Semi Flexible Monocrystalline Solar Panel (6V 1A) (FIT0600)

Support Product Questions
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This powerful monocrystalline solar panel features an A-class monocrystalline silicon panel. Due to up to 21% conversion efficiency and waterproof design, you don’t…

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I plan to use semiflex solar panel 6v 1A with DFRobot Sunflower 5v charging 900mA to charge 18650 3.7v 3400mA which charge @ 0.2C. The Sunflower will then charge @ 900/3400 = 0.265C. Will this work? Or how do I reduce the charging rate?

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Hey there, @Eddie20597,

While the solar panel is important for supplying sufficient power, the SPM is going to be the more critical factor here. The Sunflower manages the battery current using a three-stage charging cycle:

  • Below about 3 V battery voltage: trickle charge at up to roughly 90 mA
  • From about 3 V: constant-current charging at up to 900 mA
  • Approaching 4.2 V: constant-voltage charging, with current gradually tapering until charge termination

So if 900 mA is the maximum during the constant-current stage, not the current throughout the whole charge. For a 3400 mAh cell that going to be about 0.265C. If the cell datasheet lists 0.2C merely as its standard charge rate and allows a higher maximum, this should be acceptable.

However, if 0.2C (680 mA) is its absolute maximum, well, the Sunflower manager might not be the best for this one. It doesn’t have any user adjustment to reduce its current setting. In that case, you’d be better off with a charger configured for 680 mA or less.

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Hi Eddie and welcome.

I actually have the SUNNYSOLAR SYP-SP5V10W solar panel (SKU: FIT0573) which is the 2A version of the one this thread is for, with a DFRobot Solar Power Manager 5V (SKU: DFR0559) for my back yard greenhouse project. They work well together.

I found that solar panels output rarely meets the manufacturers specifications, and the fact that the sun is moving (ie changes the angle to the panel) also varies the output. What with clouds and shadows it is not possible to predict a definite amount of power which will be generated on any day … so this is where some over-thinking can be your friend :wink: And let’s not mention the string of cloudy/rainy days during winter !

This solar panel’s output is rectified to 4.5 - 6 volts during daylight hours, with the amount of current being variable (going from barely registers up to maximum when strong sunlight is direct on the panel at 90 degrees).

I am amazed that DFRobot think we are happy for our projects to stop without warning when the battery runs down … so you might like to measure your battery’s voltage, and possibly the solar panel output. I found the Adafruit INA3221 very handy for measuring battery and solar; voltage and current - though a simple voltage divider on the battery is the minimum to warn of low battery.

Note also that this panel is thin, lightweight and “showerproof” - so I am building a perspex container so mine can be outdoors in full rain.

I hope I haven’t put you off - it is worthwhile … but I found it comes down to best guesses and “try it and see”.