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Jeff,<br>
<br>
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.<br>
<br>
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.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar<br>
<br>
<br>
Jeff Yago wrote:
<blockquote cite="mid:20090803062156.CD9B16AE@resin17.mta.everyone.net"
type="cite">
<div style="font-family: Arial,sans-serif; font-size: 10pt;">
<div>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!. </div>
<div> </div>
<div>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. </div>
<div> </div>
<div>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? </div>
<div> </div>
<div>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?.</div>
<div> </div>
<div>Thanks,</div>
<div> </div>
<div>Jeff Yago</div>
<br>
<br>
<hr></div>
</blockquote>
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