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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Allen,<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'>First a minor correction: Those 100-33 cells are rated at 1920Ah
at the 20hr rate.<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'>It’s interesting that their Sr App Engineer would say 9A per 100Ah
(C/11 rate), since the operation manual and spec sheets state that the max
charging current is “5% of nominal C/100 Amp-hour rating” at 25⁰C, or C/20. The
100-33 cells have a 100-hr rating of 2100Ah to a cell voltage of 1.75V, so the
max charge rate should be 105A. However, that 5% rate is based on using a
constant-voltage charging source at the 2.35V per cell voltage setting. I’m
sure that you can charge at a higher rate if the battery voltage is lower
(still partially discharged), and that is probably what the Engineer was thinking
of. <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'>You don’t have to push AGM batteries as hard as flooded
batteries since you don’t need to stir up the electrolyte.<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 don’t think that this is particularly relevant though, since any
charge rate that replaces the used amp-hours, plus the self-discharge rate,
will work fine. So really the more important question is “what is the rate of
self-discharge for these batteries”. The spec sheet states that the
self-discharge rate is between 0.5 and 1.0% per week, but that’s with a new
battery. What the rate is on your older batteries would not be easy to find
out. The only way that I can think of would be to charge them up completely,
and let them sit, with no charge or discharge, for a few weeks to a month, and
measure the static voltage drop over that time. From that you can get an idea
of what the lost percent of charge is, but I doubt that this is a practical
experiment to do.<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'>Ultimately, the issue is whether the charging sources can keep up
with the discharge over time. Only observation and time will tell that. A good
amp-hour meter will sure help. If the batteries can’t be brought up to a full
state of charge within a few days of a major discharge, you need to add more
PV, reduce loads, or run a genny.<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>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:
"Tahoma","sans-serif";color:windowtext'>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Allan
Sindelar<br>
<b>Sent:</b> Wednesday, February 10, 2010 9:19 PM<br>
<b>To:</b> RE-wrenches<br>
<b>Subject:</b> [RE-wrenches] Absolyte Battery Question<o:p></o:p></span></p>
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</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>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: "<span style='font-size:10.0pt;
font-family:"Arial","sans-serif";color:navy'>I did discuss this with
engineering, and they recommend 2.35 volts per cell as the charge rate."<br>
<br>
</span><span style='color:navy'>So I replied: "</span> 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 style='color:navy'>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.</span><o:p></o:p></p>
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<p class=MsoNormal>-- <br>
<br>
<o:p></o:p></p>
<p class=MsoNormal><span class=il><b>Allan</b></span><b> Sindelar</b><span
style='font-size:10.0pt'><br>
<a href="mailto:Allan@positiveenergysolar.com" target="_blank"><span class=il><u>Allan</u></span><u>@positiveenergysolar.com</u></a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank"><u>www.positiveenergysolar.com</u></a></span><o:p></o:p></p>
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