Lithium-Ion charging with solarpanel

Hi,
I have 4 Varta 6600mAh 14.8V 98Wh (i think there are 12 cells) Lithium-Ion batteries which i would like to use in an audio cabinet.

I have correct Lithium-Ion chargers for 220V which are ok and run fine. I would like to do following :

1. Charge all batteries from an solar panel (something like this one http://cgi.ebay.com/15W-12VOLT-SOLAR-PANEL-BATTERY-CHARGER-7-AMP-CONTROLLER-/400105207280?pt=LH_DefaultDomain_0&hash=item5d2820f5f0)
2. Be able to use all the Ah from the batteries.
3. Need an Voltage of 11V - 14.8V for output.
4. Need to be able to charge with solar panel at the same time as i use current.

I have looked on the net and i see that there are no charge controllers where it is specified to work with Lithium-Ion batteries. I found a chip like this one http://www.national.com/profile/snip.cgi/openDS=LM3647 but it needs integration to be used and i am not entirely sure it can be used here.

I also have another issue that i cannot parallel them since that could be hazardous so how can i solve that problem ? I mean i would be perfectly satisfied to have a box/electronics that could drain the first battery first then second etc...

I looking for ideas how to use these batteries with solar energy.

donnib

Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,397 ✭✭✭✭
    Re: Lithium-Ion charging with solarpanel

    The issue with LiIon batteries is they don't take overcharging. At least, they will be damaged, at most they can catch on fire if overcharged.

    You need to look up the actual specs for your batteries. They are likely 4 LiPo packs which have a nominal cell voltage 3.8 vdc. The maximum recharge voltage is 4.20 vdc per cell or 16.8 vdc for the 4 cell array. This voltage is on the high side for a normal 12 volt (36 cell) panel. When the panel gets hot its voltage will drop to about 16.2 vdc.

    LiIon battery recharging needs several safety checks.

    Since they don't take overcharging, when cells are connected in series and diverge in state of charge from use, you need to have voltage limit shunts across the cells to allow the weaker cells to continue to charge while capping the maximum voltage on cells that have reached full charge.

    Some multi-cell packs don't have charge leveling shunts. They rely on cell matching at manufacture point. This is not as good as actually having leveling shunts on each cell and usually results in reduced longevity. If you plan on putting two or more of these 15 volt batteries in series your charger should manage the batteries to ensure they don't get overcharged.

    Typical maximum charge current is between half AH rate to 2/3 AH rate.
  • System2System2 Posts: 6,290 admin
    Re: Lithium-Ion charging with solarpanel

    Thank you for replying back.

    The only info i have on the battery is this http://db.tt/8johQgy which is a picture taken by me.

    I hope that someone have some ideas how i can acchieve what i want.

    Thx
  • RCinFLARCinFLA Solar Expert Posts: 1,397 ✭✭✭✭
    Re: Lithium-Ion charging with solarpanel

    That is LiIon polymer OEM battery. I don't believe Varta has any cells greater then about 2200 mAH's so that must be a series/parallel combination to get the voltage and capacity. That would explain twelve cells in a pack with 14.6 vdc @ 6.6 AH spec. Probably arranged as 3 cells in parallel with four of the three parallel groups in series.

    OEM battery means OEM is responsible for safely charging battery. These appear to be the raw packs for a laptop computer battery without the safety electronics board or battery plastic housing.

    Real nightmare to keep control of charge balance.

    To be frank, these would be a risky setup. Something is bound to go wrong over time and you are dealing with some sizable energy content.

    Anyway, a 15 watt panel producing a maximum of 1000 mA with a blocking diode should be okay to hook directly up to a single pack and not reach the maximum battery allowed charge voltage of 16.8 vdc or 3.3 amps max charge current. Just have to be a little careful of PV maximum voltage when panel is in cold environment where the panel voltage will go up to over 20 vdc.

    You can go to about 3.3 amps of charge rate per battery pack but must prevent battery charge voltage going above 16.8 vdc.

    You could tie all packs in parallel but again just adds more chance of charge imbalance over time. This parallel arrangement could take a charge current of 13.2 amps total or 220 watts of PV panel. Cease charging when batteries reach 16.8 vdc.

    A real charger would current limit at 3.3 amps per pack until voltage reaches 16.8 vdc then hold it at that voltage until current tapers off to about 200 mA where charging would be terminated. It would also monitor pack temperature to shut down charging if cells get too hot due to an internal cell failure. Nomally packs should barely even get warm during charging. Don't attempt to charge if battery temp is below 0 C or above 40C.

    The National semi data sheet you enclosed would not handle the current for these cells. The LM317 they are using for linear current source would get too hot. It also would need about 20 vdc minimum input voltage. You can charge with less current, just takes longer to recharge.

    I am sure you have seen the news reports over the years of laptop batteries catching fire. And this is with their safety circuits from reputal companies that are suppose to know what they are doing.

    Just make sure your fire insurance is paid up.
  • System2System2 Posts: 6,290 admin
    Re: Lithium-Ion charging with solarpanel

    Thanks again :)

    Actually i got these from my work and one of technical guys said there is safety electronics inside and that's about it whats in them. When i say 12cells i cound them by the number. I guess thats's correct ??

    I understand all your concerns and the problems with Lithium i just feel thst it would be a pitty not to be able to use these batteries. I would be willing to spend some time to find a solution like finding an charge controller maybe from Texas Instruments that fits and then make electronic for every single one so it could be charged from solar energy. I mean it should be possible in the theory to fit an charge controller on every single of them then use the solar energy powert to fit every charge controller. Yes it would charge slowly but it will charge. So what is your opinion should i even try this or should i leave it?

    Do you believe this would work?

    http://focus.ti.com/lit/ds/slusa75/slusa75.pdf
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Lithium-Ion charging with solarpanel

    Well, not kidding, if they were mine, I'd sure want to use them too, but they would be installed in a concrete out-building where they couldn't set my house on fire. No, I'm not being sarcastic, or joking. Even when recharging LI camera batteries, I dump the works in a steel pot until the recharge has finished and things have cooled down. That way, if they decide to start spitting flames, the pot will contain the fire. They're awesome batteries, and I use them. I just don't trust them.
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Lithium-Ion charging with solarpanel

    RCinFLA is spot on here - listen to what he says!

    Also keep in mind that lithium pouch batteries tend to expand when charged - preferably you want to get that pouch mounted in something that minimizes that to maximize cycle life.

    Cell management and monitoring is critical on lithium batteries to maximize life - and you really need to have each cell monitored and each cell's status tied into your battery charger so it knows how fast it can charge and when it needs to stop.

    Lipo cells like the ones you're dealing with can be very volatile when overcharged!

    Most likely the "protection" they have is undervoltage protection and not overvoltage - many cells have a circuit that will shut the cell off if voltage drops too low to avoid killing the cell - a completely discharged lipo will not come back to life.
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Lithium-Ion charging with solarpanel

    Per the label's "4S3P" they are 4-series 3-parallel cells. That's the standard nomenclature for lithium packs.

    One thing I've always wondered, though, is if it really is four-in-series, then those strings in parallel (as one would do with lead-acid banks) or if as RC said three-in-parallel then series those packs. Thanks to the charging requirements, I figured they'd have to do the latter - or have a Whole Bunch of single-cell sampling wires, which I haven't seen.
    Even when recharging LI camera batteries, I dump the works in a steel pot until the recharge has finished and things have cooled down.

    What's getting hot, the batteries themselves? I'm curious, as I bought a 2.3AH 3S1P LiFePO4 pack for ham radio / bicycle lights and am amazed it can be charged at a 4A rate (what my smart charger will do, the manufacturer's "recommended" rate is even higher!) but the cells don't even get warm to the touch.

    Compared to standard NiMH AA cells that get noticeably warm in a slow-charger...!
  • RCinFLARCinFLA Solar Expert Posts: 1,397 ✭✭✭✭
    Re: Lithium-Ion charging with solarpanel
    RandomJoe wrote: »
    I'm curious, as I bought a 2.3AH 3S1P LiFePO4 pack for ham radio / bicycle lights and am amazed it can be charged at a 4A rate (what my smart charger will do, the manufacturer's "recommended" rate is even higher!) but the cells don't even get warm to the touch.

    LiFePO4 are quite different batteries then LiPo type.
  • System2System2 Posts: 6,290 admin
    Re: Lithium-Ion charging with solarpanel

    Great thread, it's really hard to find info on charging lithium with solar.

    I have a somewhat similar project in mind, though it involves a PowerFilm 7w rollable panel attached to a kayak deck to charge a Tenergy 11.1v battery pack that would be used to power a 12v bilge pump and also charge electronics through a 12v car socket.

    I just came across this controller and this one. I wonder if one of these resolves all issues to allow for safe charging under all conditions?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Lithium-Ion charging with solarpanel

    As I understand--A big issue about safety is the battery pack itself. Each cell is supposed to have its own charging and shutdown circuitry (there are lots of different lithium chemistries out there--just a generic statement of caution)... Which adds to cost and size...

    Many people buy "unprotected" LI cells for their projects... It is always up for debate about how "sane" running unprotected cells in a flashlight may be (for example).

    And there are many types of lithium chemistry... Some are supposed to be pretty safe and others are not nearly so safe. One needs to do a lot of research on the subject before they go and start using some LI cells. (I know enough to not get involved with unprotected cells... Perhaps if I knew more--I would look into it).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Lithium-Ion charging with solarpanel

    Lithiun ion phosphate cells, 10 ah can be charged ok with a normal PWM charger but it needs to be adjustable output and no equalizing charge, if 4 cells set to15.2v max as no useful power can be put in them above that and thats the limit for most inverters. but there needs to be a voltage controlled switch for low voltage the 4 cells MUST NOT go below 9.6v or THEY WILL DIE even if done once. You dont need to try ive done it and they died. lucky for me I didnt pay for them,, 2.2v per cell is absolute bottom for survival
  • xbahaxbaha Registered Users Posts: 1
    Re: Lithium-Ion charging with solarpanel

    hi,
    i would like first to know if such a controller has a High Volt Disconnect @ 16v , and has a protection diod if the voltage of the solar dropped below the source, would it work considering overcomes the main safety requirements for charging li-ion batteries?

    thanks.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Lithium-Ion charging with solarpanel

    The more I hear and read about Lithium Ion batteries bursting into flame, the more I distrust them and am scared to have them in my house. My camera has such batteries, so when not in use I keep it in a closed metal cabinet.
    Now this latest news item, yet another Lithium Ion battery bursting into flame on an aircraft in flight: http://avherald.com/h?article=44e25cdf&opt=0
Sign In or Register to comment.