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Solar panels, charge controllers, diodes.

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Posted by Bob Wennerstrom on March 23, 2005, 2:47 am
I'm building my own solar panels from arrays of cells. If I wire them
into a Outback or Trace charge controller, do I still need to put diodes
in the circuit or does the charge controller prevent current from
flowing back through the panels at night. From what I've seen, I can
lose .7V or so from a regular blocking diode on a 12V (19Voc) panel. I
could not find a Shottky doide  that would take the 4A that these panels
would optimistically produce, and even Shottky diodes have some losses I

Mr recently-bought BP 380Us have some sort of diodes in the juction box.
Are these "blocking" diodes to prevent night discharge or are they
"bypass" diodes to improve charging in patially shaded conditions?


Posted by George Ghio on March 23, 2005, 4:29 am

Most likely By-pass.

Posted by Solar Guppy on March 23, 2005, 4:39 am
 On the Xantrex C Series , it has internally back to back MOSFETS , which
eliminates reverse losses

On the Outback MX-60 , it has a relay , that is controlled by the
microprocessor that opens when there is no power to be harvested from the

No blocking diodes are needed using these controllers

"Bob Wennerstrom" <nospam> wrote in message

Posted by Steve Spence on March 23, 2005, 3:29 pm
 The charge controller keeps battery power from flowing back to the
array. If you have many widely dispersed panels/cells, in
series/parallel configuration, you may want to install bypass diodes. I
have 3 30 watt panels in parallel, so I don't bother with bypass diodes.

Steve Spence
Dir., Green Trust

Contributing Editor

Bob Wennerstrom wrote:

Posted by Bill Kaszeta / Photovoltaic Re on March 24, 2005, 5:17 am
 On Tue, 22 Mar 2005 19:47:26 -0700, Bob Wennerstrom <nospam> wrote:

PV modules meeting UL, EU or IEC standards should have data sheets
or installation requirements included per the standards. If you did not get
the instructions, contact the dealer or look on the manufacturer's web
site.  It is likely you do not need isolation diodes, but you may need to
fuse each module to be in safety compliance.  Fuses need to be dc

BTW, if you have bypass diodes in a PV module junction box, and you
connect the module directly to a battery with reversed connections, the
bypass diodes can make a lot of noise and some smoke as they self
destruct!!  Once the smoke is out of then, they do not work.

Bill Kaszeta
Photovoltaic Resources Int'l
Tempe  Arizona  USA

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