In-circuit 9VDC Charger

Discussion in 'The Projects Forum' started by onebigfellah, Apr 3, 2012.

  1. onebigfellah

    Thread Starter New Member

    Apr 3, 2012
    9
    0
    Hello all.

    I need to develop a battery charger for an in circuit 9 VDC battery.

    Details:

    The battery is constantly in use by the PCB it is attached to. The PCB has been designed to detect tampering in our system by means of mechanical switches. When the PCB loses power from the PC it is connected to, the PCB then looks to the battery to provide power for tamper detection.

    The battery is currently a 9 VDC Lithium.

    I have two possible power sources:

    120 VAC, which can be adjusted to 9 VDC by use of a transformer.
    12 VDC, which would have to adjusted through a PCB design.


    Need:

    For someone to help me design a circuit that would provide a stable electrical voltage / current to the battery and PCB but would prevent the battery from discharging when power is off to the PCB.

    I look forward to seeing what comes up from this discussion.
     
  2. onebigfellah

    Thread Starter New Member

    Apr 3, 2012
    9
    0
    Just as a side note, the most current the PCB draws is around 60 mA and that is when a tamper is occurring.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    You need to first choose a specific, rechargeable battery. The charging and maintenance strategy will depend on the chemistry (ni-cad versus NiMH, etc.) and on the number of cells. "9V" covers a range of actual voltages.

    In general, I think a nicad is easier to deal with but Li-ion has the highest power density (and cost).
     
  4. onebigfellah

    Thread Starter New Member

    Apr 3, 2012
    9
    0
    Please see the attached files for ideas that have been generated thus far internally.

    NOTE: The Trickle Charger file is for a 12VDC source on the PCB...but the use of a 120VAC charger like the one depicted in the pdf file is preferred...

    Thanks!
     
  5. chrisw1990

    Active Member

    Oct 22, 2011
    543
    41
    question, why not buy an IC? theres a few charger ICs out there for batteries and such? see Farnell, that could be an easy solution in a compact footprint.
     
  6. onebigfellah

    Thread Starter New Member

    Apr 3, 2012
    9
    0
    I feel it is my duty to inform you that while I am a ME, I am not familiar with all of the EE terms...what do you mean "IC"?
     
  7. onebigfellah

    Thread Starter New Member

    Apr 3, 2012
    9
    0
    /bumpitty bump
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The 9V lithium battery is not 9V, it is only 7.4V. But it is 8.4V when fully-charged then its voltage slowly drops to 6.4V when its internal circuit disconnects the load.

    The manufacturer says it has a protection from over-charge circuit inside (that does not work) because they say if you use an ordinary charger then the battery might EXPLODE! They say to use their expensive charger.

    You must NEVER trickle-charge a lithium battery.
     
  9. chrisw1990

    Active Member

    Oct 22, 2011
    543
    41
    an Integrated circuit.. small chip..
    lets say, if you got look on here: Battery Charging IC's
    Then put your relevant information in, maybe youll be able to get a low-cost low component count ic, that conditions the battery too.
     
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