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I'm trying to hang some bistro lights on my balcony — specifically, the SVARTRÅ outdoor bistro lights from IKEA.

There's just one issue: the balcony has no power outlets, and I'm not going to snake a cable out my balcony door, so I'm trying to find a way to battery-power or solar-power these lights.

The lights take 5 V DC according to their power supply, and my kill-a-watt shows they draw 0.025 A at 120 V from mains when powered. I know enough about electronics to know I could power the bulbs by splicing in a D battery holder with 4 batteries in series, but I'd like to solar-power the lights if possible. My questions are:

  1. Even though the power supply is rated for 5 V, would it be safe to give the bulbs 6 V? It would make it easier to test my setups with them without worrying about blowing them.

  2. What combination of a solar panel/battery could I use that would be relatively clean while also giving the bulbs enough power to be turned on all night if desired?

EDIT: Some more info about the lights from a relevant FCC report on the power supply:

  • LED driver: KMUV-050-060-NA-2
  • Rating
    • Luminaire: 5 V DC, 3 W
    • LED driver input: 100 – 120 V, 50/60 Hz, 0.09 A
    • LED driver output: 5 V DC, 1.2 A, 6 W
  • Class
    • Luminaire: III
    • LED driver: II
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  • \$\begingroup\$ Are you measuring high voltage current from primary source? What is the voltage? \$\endgroup\$
    – user263983
    Jan 25, 2021 at 13:09
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    \$\begingroup\$ We don't know how the lamp works and what kind of power supply it has, so you need to figure it out, i.e. modifying equipment needs some understanding of the equipment. Manual says it has 12x0.2W lamps, that's 2.4 watts, or about 500mA at 5V. It could be constant current driver, or simply 5V constant voltage driver. Anyway, lamps might simply burn immediately when connected to 6V, so don't do that unless you are willing to experiment. Even if they work at 6V, they could consume excess current and heat up more and this can affect long term reliability. \$\endgroup\$
    – Justme
    Jan 25, 2021 at 13:34
  • \$\begingroup\$ More than likely your wallwart is outputting more than 5V when it's running. My guess is 6V is safe enough for the lamps. Note that your kill-a-watt measures the AC current (lets say at 110V)- so .03A @115V there is more or less equivalent to the 500mA at 5V that Justme calculated. \$\endgroup\$
    – mike65535
    Jan 25, 2021 at 14:01
  • \$\begingroup\$ Can you use a telephone jack cable to a 5V USB charger or PC PSU Molex? It's not much power \$\endgroup\$ Jan 25, 2021 at 14:01
  • \$\begingroup\$ @Justme I've added some info to the main post to clarify about the power supply. I'm not sure how to tell whether it's a constant current or constant voltage driver, since the rating plate specifies 5 V and 1.2 A, respectively. \$\endgroup\$
    – A. Vance
    Jan 25, 2021 at 14:58

1 Answer 1

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We can guess the 12 LED lamps are wired in parallel, and each has its own individual dropping resistor or driver circuit. (Because if they were wired in series the power supply voltage would have to be at least 12 times the individual LED forward voltages, probably 15V or more total).

I'd say you just need a 5V supply that can supply at least 1.2 A.

I'd suggest the easiest solar power solution is a "solar power bank" with 1 or more USB receptacle(s). You will need to cut the wire to your lights and splice a USB plug. When you make the cut, take care to test and label the wires to determine which is positive and negative, and match that to the USB voltage.

This search term Amazon solar power bank will find plenty, ranging from $25 up and supplying 2A or more. To determine if they can run all night, check the battery capacity. For example, a 20000 mAh battery is 20 ampere-hours, so it could supply 2 A for 10 hours, maybe not enough to run all night in winter. You also need to have plenty of sunlight all day to charge it. Finally, be aware these units will wear out from repeated charge/discharge cycles. Bottom line: reconsider whether you could find a way to run a wire through your door, window, or wall.

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