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<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'>The method Dave showed is the simplest and
least expensive solution – other approaches are possible as well, such as
diversion regulation with a dump load via a solid-state relay for
example. </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'>In most utility back-up applications, this
simple “on-off” approach is acceptable as the loads will be
consuming most or all of the output of the grid-tie inverter and some of the
batteries power during a power outage. The control of the relay is simply
to prevent an over-voltage condition for the batteries – not precise
recharging regulation. This is acceptable on an AC coupled back-up system
since the battery will be properly recharged by the OutBack’s built-in
battery charger once the grid has returned. </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'>For off-grid AC coupled applications –
I would advise using a more sophisticated approach to controlling the battery
recharging process by using a dump control system. This also puts the
excess power produced by the system to a good use – such as space or
water heating. </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'>If you would like more information or
assistance with these types of applications, contact myself or OutBack’s
application engineers & technical support people. </span></font></p>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'> </span></font></p>
<div>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Christopher</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Christopher Freitas</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Director of Research and Development
</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>OutBack Power Systems, Inc.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="mailto:cfreitas@outbackpower.com"><font
size=3 color=black><span style='font-size:12.0pt;color:black'>cfreitas@outbackpower.com</span></font></a></span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Tel 360 435 6030</span></font></p>
<p class=MsoNormal><font size=3 color=black face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:black'>Cell 360 202 4239</span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><font color=navy><span style='color:navy'>19009 62<sup>nd</sup>
Ave NE</span></font><font color=navy><span style='color:navy'> </span></font></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><font color=navy><span style='color:navy'>Arlington</span></font><font
color=navy><span style='color:navy'> </span></font><font color=navy><span
style='color:navy'>WA</span></font><font color=navy><span style='color:navy'> </span></font><font
color=navy><span style='color:navy'>98223</span></font><font color=navy><span
style='color:navy'> </span></font><font color=navy><span style='color:navy'>USA</span></font></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="http://www.outbackpower.com/"><font
size=3 color=black><span style='font-size:12.0pt;color:black'>www.outbackpower.com</span></font></a></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>mick abraham<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, November 05, 2008
9:39 AM<br>
<b><span style='font-weight:bold'>To:</span></b> dkatz@aeesolar.com;
RE-wrenches<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [RE-wrenches] AC coupling</span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> </span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
10.0pt'>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. <br>
<br>
<span arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><u1:p/><span
bauhaus="" 93=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span><span
arial="" ,="" sans-serif=""="" color:="" rgb(192,="" 0,="" 0);=""><u1:p/></span>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. <br>
<br>
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. <br>
<br>
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. <br>
<br>
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.
<br>
<u1:p><br>
Mick Abraham, Proprietor <br>
<a href="http://www.abrahamsolar.com/" target="_blank">www.abrahamsolar.com</a>
<br>
Voice: 970-731-4675 <br>
<u1:p/><u1:p/><span verdana="" ,="" sans-serif=""=""><u1:p/></span><span
verdana="" ,="" sans-serif=""=""><u1:p/></span> </span></font></p>
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