pulse charging or regular charging?

Discussion in 'General Electronics Chat' started by ak52, Jan 31, 2015.

  1. ak52

    Thread Starter Member

    Oct 15, 2014
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    Hello Everyone :),
    Could someone please shed some light on pulse charging. and its disadvantages if there are any.
    For my application I require to charge 4, 12v lead acid batteries in series(48v). So is it ok to send a pulsed signal or is it an absolute necessity to smooth-en the pulse using an LC filter?
    Would pulsed charging effect battery life in an adverse way?

    I have opened up a few chargers of the same ratings and found that some of them are using a filter and some of them are not. So i am really confused which way to go..

    Please help,
    AK
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I would use a steady voltage of about 54-56 volts.
     
  3. ak52

    Thread Starter Member

    Oct 15, 2014
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    Hello dave,
    So you are saying i should smooth-en the pulsed signal first?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    yes, have you got a circuit for the charger?
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Is the pulsing a consequence of using PWM to generate the charging voltage? What is the pulse frequency? What is the rise time of the unfiltered pulse?
     
  6. ak52

    Thread Starter Member

    Oct 15, 2014
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    I am designing a draft at the moment.Its still incomplete.
    Yes,the pwm signals are from a micro-controller.,driving two mosfets in an half bridge configuration.
    Pwm frequency is 10KHz

    In would like to know the effects of pulse charging,if anybody has already done it.Because if it is suitable ,i can eliminate the LC filter,which will have a bulky inductor in enclosure.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    A couple of points of reference that I know of:

    The automotive industry opted for 3-phase alternators because high ripple charging current (allegedly) isn't good for the battery.

    There's a blog online somewhere, written by someone living "off grid" who has a lot of theories about care and maintenance of lead acid batteries.

    One of the theories suggests that the batteries have a preferential frequency of a few MHz. Supposedly this is good for de-sulphating.

    A battery reconditioning charger I bought (Optimate) touts pulse charging among its various features - unsurprisingly, they don't give much in the way of technical details.

    My own appraisal of the Optimate - if a battery is so sulphated that the Optimate can't revive it, then the battery isn't worth any further messing about.
     
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  8. bwilliams60

    Active Member

    Nov 18, 2012
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    I have to agree with Ian on most of this. The automotive industry which I am part of, uses both types of charging. If the battery is fairly new and/or in very good condition (low-sulfation), we would tend to use a smooth charge. A pulse charger of low amperage is recommended when the battery is medium to heavily sulphated and we want to try and knock the sulfation off the plates and restore the battery. My personal belief from working with batteries is that if they are lightly sulfated, pulse charging will help restore the battery. If they are heavily sulfated, you will not entirely remove the sulfate and the stuff you do remove, will also take some of the sponge lead or lead peroxide with it and the battery will be less effective. Each battery will present it's own case. You should run an analysis of the degree of sulfation on the battery using an electrochemical impedance spectroscopy test on it or a three minute charge test. Then you can decide which charger to use. Normal automotive battery life can be expected to be around five years. After that you are gambling.
     
  9. ian field

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    Oct 27, 2012
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    My theory is; you never quite get rid of sulphation once its appeared, and it provides seed-crystals that make the next growth easier to form.
     
  10. bwilliams60

    Active Member

    Nov 18, 2012
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    Totally agree with you. In addition, if you are able to knock it off the grid, paste goes with it and renders cell less effective. Bottom line is every time it happens, battery life is shortened. I have seen a lot of posts on here and other forums where people say these batteries can be brought back to life. I am willing to bet that they never put a carbon pile load test on them afterwards to check the condition of them under load. Real life and 35 years tells me that they will fail.
     
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  11. crutschow

    Expert

    Mar 14, 2008
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    The reason for automobiles going to 3-phase with the alternators is that 3-phase is more efficient (takes less copper and magnetic material for a given power output) and generates a steady-power output (the sum of the three outputs gives a DC power value into a resistive load). This means there also is no fluctuation in the driven torque as there is with a single-phase alternator. That fact that 3-phase has lower ripple is an added bonus.

    I don't see that a pulsed current (such as from an unfiltered full-wave rectifier) would have any adverse affect on the battery as long as the average current is within spec.

    ak52, note that with a PWM drive you may still need an inductor to limit the peak current (which would be otherwise limited only by the resistance in the circuit) although you should be able to eliminate the capacitor since a battery basically looks like a very large capacitor.
     
    Last edited: May 7, 2015
  12. ak52

    Thread Starter Member

    Oct 15, 2014
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    Thanks guys for all your replies.
    But i have another problem.
    Lets say the charger uses pulsed charging topology(i.e without the filter).
    My charger is used to charge batteries(charging current coming from PV panels) which are already connected to an inverter.Assuming that my batteries are fully charged.The excess pulsed charging current directly bypasses the batteries and goes to the inverter.The inverter i am assuming is expected a pure DC signal,could this pulsed DC signal adversely effect the inverter operations?
     
  13. crutschow

    Expert

    Mar 14, 2008
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    As I previously noted, batteries look much like a large capacitor (with a very low impedance) so any pulses will be absorbed by the battery as overcharge current and will not be seen by the inverter.
     
  14. vikasbly44

    New Member

    Jan 19, 2015
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    Lead acid battery,which cells have low energy density and have relatively low life-cycle, yet
    because of their cost effectiveness they are still considered the preferred choice by
    many electric vehicle (EV) developers and are likely to continue to be so for the
    next 5-10 years. One method of improving the performance of a battery powered
    EV is to improve the battery charging methodology.
     
  15. Punkdunk69

    New Member

    Apr 25, 2015
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    Pulse charging works on crystal resonant frequency of 3.6Mhz.Which means PbSO4 crystl will vibrate and then eventually dissociate into electrolte as sulphates.Is there possibility of short circuit of battery during pulse charging???
     
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Pure bunk, unless you can cite some research to support this...
     
  17. ian field

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    Oct 27, 2012
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    There was a blog about living off grid with wind & solar power and a few pages on recovering S/hand lead-acid batteries.

    That's where I remember 3.6MHz being mentioned, but I haven't been able to find that site for some time.
     
  18. MikeML

    AAC Fanatic!

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    Yeah, I saw that stuff a few years ago. I didn't believe it then, and I don't believe it now...

    However, it was on the internet, therefore it must be credible...
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    I'd be up for giving it a try - but I'm not going to sulphate a perfectly good battery just to try out an experimental circuit.

    There are off the shelf battery reconditioners that can handle mild sulphation - anything heavily sulphated pretty much isn't worth investing time and effort.
     
  20. Punkdunk69

    New Member

    Apr 25, 2015
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    Hi MikeML thanx for your honest reply.But i have seen in come cases even vibrating(very less frequency as conpared to pulse charging) the battery before discharging leads to increased capacity and im talking of newly formed battery that is not subjected to any electrolyte straticification.Is pulse charging really that great??
     
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