Jeff I agree with Kent, The OB is in the 'no grid mode' and as such is regulating the AC to be a perfect grid signal. The thing to do is to use a second controlled load. On smaller DGI inverters I use a Tristar 60 set for diversion load or use the DAvid Katz method and let the Outback Aux relay or the FNDC relay open a power relay that breaks the connection between the DGI inverter and the Bimodal inverter.
DT --- On Mon, 8/3/09, Kent Osterberg <[email protected]> wrote: > From: Kent Osterberg <[email protected]> > Subject: Re: [RE-wrenches] AC Backfeed Battery Over-Charging > To: [email protected], "RE-wrenches" <[email protected]> > Date: Monday, August 3, 2009, 9:23 AM > > > > > > > > Jeff, > > > > The Outback inverters have no battery charge regulation > while operating > in ac coupled mode because the inverter is regulating the > ac output > voltage (preventing it from going too high) by charging the > batteries. > The SMA Sunny Island can regulate the battery voltage if > the other > inverters are SMA products (Sunny Boy, Windy Boy ...) by > shifting the > ac output frequency to tell the inverters to shift off the > max power > point. > > > > Usually the input voltage to a grid-tie inverter is higher > than 240 > volts so, even with ac coupling, it is more efficient for > the long > feeder to be on the dc side. The dc side also has a > wider operating > window too. > > > > Kent Osterberg > > Blue Mountain Solar > > > > > > Jeff Yago wrote: > > > I have a question that may be one of those that > everyone wants > to know the answer but feel they are the only one that > doesn't know the > answer, or perhaps I am the only one that doesn't > know!. > > In an AC-coupled system, i.e. the 240 VAC output > solar inverter > mounted at a distant array (240 VAC out to reduce long > line loss) > is wired to the 120/240 VAC output > emergency panel supplied from a > battery based inverter. This allows the > solar inverter to stay up when > the grid goes down since it thinks the grid is still up on > the load > side of the battery based inverter. The battery based > inverter will > use any excess backfed power from the solar > inverter that is in excess > of the other supplied loads to re-charge the > battery. However, when > this happens the battery charging process can boil the > batteries when > there are no other loads running. > > I have been told this is because the battery based > inverter does > not regulate its charging of the battery when using > backfed power from > its output panel, but I still don't understand > why. If the battery > charger in the inverter can provide regulated 3-stage > battery charging > when the power is supplied from the grid or a generator, > why does it > suddenly become a full output un-regulated battery charger > when power > is supplied from backfeed and will keep charging > regardless of reaching > a high battery voltage? > > I would have assumed the battery charger section > would charge > the same way regardless of where the power is being > supplied from, or > perhaps just shutdown on some kind of backfeed > safety. As far as I > know, this over-charging problem in an AC coupled dual > inverter system > is true for all battery-based inverters. Any > inverter techs out there > that can explain why? Perhaps this would be > a nice feature in future > high-end battery-based inverters so we no longer need the > custom power > relay field wiring to provide this high voltage > cut-out?. > > Thanks, > > Jeff Yago > > > > > > > > > > -----Inline Attachment Follows----- > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: [email protected] > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
