I recently purchased too many of these fold-able type solar chargers. Some of them have many reviews, and some have very few, but almost no reviews discuss how the panel deals with shady interruptions like clouds.
NOTE: This is only a test of one aspect of this charger, not a full review.
Charge Restart Feature
Background
These solar chargers are marketed toward backpackers, campers, and/or emergency situations. In my opinion it makes sense to charge a battery bank with one of these, and then charge your mobile phone with the battery bank later on (after dark?). These chargers can also work directly with your mobile phones, but that is a tricky endeavor.
Many mobile phones (and some battery banks) will not adapt to the changing power provided by a solar charger. For example, current generation apple devices will start charging at full power, but if a cloud reduces the output temporarily, the apple device will not resume charging at full power.
In response to this, some solar chargers have begun adding charge-restart features to their circuitry. The theory is nice, the panel detects an interruption in solar energy, and briefly cuts power to the usb ports. This should trigger an apple device to automatically resume charging at full power.
Drawbacks
Depending on how the charge-restart feature is implemented, there could be some serious drawbacks. Ideally the solar charger would reset the usb ports only once, after the cloud has passed. That means the charger has to notice a sudden increase in sunlight, and reset the device.
Some solar chargers are taking the easy way out, and just cutting the ports off when the output voltage drops below a certain threshold, say 4.4v. This method means that when a cloud obstructs the sun, power is cycled immediately. But as soon as your device begins charging, the voltage will drop again, and power will be cycled again. This will repeat until the obstacle passes. This method could be very bad for your device. This method also makes it impossible to trickle-charge your device.
In this test I will try to determine if these solar chargers have a 'charge restart' feature, and if so how well it works.
The AUKEY 20W (pb-p2, purchased on amazon, March 13, 2016)
Some Pictures
IMG_20161112_133521.jpg
IMG_20161112_133529.jpg
IMG_20161112_133548.jpg
IMG_20161112_133649.jpg
The Test
In my test, I tried to obscure the sun as much as possible without cutting power to the device being charged. For this charger, I closed the third panel over the second panel, leaving only the first panel exposed to sunlight. Then I used a semi-transparent piece of plastic over the last panel to further reduce the output. I monitored the charge rate with a simple USB charging meter.
After the charge rate slowed to almost nothing, I removed the plastic and opened the panels back up. Here are the results:
From what I can tell, the Aukey 20w (pb-p2) does not have charge restart technology.
NOTE: This is not necessarily bad, see the 'Drawbacks' section above.
The Specifics
| Resting Voltage 3 panels exposed |
Charging Tesa PB 3 panels exposed |
Charging Tesa PB 1 panel exposed |
Charging Tesa PB |
| 5.26v | 4.86v/1.55a | 4.4v/0.69a | 4.11v/0.06a |
Additionally for this panel, I tested an iPhone 6 with an obstruction. I closed the third panel over the second, and covered the first panel with my plastic cloud. The iphone charge rate dropped to 0.08a. After I removed the plastic cloud and exposed all panels, the iphone still only charged at 0.08a. This is what the charge-restart feature is supposed to help with. I will be testing more fold-able panels in the future...
Conclusion
In my opinion, the AUKEY 20W will work great for charging a power bank or android phone, so long as the PB or Phone dont stop charging after temporary reductions in power. It would also be great for trickle charging devices in not-so sunny conditions.
The AUKEY 20W will have trouble charging an IOS device on a partly to mostly cloudy day.
I always recommend you fully test your setup in varying conditions before you rely on it.
EDIT: typos
EDIT: add a conclusion