Matthew Miller wrote:
> http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1031,C1115,P1597
> 
> My trouble is that I connected the converter ground to the battery pack and
> then when I touched the positive wire to the battery terminal there was a
> big blue spark and now the converter is no longer working. :( I haven't
> repaired the converter yet, but I'm wondering if the converter design I used
> is appropriate for this application?
> 
> I would appreciate any suggestions, insight, or questions.
> 

Your cells provide 15V "under load"; thus some amount of current flows 
and your cells provide some amount of power (V*I).  If the charger and 
battery draw more current than is available, the solar cell voltage will 
drop requiring even more current (it's a switcher: think constant 
power).  Depending on how the switcher reacts (shuts down until power 
cycled?, current limits?, foldback limits?, oscillates?, etc.) anything 
can happen.

To proceed, here's some things to check.

Repair the supply noting what went wrong. Try to figure out why it 
failed.  Connecting the battery to the supply with no current limiting 
could easily induce transient conditions that will prevent proper operation.

Characterize both the supply and the battery.  Either get a bunch of 
resistors or build a constant current sink and load the supply taking 
V*I data points.

Do the same for the battery.  If it's 48V and you connect a 48V charger 
to it, it should draw very little current.  How much does it draw when 
it is 47V?  46V? 40V?  At some point, a heavily discharged battery may 
draw more than your supply can deliver.

Think about a current limit scheme to put between the supply and the 
battery.  Limit the current to something the supply can handle.

Diode isolation (or FET isolation) may be needed also.  What happens 
when clouds block the sun during high power charging?  The cells can't 
deliver the power, the voltage drops, the supply draws more current, bang.

Good luck!
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