For an updated look at how to charge your digital camera from solar, view our Solar for Photography Guide.

For all of you shutter bugs out there who are looking for solar solutions for charging your devices on the go or for simply cutting back on your grid power usage, Voltaic Systems is testing a variety of battery charger units and some interesting peripherals as well.

SIMA camera light charged by two 2W panels

SIMA camera light charged by two 2W panels

Charging the SIMA model SL-20LX
A friend of mine, who does a lot of freelance photography and videography, approached me about charging a rechargeable LED camera light light made by Sima, model SL-20LX, from solar. Before connecting the light to the solar panels, we did some figuring to see what system would be most appropriate.

How Much Power is in the Battery?
The SL-20LX is outfitted with a 3.7 Volt (V) lithium ion battery pack with 730 Milliamp Hour (mAh) storage capacity or about 2.7 Watt Hours (Wh) of power (Volts x Amp Hours = Watt Hours).

How long will it take to charge?
According to their documentation, the light charges in 3 hours from their AC adapter. The input jack on the back is rated at 5v and 300mA or 1.5W, so we can figure that the AC adapter will provide roughly 4.5Wh through the entire 3 hour charge cycle. But wait, the battery only holds 2.7Wh of power. This means that only 60% of the power from the adapter makes it into the battery (power stored in battery / power consumed by the charger).

If we want to charge the Sima light in roughly the same amount of time from our solar panels, we need to select a panel configuration that will provide roughly the same amount of power as the AC adapter. A single 2W solar panel should do the trick. But how long will it take? With other batteries, we’ve seen that it takes about 2.5 times as long to charge than if you simply divide the Watt hours of the battery by the Wattage of the panels. So to charge a 2.7Wh battery it should take about 3.4 hours (2.7Wh*2.5/ 2Watts) in full sun. For the 4W system using two panels, the light should charge in a bit under two hours.

Test Results
In full sun, a single 2W panel charged the Sima light in just over 6 hours. The two-panel 4W system charged the light in just under 4 hours. This means that the charge from solar isn’t perfectly efficient but that the Sima lights will charge from any of the 4W systems (Amp, Fuse, Switch, Converter, Off Grid) in about the same amount of time that it would take to charge them from the AC adapter. All you need is an adapter to fit into the Sima’s power jack, 3.7mm x 1.3mm.

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