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Help! Newbie Question - Junction Box on solar panel

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Posted by Jay Javor on July 7, 2004, 12:17 am
All right, I would appreciate it if any of you smart people could help
me out.  I recently purchased 2 solar panels (SE-120) from Sun
Electronics.  These are supposed to be dual voltage panels (12 or 24
volt).  When I received them, the panels appeared to be the same but,
there was a difference in the junction box.  One panel had 7 terminals
inside the box (and matched the instruction booklet) while the other
had only 6 terminals.  Of course, Sun Electronics was no help at all.
There response was "use a volt meter".  That's all fine and dandy but,
what am I looking for?   How do you figure out what is positive,
negative, 12volt, 24 volt, and any other wiring issues?  I am new to
this and want to get on the right track.  Any help would be greatly

Thank you so much for your help!!!


Posted by John Beardmore on July 7, 2004, 11:37 am

:)   Ok, first of all, do you have a volt meter, and is it analogue or
digital ?

Start by finding pairs of terminals that give a reading on the meter.

The voltmeter must be set to measure DC, and will have terminals marked
+ and  - .

When you get a clockwise movement of the pointer on your analogue meter,
the + terminal of the PV is connected to the + terminal of the meter.

On a digital meter, the + terminal of the PV is connected to the +
terminal of the meter when there isn't a minus sign in front of the

Presumably these panels offer two 12 volt banks of cells which can be
wired in parallel to give 12 volts at a high current or in series to
offer 24 volts at a lower current.

If this doesn't make sense, ask us more questions !

Cheers, J/.
John Beardmore

Posted by Fred B. McGalliard on July 7, 2004, 2:29 pm

Two banks of 12V each require a total of 4 terminals, not 6 or 7. Checking
these with the voltmeter should quickly tell you if you have 4 powered
terminals and some spares.

Posted by Solar Guppy on July 7, 2004, 5:33 pm
 Wrong ...

Your are forgetting the connection for the bypass diodes , most likely these
panels have 4 bypass diodes.

Looking right to left , if you have 4 bypass diodes. Each 12 volt string is
"across" each pair of diodes. The diodes have a white band on them (the
cathode) and this is connected to the higher potential of the string.

get a 8 dollar dvm at home depot (there located in the electrical
department) , put the panel in the sun and make a few measurements and you
should have it figured out

Posted by John Beardmore on July 7, 2004, 10:54 pm

Well, maybe.  I've seen panels without and without bypass diodes and
occasionally with blocking diodes.

I'm not forgetting them, but he didn't mention any components.

Why 4 ?

If he needs to ask the question he has, that may not be a good

Cheers, J/.
John Beardmore

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