<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Consider a pair of MX 60s instead of the MX(oops).....FM80. We had customer complaints about the fan noise on the 80, and went to pairs of 60s.<div>120 amps total is worth it for future modules. Those amps go fast at 24 vdc.</div><div>Redundancy is a 3rd valuable asset.</div><div><div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div>R. Walters</div><div><a href="mailto:ray@solarray.com">ray@solarray.com</a></div><div>Solar Engineer</div><div><br class="khtml-block-placeholder"></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span>
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<br><div><div>On Feb 10, 2010, at 10:18 PM, Allan Sindelar wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
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Wrenches,<br>
I am working extensive cleanup on a five year old 24V Outback off-grid
system for a neighbor. The original installation work was pretty
amateur. The BOS is standard PS2, with 2100 watts of tracked PV and a
single VFX3524
and MX60 (which will need to be replaced with an FM80 to handle this
much array). The batteries are GNB Absolyte II, the 100/33s with "1600
amp-hours, 8 hour rate" on each.<br>
<br>
I believe the 8 hour rate multiplies by 1.23 to determine our more
familiar 20 hour rate, so each set is rated 1968 amp-hours. There are
two sets; apparently a crane was used and the stairs removed (and
replaced) in order to get these bad boys settled in the basement. The
batteries are used telecomm batteries, and the one string currently in
operation appears to be in quite good condition, as it is holding up
well under extended discharge due to cloudy weather and weak input
during rewiring.<br>
<br>
My questions: I can safely assume that when the rework is done PV input
will be about 70A PV input in good sun. That's a C/28 charge rate on
one string; C/56 if both are hooked up. <br>
1. What is the minimum charge rate needed to properly charge these
batteries? Flooded batteries like at least a C/20 or higher to overcome
internal resistance and get the voltage well up, but I don't have much
experience with these.<br>
2. Put the question another way: given that the batteries are already
in the basement, will the customer get better performance and longer
life with one string or both connected in this particular situation?<br>
<br>
<br>
Back story: I tried to get answers first from GNB. I asked for the
minimum necessary charge rate and got this back: "<font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">I did
discuss this with engineering, and they recommend 2.35 volts per cell
as the charge rate."<br>
<br>
<big><font face="Times New Roman, Times, serif">So I replied: "</font></big></span></font><big><font color="black" face="Times New Roman, Times, serif" size="3"><big><span style="font-size: 12pt;">
I'm sorry to be a pain, but let's try again. A cell voltage is not a
charge rate. That's a charge voltage. We already discussed this last
week. I am asking for a minimum current - in amps, not volts -
necessary for good battery care. Could you ask them again, please?"<br>
<br>
And got back: "</span></big></font></big><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"><big><font face="Times New Roman, Times, serif">I spoke with Sr. App Engineer,
and said 9 amps per 100 amp-hours."<br>
<br>
OK, so if I use the C/20 rate, I need to charge at 177 amps. Double
that if both strings are used. Right.<br>
<br>
I need better advice, so it's time to request it here.<br>
<br>
Thank you.<br>
</font></big></span></font>
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<div class="Section1"><p class="MsoNormal" style=""><span class="il"><b style="">Allan</b></span><b style=""> Sindelar</b><span style="font-size: 10pt;"><br>
<a href="mailto:Allan@positiveenergysolar.com" target="_blank"><span class="il">Allan</span>@positiveenergysolar.com</a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b style="">Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b style="">505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank">www.positiveenergysolar.com</a></span></p>
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