Solar charges and powerpacks

I've used solar chargers and power packs to charge things for a while now whilst possuming. They came up in a separate thread, so here's my experiences. Summary ================================ Powerpacks alone: You can use a powerpack to charge most things there days - phone, gps, etc. This seems handy as it avoids carrying all shapes & sizes of spare batteries. However, powerpacks alone, plus assorted cabling to connect devices to them, were much bulkier and heavier than just carrying spare phone/gps lithium ion batteries. They were, however, effective at doing their job, but delivered 1/2 of their nominal charge into the battery they were charging. They were also near-useless for charging AA/AAA batteries. Solar charging: Solar->USB chargers were great for some devices (qstarz gps, degan radio) which would trickle charge off them in any light conditions. However, for phones the only way to charge the phone in anything other than direct sunlight was to go solar -> powerpack -> phone, as the current requirements of the phones charging exceeded that generated by both solar panels tested. For extended stays in one place the power packs have the advantage that you can leave the powerpack charging off solar panels at camp/hut all day, whilst you use your devices in the field, then can charge from the power pack to the device at night. Details ======================== Powerpacks Power ratings: The process of charging a lithium ion battery seems about 60% efficient - i.e. the power required to do: charger -> powerpack -> phone was approx 2x the amount of power required to do: charger -> phone So if the power pack says 9000mAh, you get closer to 5000mAh into your phone batteries Weight worth it? My goal zero 8700mAh power pack (~5000mAh to phone) weighs 250g. Spare phone batteries weigh 45g. So on a weight-for-weight basis it's not worth using the powerpack. Plus, to charge camera, gps, phone I required 3 different USB cables to got from the powerpack to the device. Solar charging ========= I've bought a couple of USB-output solar panel sets. One from goal zero for $150 including above power pack, another online, unnamed one from dx.com for $30. Both weigh 250g and are 140x150x20mm, and 120x120x30mm respectively. Both give pretty-much identical output under load, despite the dx.com one being rated 5W output and the goalzero one being 3.5W. Charging devices: QStarz GPS, Degan radio Both of these devices will charge off the panel direct in most light conditions, only cutting off when it gets dark. Samsung galaxy phone This only charges directly in bright sunlight. In other conditions (under cloud) it shuts-down the charging process Charging powerpacks My 8700mAh powerpack took about 2 days to charge completely in normal conditions (sun with occasional cloud). This could be improved if you're around to reorientate the panels to the sum at all times. Charging AA/AAA batteries. I tried 2 different USB AA/AAA chargers from dicksmith and dx.com. To charge a AA/AAA you need a voltage somewhere just over 1.2V The powerpacks produce approx 5v. Both chargers I tried appeared to drop the 5v out of the powerpack down to the 1.2v+ required to charge the battery by disapating the remainder as heat. This was hugely inefficient. A fully charged 8700 mAh (holding about 40 watt-hours of power) power pack could only just charge two 2200mAh 1.2v AA batteries simultaneously (holding 5.2 watt-hours) before going flat. Both chargers would just run direct off the solar panels in full sun conditions, but shut down if cloud was present, of the sun panel was not pointing directly at the sun. More efficient USB->AA/AAA chargers may exist, but I failed to find any for sale with enough details in their technical specifications to convince me to try them.

I’ve been deliberating over solar chargers and how effective they really are. A friend bought the PowerMonkey Extreme and from a distance it looked pretty good but weighs nearly 450g… The manufacturer claims it recharges in optimum conditions within 18-22 hours. Because I lack the expertise in this department I asked a friend to comment on the matter of solar chargers and being a Chartered Engineer and member of the Energy Institute in the UK with 30 years energy management experience he came up with an illuminating answer... “Quoted energy from the PowerMonkey Extreme is 33.3 Wh. My calcs of available sun energy for input into the device battery in ChCh per January day, is 16 Wh, which means 2 days charging. Based on the following assumptions: 1. Using the NIWA data, average Insolation per day in January is 373.5 W/m2, 6am to 6pm 2. Solar panels on the device are approx 150 x 80 mm, 2 of them giving a total of 0.024 m2 3. Therefore ave Watts sunlight on the panel area is 8.96 W 4. Assume 15% efficiency for the panel (that’s pretty good) and 12 hours charging, this gives 16.13 Wh. 5. This also assumes the panel is at the NIWA’s optimum tilt angle to the sun for ALL of the day (but fixed orientation bearing i.e. due north). 6. If the days were totally cloudless, available sunlight would be around 60% higher. 7. This doesn’t take into account any charging losses – and there will be some, say 5-10%. Sorry, but there is a lot of smoke and mirrors out there.” I bought an external battery pack in the end… but still keep an eye on progressing solar technology…

Problem is they are all so damn heavy. It would be nice to be able to charge the camera battery and MP3 player on those longer trips though... Have a look at the one Lightweight Rob uses, only 250gm's... http://www.lightweightrob.com/2014/12/first-tramp-of-2015.html

I just bought a couple a week or so ago. 8000mAh, Solar Charging 5V/200mA, input DC 5V/1A, Output DC 5V/1A. Made in China, Measures 75mm x 130mm x 15mm, Weighs 125 gms. Just checked that weight on a set of digital scales. I fully charged both from mains, carried them around for 5 days in window of car when driving, on window sill when at work. Cloudy days, bright sun days, even found some artificial lights turned the charging trickle maintenance light on. I then used one to charge my Samsung note two. Then left the solar pack sitting on bedside table until phone required charging again. I then used it to charge phone again, in each instance the phone battery was indicating approx 25% remaining. The phone was charged to 100% in both instances and the solar unit looked as if it might do another charge. I haven't conducted any further tests to date as I was satisfied these two units would suffice for anything I would need.