Blocking Diodes for Solar

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August 2008 --

With three different banks of solar panels, I need blocking diodes to prevent a shaded panel from pulling power away from working panels.

Also, at night, the blocking diodes will keep the panel from sucking power out of the batteries. Note: my solar voltage controller will also shut down at night, when it senses that the panels are not producing.

I went to a local electronics superstore, and looked for diodes. They had thousands of them, and I had no idea what type to get. So, I bought four diodes on the internet from a solar power web site.

These are rated at 15 Amps maximum. Each of my panels will output no more than 3 Amps, so I don't have to worry about blowing the diodes.

Here's a close up of the diode, so you can look for these at a local electronics store or Radio Shack, and not have to pay $20 shipping by getting them on the internet.

My multimeter has a diode testing function, but I really don't know what to do with it. So I created a circuit with a small load to determine which lead is positive and which is ground. On this diode, the solar panel is connected to the lead on the right. Power will flow from right to left,
and is blocked from left to right.

I soldered wires directly to the diodes, using a small heat sink to protect the diode.

Blue goes to the panel,
and red goes to the fuse.

Each bank of panels has a 5 Amp
in-line fuse, before being connected to the main "Solar" breaker switch.


The soldered connections are physically supported,
and electrically protected,
using marine heat shrink with an adhesive lining.

The glue melts when the tube is heated,
so these connections are good and strong.

Finally, the diodes and wires were screwed down to a little block of
scrap mahogany.

A small piece of plexiglas covers the whole thing.

The wires are connected into the circuits using Ancor butt connectors, and covered with heat shrink.

I only have three banks of solar, so I have a spare diode in case of failure, or if I add more solar later.