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Li-ion battery charging from solar?

Discussion in 'Off Grid Living' started by natshare, Sep 13, 2013.

  1. natshare

    natshare Monkey+

    Was wondering if anyone knew of a good solar based method for charging Lithium-ion batteries, like AA or AAA??
    With the little bit of research I've done, it seems that while it's easy to recharge NiCad or NiMH batteries with solar panels, Li-ion batteries have their own special peculiarities for recharging, and may not be as easy to recharge with a solar panel.
    It seems that while Li-ion batteries charge well off of a stable power source (wall voltage, via charging block, or computer USB power), they don't do well with the fluctuating power that solar panels put out. In fact, most of the time, what I've seen is "use the solar to charge another battery, then use that to charge the Li-ion battery" type of response! The problem with that, of course, is that every time you go through a charging system, you're going to have losses (no system is 100% efficient), so why take a double-loss by charging one battery, then using it to charge another?
    While I have no problems with using NiMH batteries, the inherent stability of a charged Li-ion battery, plus their lack of charging "memory", makes them more attractive of a power source, for small electronics (flashlights, radios, etc.).
    Does anyone have any insight on this, or know of a good solar charger that can recharge both an installed battery pack AND small (AA/AAA) battery charging, straight off of the solar panel?

    Thanks, in advance! [winkthumb]
  2. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    You are dealing with two incompatible issues. An uneven power source, and a battery that requires a steady power source. That is why you need the second battery, to even out the power source. I use AA and AAA batteries, all of them rechargeable. I use a wall charger now, but will be switching to solar as possible. Charge the 12vt bank through the solar panel (and as needed, a charge controller) then either step down for the proper voltage( if you are handy) or run it through the inverter. Or, I believe the better controllers have adjustable / programmable loads available to be custom set.
    natshare likes this.
  3. Airtime

    Airtime Monkey+++ Site Supporter

    The RC airplane and helicopter folks have latched onto Li-ion and polymer batteries in a big way. That industry has numerous charging products many of which operate from 12 volts. Tower Hobbies based in Champaign, Illinois is a very good and reasonable priced source. I'd look for a 12 volt input charger that does what you want, find a solar panel(s) that will more than meet the supply requirements and put a small lead acid battery in the middle. If the solar panels were not setup to charge a 12 v battery directly, then you'll need a charge controller. Many smaller panels don't put out that much juice and their internal impedance is high enough that while they may put out 25-30 volts with nothing attached, hook a Lead acid battery to them, even a smaller one, and suck some current from the panel the voltage will drop right down to normal charging voltages. Connect the Li battery charger to them both and the lead acid battery will act like a buffer right around 12.5-13 volts. If the Li charger pulls more current than the panel can supply, the panel's output voltage would normally drop but the lead battery is there to supply some current the panel can't and keep the voltage up above 12 volts as long as it has the capacity to do so. If the charger is drawing less current than the panel is supplying, the lead acid battery will absorb this and start charging itself keeping voltages generally well below 14 volts. Watch the specs but I suspect most Li chargers would be happly between 12 and 14 volts input to them.

    Now if you are using some big panels or multiple panels such that if they are connected straight to a lead acid battery directly it would be too much and create over-charging issues, then those panels would need to go through a charge controller before connection to the lead acid battery to prevent excessive voltages and over charging. Hook your Li charger to the lead battery and proceed as before.

    The described set up would be more efficient than first charging a battery and then charging the Li battery packs as much of the solar panel output goes straight to the Li charger and the efficiency loss in charging and then discharging the lead acid battery is avoided. Just a final note, while I haven't done this thing with Li chargers, I have done this exact same thing with 7.2 volt NiMH battery pack chargers and it worked well. My solar panel was a bit whimply so some power would come from the acid battery and then it would recharge in-between. Yes this was less electrically efficient overall but then I got by with a smaller panel.

    jollyrodger13, natshare and kellory like this.
  4. BTPost

    BTPost Old Fart Snow Monkey Moderator

    The technical issues in charging Li-Ion and Li Polymer Batteries can be overcome with a Buck/Boost Switching DC/DC Power Supply... These are designed to take a very WIDE DC Input Voltage, and supply a constant Output Voltage, or Output Current, to a specific Impedance. The Li Batteries have a VERY Low internal Impedance, thus they need an Active Charger Design for charging. This means that one must first make a Constant Voltage from a wide variable Input Voltage, and then buffer that with a fair sized Capacitor Bank. (1000+ uF) Then feed the Active Charger Chip that knows how to deal with the specific Battery Type (Li - something) that you want to charge. Most outfits just deal with 12 VDC as an Input to the Active Charger System, but if you put a Buck/Boost Switching DC/DC Power Supply that outputs 12Vdc, in front of it to feed it 12 Vdc, you have what your looking for.... You could run it off anything from 5 Vdc from one of those Thermo-electric Stoves thingies, Solar, Hand Cranked, Car battery, or whatever you can come up with.... ......
    jollyrodger13, natshare and kellory like this.
  5. natshare

    natshare Monkey+

    Sorry for my stupidity! I forgot to add that I'm primarily looking for a man-portable method, NOT for home use! :oops:

    I didn't think of that little tidbit of information until AFTER I was in a place where I didn't have computer access today! :rolleyes:

    I will, however, utilize the knowledge you guys have already taken the time to share, for home use, as I was also looking into doing Li-ion solar charging at home. I just had a senior moment, while typing in my request, and forgot to mention this was more for a SHTF situation. Seems I [own] myself!!
  6. Airtime

    Airtime Monkey+++ Site Supporter

    The system I was talking about need not be huge. Probably beyond BOB consideration but worthy of putting in the trunk or back of BOV. A small lead acid battery could be like the ones in an UPS stand by system which isnt much bigger than a pint of milk.
    TowerHobbies.com |Duratrax Onyx 235 AC/DC Advanced Charger
    natshare likes this.
  7. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

    You might already have one in the trunk of your car in the form of a emergency air pump/ flashlight/ jumper battery pack with cables. These things have 12vt female jacks on them to power other things, just add a male 12vt jack in parallel with the solar panel and that should level out the source power to your charger.
    jollyrodger13, natshare and Airtime like this.
  8. Airtime

    Airtime Monkey+++ Site Supporter

    Great thinking! Something like that would do the trick.
    kellory likes this.
  9. natshare

    natshare Monkey+

    Thanks again for all the great ideas/thoughts you guys are bringing me! [winkthumb]

    I did run across this list, at Amazon, that has some good products already on the market, that I'm going to look at (more in depth) when I get a chance:
    Solar Battery charger list at Amazon

    I'm also going to cruise through the site "Instructables" (if you've never seen it, go check it out!), and see what other people have done. Seems that if I can take some inexpensive solar lights, and change them into inexpensive battery chargers, it's worth the time spent. Oh, and I'm also thinking that I'll stick with NiMH for the replaceable (AA/AAA) batteries, and just find a good solar charger that can has an onboard battery, and can do a USB output, to recharge those devices.
  10. kellory

    kellory An unemployed Jester, is nobody's fool. Banned

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