push. I think I remember it to be around 1998 or 1999 with software rev 4.01 allowing it.

Then came UL1741 and the design got in trouble that was not easy to remedy. They tried a rather bad grid tie adaptor that was a large series inductor in the grid input line to allow the rather coarse adjustments of SW series to test for grid presences without overloading the inverter and stressing the batteries. It was a bad bandaid.

On the earlier software if battery voltage is raised above the charger set point the inverter will push out the excess trying to keep the battery charger regulated voltage. It will either be consumed by ACout load or go back out the AC in port. On later software, without the GTI adaptor box there will be a short period of reverse push to grid (or AC loads), if excesss battery voltage continues beyond the allowed time period then the inverter will shut off to prevent reverse power push. (AC passthough to output in not interrupted) Your PV controller would then control the battery charge voltage regulation.

As to old units in use, they don't pass the present regulations (UL1741) but no damage will occur to your equipment. This is is when the grid goes open circuit with a light enough load to not overload the inverter. This case probably happens about 0.001% of the time the grid goes down. Usually when the grid goes down the inverter see a very heavy load that trips the overload sense immediately releasing the relay that couples the inverter to the grid. (your AC continues on inverter battery supply)

A case for the 0.001% grid drop might be your common pole transformer primary breaker releasing due to some momentary overload on your particular pole transformer. If your neighbor is also connected and not drawing too much power, your SW4024 could supply you and your neighbor. The primary high voltage side of the pole transformer (with open circuit breaker) will have the the 25kV (depends on your neighborhood setup) which might surprise the power company service man. They are taught to always assume the line they work on is live. Once I had a wild parrot poking around the high voltage primary side transformer insulator. There was a loud pop, toasting the parrot and causing the transformer's primary side breaker to blow. This is exactly what the UL1741 spec is designed to detect but the old SW series would not, unless the neighbor's load overloaded the SW inverter.

Re: SW 4024

The SWs will not sell (with or without the GTI) unless you set it to "SELL" in menu 9.

Inverter Setup 9
Set Grid Usage
FLT SELL SLT LBX

"FLT mode does not sell excess power into the utility grid" - SW manual (With Revision 4.01 Software)

-Alex Aragon