[RE-wrenches] dual stacked inverters on 208V service

[Phil Undercuffler]

Kent is correct, but you have to go a little further.  We're all still
guessing that you've got Outback G series inverters and FM charge
controllers.  If that's not the case, change some of the nouns below.  In
any case, if the inverters are kept at default programming at some point
down the road (takes about a month before I usually got the call from the
installer) the system will get into a locked cycle and either the charge
controllers will go to float when grid & sun are available, or one inverter
will try to sell while the other is charging.

If you have two inverters and two FM charge controllers, you'll need two
Hubs too (to let the controller know when grid is available so it stays in
bulk). You can share one Mate, but it will have to be manually shuttled back
and forth between the "pair" that you wish to see/program.  In addition, if
you want to share one battery bank you'll need to disable the inverter
charging from the grid, by backing the charge rate back to zero.  After a
power outage, the system will not begin to sell back until after the
renewables have recharged the battery.

Phil Undercuffler
Conergy





On Thu, Dec 31, 2009 at 3:23 PM, Kent Osterberg <kent at coveoregon.com> wrote:

>  Nik,
>
> 120/208 has a 120 degree phase angle between legs, same as three-phase but
> you only have two legs.  Check with Outback tech support, but I believe the
> GTFX inverter can only be stacked in systems with 120/240 split phase (180
> degrees between legs).
>
> If there are no 208 loads, just unplug the second inverter from the Hub and
> program both inverters to be a Master so you have two independent 120-volt
> systems.  With two independent 120-volt systems you should have a separate
> neutral conductor for each inverter, on the load side because the two
> inverters aren't synchronized when there is no utility power.  On the source
> side they can share a neutral, but it has to be the same size as the hot
> legs, because line power keeps them in sync.
>
> If you have 208 loads on the backup power panel; well -- you can't do it
> unless Outback has support for three-phase grid connected systems.
>
> Kent Osterberg
> Blue Mountain Solar, Inc.
>
>
> Nik Ponzio wrote:
>
> Hi Gang,
>
> I have a problem. We are installing a gridtie PV system with 2
> battery-based inverters for 240V. The service coming in to the condo is
> 120/208 split-phase fed from 3-phase 208 in main building. The master
> inverter pickups up L1 but the slave inverter will not sync. What am I
> missing?
>
> Thanks and Happy New Year to all!
>
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