How does the intelligent 12v lead acid battery know that the battery sulfated?

Discussion in 'General Electronics Chat' started by xchcui, May 12, 2014.

  1. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi.

    I read that when i charge 12v car lead acid battery with intelligent battery charger,the charger first check if the battery is sulfated before it starts to charge it.
    If it detect sulfated battery,it starts to charge the battery with max voltage of +/-20v and max current of 200mA in order to recover the battery.
    But how does the charger detect(know) that the battery is sulfated?what are the parameters that it checks?

    Thanks in advance.
     
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
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    The charger applies a voltage and measures the resulting current. A sulfated battery will have higher than normal internal resistance and therefore lower than normal current. Chargers designed to "recondition" partially sulfated batteries apply pulses of higher than typical charging voltage.
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    Basically, the formation of sulphate is an insulating skin over the surface of the lead plates, a dumb charger doesn't output enough voltage to push any charging current through the insulation.

    The charger I've had long enough to read the instructions is the Optimate - on a sulphated battery that doesn't want to take charging current the voltage goes up to around 30V or so, the micro senses this and most types introduce a puls mode to try to dislodge the sulphate.

    If that is successful, the charge current steadily rises - usually the charger will start desulph mode with constant current pulses, when the terminal voltage is drawn down to a preset level, the charger switches to fixed voltage bulk charge mode - usually somewhere between 13.8 - 14.2V, in this mode the charger monitors current draw and at a set point switches to maintaining mode at about 13.6V.

    The Optimate has a regular iron-cored transformer providing an intermediate voltage, followed by an industry standard SMPSU chip hooked up to their custom MPU.

    Generally, any battery so badly sulphated that one of these chargers can't get it going, isn't worth saving - once or twice before I got the Optimate, I was desperate enough to splice a bridge rectifier into the neutral lead of a table top oven for electrocuting sulphated batteries - it can start with a terminal voltage over 200V! - whether the voltage sinks down to something more like it, is a good indication whether it'll get you to the shop to buy a new one.
     
  4. xchcui

    Thread Starter Member

    May 12, 2014
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    Thanks for your explanation.
    The issue is much more clear now.
    thanks:)
     
  5. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi again.

    I have one more thing refer to the intelligent charger.
    I understand that the charger at the desulfated mode uses pulses.
    Does the charger in the bulk stage when the current is limited,also,use pulses?i mean,does the chip use current pulses in order to get the sum average of the limited charging current or the current is "steady"?
    When i say steady i mean that the current is flow in flat line(if i can draw on a graph)the same as in the traditional charger and not in pulsed line that give average current.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    The Optimate uses a SMPSU chip - so there are pulses unless there's smoothing caps on the output (I didn't look that closely).

    I read somewhere that when manufacturers switched to alternators in cars, they went for 3-PH type because lead acid batteries don't take kindly to ripple - so I don't know how they got on with the crude half wave rectified battery chargers of old!

    Various magazines have published circuits to keep batteries lively, these pass current through an inductor then break the current causing a spike fed back to the battery. They don't contribute any charge current, so if you forget all about them they'll eventually run the battery flat and *CAUSE* sulphation.
     
  7. xchcui

    Thread Starter Member

    May 12, 2014
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    Thanks ian field:)
     
  8. xchcui

    Thread Starter Member

    May 12, 2014
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    Besides the Optimate there are many brands of chargers that are using the same method to charge the lead acid battery.
    And what i try to understand is if in opposed to the old traditional charger which charge the battery with steady direct current and voltage(i mean no pulses),the new type are charge them with voltage and current pulses during all the stages besides the sulfated stage?(On and Off periods)?
    I know that we put capacitors and conductors in order to smooth the ripples because it is not good to the battery,so how does the pulses with the new technology is not bad for the battery:confused:
     
    Last edited: May 18, 2014
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    There was/is a blog somewhere about living off-grid and depending on solar panels to maintain lead acid batteries.

    There is a specific frequency mentioned which is allegedly very good for lead batteries - but I didn't see too much in the way of hard scientific fact on the blog.
     
  10. xchcui

    Thread Starter Member

    May 12, 2014
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    I am not exactly look for the best method to charge lead acid battery.I am more trying to understand the idea about the new type charger vs the old one refer to what is the characteristics of the charging voltage and current that get into the battery.
    And the main question is :eek:pposed to the old traditional charger which charge the battery with steady direct current and voltage(i mean no pulses),Are the lead acid battery recieves pulses voltage and current from the new type chargers during all the stages besides the sulfated stage?(On and Off periods)?
    And in short-Does the battery get steady direct voltage/current or pulsed ones?
     
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