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My solar lights charges the rechargeable batteries. But in the winter there is not enough sunlight to keep the lights on all night.

The solar cells and batteries are in parallel; can I add an AC 3 volt DC output power supply to augment the existing solar cells?

It's an address light with 5 LEDs. The batteries are two 2.1 rechargeable in parallel with unknown spec solar cells. My idea is to add a 3V solar panel with diode in a south direction connected by a long wire to the unit.

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    Can you give a few more details about the system? type of panel, voltage/current/power ratings, battery chemistry and size, etc? It's possible this question may fit better over on electronics.SE – LShaver Dec 7 '16 at 20:39
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    There's still not enough detail here, but I don't think your solution makes sense. The problem could have less to do with how much sunlight is available for charging batteries, and more to do with the batteries not having enough charge to last through long winter nights. I would try adding additional batteries before adding more solar panels. – LShaver Dec 12 '16 at 20:43
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You need to diagnose why the cells are failing to keep the lights on.

A: Depending on the battery chemistry they may not work well in cold weather. You may be able to get better lighting by putting the batteries inside, and running longer wires.

B: If the solar cells aren't getting enough light to charge the batteries, look at:

  • Reorienting the cells to be at right angles to the sun at noon.

  • Adding reflectors to concentrate more light on the cells.


The problem with just adding an arbitrary solar array in parallel is the risk of overcharging the batteries. I don't know the setup of small units like this. It should be simple to make a circuit that periodically measures the battery voltage and disconnects the solar array when it's charged. But if they are cheap, they may figure, "Let the batteries cook. They won't remember where they bought it 6 months from now." Sadly the latter is the more common scenario.

  • On a 3 VDC system, you won't be able to lengthen the wires much before the voltage drops too low. – LShaver Jan 14 '17 at 5:14
  • @LShaver depends on the current - with a 1W panel (be generous, probably very generous) 3V means 333mA, losing about 0.0011V/m with 1mm^2 conductors (via voltagedropcalculator.com.au/…) Just because the panel comes with 0.02mm^2 wires doesn't mean you have to use the same wire for a longer run. Thicker wire is more robust, which you probably want for the longer run anyway. – Móż Jan 14 '17 at 23:12
  • @Móż good point. However I'm still suspicious that battery capacity is the issue here. – LShaver Jan 15 '17 at 5:02
  • Adding a parallel source does not increase the open circuit voltage, so it is unlikely to cause battery overcharge. Even the simplest charging circuits protect against it anyway. – FauChristian Feb 21 '17 at 8:04
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The longevity of batteries often depend on maintaining the charge current within a particular range, so it is not advisable to add a 3 Volt AC-to-DC converter in parallel with the batteries.

Here are some simple solutions that do not require electrical engineering expertise.

  • Use a second set of lights for when the solar devices are low on battery power. If you get a second set with sensors, they might be adjustable enough to get them to automatically turn on when the solar lights die out.
  • Get an additional battery holder and Wire the batteries so that they are indoors and out of the cold.
  • Ensure that there are no parts of the building or landscaping that shadow the solar cells during brightest parts of the day. You may be able to relocate the cells themselves or the entire units to catch more sunlight even during the increased declination of winter.
  • Ensure that the angle of the cells is close to perpendicular relative to the winter's noon time sunlight.
  • Clean the cell surface in the way instructed by the device manual.
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    This assumes the existing batteries have enough capacity to last through the longer winter nights. – LShaver Jan 14 '17 at 5:16
  • I think OP first needs to find out if the problem is the batteries not charging fully, or not having enough capacity. If it's the latter, none of your suggestions will help. – LShaver Jan 21 '17 at 6:12

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