# Solar battery charger?



## spiritofold (Dec 11, 2010)

Im not sure if a decent one has been invented yet, but what do you reckon is the best solar battery charger? I mean something for reliably charging AA and AAA batteries?

Over the years i've had a few and tbh they have all been crap. Im ever hopefull that something decent is available now that will do the job ;-)

Andy


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## UncleJoe (Jan 11, 2009)

Solar landscape lights make great "AA" battery charges. You just have to make sure to pull them out at night so the lights don't come on. It might take a couple days to get them to full charge but it does work.


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## Wallrat (Oct 28, 2011)

UncleJoe said:


> Solar landscape lights make great "AA" battery charges. You just have to make sure to pull them out at night so the lights don't come on. It might take a couple days to get them to full charge but it does work.


Brilliant solution, and cheap too!


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## spiritofold (Dec 11, 2010)

I'll take a look at them, cheers ;-)


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## The_Blob (Dec 24, 2008)

you can find them @ Dollar Tree


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## LincTex (Apr 1, 2011)

Be careful with those "Path Lights" - many have a clear epoxy poured over the surface of the solar panel that only lasts ONE YEAR in sunlight before clouding over (at least in Texas sun). 

DO NOT BUY THESE as the solar panel is junk in one year. You can identify these in the store because you can "catch" this surface with your fingernail.

The ones you want have "Amorphous" silicon solar panels. These are a very dark red color and are smooth glass, not chips/strips of blue ("polycrystalline") under cheap epoxy that is NOT U.V. resistant.

Also, buy one and take it apart. If all of the components are "surface mount", I would avoid it. If it has "Real" resistors, transistors and diodes soldered onto a PCB, I would buy that.

I have built my own: I use a "Good" PCB with "Real" components from a bad light (with the solar panel clouded over). The components are pretty heavy duty, so I married this circuit board to a battery holder that can hold either two "AA" (for the Mini-Mag Lite) or 3 "AAA" (for the LED headlamp). The first one I built, I can charge a pair of AA or the AAA's, but not both at the same time.... so I built a pair in each configuration - - - so now I can charge 2 pairs of AA and also six AAA all at once.

To do that, you need a bigger solar panel! 
The little ones on top of the garden lights can not do this, and they are pretty cheaply made anyway. Solar panel "cells" as formed are only .5 volts each... you will need a panel with 4 cells soldered in series (2 volts total). These are pretty easy to find on ebay, about the size of a 3x5 recipe card (close enough). You must be able to see the four cells soldered in series before you buy it.

You can also buy four high-quality "cells" (at .5 volts each) VERY cheaply and solder them in series to get 2 volts. This isn't hard to do.


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## LincTex (Apr 1, 2011)

here's a "do-it-yourself" solar path light kit if you like stuff like this:

Solar Lawn Light Self DIY Kit | eBay


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## NaeKid (Oct 17, 2008)

I have a solar-charger for upto 8 AA and AAA batteries at home. The charger works off of 110v, 12v or solar for the widest range of connection possibilities by unplugging the cord to the charger and plugging in a seperate cord.

I have found it works quite well for the most part keeping batteries topped-up and ready for use. If I remember correctly (IIRC), the unit was manufactured by Energizer ..


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## GetPreparedStuff (Dec 16, 2009)

Over the last 5-6 years I've gone down a number of different paths in the search of solar charging solution for AA & AAA batteries. Here's some of what I've discovered.

The engineering of a decent solar AA battery charger requires some trade offs to accommodate the charge characteristics of a typical NiMH rechargeable AA cell. A typical modern AA battery charger that is plugged into your AC household current will use currents from 500mA to 2000mA and will shut off the charge once the charger senses a -delta V during the charge cycle. However, depending on conditions this -delta V signal isn't always detectable and can be missed or be absent so a good charger will also have a timer that will shut off the charge cycle after a period of time to prevent run away over charging. This routine requires a constant power source, a constant current and normal temperature being supplied to the battery makes this type of charge process possible but trying to adapt the -delta V sensing to a solar charger is very problematic because of temperature and current fluctuations and the constant potential of a power interruption due to a cloud or shade source which could cover the solar panel at any point during the cycle effectively shutting off the power to the charger and causing a reset before the charge cycle can finish making an over charge condition likely unless some other means is used to terminate the charge cycle.

Because of the inherent inconsistent and variable power supply of solar most of the solar battery chargers available have chosen the low current trickle charge method to charge batteries. They use a small solar panel that doesn't output more than 100-200mA (which is still high for trickle charging AA cells) and will slowly charge the batteries during a long sunny day after which you hopefully have a mostly charged battery. This method worked better with older NiCad and low capacity AA batteries that had a chance to be charged fully in one day but as capacities of NiMH cells have increased (2000mA - 2500mA) it would take a solar trickle charger 10-25+ hours (1 to 3 days) of sun to charge AA cells fully.

Most if not all landscape type lights use this trickle charge method and on average produce enough power to charge the battery enough to run the LED emitter for a few hours each night. The capacity of the batteries in these lights are 500-800mAh size so the batteries are sized to match the max amount of power that a days sun on the little panels would charge them. The better quality lights use NiCad batteries because of of the next issue.

Another issue with solar charging is the sensitivity of NiMH cells to heat. NiMH cells can lose over 40% of their cycle life if used and charged in temperatures above 104F and 50% of their life at temps over 110F. High temps also reduces the efficiency a NiMH cell charges at so at higher temps it takes much longer and more power is used to recharge the cell to full. Many solar battery chargers are "all in one type units" that "trap" the cells inside the unit with the solar panel over top creating an oven that cooks the cells as it tries to charge them. An average NiMH AA cell has a rated cycle life of 1000. A solar charger can easily reach temps above 104-110F which will quickly reduce the life expectancy of a cell to way below 500 cycles. Note: NiCad batteries are more robust under these high temperature extremes but have less capacity than NiMH cells.

I've gone through a number of solutions to these issues and cost is the big variable.

The least expensive solar charging option is the cheap trickle charge method. If you have the time to wait for batteries to be charged and can buy extra batteries to replace those that go bad earlier, go with the cheap under $25 solution. I personally have bypassed this option as my minimum requirement was the need and ability to charge four AA cells (2000mAh capacity) in one day of sun.

The best solar AA charger I've found that does this and meets my minimum requirement is the Goal Zero Guide 10 adventure kit. The Guide 10 plus charger can charge 4 AA 2000mAh NiMH batteries in 3-6 hours in good sun when plugged into the Nomad 7 solar panel. The charger is connected to the solar panel by a short cable so I can place the charger behind the panel protecting it from direct sun and the higher heat that other solar charger designs subject the batteries to. The Guide 10 charger has had to make some design decisions as to it's charge cycle to work well with solar panels and from what I've measured it does a good job of charging the four cells without threat of overcharging them.

Some of the quirks I've experienced is that the Guide 10 requires that four AA cells must be loaded in order for charging to take place. It will not charge just one, two or three cells by themselves. The Guide 10 will balance charge the cells so if you placed inside 3 fully charged cells and 1 discharged cell it will charge primarily the 1 discharged cell. The reason for this is that the Guide 10 is also a USB power pack giving you the ability to use the power from the 4 AA cells to charge any USB device. The Guide 10 will charge AAA cells but it needs an optional adapter cartridge/caddy that must be inserted into the battery compartment to hold the four AAA sized cells.

Because of the issues presented by the charging characteristics of NiMH batteries. The best solar charging option for AA batteries is to use a larger solar panel system to charge a good capacity 12v battery of a different chemistry such as a lead acid or LiFePo4 and then use a quality 12v DC AA battery charger that can be run directly off the 12v battery and constant power source. Lead acid and lithium iron phosphate batteries can be charged more effectively under the variable power produced by solar panels. From a number of the AA battery chargers I've tested It takes on average about 20-24 watt hours (2AH) to fully charge four AA 2000mAh cells.

A 15 watt 12v solar panel is the very minimum size I'd recommend to generate enough power on a typical day to be able to in turn charge four AA cells. I say very minimum because I'm also interested in using this system year round under a lot more conditions than just a nice cloudless sunny day. A 30 watt panel is actually more to my liking in being able to produce enough power to charge at least four AA cells in a single day under a greater number of weather conditions seen through out the year.


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## Redtail (Oct 17, 2008)

Does anyone know of an AA/AAA charger that will interface with MOLLE/PALS webbing? I've read about them all over and would really like one to strap to my pack. 

RIght now I can interface to a USB solar charger and use my low-power radio, a Motorola EM1011R, as a AA charger, but to do this, I lose use of the radio while it's charging. And solar charging takes a long, long time. 
Not to mention, the USB solar charger doesn't really attach to anything because it's meant for yuppie hipsters to leave on the dashboard of their Prius with their mop-head designer dogs to bake in the sun, to charge their various iBortions.


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## NaeKid (Oct 17, 2008)

I have several christmas-light solar-panels where the panel will charge-up three AA-batteries and automatically turn-on the string-of-lights at dark. There is a switch on the back of the panel to turn off the night-light option, but, keep the batteries charged up.

Would something like that do the trick for you (pictures attached).


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## NaeKid (Oct 17, 2008)

Had another thought for you. There is a product called BatteryTender that is normally used for motorbikes to keep the battery topped-up all winter (or summer when you are not riding all of your bikes) and they have a solar-panel version of their normal 120-volt product.

You can see what it is like through eBay (link to the quick-search) ... battery tender solar | eBay

Hope it helps in your quest.


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## GetPreparedStuff (Dec 16, 2009)

Redtail, the solar panel system that I've seen compatible with MOLLE are a few of the Voltaic panels (Voltaic Fuse 10W Solar Laptop Charger)

It's more of a solar panel/battery pack combo system that has it's own internal lithium battery that charges direct from the solar panel. You would then plug a AA battery charger into the lithium battery for recharging your AA/AAA cells.

I don't know of a AA charger unit by itself that specifically integrates with the MOLLE/PALS webbing. A silicon sleeve for the Guide 10 battery pack can be purchased and the sleeve could be adapted by cutting slots into it to fit into a webbing system, but the better option might be to just let the charger sit inside the Nomad 7's built in pocket or the Voltaic's pouch.

The Nomad 7 solar panel doesn't have anything specifically designed to work with MOLLE/PALS but it does have loops at each corner, end and side that a small carbiner will latch into and then into the webbing on a pack.









Also, thanks for the info on the EM1011R radio and it's ability to charge AA cells in a pinch with a USB connection. It maybe slow but it's a nice option to have available when nothing else is.


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## Redtail (Oct 17, 2008)

Versatility is always a huge plus in my book. 
I like redundancy, but if I can multitask a number of tools with overlapping roles, I can have redundancy with less weight. 
That radio, I actually found dead on the side of the road when I was policing the edge of a reenactment field back in October. I took it apart, silicone'd all the gaskets and O-rings, stuffed a NiMH battery pack in and it started right up. 

I just used it the other night to charge up some NiMH AA's for my night-vision goggles, someone ran off with my wall charger.


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## swensor (Mar 10, 2012)

These days more and more products are migrating to USB power. Many of the Goal Zero kits are using it as an interface, and lots of new products are using it to charge and/or power themselves. A good example is this camelbak water purifier. Pretty cool stuff.


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## swensor (Mar 10, 2012)

so... another cool charging option, in addition to solar is geothermal, like this product called The PowerPot . It doesn't require sun so it will work regardless of weather or time of day. There are other similar models out there... so far this one looks the most promising. I reserved a pot on their home page when it becomes available. Ye!


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