Mark,<div><br></div><div>The battery is marked with a 6 hour rate because if it's used in a forklift in a warehouse, they figure on a 6 hour discharge cycle -- they hammer it hard for most of the day, then park it for the night, plug it in and let it recharge. They also mark it with a 20 hour rate because that's the "standard" discharge rate for comparisons -- as you notice, the 6 hour rate is considerably smaller than the 20 hour rate, so it helps to make sure you're comparing apples to apples.</div>
<div><br></div><div>If your standard discharge cycle is a ~24 hour period, then you can use the 20 hour rate to evaluate charger setpoints.</div><div><br></div><div><span class="Apple-style-span" style="font-family: Arial; ">Also, in regard to your question: </span></div>
<blockquote class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: 0px;"><div><span class="Apple-style-span" style="font-family: Arial; ">Is it fair to say the following: For rapid bulk charging to bring the voltage up from some discharged voltage of say 48VDC to a bulk charged voltage of say 60VDC, I want a charger that can provided a constant current of C/10 or 1320/10 = 132 A across that voltage range. </span></div>
</blockquote><div><span class="Apple-style-span" style="font-family: Arial; ">I would say that is not correct. Use the C/20 rated capacity, not the C/10. That means you want a charger that can provide 169 amps if you want to push the battery as hard as it can reasonably be charged. Charging that bank with anything less than ~85 amps of charging current (after you account for daytime loads) is really more of a trickle than a charge. Ideally, your charging source should be somewhere between those two numbers, and when in doubt err to the higher side. </span></div>
<div><span class="Apple-style-span" style="font-family: Arial; "><br></span></div><div><span class="Apple-style-span" style="font-family: Arial; ">Also, you mentioned:</span></div><blockquote class="webkit-indent-blockquote" style="margin: 0 0 0 40px; border: none; padding: 0px;">
<div><span class="Apple-style-span" style="font-family: Arial; ">And at the time that I complete this bulk charge, the battery bank will be restored to 1320/1690 = 78% of its starting capacity.</span></div></blockquote><font class="Apple-style-span" face="Arial">I think you're swinging at the fences there. You can't tell anything by comparing the various C/numbers, and besides they really only apply to the discharge cycle. I think it would be more accurate to say that once your constant current charger brought the battery voltage up to somewhere around 58.8 to 59.2 (temperature compensated), then it should begin to taper the current to hold the battery voltage at that point while still flowing as much current as possible. Once the bank has been held at that voltage for some period of time (which can be confirmed by specific gravity measurements, guesstimated by calculations based on depth of previous discharge, or ballparked at 3-4 hours for a bank that size), then the bank can be considered full.</font><div>
<font class="Apple-style-span" face="Arial"><br></font></div><div><font class="Apple-style-span" face="Arial">Phil Undercuffler</font></div><div><font class="Apple-style-span" face="Arial">Enjoying solar independence since a week ago last Friday</font></div>
<div><font class="Apple-style-span" face="Arial"><br></font><div><br><div class="gmail_quote">On Sun, Jun 20, 2010 at 9:59 AM, Mark Frye <span dir="ltr"><<a href="mailto:markf@berkeleysolar.com">markf@berkeleysolar.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div>
<p><font size="2" face="Arial">Suppose I have a battery bank made up of 4 - 12V Enersys HUP flooded lead acid batteries. The batteries are wired in series for a nominal 48VDC system.<br>
<br>
The side of the battery, which is actually a forklift battery, is marked as 1320 Ah @ C/6. The vendor also rates the battery as 1690 Ah @ C/20.<br>
<br>
So, for the purpose of evaluating the battery back relative to the charging system settings, what size is the battery bank?<br>
<br>
It is interesting to think that at a normal discharge rate of C/20 I can get 128% more energy out of the bank (1690 Ah) than I can put back in at a C/6 charging rate (1320 Ah)?<br>
<br>
Is it fair to say the following: For rapid bulk charging to bring the voltage up from some discharged voltage of say 48VDC to a bulk charged voltage of say 60VDC, I want a charger that can provided a constant current of C/10 or 1320/10 = 132 A across that voltage range. And at the time that I complete this bulk charge, the battery bank will be restored to 1320/1690 = 78% of its starting capacity. </font></p>
<p><font size="2" face="Arial"> </font>
<br><font color="#888888"><font size="2" face="Arial">Mark Frye</font>
<br><font size="2" face="Arial">Berkeley Solar Electric Systems</font>
<br><font size="2" face="Arial">303 Redbud Way</font>
<br><font size="2" face="Arial">Nevada City, CA 95959</font>
<br><font size="2" face="Arial">(530) 401-8024</font>
<br><a href="http://www.berkeleysolar.com" target="_blank"><u><font color="#0000FF" size="2" face="Arial">www.berkeleysolar.com</font></u></a><font size="2" face="Arial"> </font>
</font></p>
</div>
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