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14.4 V Lithium battery - re-purposing question

Discussion in 'Power Electronics' started by peterlonz, May 29, 2018.

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  1. peterlonz


    Feb 11, 2010
    I have a portable power tool battery, Lithium-ion, brand Einhell, 14.4V, 1300mAh.
    This battery, though maybe over one year old, has seen no use.
    The tool (drill) & original battery & charger are not compatible due to model/design changes .

    So I figured why not use this battery as the basis of a bench power supply; I could use with either a step up or step down converter if necessary for a wider voltage range.
    The problem (for me) is I can't be sure about the battery terminations:
    There are 5 "slots" but only 3 have the usual sliding contact grips.

    Markings in order: (-), (N), (T), (D), (+) - sliding contacts indicated by underline.
    Measure 16V across (D) & (+) and 5.6V across (-) & (+) - the 3 "terminals" with the slide in contacts.

    So to my questions:
    Since I expect to obtain 14 to 16v (depending upon battery charge condition) by using (D) & (+), what the heck do (-), (N), and (T) do?
    If I proceed I intend to charge with17V (I have a small basic charger that delivers 17V)using a DMM to monitor, but is this safe & will it harm the battery?

    I know this at first looks confusing, I could take a pic if that was thought desirable.

  2. davenn

    davenn Moderator

    Sep 5, 2009

    A really good idea else difficult to visualise what you are saying


    May 20, 2017
    17V is just a tad high. 4.2V per cell is the norm. You will also have to limit the charge current according to what ever is says on the battery pack. When a battery is fully discharged (in the case of your LiPo it will be 12V) a substantial amount of current can be drawn due to the difference in charge volts and battery volts and will only be limited by the batteries internal impedance and the power supply's current ability.
    So. photo's including this info will be very useful.
  4. dave9


    Mar 5, 2017
    You should open the battery and assess whether it has charge and discharge termination protection, or carefully monitor a charge and discharge cycle to determine it, keeping in mind what WHONOES wrote. If it doesn't I'd move on and pick something that does or just make a normal bench power supply instead.

    Frankly it seems like a big hassle, to bother making this then have to monitor charge and discharge over and over instead of something as simple as buying a transformer and throwing a bridge rectifier and capacitor after it... then add whatever boost/buck regulator you want.
  5. Audioguru


    Sep 24, 2016
    A 14.4V lithium battery has 4 cells. It must be charged with a "balanced" charger that senses and adjusts the amount of charge for each cell. Then the battery must have 5 wires. The battery or the product it is used in (your new power supply idea) must detect "low battery voltage" of about 12V then disconnect the battery so that it never becomes discharged too low. If the battery voltage is too low and you try charging it then it might explode or catch on fire.

    If you try to charge the lithium battery with 17V then one battery cell might explode or catch on fire. You do not want to be near a lithium fire.
    BobK likes this.
  6. peterlonz


    Feb 11, 2010
    Thanks to those kind folk who responded.Answering some of the questions:
    1) The battery does have 5 "slots" but it appears only 3 actually have the sliding contacts to allow a male part to engage.
    2) I had supposed 2 slots were for discharging to a power tool. One was to monitor battery temperature on charging, maybe thus allowing the charger to shut down. And 2 slots for monitoring the actual battery voltage during charging, so restricting the final voltage to 16.4 (IE 4.1V per cell). Since only 3 slots will allow contacts I am totally unsure about this supposition.
    3) The 17 V charger I have was designed to charge 14.4 lithion batteries for power tool use. It's clearly a "basic" unit & as I have said it will not engage with this newer battery Style & model changes).
    4) I never trust chargers, "balanced" or not & I never allow a cell to fall below 3.4V. I don't have the means to easily check charge or discharge current. Generally I charge on a large porcelain tile & keep checking progress with my DMM. Of course with the packages now available I can use the battery & charger combo of the particular power tool without this sort of hassle. BTW my power tool collection are all 18/20V.
    5) Simple pics attached, but need ref to the original post due to camera/skill limitations.
    6) I do recognise that all round this seems a fair bit of effort but I want to know what's going on, or rather how it goes on

    Attached Files:

  7. Audioguru


    Sep 24, 2016
    The battery might have the charge balancing circuit inside it.
  8. Externet


    Aug 24, 2009
    Typically, in the battery end there is a power terminal for charging, sometimes there is a diode to ensure it is never fed in reverse polarity that would destroy the charging management circuitry;
    another for power delivery to the tool,
    another power common,
    another temperature sensing that tell the charger to suspend/refuse until cool,
    and also a terminal that feeds a 'signature' that identifies the voltage the battery is (like 14K Ω to common for a 14.4 V battery type, that way the charger microcontroller knows the battery is the one allowed to be plugged in)
    another may have a clock for any microcontroller in the battery circuitry...
    Every manufacturer implements the safety systems they consider to have built in, and at the terminal sequence of their choice.
    Never seen an explanation from a particular brand/model.

    At the charger end, they may implement different -or more- terminals to sense if the battery pack is of one type or another when the charger is designed to serve different batteries.

    Mostly no solid information about, and perhaps the nomenclatures N, D, T... is meaningful only for them. T is usually the thermistor sense inside.
    Guessing, D could be D ischarged beyond specs, like one cell under 2.5V signals it, then the charger is D isabled from performing.
    (+) and (-) usually output power to tool,
    C the charging power in. (But you cannot tell if common is positive or negative unless visual inspected)
    Found that opening the pack and charging only the measured problem cell with alligator clips just until gets above 3V restores all functionality to everything.

    To prevent other battery brands to slide in; slightly different plastic rails, blocked slots, stop nibs do the prevention in battery packs that appear to be the same size and architecture.

    In very early packs, I found a dedicated weird component that destroyed the fuse and something else irreversibly by sensing tampering like trying to replace a bad cell within it. :eek:

    For the re-purposing part, I usually use one canibalized lithium cell to replace three 1.2 or 1.5V cells in flashlights or anything. I even replaced the memory backup 3.6V battery in my spectrum analyzer with a lithium 18650. My old NiCd drills work now on 18650s out of their original housings...
    Last edited: May 31, 2018
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