Build a NIMH battery charger ( Smart one).

Discussion in 'The Projects Forum' started by CounterLeone, Feb 6, 2013.

I dont know what it is

Poll closed Feb 7, 2013.
  1. I dont know what it is

    0 vote(s)
    0.0%
  2. I dont know what it is

    1 vote(s)
    100.0%
  3. I dont know what it is

    0 vote(s)
    0.0%
  4. I dont know what it is

    0 vote(s)
    0.0%
  1. CounterLeone

    Thread Starter New Member

    Feb 6, 2013
    6
    0
    OK, Now this IS An EMERGENCY!!!
    Do any of you guys know how I can Make A NIMH Battery charger? I Mean a SMART one. Eg: It will automatically shut off when it is fully charged. I have 2 Sony cycle energy 2700mah NIMH batteries.

    Things i can use:
    1xLM317T Ic
    Resistors (250, 500, 1k, 10k, 100k,)
    Capacitors(220u, 0.1u, 2.2u, 6.3u, 100u)
    Diodes (1n4007)
    LEDs
    1xBattery holders(2 batt)
    Voltage output supply(9v-0.6A, 12v-2a)[If other required, please tell]

    And plz tell me whether my batteries are of good quality or not. After charging, one has 1.43v and another has 1.418v. I charged them in a manual charger. it has 2 LEDs. I put the batteries in corners So that Both Leds Light up. It is a manual charger and does not turn off after full charge. So PLEASE Give me the schematic that uses any/all of the above mentioned components.It must shut off when the 2 batts Are fully charged. i am only 13 and my father is not going to buy any more things. So plz try to make it simple but not ineffective. Is the voltage of the batts after fully charged alright? It would be good if the circuit charged the batts separately.

    Thanks in advance for your help
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    You could charge the two batteries (cells) in parallel, using a fixed voltage from the LM317 IC. The fixed voltage will give a crude type of "auto shut off", it will at least make sure the cells are not overcharged.

    Have you googled for "charging voltages for NiMH cells"? That will give you some important info. :)
     
  3. CounterLeone

    Thread Starter New Member

    Feb 6, 2013
    6
    0
    I googled it and it says that at max it can be 4.5v without any load. The main factor is CURRENT. Never mind, Can you plz just Give me the schematic of the charging circuit?:(
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Can you get one of those charger ICs. probably the most simple thing. Most of those ICs can detect a fully charged battery and switch to maintenance charging
     
  5. CounterLeone

    Thread Starter New Member

    Feb 6, 2013
    6
    0
    I TOLD you that I am ONLY 13 years old And my father is not going to Buy any more Things Since my monthly exams is near. So can you please tell me how to make the auto shut off charger with the listed components?
     
  6. CounterLeone

    Thread Starter New Member

    Feb 6, 2013
    6
    0
    Oh and by the way are SONY cycle energy (2700 mah) NIMH a good battery brand?:confused:
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Sorry to say. But with that component list you will also need a magic wand. If you want to have automatic shutdown after the battery is fully charged. A simple way is to use some sort timer. And cut of charging after a given time. A short period of overcharging say 15 minutes will not kill your batteries. If you are lucky maybe you have some sort of timer at home
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    I have to ask: how can it possibly be an EMERGENCY to build something you can buy at many places? Unless the batteries are used to power an artificial heart, I kind of doubt it's an emergency.

    The NI-MH chemistry requires an end of charge (EOC) detection mode called dT/dt, which means rate of change of temperature versus time. Ni-MH batteries gradually get warmer as they charge, but the rate at which the temp increases abruptly changes (temp increases faster) at the full charge point.

    http://www.buchmann.ca/chap4-page5.asp

    IMHO, if you don't understand the battery characteristics, you can't build a smart charger.

    Google is your best friend.
     
    Last edited: Feb 6, 2013
  9. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    depends. Ni-MH do not tolerate overcharge at all. If the charging rate is fast (like 0.5c or higher) a 15 minute overcharge might cause the battery to vent gas through it's valve.

    http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride
     
    Last edited: Feb 6, 2013
  10. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    I guarantee you can not build a NI-MH smart charger with those parts.

    And yes, Sony cells are among the best made but they won't tolerate incorrect charging so buy the charger that was designed for them.
     
  11. CounterLeone

    Thread Starter New Member

    Feb 6, 2013
    6
    0
    OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, OK, !

    I understand that I cannot Build a Smart nimh battery charger using The conponents. But at least I Guess I can make a Charger (with LM317) better than the dumbest chargers called value chargers(using 2 resistors, a transformer and a diode-I know cause I hacked it!). So PLEASE PLEASE Give me a Schematic of a Circuit that uses LM317 But it does not need to be smart. Make sure it is effective
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I have an Energizer charger that came with four of their AA Ni-MH cells.
    It is so STUPID that it severely overcharges and cooks cells that are not completely dead because all it has is a timer. Maybe they want it to destroy cells so you buy more to replace them?

    The datasheet for an LM317 shows a current regulator that is an LM317 plus only one resistor. It can charge a battery then it will overcharge and destroy it.
     
  13. CVMichael

    Senior Member

    Aug 3, 2007
    416
    17
    I used MAX712 to make my NiMH charger, and it works well
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    That was my point earlier. I (stupidly) believed if I posted information and links he might read them and understand there is no way to build a usable charger in this way but clearly that was an incorrect assumption.
     
  15. CounterLeone

    Thread Starter New Member

    Feb 6, 2013
    6
    0
    OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK.!

    I understand that I cant make a SMART charger with the components. But at least I guess that I can make a charger(with LM317) Better than the cheapest manual chargers known as value chargers(using 2 resistors, a transformer, 1 diode--I know cause I hacked it). So PLEASE PLEASE Give me the schematic of a Nimh charger Using LM317 that is not THAT Simple and ineffective. I forgot to mention That I have 555 Timers and transistors( BC547, 2N2222, 2N3904, BC108, 2N3055).
     
  16. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Please don't repeat your posts! Also please be patient, it can take a day or two for someone to read your last post and get around to replying. :)

    You can make a "safe enough" NiMH battery charger using a LM317 as a voltage regulator, this will have a fixed voltage output and that makes sure the NiMH will not overcharge.

    You can limit the max current by putting a resistor between the power supply and the LM317, that will limit max charging current of a flat battery.

    You said you have a 9v 0.6A DC power supply. I assume that is a plugpack? Have you measured those voltages, or are those the voltages shown on the label?

    (edit) I looked up some charging voltage charts for NiMH. If you set the regulator voltage at about 1.50 or 1.52v, this should end charging (or greatly reduce charging current) when the battery is about 90% full.

    [​IMG]

    If you put your two cells in series for charging you set the LM317 to a fixed voltage of about 1.52*2 = 3.04v.

    Assuming your "9v 600mA supply" puts out 9v, you can use a series resistor before the LM317 to limit max current to about 400mA, the resistor will have (worst case) a voltage drop of about 9-3.04-1.5 = 4.5v so the resistor should be R = V/I = 4.5/0.4 = 12 ohms. Heat in that resistor will be 1.8 watts worst case so you need to get a big 5W resistor.

    That won't make a proper "smart charger" but it will limit max current to about 400mA, and will greatly reduce the charge current when the batteries get >90% full. Total parts cost; a 5W resistor, LM317, and a couple of resistors, (and maybe a trimpot) to set the fixed voltage to 3.04v.
     
    Last edited: Feb 8, 2013
    absf likes this.
  17. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Hey kid, your attitude stinks. You need to recognize who holds the power here. You come here with no knowledge and demand knowledge from the people who have it. You give absolutely no incentive for anybody to help you. You need to learn respect or at least how to disingenuously kiss ass long enough to get what you want.

    Don't demand, ask (politely).
    Don't be pushy; persistent is good, but "OK OK OK OK OK" makes people want to slap you.
    Say thank you, even if you haven't been handed exactly what you wanted on the silver platter that you wanted. If someone took the time to respond, that time is a gift that can't be given back, and deserves your thanks.


    This has been a free lesson from Strantor.
     
    RodneyB, kaning, MMH and 1 other person like this.
  18. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    That will destroy the battery. That voltage in the graph corresponds to warm temp and also with current being forced into the cell. At normal temp, both NI-CD and NI-MH full charge voltages correspond to about 1.40V. If you hook them to a voltage source set to 1.5V, it will overcharge them to death.
     
    absf likes this.
  19. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Thanks for the correction Bountyhunter, so the LM317 voltage needs to be set slightly lower, and likely still needs to be checked after X hours to disconnect the batteries. I have NiCd charged like that, hook them up to a constant current regulated voltage at night and the next morning (after X hours total) turn it off they are nicely charged.

    It's still far from a "smart charger", but was given in context (ie a 13yr old with only a few parts in the junkbox and an "emergency") and is safer than charging through a resistor and checking the battery every 15 minutes.
     
  20. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    You can't use a constant voltage charger with NI-MH. You also can't do sustained trickle charging unless the rate is very low like about C/40 or less. NI-MH just don't tolerate overcharge the way NI-CADs do.

    As AG pointed out, using a timer with NI-MH is a sure road to dead cells since you don't know if the cells are discharged or charged starting out. Timers are used in some NI-MH chargers, probably because it increases battery sales.
     
Loading...