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Not being able to understand simple LM317 lead acid battery charger

Discussion in 'General Electronics Chat' started by Willen, Nov 25, 2015.

  1. gary350

    gary350 Well-Known Member

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    If you use too much voltage to charge a battery that will boil the acid. A 16 or 17 or 18 volts good filtered DC power supply with amp meter is all you need. I have a battery charger that I built many years ago output is 16 volts with a selector switch for 17 and 18 volts DC. The transformer is 100 amp output. The amp meter shows battery will not take more amps than it needs. I can charge a small motor cycle battery, lawn mower battery, or any size car battery even a deep cycle 2000 amp boat battery on 100a 16v. A dead battery might pull 40 amps at first, the meter slowly drops as the battery charges, when the batteries is almost fully charged meter shows .1 amp. Changing the voltage from 16 to 17 speeds up charge time and 18 volts is faster. If you put a small 10 amp battery charger on a large battery that tries to pull 30 amps it will over load the charger if it does not have current limiting. If you put a larger 100 amp charger on the same battery it only pulls 30 amps even though 100 amps is available. The 100 amp charger is good to get a car started with a dead battery then let the alternator charge the battery.

    I worked at Interstate Battery company in KY 1995 they had a continuous battery plate casting machine, injection molding machines to make battery boxes of all sizes, battery post casting machines, assembly lines built batteries then they all went to ware houses where they were all computer charged over a period of time 1 week or longer. Batteries were all charge as some pre determined rate that was best for that battery to condition the lead plates. A computer changed the voltage and changed the current all the time for a week. Voltage and amps were up and down all the time, sometimes 18v at 50a, 16v at 5a, 16v at 1a, 17v at 20a, etc. They learned from experience by charging a battery at all these different charge rates for a week it created a better long lasting battery. I was told to let an existing battery charge at its own rate with a 16v at 100a charger.
     
  2. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    I think the only problem was that you said something like you could connect anything to the battery and it will take what it wants, which of course is not true. If you use a REGULATED voltage source then you might get away with it because as the battery charges the current comes down and so the battery does not overcharge.

    I've gone as high as 15v for mine, but never as high as 16v. I didnt want to push it that hard. In fact, with a little more lead resistance (leads to the battery from the power supply) i got a nice taper toward the end of the charge. The battery always worked much better in the car after that kind of treatment.
     
  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    gary350: Your technique works for large, flooded-cell, automotive starting batteries, traction batteries, and deep-cycle batteries provided that:

    1. The batteries have caps to replace the electrolyte you loose after the battery voltage reaches >15V (2.5V per Cell).

    2. You are constantly monitoring the charging process, and you disconnect the battery from your brute-force charger at the moment that the current into the battery drops below about 0.02C, or about 2A for a 50Ah battery.

    Your technique will ruin modern Sealed LA, AGM, VRLA batteries, and void the manufacturer's warranty...

    It is time for you to get out of the dark ages, and learn about three-step automatic chargers, and dealing with sealed lead-acid batteries.
     
    Last edited: Apr 22, 2016
  4. dave

    Dave New Member

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  5. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    That datasheet is old (Rev E). Here's the newer rev (Rev H): http://cds.linear.com/docs/en/datasheet/108345fh.pdf

    Definitely looks like a significant error on LT's part. Seems strange a part would jump from a fixed voltage regulator to an adjustable one.
     
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Looks like LT needs to merge the two files. As far as i know they come in both fixed and adjustable versions.
     
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  7. bountyhunter

    bountyhunter Well-Known Member

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    And that regulated output had better not be more than 14V or the lead acid will be overcharged. Continuous float charge is even less, more like about 13.4V.
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    I cant agree with that 14v quote because i have seen my battery in my older vehicle always undercharge at that voltage level, and that is why i had to bring it into the house periodically to charge it at a higher voltage. 14.2 was a little better though. The problem at 14v is that the internal resistance was too high so it would not draw much current at 14v, but at a higher voltage like 14.5v it would draw some current and then eventually the battery would charge and then take a better charge at the lower voltage of 14v.
     
  9. bountyhunter

    bountyhunter Well-Known Member

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    Just ask the battery makers. We designed the charging IC's that Chrysler and Ford use in their electrical systems. The current consensus is to use 14V for the system voltage for faster restore of charge. But for long term charging (float charge) it is less to reduce boil out. All you have to do is ask the battery makers, they supply exact values (per cell) for optimum charging.

    And it definitely is not 15V for a six cell battery.

    "The problem at 14v is that the internal resistance was too high so it would not draw much current at 14v, but at a higher voltage like 14.5v it would draw some current and then eventually the battery would charge and then take a better charge at the lower voltage of 14v."

    Sounds like you are describing a battery which has been damaged or has sulphation or some other problem.
     
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Well this happened with two batteries, one new and one used. Once charged properly however, they both worked fine.

    I dont believe the 14v spec i dont care what anybody says and wonder why they would say that anyway. I have measured other systems that are higher like 14.5v during charge. My older car system was 14.2 for example and then with the new alternator it dropped to 14v which caused problems. At 14.2 it was not too bad.
    That 14.5v was on two different model cars, and i have read other posts that spec something similar to that.
     
  11. bountyhunter

    bountyhunter Well-Known Member

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    Maybe because they make the batteries and know how to charge them. Here are the manufacturer's specs for the lead acid batteries made by Scorpion about sustained charge:

    "Next comes the Float Step. This is a regulated voltage of not more than 13.4 volts and usually less than 1 amp of current. This in time will bring the battery to 100% charged or close to it. The float charge will not boil or heat batteries but will maintain the batteries at 100% readiness and prevent cycling during long term inactivity."

    I have a temp compensated charger I designed many years ago to keep my motorcycle battery peaked up exactly as stated, voltage set point is 13.4V. The battery I am currently using is EIGHT YEARS OLD and still spins the starter like when it was new.

    I trust the battery makers to know about batteries.

    BTW: do you have a voltmeter? Put it on the battery terminals in your car and rev the engine. You will see it read 14V give or take tolerance. 14V is used in cars to replenish charge faster, long term charge should be as stated (13.4V).
     
  12. bountyhunter

    bountyhunter Well-Known Member

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    You can see from the attached document that at 14.34V (room temp) a lead acid battery starts outgassing which will ruin any sealed battery and dry out any water filled battery.
     

    Attached Files:

  13. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again,

    Well i am not sure what kind of battery that chart is for, or where it came from.

    I ran my older car for years with the alternator charging at 14.2 volts.
    The other cars i measured first hand were (1) a 2002 Chevy, and (2) a 2000 Ford Mustang. They were both 14.5v charging.
    My current car however measures 14.0v or pretty close.

    So you see there is some variation and it doesnt matter what the battery manufacturer says it matters what works in real life. If yours worked in real life then you were lucky to get the right battery. I have also read that changes in battery chemistry caused some manufacturers to raise their charge voltage but others refused to do so. So there must be some disagreement in the industry. Also keep in mind that battery manufacturers want to constantly sell batteries.

    I cant help it if you dont agree with what is happening in the real world, i can only present the facts as i have observed them first hand. There could be unknown differences that we dont know about yet.
     
  14. bountyhunter

    bountyhunter Well-Known Member

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    To answer your question about where the info I posted came from, one was from the web site of the Scorpion battery manufacturer and the other was from the Battery University article on charging lead acids.

    As for:

    " it doesnt matter what the battery manufacturer says "

    It may not matter to you, it matters to me. I posted the info I did to keep people from screwing up their batteries by over charging them.

    As for:

    "Also keep in mind that battery manufacturers want to constantly sell batteries."

    The one I just bought has a 96 month warranty so I doubt very seriously they are building the charging systems to intentionally kill the batteries.

    "I cant help it if you dont agree with what is happening in the real world"

    The real world is in my garage and the float charger I built 25 years ago to maintain the lead acid battery in my motorcycle has a voltage set point of 13.4V (exactly as stated by the battery maker) and I currently have eight years of use on the Scorpion battery I am running. That's real life. It's a sealed AGM type and if I had been stupid enough to over charge it, it would have been ruined years ago.

    The info supplied by battery makers reflects testing of many thousands of batteries, not anecdotal one offs. That's why I follow their specs.
     
    Last edited: Apr 24, 2016
  15. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Automotive starting battery makers started adding Calcium to their battery plates a few years ago. That increased the set-point charging voltage of the alternator voltage controller to progressively higher settings. For example, my 2015 Subaru has the ACU putting out ~14.6V, as does my 2004 GMC, while my old 1982 AMC Jeep sits at 13.95V. The tables that BH posted are likely for the older batteries with pure lead plates.

    Guess what happens if I go buy a "new" current-production battery with Ca plates, and put it in my old Jeep? No mystery, the battery is chronically undercharged as determined with a hydrometer measurement of its S.G. The ACU is potted and sealed, and has no provision for adjustment. My fix is to float the battery (while the Jeep is parked) with a modern Battery Minder type of charger. One of my future projects is to replace the Jeep's OEM ACU with one where I can diddle the set point Voltage...
     
    Last edited: Apr 24, 2016
  16. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    I am not sure what you want me to say here. I measure one thing, you say another thing. I believe what i measure and I believe what you are saying so it must be that both scenarios are correct in so much as the way they are applied. So whatever you are doing with whatever products you are using must be working for you, but whatever i am doing with whatever products i am using works for me, so the difference, as i tried to explain, must be in the materials we are working with. I also mentioned that i have read that some manufacturers do not accept the newer standards.

    There is another aspect too though, and that is the way the setup is used over time. If i drove my car every single day for 1 hour straight non stop it might have charged ok at 14v, but my usage was lower too, like 15 minutes per day but only 2 days per week. If any of that was at night then that probably did not allow the battery to get fully charged either.
    So there is a time factor too here, and that is that if we charge at a lower voltage for a long time it's almost the same as if we charge for a short time with a higher voltage. 14v for several minutes might be ok, but 14.5 for just a few minutes seems to work too. The battery only gets damaged if it is left on charge too long at a voltage that is considered too high for it, and even then it's a matter of time not just a "go, no-go" situation. The battery doesnt die after five seconds of charging at 15v.

    This isnt the only time i had issues with web sites that claim to know it all. I find this with various battery chemistries as well as many other topics. Some sites quote specs for Li-ion batteries too, but if we look at the numbers from actual tests of a huge number of batteries, we find it differs quite a bit.

    You might also want to read Mike's reply in this thread that came just before this reply.
     
  17. bountyhunter

    bountyhunter Well-Known Member

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    The charging information I posted are for new AGM lead acid batteries.

    Here is the data for recommended continuous charging voltage from Exide who is probably the largest maker of car batteries in the USA. Note that this data is for calcium type.

    http://www.exide.com/Media/files/Downloads/TransAmer/Battery Care and Maintenance/Battery Charging & Storage Guidelines 5_9_13.pdf

    This shows exactly why I said that for continuous charging, the set voltage should be 14V or less. The spec listed below is 13.5 - 13.8V. See the attached image, fourth and fifth columns. The only charge modes that use a higher set voltage are current limited/timed for short duration which means they do not apply to automotive use or continuous charging such as the OP of this thread was asking about.

    Like I said: I go with the battery maker's data. You do what you want. If you think the maker publishes incorrect data, you can ignore it.

    View attachment 99132 float2.jpg
     
    Last edited: Apr 25, 2016
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  18. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi again,

    Thanks for the chart. I think this is starting to make some sense now.

    If we intend to charge for long periods, 14 volts is probably better than say 14. 5 volts. If we intend to charge for a shorter time period, then 14.5 volts would be better than 14 volts.

    What may help to explain the readings i have taken on other vehicles is that maybe when the car is first started from cold (not necessarily very cold, just a cold engine that did not reach operating temperature yet) the voltage is higher, then as the alternator heats up it cranks the voltage down to 14 volts. That is a possibility that i did not look for because most of the measurements i have made over the years were after cold starts not after the engine/alternator has warmed up.
    On my own vehicles however i did measure before and after cold starts, and sometimes long after the engine had warmed up. I noticed that the alternator cuts back the voltage slightly, from maybe 14.2 or 14.0 volts down to maybe 13.5 volts. That indicates that it knew enough to charge faster for a short time and then cut back and charge at the safer level.

    To show that the user's drive cycle has a lot to do with the optimum voltage, back when i had my Hyndai, i would have been VERY happy to be able to crank the alternator voltage up to 14.5 volts from 14.0 to 14.2 volts that it was on cold start. That would have meant that i would have never had to carry that battery into the house to charge it on a power supply :)
    This is because the vehicle was not used every day, maybe only 2 times per week for a short drive. That meant that the battery had to be charged faster. On a short trip like that, the car has to be started at least two times: once leaving, and once leaving the destination location. Sometimes i would hop around a little too, from one location to another, which would mean starting the car 3 or more times over a very short time period. That would use more battery power and therefore require a longer charge time with a lower voltage like 14 volts.
     
  19. spec

    spec Well-Known Member Most Helpful Member

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    Interesting and informative thread.

    When the old mechanical regulators with dynamos, especially on Minis, aged, they either undercharged or boiled batteries. The modern alternator and solid state regulators are much better. You can still get all sorts of weird charging scenarios though due to bad/corroded connections. The 1970s Delco charging systems were a nightmare and the same period Lucas were worse. The German alternators were in a different league though.

    spec
     
    Last edited: Apr 28, 2016

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