New folks trying to build a Lithium Ion Battery, not burn down our house.

Discussion in 'Power Electronics' started by CaveManNeil, Jan 10, 2017.

  1. CaveManNeil

    Thread Starter New Member

    Jan 10, 2017
    Hello and thank you for reading our post, what we are trying to achieve is a Lithium Ion Battery that will operate at least 8 to 16 hours of use, with a preferred weight is half a lb or Less per battery. We are trying to create a reliable LI battery that is easily charged by both solar power and or wall charging either indoors or outdoors for backpack purposes so as not to be limited by weight or capacity. Any guidance on configuration, pitfalls and potential hazards is welcome. Here is what we have learned so far that in order to build the power pack from the inside out to the completed, usable product we will require: IE from the battery cells to the PCB to the power cable to the barrel plug, please keep in mind we are not experts this is a home created item to fit our needs. We are looking for advice on creation or possible schematic design. Question, if you know of a source of supply that will meet our needs would you recommend we purchase the battery pack or rather build the battery pack? What are the advantages to either scenario?

    What we are trying to build is a Lithium Ion Battery for a device that’s design parameters are rated for the following sources:

    PSA2 (Wall Unit Charger w/ Interchangeable International Plugs)

    BAT4 (8 Hour Battery Pack) 4SP1

    BAT8 (16 Hour Battery Pack) 4SP2

    The existing Lithium ion Battery Unit in use is a:


    14.4V, 5200mAH, 75Wh

    Configuration 4SP2

    With what we think is a EIAJ-05 or a J5BP5 barrel plug that goes from the battery to the device specification can be provided as soon as we can acquire a caliper

    The Wall Plug in Current Use is a :


    Input: 100-240V

    50-60Hz, 1.0A

    Output: +18V---, 1.67A

    The components we must specify, if we are to fabricate, are:

    Male Barrel Plug (From Device to Battery Pack)

    Wire that goes from plug to Core question what kind of wire would you recommend? Or how do I gauge the existing wire?

    PCB & Charge Indicator Light On the Housing

    LI core that is configured in a 4SP2 w/ UL parameters of 14.4V, at least 5200 mAH (What might happen if we up the mAH?)

    Female Barrel Plug in the Housing(to accommodate wall or Solar Panel charger)

    Housing to Accommodate Everything

    We are considering a EarthTech R14 (14W) as a solar source in the field. Our existing wall plugs should be fine for locations where electricity is available.
  2. wayneh


    Sep 9, 2010
    Pardon me if I missed it, but what are you hoping to power with this?
  3. CaveManNeil

    Thread Starter New Member

    Jan 10, 2017
    a mobile CPAP device. Hence the issue with weight.
  4. wayneh


    Sep 9, 2010
    Well, more to the point, what are its power requirements? That's what will dictate the battery capacity you need to get the operating time you want.
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Does the CPAP device already include a charger specifically rated for charging lithium cells?
    How will you control the voltage/current provided by the solar panel?
  6. EM Fields

    Active Member

    Jun 8, 2016
    Symantec reports your site as a dangerous virus threat.
    Last edited by a moderator: Jan 12, 2017
    spinnaker and GopherT like this.
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
    If your CPAP power supply is 18v @ 1.67A (30 W) that is the peak and let's say the average 50% or 15 watts.

    15watts at 18V is 0.87 A (866 mA).

    To keep a sleeping person happy, this should work for 8 hours. You'll need a 7,000 mA hour battery pack (minimum).
  8. spinnaker

    AAC Fanatic!

    Oct 29, 2009

    Engineers that have spent years in study and specializing in design of lithium batteries have built batteries that have burst into flames. And you think you are going to do better by posting on an electronics forum, asking anonymous people for advice?
  9. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    Are you saying there is something wrong with my skills lol ??
    ErnieM likes this.
  10. MrSoftware

    Active Member

    Oct 29, 2013
    LiPo batteries are nothing to fool with. Buy a pre-built pack and use a charger specifically designed for the battery chemistry that you use. Also you're going to need batteries with more capacity that you need, if you expect them to last. i.e. if you need 8Ah total, get a battery rated for more than 8Ah. Draining LiPo batteries all the way dead really shortens their life. I recommend reading all of the Lithium articles here:
    spinnaker likes this.
  11. MrAl

    Distinguished Member

    Jun 17, 2014

    To be safe the best way is to charge each cell independently. For example, if you had two cells in series and you had two completely independent battery chargers, you could charge each cell with the two chargers even without disconnecting the cells. That would act the same as two separate batteries being charged by two separate chargers and so would be as safe a way to charge as you can possibly get. The voltage set points obviously have to be accurate.

    Second, the battery voltage of each cell must be monitored while in use. That's not while charging, that is while the current is being drawn from them in the actual application. If the battery voltage of even ONE cell gets too low, the pack has to be disconnected because that one battery could easily be ruined and then during the next charge cycle explode or catch fire.

    Third, each cell has to have room for expansion as we found out from the Samsung incident.

    This is one kind of circuit where we cant take ANY shortcuts. Everything has to be done right, and then we hope that everything works out in the long run, similar to a missile tower only worse because it might be in our own livingroom :)
    CaveManNeil likes this.
  12. MrSoftware

    Active Member

    Oct 29, 2013
    The term you're looking for is balance charger. There are many available, and they ensure that all cells are charged to the same potential.
    CaveManNeil likes this.
  13. tcmtech

    Distinguished Member

    Nov 4, 2013
    I for one wouldn't have major problem with building a battery system for such a device out of common quality lithium cells.
    I would however use off the shelf components like dedicated properly made cell balancing and charging devices rather than build my own.
    Making a ~18 - 20 volt 8 - 10 Ah battery pack from common 18650 cells is easily done and a common configuration used in millions of higher end RC hobby devices and a well supported DIY fabrication project.

    Or just buy a off the shelf ready made CPAP battery pack and be done with it.

    Or as an extreme last resort just eat less, get more exercise and lose the necessary weight to not need a CPAP to begin with assuming you're not already beyond that point of no return. :oops:
    hparker likes this.
  14. bulrush


    Jan 1, 2017
    I don't think you will reach the price point you want with solar panels. To get efficient PV panels is super expensive, and cheaper panels are not that efficient, and cheaper per sqft, but larger panels are yet more expensive. My solar panels are useless in the winter, because our winters are super cloudy for 3-4 months. My solar panels are only useful during the brightest 3 months of the year: June, July, and August, and for the rest of the year they have limited, or no usefulness at all.

    So, for a CPAP device the person will have to recharge it from the wall for 9 out of 12 months of the year. Besides, if you leave a battery in the car with a solar panel in the window, the inside of the car can get 120-130F or higher in temperature. That will probably damage electronics in the charger.

    If the CPAP device must be worn 24 hours a day, you should not rely on solar power to charge it, this is a life-critical application. Also, if the CPAP uses a pump, the power usage will be high, which requires bigger heavier batteries, which will turn off most consumers.
  15. CaveManNeil

    Thread Starter New Member

    Jan 10, 2017
    thank you very much
    Last edited by a moderator: Jan 12, 2017
  16. CaveManNeil

    Thread Starter New Member

    Jan 10, 2017

    thank you very much for your information, im guessing you dont recommend i use that site??