Dave Katz sent a drawing which breaks the AC connection between grid-tie
inverter and battery based inverters when the battery voltage is high.I've seen
similar sketches from others.
Thanks as always, Dave...but it seems that in this arrangement the amperage to
the battery is either 100% on or 100% off, with no finely tapering pulse width
modulation as is commonly preferred for a good finish charge. On/off hysteresis
would be relatively slow just as in the days of Trace C-30 type charge
controllers.
Is there a "shift to float voltage" with this simple setup? What about
temperature compensation? Those are not accusations, just questions because I'm
unsure whether the Outback auxiliary control output manages using those factors.
If the battery lifetime suffers because of rough management at the end of
charge, that's a hidden cost which reduces the appeal of using a simple AC
relay. "Pulse width modulated" diversion into a dump load may be better for the
battery (especially with float mode and temperature compensation)...but that
requires a controller, dump resistor, & circuit for relatively high amperage DC
at the battery voltage, so there goes part of the cost benefit of AC coupling.
One must weigh the cost of fancy charge control methods against the cost of
possible battery degradation using the simple method in Dave's drawing. The
battery degradation cost (if any) is difficult to predict, and may vary from
one installation to another. If the AC loads during the daytime are big
relative to the array size, the battery may only be receiving a trickle charge
anyway.
Mick Abraham, Proprietor
www.abrahamsolar.com
Voice: 970-731-4675
-----------------------------------------------------------------------
_______________________________________________
List sponsored by Home Power
magazine
List Address: RE-wrenches@lists.re-wrenches.org
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
------- End of Original Message -------
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@lists.re-wrenches.org
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
