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I'm using a solar panel to power an Arduino + a LiPo battery charger. I'd like to increase the amount of current at the same voltage, so would like to wire up a second solar panel in parallel to the current one.

The panels are slightly different:

One is a 6V; the other an 8V.

Assuming my charger can take the voltage (it can), is there anything special I need to do to wire these in parallel? Do I need blocking diodes on both?

EDIT: I'm reopening this because putting these panels in parallel did not work. I'm certain of the wiring, and each individual panel works fine, but putting them together drops the voltage down to <1V. I'm assuming the voltage imbalance is creating some kind of issue. Is this something that can be addressed with additional (simple) circuitry, or should I just buy another matching panel?

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  • \$\begingroup\$ I disagree. The circuit is quite discrete - two solar panels, of specified parameters, wired together in parallel, providing power to a LiPo charger. What additional detail would you like? \$\endgroup\$
    – kolosy
    Commented Sep 9, 2013 at 3:48

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Putting the two dissimilar panes in parallel is not a good idea. Mostly, the higher voltage panel will deliver most of the current and the low voltage panel does little.

If the two panels have similar current ratings but different voltage rating, you can put them in series to get the sum of the voltages at the single current rating. Then use a switching power supply to buck the higher voltage down to what you want. For maximum voltages under 30 V, it's actually not hard to make your own buck converter. There are many off the shelf chips that you only need to add a inductor, diode, and a few other parts too. You can even make your own with a microcontroller if you want to learn more about buck converters.

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  • \$\begingroup\$ Actually, since one is 310mA Isc and the other 500mA Iopt, putting them in series is also not a good idea. They are much better matched in voltage than in current. \$\endgroup\$
    – Bobbi Bennett
    Commented Sep 9, 2013 at 15:24
  • \$\begingroup\$ @Bobbi: Like I said "If the two panels have similar current ratings ..." \$\endgroup\$
    – Olin Lathrop
    Commented Sep 9, 2013 at 15:38
  • \$\begingroup\$ These are not exactly dissimilar panels, though, in the context of your first statement. They actually should have very similar Voc and Vopt. \$\endgroup\$
    – Bobbi Bennett
    Commented Sep 9, 2013 at 16:08
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    \$\begingroup\$ In the situation you describe I see a couple of issues. First, a LiPo charger needs very stable voltages. We've all seen what can happen to Li batteries when not treated well. Second, when you hook two panels in parallel like described, one will likely discharge into the other. You are better off with one panel that can handle the whole load. \$\endgroup\$
    – SDsolar
    Commented Feb 26, 2017 at 2:13
  • \$\begingroup\$ that's very close to my concern I described here as well: electronics.stackexchange.com/questions/387164/… \$\endgroup\$
    – Tagar
    Commented Jul 23, 2018 at 20:04
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Use a DC/DC converter, it's a DC voltage regulator and put the output in parallel. A 5V regulator, for example.

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You cannot successfully parallel two different voltage sources. The higher voltage one will simply try to drive current through the other one. In your case, the sources are diodes, so you might not get reverse current, but your report that the combined voltage drops to 1 V indicates that the sources are very unhappy. Maybe you didn't connect + to + and - to -, but whichever way you connect, it won't work. You need to panels of the same voltage.

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