PSPV combiner and blocking diodes

Discussion about the Power System PV Combiner (PSPV)

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kona
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PSPV combiner and blocking diodes

Post by kona » Sat Apr 08, 2006 11:27 am

If my solar panels do not have blocking diodes, should I add one in front of the breakers in the combiner box?

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mvrck
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Post by mvrck » Sat Apr 08, 2006 3:46 pm

Blocking diodes are for preventing current from flowing into the panels from the battery, particulary at night. If you have a charge controller, it should do that job for you.

Bypass diodes are sometimes used to reduce the effect of shading on strings of panels. I will never have shade on my panels and therefore did not install any.
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kona
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Post by kona » Sat Apr 08, 2006 4:24 pm

It would be for shading...

Jay

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mvrck
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My RE system: 3.1 kW (BP 60W) on 2x MX60s
560W (Kaneka 60W) on 1 Classic 150
1080W (Day4) on 1 Tristar MPPT 60
GVFX3524 + PS2AC/DC, MATE, HUB4, Charles 24V 30A Charger, Generac S4001, Trimetric 2020, WattPlot, greenMonitor Lite, 400AH Bank (4 ea Rolls Surrette S530 Batteries), and a lot of other solar refuse...
Location: Austin, Texas
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Post by mvrck » Sat Apr 08, 2006 7:48 pm

Bypass diodes should be placed in parallel with each series string of cells. My panels have two series strings inside each panel. So, if I had a shading concern, I would put two diodes in each panel. If shade covered one part of one panel, then the current would flow through the bypass diode instead of being stopped by the inactive cells under the shade. I looked around the net for a good diagram of this concept. I found a poor copy of a good diagram here at www.windsun.com/tech_tips.htm (the diodes don't touch each other, just the connections in the terminal block of each panel)

Image

The diode at the end of the string is the blocking diode. The diode in parallel with the panel is the bypass diode.

The Bypass diode should be rated for an amount of current the panel could produce, plus some safety margin. Check the Isc rating and get a diode that can take at least that much current.

Thanks
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Post by kona » Sun Apr 09, 2006 10:08 am

Tnx! That's what I needed to know.

My Evergreen panels have built-in "bypass diodes" but I will need to install "blocking diodes". I thought the built-in "bypass diodes" were for ESD. But your explaination makes more sense.

Tnx again,
Jayjavascript:emoticon(':cool:')
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Post by rock » Wed May 10, 2006 3:05 pm

If you only have one panel and it has bypass diodes in it, does the system need a blocking diode too? Assuming no charge controller.

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