rechargeable batteries question

Discussion in 'General Electronics Chat' started by Tesla00010010, Jul 24, 2008.

  1. Tesla00010010

    Thread Starter Member

    Jun 20, 2008
    21
    0
    Hello,this question may be obviosu to many of you but i just decide to start using rechargeable batteries instead of the normal ones.So,i needed 0.23 A in a circuit and i went to buy a rechargeable one,and i got one "Gold-Peak" Ni-mh 9v one(8.4V actually)with the rating of 170ma-H.I read the article on the lessons in this website("Battery Ratings")and it sais that even if you give more charge to the battery than what it is rated it should give you the charge,but for a less time obviously.So the battery was planned to give 0,17 A in an hour and i put it to 0.23(to light those 3.5V tiny bulbs that work at 0.25 A),and my surprise was that the bulb just lighted for 5 seconds and then it was not lighting anymore.

    When i measured with the voltmeter to the battery terminals,it was around 3 V and going up quickly but it never reached its value(8.4V).On the battery it says "short-circuit proof",and im not sure if this has something to do about it.The battery says 16 hrs at 17 ma too,but i dont understand why cant it give me 0.23 A it should give that charged for less than an hour,right?

    I have read that if u overcharge the batteries u can damage,so if somebody could explain this to me it would be great,because im planning to light 4 bulbs and this time i would need 1/2 A.I have 3 pairs of 1.2v batteries of the same brand and they have the rating of 1800ma-H.I think now i shouldnt have problems because im not gonna use even 1 A but i dont understand what happeend with the 8.4V battery.

    Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    9v rechargeable batteries are usually made up of seven very small 1.2v batteries. Batteries become very inefficient if you place loads on them which would cause complete discharge in less than an hour. It causes the batteries to heat up due to the power dissipated across the battery's own internal resistance, which makes the problem worse.

    You would be much better off to use "AA" size or larger batteries.

    Better yet, consider using super-bright LEDs; they are far more efficient than incandescent bulbs, as they generate very little heat. A super-bright white LED generally has a Vf of 3.6-4.0V, and can produce a lot of light on 25mA-30mA of current. You could put two of them in series with a resistor to limit the current to 30mA, and run them for over 5 hours on your 9v 170mAh battery.
     
  3. theamber

    Active Member

    Jun 13, 2008
    318
    0
    If you overcharge a battery it can even explode releasing corrosive chemicals! or it will retain the higher charge for a very short time. Rechargable batteries have what is called "memory".
    http://www.batterybank.com/page18.html
    You can check youtube for battery explosions.
    The sarge is right, if you use a battery at full load it will overheat therefore discharging very fast. It is a good idea to be generous in the current capabilities of batteries if you intent to use them in a continous mode.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The battery says to charge it at 17mA and you tried to charge it at 230mA or more and it doesn't work properly any more. I wonder why? Duh!

    An 8.4V Ni-MH battery will be about 9.8V when it is fully charged, if it is charged properly at 17mA for 16 hours.

    You used a charger but forgot to say its output voltage and current. Then you connected a 3.5V/250mA light bulb in series with the charger and the battery? Why??

    You want the tiny "9V" battery to power 4 incandescent light bulbs. If two 3.5V/250mA bulbs are in series then their current is 250mA at 7.0V and will be higher at 8.4v. Two of these series strings will probably try to use a current of 600mA at 8.4V.

    Energizer battery company have a website with datasheets for every battery. Their 9V Ni-MH battery has 7.2V at 175mAh and its voltage drops to 5.5V in only about 5 minutes when the load draws 600mA. You will see the lights dimming as the tiny battery runs down.

    Incandescent bulbs are heaters that waste a lot of power making heat. Use efficient LEDs instead.
     
  5. Tesla00010010

    Thread Starter Member

    Jun 20, 2008
    21
    0
    Well actually what i wanted was to light 4 bulbs 2 in parallel in series with 2 in parallel and all in series with a 3.9 resistor.The networks should complete the 9V at 0.54 A,so i was using a duracell battery which gave me 0.5 A for some time but i tried then with a rechargeable instead.Yes.i suppose i will better use AA batteries then...and i know LEDs use not much power as the bulbs but,arent they supposed to give better illumination?thanks for the help
     
  6. Tesla00010010

    Thread Starter Member

    Jun 20, 2008
    21
    0
    i mean one 3,.5 bulbs should light more than a white LED at 3.5V or 4V
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    There are tiny dim lightbulbs and there are very bright big ones.

    There are tiny dim white LEDs and there are very bright big ones.

    The light bulbs waste about 80% of the power making heat.
    the LEDs waste only a small amount of power making heat.
     
Loading...