Amps are Everything

It’s hard to find a solar panel which fits on top of a backpack and which can reliably charge eg an 18650 battery/powerbank. This one from Alexpress looks pretty good.

 It is 275 x 150 mm  (10 ¾” x 6”) and weighs:141 grams. so it should just fit on top of your pack, particularly suitable if your backpack has a lid like the cheapies we took on the EBC.

It puts out 2 amps at 5 volts (10 watts) so it should technically just about charge a single 18650 in an hour supposing you can find a 2 amp charger and cord to go with it.

It would be safer to charge two 18650s together at 1 amp each through 2-3 amp charging cords (below) and a 2 amp charger if you can find one. Or you can buy usb splitters  for a bit over a dollar to turn the single usb outlet on this solar panel into two. If you connect each outlet  to a 1 amp only power bank charger they should both be charged safely in just over two hours.

Above is a Buheshui solar panel from Aliexpress. They also have a larger folding one. This manufacturer’s panels are amongst the best I have tested. I have tested many.

Even on the top of your backpack you should get the equivalent of two hours of bright sunshine during the course eg of an eight hour hiking day. The 3700 milliamp hours available from a single 1860 battery ought to be enough to charge a small phone, camera battery and torch each day. Given that most of these will only need charging at most every second day that should be quite enough to keep them topped up and any other electrical gadgets such as an emergency sat phone/communicator and emergency radio text messager such as the Go Tenna. At US$12.90 delivered (Feb 2019) it is worth a try.

The diameter of the charging cord is vital to successful charging. Wires are measured in AWG (gauges) the lower the number being the thicker, as seen below
 Here are some cheap 3 amp charging cables (pictured above –  5 for US 6.99).

You need to check what amperage your (eg 18650) batteries can handle and how many amps your charger delivers to each battery. Many such batteries can handle around 1.7 amps (each) so that a power bank/charger) which contains two such batteries and can take 3 amps should be fine. I am using the 18650GA flat tops in mine.

Each battery is approximately 12 watts  (at 5 volts times 1 amp each = 5 watts per hour) they will take a bit over two hours to charge in two single chargers. It is quite difficult to find a power bank/charger which delivers more than 1 amp each to the contained batteries. The batteries are always wired in parallel so the current is divided between the batteries.

Indeed it it difficult enough to find one which delivers 1 amp each (.5 amp is more typical) Now perhaps you see why your device/s take so long to charge. Practically all my charging cables proved to be 28AWG wire and so delivered at most .5 amps.

As you can see the one above is 20 awg wire and will deliver 3 amps plus to the power bank/charger. There are other cables which promise to deliver 5 amps. Of course length/weight is also a factor. You may have to do some hunting through Aliexpress and etc to get the perfect setup.

A USB digital amp meter will also be a useful tool so you can see just how many volts/amps your setup is delivering. These can be bought for a couple of dollars.

PS: This 3 cell powerbank charger looks like the perfect match. 2 amps in and out. I like the digital percentage charged function. Also only a couple of dollars.

PS: I bought these 3+ amp charging cables from Amazon. Pack of 5 x 7″ cab;les for US7.99 the lot (may 2020)  They weigh 7 grams each.

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