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--></style><title>Re: [RE-wrenches] 24 volt Battery Bank
comparison</title></head><body>
<div>I am glad to see this issue with series strings being brought
into the discussion. </div>
<div><br></div>
<div>At 11:53 -0600 3/6/11, Ray Walters wrote:</div>
<blockquote type="cite" cite>I've had single strings with equal
current through each battery, but some batteries would be at 15.5
volts, while others next to it would be at 13. The charge controller
shuts off when the sum of the voltages hits the bulk charge V, but
meanwhile some cells are chronically overcharged or undercharged.
(parallel strings no where to be seen)</blockquote>
<div><br></div>
<div>and......</div>
<div><br></div>
<div>At 15:10 -0300 3/6/11, James Surrette wrote:</div>
<blockquote type="cite" cite><font face="Arial">If you hook up 4 x 12V
monoblocks for a small 48VDC system and begin charging at 58.8V, total
voltage will be 58.8V very quickly but individual battery voltage will
not be 14.7V. Battery voltage will have a large range from 14 to
almost 17V.</font></blockquote>
<div><br></div>
<div>If you have 4 x 12V monoblocks, they will thrive much better
connected in parallel than they will in series. The parallel strings
discussion reappears regularly on this list, and always produces a
chorus of disapproval, but I think the downsides are
over-stated.</div>
<div><br></div>
<div>Most battery charging regimes are based on bringing the battery
up to a specific voltage and holding the voltage there for a period of
time. This can he achieved with perfect equality for strings of
batteries in parallel. (Yes technically you may need to use
bus-bars to get within millivolts of each other but to be honest who
really knows the optimum absorption voltage that exactly, and does it
matter?) So long as the battery as a whole gets up to and
stays at the prescribed voltage for long enough, then all the parallel
batteries will get charged according to the manufacturer's
instructions.</div>
<div><br></div>
<div>With batteries in series I am finding that 48V systems are much
harder to keep properly balanced than in the old days of 12V systems,
since the current in one string is the same in every cell, whether it
needs it or not. Yes you could put diversion load
regulators on individual 12V batteries in the string, but given the
way they are priced (by amps) you would end up spending four times as
much on charge controllers.</div>
<div><br></div>
<div>To me the issues of unbalanced charging are much worse for
batteries in series than they are for batteries in parallel. Now
I will go and hide from the wrath of the list :-)</div>
<div><br></div>
<div>have fun,</div>
<x-sigsep><pre>--
</pre></x-sigsep>
<div>Hugh Piggott<br>
<br>
Scoraig<br>
http://www.scoraigwind.co.uk</div>
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