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<br>
I didn't see that Brian T had the same idea until after I sent
that email off to Allan...<br>
boB<br>
<br>
<br>
<br>
<br>
On 7/19/2012 7:53 PM, Allan Sindelar wrote:<br>
</div>
<blockquote cite="mid:5008C846.8020501@positiveenergysolar.com"
type="cite">
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<div class="moz-cite-prefix">Wrenches,<br>
I forwarded Brian's post on to Robin at Midnite, as I thought it
was an interesting idea. Below is his response, as well as
boB's.<br>
Allan<br>
<br>
<div class="moz-signature">
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charset=ISO-8859-1">
<title></title>
<font face="Times New Roman, Times, serif"><b>Allan Sindelar</b></font><br>
<small><a moz-do-not-send="true"
href="mailto:Allan@positiveenergysolar.com"><font
color="#000099" face="Times New Roman, Times, serif"><u>Allan@positiveenergysolar.com</u></font></a></small><font
face="Times New Roman, Times, serif"><br>
<span style="font-size: 10pt;">NABCEP Certified Photovoltaic
Installer<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder and Chief Technology Officer<br>
<b>Positive Energy, Inc.</b><br>
3209 Richards Lane (note new address)<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a moz-do-not-send="true"
href="http://www.positiveenergysolar.com/"
target="_blank"><u>www.positiveenergysolar.com</u></a><br>
<br>
</span></font>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Allan,
It is simpler than what is being suggested. The reason
they want to limit to 20 amps is because the battery
doesn’t need anymore than that. The controller will
automatically limit the charge current as the battery gets
full. If a large load is turned on, the controller will
try to refill the battery up to its capacity. The 80 amps
will quickly be reduced because the voltage will rise to
the point where the charge tapers off.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">There
is nothing else that needs to be done. If the problem is
that the battery bank is too small for a big controller,
the best answer is to get more batteries. A 80 amp charger
into a 200 amp hour battery is going to raise the battery
voltage so quick, it will not affect the battery at all.
By the way, discharging a battery at 60 or 80 amps is
probably going to do damage to a small battery also. We do
have an input on the Classic that could probably be
programmed to do as requested. That input feature has yet
to be implemented. I’m sure we will have discussions about
this when the time comes to write the input code. Maybe
this feature will be designed in, but it doesn’t sound
like it is a very good feature to spend a bunch of time
on. After all, the main problem is that the battery bank
is just too darned small. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Bob,
Tom and Ryan do you have any comments on the subject?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thanks,<o:p></o:p></span></p>
<span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Robin</span>
<p class="MsoNormal" style="margin-right: 722.25pt;"><span
style="font-size: 10pt;"><font face="Times New Roman,
Times, serif"><st1:place w:st="on"><st1:city w:st="on"></st1:city><st1:state
w:st="on"></st1:state><st1:postalcode w:st="on"></st1:postalcode></st1:place></font><b
style=""><br>
</b></span></p>
<br>
One idea I had in mind was to have an option, in software, to
limit the current into the battery,<br>
when the charging current goes above some set threshold. The
controller would have to get its information from<br>
the battery monitor over the network.<br>
<br>
If it is a grid tie system and grid is there and GT inverter
is selling, then no problem... The controller<br>
can work at its full output. If grid or loads go away, then
the CC will know and it can throttle back at<br>
that time.<br>
<br>
We don't have a battery monitor yet, but we will have one.
This will be one of the settings as well as<br>
Re-Bulk based on state of charge, ending amps and those types
of things.<br>
<br>
boB<br>
<br>
</div>
On 7/19/2012 8:34 PM, <a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:maverick@mavericksolar.com">maverick@mavericksolar.com</a>
wrote:<br>
</div>
<blockquote
cite="mid:8E7291AE-7BB4-4677-81C2-66250F555B0A@mavericksolar.com"
type="cite">
<div>I say it is waste of time. </div>
<div><br>
</div>
<div>1. AGM batteries can take the high current and you are
right, the absorb voltage is reached and the absorb current is
tapered rather quickly. Current generation charge controllers
are rather fast at the transitions. I have a bunch of data
from a system with a PentaMetric that shows the battery bank
going to absorb voltage at grid tie, during cloud events, but
only for a few seconds at a time.</div>
<div><br>
</div>
<div>2. A properly designed GTBB system should cover the
connected loads for 24 hours of each sunny day, at a minimum.
Keep in mind, off grid systems are designed for that, and 3
days + of backup, etc.</div>
<div><br>
</div>
<div>3. I would say, based on my experience, the minimum battery
bank should be 400Ah. I personally try to set it at 600Ah
(48V). It is a backup system after all. But the key is the
customer's expectations...who are they going to call after the
lights go out?<br>
<br>
<div><br>
</div>
<div>Thank you,</div>
<div><br>
</div>
<div>Maverick</div>
<div><br>
</div>
<div><br>
</div>
<div>Maverick Brown</div>
<div>BSEET, NABCEP Certified Solar PV Installer ®</div>
<div>President & CEO</div>
<div>Maverick Solar Enterprises, Inc.</div>
<div>Office: 512-919-4493</div>
<div>Cell: 512-460-9825</div>
<div><br>
</div>
Sent from my HondaJet!</div>
<div><br>
On Jul 19, 2012, at 6:35 PM, Brian Teitelbaum <<a
moz-do-not-send="true"
href="mailto:bteitelbaum@aeesolar.com">bteitelbaum@aeesolar.com</a>>
wrote:<br>
<br>
</div>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Drake,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I’ve
been hounding a couple of the charge controller
manufactures about this issue, but so far I just
haven’t seen a light bulb go off in their heads, but
I’ll keep trying, and maybe this is a better forum to
do it.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">MPPT
controllers can be adjusted to current limit at
amperage values below their rating, but if you do
that, you are also limiting the output of the array in
general, and the amount of PV power available to run
the loads directly from the array (through the
inverter). Not the best use of available PV power.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Say
you have an 80A controller and a 200AH battery. With
current technology, you have two choices:<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Let
the controller operate at 80A. If you have loads to
draw off some of the current (or sell to the grid),
great, but if not you could be seeing a charge rate of
C/2.5, which would be pretty hard on a sealed 200AH
battery, to say the least. Granted, the battery
voltage would rise pretty quickly, and the controller
would start to taper off, but it would still see high
currents especially if the absorption time is set
long. Not a happy scenario.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Or,
you can set the current limiting on the controller to
20A for a C/10 charge rate. But if you had loads
drawing 60A, you would be pulling that additional 40A
from the battery and not using the array’s full power.
Also not a happy scenario.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">What
we need is a controller that can read the signal from
a shunt at the battery, and use that as the basis of
current limiting control. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">For
example, if we have an array that can produce 80A of
current, but we want to limit the battery to 20A of
charge, there would be 60A of potential current there
to run loads without drawing on the battery. If there
are no loads running, the controller should current
limit at 20A (reading from a shunt), but if loads are
turned on, the controller should be able to let more
current through while still limiting the battery to
20A. When loads are shut off, the controller should go
back to a 20A limit.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">This
doesn’t all have to happen very quickly as a battery
can take a heavier charge for a short period of time,
but I think that this would be a major improvement of
controller function.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Of
course, if you are grid-tied you can sell all the
excess power, but if the grid goes down, or you are
off-grid….?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Because
of the low cost of PV and the high cost of batteries
these days, I’m seeing more and more requests for
large arrays with smaller batteries. I also think that
PV is now cheap enough to allow for oversizing of
arrays for better battery charging on cloudy days,
which can reduce generator run times. We need smarter
controllers.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">What
say ye, charge controller gurus?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Brian
Teitelbaum<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">AEE
Solar<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<a moz-do-not-send="true"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org">re-wrenches-bounces@lists.re-wrenches.org</a>
[<a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="mailto:re-wrenches-bounces@lists.re-wrenches.org">mailto:re-wrenches-bounces@lists.re-wrenches.org</a>]
<b>On Behalf Of </b>Drake<br>
<b>Sent:</b> Thursday, July 19, 2012 2:21 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] Small battery bank
vs too large array<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hello Wrenches,<br>
<br>
Where can I get a device that will measure current
through a shunt and create a signal to trigger a
relay? <br>
<br>
We want to be able to use a 2 kW array with four, 200 AH
sealed batteries on an Outback system. 2 kW of PV would
be too much amperage for the batteries. The idea is to
open relays to disengage strings in conditions of high
current to the batteries.<br>
<br>
The reason for this is to create backup systems where
power will be abundantly available when the sun shines.
The system will normally connect to the grid, except
during outages. In normal charging conditions the power
will go straight to the grid. When the grid is down,
power will be available for loads and battery charging,
but batteries will be protected from overcharge?<br>
<br>
Any suggestions on ways to accomplish this are welcome!<br>
<br>
Thanks<br>
<br>
Drake <br>
<br>
<br>
Drake Chamberlin<br>
<i>Athens Electric LLC<br>
OH License 44810<br>
CO License 3773<br>
NABCEP Certified Solar PV Installer<br>
740-448-7328<br>
</i><a moz-do-not-send="true"
href="http://athens-electric.com/">http://athens-electric.com/</a>
<o:p></o:p></p>
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