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Battery Charger

Discussion in 'Electronic Design' started by [email protected], Jul 17, 2013.

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  1. Guest

  2. Glenn

    Glenn Guest

  3. Glenn

    Glenn Guest

    If so - do you have other batterypack criterias?

  4. Guest

    I am charging a 3.7 V 1200mAh LiIon battery. I want to isolate the AC to DC adapter because of safety issue.

  5. Glenn

    Glenn Guest

    The ac to dc adapter should have adequate isolation. Is that not good

  6. Guest

    I am trying to provide user more protection. The other thing is that its an interesting problem to solve. But I do need some direction here.

  7. whit3rd

    whit3rd Guest

    More than what? There's some common test protocols, and models of human-body
    load, involved. If you want an UNCOMMON test or model, it'll cost ya.

    Easiest way to provide 'user' more protection, of course, is to use connections that
    the user doesn't come in contact with. My electric toothbrush charges by proximity,
    not an electrical contact anywhere you can see or touch.
  8. Guest

    I was told by a collegue that this is a challenging problem. i took sometime and tired to figure out but could not figure it out. You can take the AC to DC adapter out of the picture and use a +5v power bench power supply.
  9. John S

    John S Guest

    Please explain in detail what makes it challenging.

    Please explain what level of isolation you are seeking.

    Please quote any specifications you must meet.
  10. Guest

    Could your colleague specify where the challenge
    is ? Most wall warts and bench power supplies use
    the standard step-down transformer->bridge rectifier->
    capacitor bank->voltage regulator/overvoltage
    protection design. So the isolation is there right
    at the start. Is there anything special - a biomedical
    device with some special requirements ?
  11. Phil Allison

    Phil Allison Guest

    ** Lose that switching AC adaptor and use one that incorporates an iron
    transformer - no need for regulation as the IC can take up to 8v input.

    Iron transformer adaptors, with Class 2 or Double Insulation, have a long
    track record of being exceptionally safe - the same cannot be said for most
    of the switching types pouring out of China.

    Another idea is to change the plug on the output cable to a non touchable
    kind - but it cannot be any connector that is associated with AC power.

    You have not indicated whether the imagined " safety issue " originates
    from the adaptor or the battery side of things ?

    .... Phil
  12. miso

    miso Guest

    The wall wart she picked is a switcher. Actually most modern wall warts
    are switchers these days...for better or worse.

    It is certainly possible to add a second DC/DC with isolation, but that
    is a lot of work for a dubious return on investment. It would most
    certainly reduce the efficiency.

    I suppose if you really didn't trust the wall wart peddlers, you could
    go AC on the output. Then all the peddler is supplying is a low tech
    transformer and some sort of short circuit protection element.
  13. Glenn

    Glenn Guest

    Hi Melissa

    Please read:

    The "old" way is to use a 50Hz or 60Hz insulation certified (5000V)
    transformer. E.g. the transformer could have the primary winding
    separated from the rest of the windings on the bobbin. Combined with a
    linear regulator this is normally a very robust solution, that works for

    The "new" way is to use a insulation certified (5000V) high frequency
    transformer in some SMPS circuit. The problem with these is that the
    designer or component-buyer sometimes use bad capacitors or bad designs
    (incl. to little filtering) so they to often fails prematurely. The most
    used way of signalling back from the secondary circuit the primary
    circuit is to use an optocoupler that can 5000V (most can). The good
    thing about SMPS is that they can be efficient. Some can even use almost
    zero power from the grid when not loaded on the secondary side.

    Another way is to transfer the power wirelessly. There is ongoing
    research and development to make this a public reality. The area has of
    cause been littered with patents.


    Please note that the primary to secondary circuits must also be
    insulation certified (5000V).

    Anything that bridges (e.g. noise suppression capacitors) between
    primary and secondary circuit must withstand 5000V.

    Note that the term isolation transformer (e.g. 110V->110V - or
    230V->230V) has a special meaning. They are used by repair technicians:


    October 27, 2012, A dozen USB chargers in the lab: Apple is very good,
    but not quite the best:

    USB Power Supply/charger Test: UK.html

    February 12, 2013, Teardown of a HomePlug Adapter:



    Professional insulation meter with test voltage programmable up to 10kVDC:

    Fluke 1550C Insulation measuring device, 250 V - 5 kV Manufacturers
    guarantee 3*:

    Comparison table - insulation measuring instruments:


    Back to Basics: Voltage Regulator ICs, Part 1
    There are two basic types of regulator ICs, linear and switch-mode. The
    linear regulator operates in the linear region and is always on, whereas
    basic the switch-mode type turns on and off and requires a rectifier to
    produce a dc output voltage.

    Back to Basics: Voltage Regulators, Part 2.
    In this second part of the Back to Basics series on regulators, we
    examine buck (step-down) and the boost (step-up) forward and flyback
    topologies, as well as the SEPIC, hysteretic and multiphase converters.

    Off-Line SMPS Failure Modes PWM Switchers and DC-DC Converters
    Quote: "...
    This transistor failure is often caused by bad capacitors. It is
    extremely common to find output filter capacitors that are swollen or
    leaking electrolytic material.
    ...." - What Causes This:

    How-To Repair a Desktop LCD with Bad Capacitors:


    7 June 2007, Wireless power a reality:

    13 August 2012, Tiny transmitters that cost a penny to print unveiled:
    Institute of Physics (2012, August 9). Wireless power for the price of a
    penny?. ScienceDaily:

    Dec 12, 2012, Magnetic metamaterials could boost wireless energy

    DIY: Wireless Battery Charger: 1-pg-4.htm

  14. Glenn

    Glenn Guest

  15. Glenn

    Glenn Guest

  16. Joerg

    Joerg Guest

    That's the way it's done. If the voltage on the other side doesn't have
    to be regulated there would be no need for a feedback path. Since
    Melissa uses a LTC4062 to post-regulate she has some wiggle room on the
    secondary voltage. But not much, I believe these don't like more than 8V
    on the input.

    But she has to come forward with some detailed specs to see what's
    really needed here.

  17. Phil Allison

    Phil Allison Guest

    "Tim Wescott"

    ** Irrelevant, crazy bullshit.

    YOU are not SURE of any such thing.

    **** off - wanker.
  18. Guest

  19. Glenn

    Glenn Guest


    This group need some information about what your purpose with the
    isolation/charger is e.g.:
    * fun
    * learn
    * save money
    * design a professional charger
    * safer charging

    Please note that standard li-ion cells are potentially very unstable if
    you do not follow some security rules. They can explode and catch fire
    instantly - or sometimes long after they have been mishandled.

    So do not start with standard li-ion chemistry cells.


    Instead start with LiFePO4 li-ion - or LSD-NiMH.

    LiFePO4 - please note the pdf-papers. This accumulator very robust, but
    still needs care when used. Can under optimally circumstances be fully
    cycled more than 7000 times. Will not catch fire even if shot with a nail:



    These might work 5 years and/or up to 1800 cycles under optimally
    circumstances. An unloaded LSD-NiMH can keep the charge for more than a



    Test of another LiFePO4 (LFP) accumulator:

    Unlimited Release
    Printed September 2008
    Selected Test Results from the LiFeBatt
    Iron Phosphate Li-ion Battery
    Thomas D. Hund and David Ingersoll
    Prepared by
    Sandia National Laboratories
    Albuquerque, New Mexico 87185 and Livermore, California
    Citat: "...
    Test results have indicated that the LiFeBatt battery technology can
    function up to a 10C discharge rate with minimal energy loss compared to
    the 1 h discharged rate (1C).
    The majority of the capacity loss occurred during the initial [!] 2,000
    cycles, so it is projected that the LiFeBatt should PSOC cycle well
    beyond 8,394 cycles with less than 20% capacity loss.
    [See graph pdf-page 23]
    [ Read: 48% capacity available at -30°C. ] [ very useable! ]
    [ Read: 65% capacity available at -20°C. ]
    [ Read: 74% capacity available at 0°C. ]
    3.8 Over Voltage/Charge Abuse Test
    In Figure 16 the events in an over charge/voltage abuse test are
    documented. Initially, as expected, the cell voltage increases quickly
    while being charged at 10 A, but then slowly increases after 4.7 V. The
    cell voltage slowly increases for about 30 minutes while the cell
    temperature continues to slowly rise to about 100 °C at which time cell
    voltage spikes to the maximum value of 12 V. At about 110 °C the cell
    vents liquid electrolyte without any fire or sparks and then
    open-circuits at 116 °C. After open-circuiting and a loss of
    electrolyte, the cell looses all voltage at 120 °C. The data acquisition
    shuts down due to a no voltage condition, but temperature is manually
    monitored until the cell reaches its maximum value at 160 °C about 20
    minutes after the cell open-circuited.


    Test of LiFePO4-accumulator:

    Nail penetration testing A123 Li-ion [ one of the best
    LiFePO4-accumulators ]:


    Comparison with other Li-ion chemistries (non-LiFePO4):

    Exploding Laptops on Good Morning America:

    Nail penetration testing Standard Li-ion:

    World's Most Dangerous Battery!:

    Modify Li-Po Battery Nail Penetration Test:

  20. Glenn

    Glenn Guest

    Even Boing have problems with li-ion:
    Quote: "...
    It is reported that the plane has had two major battery thermal runaway
    events in 52,000 flight hours, which was substantially below the 10
    million flight hours predicted by Boeing, and had done so in a dangerous

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