Charging a power bank with a solar panel

Question

Is there either a simple circuit that I could build, or a good circuit/pre-made board that will charge up a 6700mAh/5V/2A power bank with a small solar panel that is attached to the cover of an Altoids tin?

If I took the pre-made path, would it be sufficient to just buy an AdaFruit mintyboost kit or is there some additional circuitry required?

Panel specification:

• Typical voltage: 5.5V
• Typical current: 170mA
• Open-circuit voltage: 8.2 V
• Maximum load voltage: 6.4V.

The charging time is the biggest bottleneck here but I'm mainly doing this for fun and learning power electronics so I'll try it out.

Answer 1

This addresses th "make it myself" approach:

An extremely simple design should be adequate. As long as the panel voltage never exceeds the power bank maximum input voltage you can connect the panel you describe to the power bank 5V input. Some devices specify Vinmax, while others assume USB-5V specification compliance. Usually up to 6V in woul be safe but there are a very few devices with 5.5V max specifications.

A voltage clamp at 5V or slightly will work - as above, Vin_powerbank must be below its specified Vinmax. A zener diode of suitable voltage will work but a sharper cutoff clamp would be better. A 5.1V 1 watt zener or maybe a 5.6V should suit. For 1 Watt devices here rated voltage is achieved at about 50 mA. Some simple real world test will show what zener voltage is required to keep Vpanel below the maximum power bank input voltage. Two or three inparallel may be required.

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Older - retained for relevance:

An Altoids tin panel output will be small - probably under 100 mA.
Do you have a specification for the panel?
At 100 mA it would take 67 Sunshine hours to charge fully from flat or about 12 days in typical summer sun with the panel moved occasionally to optimum angle.