Is my new battery charger faulty?

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

  1. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi.

    I have new 12v small battery charger,which designed to charge all the types of lead acid batteries(up to 70AH).
    It has 4 stage:
    1)recovery mode(desulfation mode)-uses pulse mode.
    2)bulk mode.
    3)absorption mode.
    4)maintainance mode-uses pulse mode.
    and i have two option of max charging current.
    I measured the charging current and voltage on car battery and i try to figure out if what i observed is charger fault or it should work this way.

    I start charging 12V/55AH(12.4v,state of charge)car battery with the higher max charging current.
    At first the voltage start to rise smoothly up to 14.5v(rise smoothly at the bulk stage)while the charging current was the max that the charger could give.
    And when the voltage reached this 14.5v,the voltage started to fall and rise instantly and repeatedly from 14.5v to about ~12v or ~13v,again and again...
    It is happened in the beginning of the absorption stage.
    As far as i know,it should be stayed at a round 14.4v and stay fixed on that voltage until the current decrease to a minimum set current,rather than,repeatedly fall and rise,shouldn't it?(i familiar only with traditional old chargers)
    Isn't it a fault?
    By the way,also,the charging current was instantly and repeatedly fall and rise in that absorption stage,instead of decrease smoothly down forward the minimum set current.
    I know that the charger provides pulses on the recovery and the maintenance stages,but could it be that the smart charger uses pulses also in the absorption stage,and that is the reason that i saw in the multimeter that phenomenon?
    or it could indicate faulty charger?

    For certain reasons,i didn't mention the brand of the charger and omit some characters that could reveal it.
    But the main idea is to understand if todays new technology smart chargers
    are using charging method that give that behavior in the multimeter so what i had been experienced is,actually,not a fault.
    Or it does?

    Thanks in advance.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I may be wrong but isn't 14.4V a bit higher. I think it should be 13.8V
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    14.4V is the correct charging voltage. When the battery reaches this voltage the charging voltage is reduced to 13.8V to provide a float charge (maintenance mode). It appears that your charger is working properly.
     
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  4. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi everyone.

    The 14.4v value and the float charge when the voltage decrease to about 13.6v is not the issue.
    My question is why the charging current and voltage that i see in DMM is jumping and falling steeply in that smart charge.
    For example(don't focus on the values,the main issue is the way that the charger is charging) at old traditional charger on the absorption stage the voltage stays steady on 14.4v and the current slowly and smoothly decrease from(for example)4A to 0.4A like that 4A to 3.99,3.98,3.97.....0.4A.and then change to float voltage.
    But in that smart charge,the voltage doesn't stay steady it falling and jumping like that:14.5V to 14.3V to 14.5, 14.2,14.5,14.3A....
    And the current indeed decrease toward the 0.4A but in strange way.similar to the voltage behavior,it also jumping and falling steeply and rapidly up and down like that:4A to 0.2A to 4A to 0.3A to 3.98A to 0.3A ....
    Why does the value in the DMM go wild like that?
    Is it normal behavior of the smart charger?
    When i saw that behavior(for example) on the alternator i know that something is wrong with the regulator.But in this case i don't know if its behavior indicating on a faulty charger?
     
    Last edited: Jun 12, 2014
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Sounds like your charger is working OK. The 'jumping' your seeing is most likely called PWM(pulse width modulation) a method of regulating current in a voltage. PWM is used also in DC motor speed control and other things.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Why is 14.4V selected as charging voltage ?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Most manuf recommend a maintenance charge of 2.37v to 2.4v/cell.
    Automotive Alternators usually cap out around 14.5v.
    Max.
     
  8. xchcui

    Thread Starter Member

    May 12, 2014
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    I know more or less how the SMPS work and the issue of the PWM.
    But i was pretty sure that the value of the charging voltage and current on the DMM will be appeared as a steady average value(steady increasing or steady decreasing),but not "jumping"crazy values.
    I checked current and voltage in flashlight with pwm(when changing mode high,low and etc.)and it show me average steady values with no jumping or something like that.So this smart charger behavior looked to me like a fault.

    Thanks for your help.:)
     
  9. Lestraveled

    Well-Known Member

    May 19, 2014
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    I have a "smart charger" that does the same thing. It is a Soneil 1212RS. It was a little disconcerting at first. I, like you, expected to see the traditional absorption mode after the bulk charge. If you download the data sheet for a BQ2031 (Unitrode lead acid battery charger controller) you will see that it has a mode that matches your description.

    Mark
     
  10. xchcui

    Thread Starter Member

    May 12, 2014
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    Hi Lestraveled.
    Do you mean that you also read on the DMM rapidly up and down currents values("jumping),in the bulk stage until the voltage rise to a max set voltage.
    And the same"jumping"current and voltage values on the stage which the current decrease(of course,by jumping manner) until the charger turn into the float level(and continue the crazy dance).
     
  11. Lestraveled

    Well-Known Member

    May 19, 2014
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    No, while in the bulk charge state I get a well behaved constant current until the battery reaches 14.5 volts. THEN, the on/off pulsing begins. The duty factor of the pulsing gets less and less over time.
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Things like flashlights and motor control use a much higher frequency on the PWM. On flashlights, so you don't see 'blinking' of the light. Motors, so you don't hear the PWM.

    Wait till you try to charge a completely dead battery, under ~9V. It won't even give you a charge when battery is that low. The "smart" chargers are pretty dumb then. Had to use my old "dumb" charger to get it up to ~11V, first.
     
  13. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Is this charger designed for SLA (Yuasa for example) or car batteries?

    In my experience a "12V small battery charger" isn't suitable for a 70Ah battery.
     
  14. Lestraveled

    Well-Known Member

    May 19, 2014
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    To follow up, here is a picture from the BQ2031 app note. It is one of the three modes that the charger controller can operate in. I think it is how your charger is working. It is how my Soneil 1212SR is operating.

    What is the make and model of your charger?

    Mark
     
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  15. xchcui

    Thread Starter Member

    May 12, 2014
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    So,how should i relate to the"jumping"behavior in my charger on the Bulk stage(besides on the absorption stage)?
    It seems that it is not,after all,behave as my charger.what make me wonder again if could it be fault.
    The voltage is increase well up to 14.5v without jumping(opposed to the absorption stage)but the current numbers value,opposed to your well behaved constant current,jumping up and down,up and down.
    As i mentioned, for certain reasons i didn't mention the brand,but the charger is suitable for all the lead acid battery types up to 70AH included car battery.(of course,higher capacity battery need more time to charge).
    I still do not understand yet,if what i see on the DMM is what i should see as the action of the PWM(PULSES) or it is a fault?
     
  16. Lestraveled

    Well-Known Member

    May 19, 2014
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    Perhaps I missed something. In your first post you said,"At first the voltage start to rise smoothly up to 14.5v(rise smoothly at the bulk stage)." This indicates a constant current.

    Now, what may be happening is that you are trying to charge a full charged battery. In which case the charger will immediately go to the maintenance mode ,(on off behavior). Discharge your battery for while and try charging it again and see what happens.

    You may also have a bad battery.

    Mark
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    IIRC - the Optimate charger I have backs off to 13.6V at the end of the bulk charging stage.

    One car battery that was in my possession had a big sticker on top; "Charging voltage not to exceed 14.4V" - it was a regular flooded cell run of the mill car battery.
     
  18. xchcui

    Thread Starter Member

    May 12, 2014
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    Thank you for your advice.
    Maybe the charger has an intermittent fault,maybe it doesn't,maybe the battery is the problem,maybe it is not.The reason for these thought came since i charged the car battery again(SOC-12.4V)and now the current is steady on the bulk stage but the on/off behavior started
    when the battery reached to 14.2V(opposed 14.5V)on my last charging from the same starting SOC.

    What could be the reason for getting into the maintainance stage at different voltage?
    (the state of charge on both cases was ~12.4V SOC).

    I was trying,also, to charge small AGM 12V/7.5AH battery with SOC of 12.9V,while the charger got into the on/off behavior immediately and very quick finished the charging.The SOC stayed 12.9V.
    But when i discharge the battery a while,as you adviced,the charger got into the bulk stage(steady current with increasing voltage)and when it finished the state of charge was 13.2V(i know that 12.9v is considered full charge but 13.2 is really full charge).What i am trying to say is that the smart charging was thinking that the battery was full charge,while the battery could be charged more opposed to a "dump charger"that was keep charging the battery until it was 100% full charge charged,without needing to discharge it a while first,like with the smart one.

    And last more thing.if your charger get into the desulfated(recovery)mode(soc to low) and the charger find out that it can not recover the battery(maybe because of bad plates,a shorts between the plates and etc.) ,How does your charger behave?
    Is it shut down,immediately?
    How much time is it working until it tell you that it can't recover the battery?
    Does it give you any sign(like a special led light)that show you that it can't recover the battery?
    I asked those questions because when i try to charge a 7V battery,the charger get into recover mode work for 5-10 minutes and shut down while only the power-on led was lights without any special indicating sign that it can't recover the battery.
     
    Last edited: Jun 23, 2014
  19. xchcui

    Thread Starter Member

    May 12, 2014
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    Thanks everyone for your help:)
     
  20. K7GUH

    Member

    Jan 28, 2011
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    Your charger is working properly, using one or more pulse methods to charge. The DVM readings are trying to track the pulse(s), but are probably a lot slower than the pulse(s) in real time. An oscilloscope, even an inexpensive one, would be able to display the shape and duration of the pulse(s). There is, no doubt, some extensive discussion of why this technique has been adopted for charging lead acid batteries, but I can't direct you to that discussion without doing a lot of research.
     
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