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Lm317 battery charger

Discussion in 'General Electronics Chat' started by baxterdmutt, Dec 21, 2016.

  1. spec

    spec Well-Known Member Most Helpful Member

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    Thanks BM,

    I will give what you say some thought.

    What supply voltage and type are you using for these tests?

    spec
     
  2. spec

    spec Well-Known Member Most Helpful Member

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    Ah yes, but Chemlec was talking about a standard 6 cell 12 Volt battery, but your batteries are 3 cell 6V types.

    spec
     
  3. baxterdmutt

    baxterdmutt Member

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    Well the plan for the final project was to use a 12v 1a (or I guess a 300ma adapter would be plenty) wall adapter. Those things vary widely so on the bench I've been using 16v.
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    BM can you do this with the circuit of post #76

    (1) Remove R7
    (2) Remove Q3
    (3) Without the battery connected set the charger output voltage to 7.4V
    (4) Connect the battery to the charger and monitor the charging current.

    spec
     
  6. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Although battery ESR and Ah capacity is not a great indicator for LiPo, it is pretty good for Lead acid. The reason is Ah capacity is a combination of plate sulphation ESR and dielectric contamination and acid level or Specific Gravity which is the best indicator. Both high and equal s.g. correlates well with batteries with low ESR in each cell. ESR rise with lower SoC as well. Refurbishing sulphated batteries is a tradeoff between burning off sulphation and boiling electrolyte so large fast pulse currents of many amps for <<0.1us is best, not necessarily charging the battery but disturbing the lead sulphate crystals insulation. So often products with slow charge and high pulse desulphation during charge only are good for battery maintenance.
     
  7. chemelec

    chemelec Well-Known Member

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    I Originally understood your battery was rated at 12 Volts.
    Sorry if I was Wrong.

    If your battery is 6 Volts, the Charge Voltage should NOT Exceed 7.35 Volts.
    Normal Charge Current is 1/10 Capacity, so for a 1.4 A/H Battery, it should be 140 mA.
    Or for a 1.2 A/H Battery it would be 120 mA.

    If your battery is LOW in Voltage and Does NOT Accept this Current, Than it is Either SULFATED or has a BAD Cell.

    INCREASING the Charge Voltage Just to DRIVE MORE CURRENT will NOT Fix the Battery.

    Hope this Helps

    IF YOU WANT TO TALK by PHONE, It is a FREE CALL FOR ME.
     
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  8. spec

    spec Well-Known Member Most Helpful Member

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    Hi Chemelec,

    Quite true for most LA batteries, but the label on BM's battery says 7.5V maximum charge voltage.
    (it may be a polymer LA battery or other higher voltage LA type)

    spec
     
  9. baxterdmutt

    baxterdmutt Member

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    No problem

    Thanks. I appreciate that. I was only confused when you said I should charge the battery at 14V. I wasn't sure why you would say that so that's why I connected it at that voltage just long enough to read the amps (1-2 seconds). I thought that's what you wanted for some diagnostic reason, but I had no idea why.

    In general I have an ok understanding of sulphation and charging volts and amps.

    I do very much appreciate the help and the offer to talk on the phone but as far as the battery goes, I'm ok. Getting a charge circuit with at least a vague charge complete indication is my problem. I'm about to give up on that plan though. It's getting too complicated for a simple charger for an LED lantern that I've rebuilt.
     
  10. chemelec

    chemelec Well-Known Member

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    Well if you ever need help, I am just over in the Okanagan Area.
    And I have Thousands of New Parts, many that I can give away for free.
    Although Mailing Costs can be a problem for larger ones.

    Take care.......Gary
     
  11. baxterdmutt

    baxterdmutt Member

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    Wow! Thanks Gary. That's very nice of you.
     
  12. baxterdmutt

    baxterdmutt Member

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    So...I'm not committed to a charger that uses the Lm317. Would it be better to do this another way. Keep in mind that this is the project:
    -The battery will be placed in an led lantern that I have rebuilt for power outages.
    -The battery is 6v, 1.4Ah lead acid SLA.
    -I'd prefer some kind of indicator (mostly just to give me an idea that it's close to charged.
    Thanks.
     
  13. baxterdmutt

    baxterdmutt Member

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    Spec,
    I'll get to that in a little while. I'll have to put it back on the breadboard because I had changed to another circuit. I really need more than one breadboard
     
  14. baxterdmutt

    baxterdmutt Member

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    Chemlec,
    Do SLA batteries prefer a constant current (140ma on mine, for example) or constant voltage (7.25) with a varied current (higher, 140ma at the start and lower, 10ma or less, towards the end)?
     
  15. chemelec

    chemelec Well-Known Member

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    Constant Voltage.
     
  16. spec

    spec Well-Known Member Most Helpful Member

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    Hi chemelec,

    While constant voltage is a good way to simply charge a LA battery, ideally the charger should also have current limit. For most batteries a good value of current limit is capacity/10 or, for BMs batteries, 0.120A.

    spec
     
  17. chemelec

    chemelec Well-Known Member

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    YES, I Mentioned that Current Limit Numerous times before.
     
  18. spec

    spec Well-Known Member Most Helpful Member

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    Steady on chemelec.:)

    spec
     
  19. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    I am not sure if you have looked at the entire process of charging a LA battery because that entails BOTH constant current AND constant voltage, at least basically. It also depends on time which the battery takes to start to charge more and more.

    "constant current" in this case however does not really mean constant current, that's just a way to describe the starting conditions. It should really be called, "current limit" because that's really what it is. The current is limited during the start of charge, and gradually as the voltage gets higher the circuit switches to constant voltage, but constant voltage here does mean constant voltage (or 'regulated' voltage).

    For a 12v battery, if we start with say 14v constant voltage, we might see a very large current like 10 amps. To avoid that, we limit the current to the safe level. Lets say that it is 140ma as is your battery. That means we have the circuit set up so that it can put out a constant 14v BUT the current in that circuit is limited to 140ma also. So when the battery starts to charge and it wants to draw 10 amps, the circuit does not let it. The circuit cuts the current back to 140ma and that means the voltage of the battery is automatically lower, like maybe 13.6v or something.
    As the battery charges, the current remains at 140ma but the voltage starts to creep up slowly, 13.60, 13.61, 13.62, 13.63, etc., until it gets close to the set point of 14.00v. At that time the current will NATURALLY be lower, even without the current limit, because of the internal resistances of the battery and the charger. That means that at 13.98v the battery might only draw 100ma (not 140ma anymore and certainly not 10 amps) so the constant current is not needed anymore and so the charger starts to limit the voltage and as the battery gets up to 14.00v it only draws a very small current which may only be 20ma or something.

    So you see the process starts out with the max current, then when the current tapers off naturally the charger starts to limit the voltage so the battery does not overcharge. That is the basic charge method for LA and for Li-ion although the set point voltage for Li-ion is more critical and has to be more accurate. The set point for LA is also based on temperature, but often a temperature of 20 degrees C is assumed so if the temperature is significantly different than that, the set point voltage has to be changed a little. Some batteries actually have this stamped on them.

    The simple characterization of the LA charger is that it is basically just a voltage source (power supply that puts out voltage) with an included current limit. It can put out the full voltage of say 14v but only if the load does not draw more than 140ma (in your case).
     
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  20. spec

    spec Well-Known Member Most Helpful Member

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    What a wonderful description MrAl. :cool:

    spec
     
  21. schmitt trigger

    schmitt trigger Active Member

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    On the Mars lander story, which crashed because the contractor used Imperial units and NASA used Metric units......there is an interesting twist.

    This was at the time when NASA had its budget significantly reduced. In addition to firing people, what most organizations do is limit business travel. They had this new wonderful technology called "teleconference".
    Well guess what, a teleconference, with all its advantages, never truly replaces a face to face meeting, with the ability to touch the unit, go into the lab or machine shop, and actually see it perform in real time.

    When the mistake was discovered, legend tells that the managers involved almost came to blows...............
     
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