Lipo battery pack and LEDs

Discussion in 'General Electronics Chat' started by Medowin, Jun 1, 2011.

  1. Medowin

    Thread Starter New Member

    Jun 23, 2010
    16
    0
    Hello!

    I am a complete noob to electrical wiring and am looking into a project that involves 30 or so LEDs powered portably. It appears as though most conventional batteries don't have enough "juice" to power them so I was looking into a higher powered LiPo battery pack to power them. The battery pack I am considering is this. However, I am unsure so I have just a few questions:

    *Would this battery pack be enough to power 30 LEDs rated at 2.2v / 20ma for several hours?
    *How exactly could I hook a battery like this up to an LED circuit? It doesn't appear to have typical exposed positive/negative ends like a normal battery.
    *If I have to strip the connector ends to hook up the battery to the LED circuit how will I be able to later recharge the battery pack in a charger?


    Any help would be appreciated. Thanks! :)
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    I would leave the battery connectors intact and try to get the counter connections for them.
    The battery is stated to be 11.1 Volts.
    You say you want to connect 2.2 Volts leds.
    You can connect 4 leds in series with a current limiting resistor to the battery.
    The resistor will have the following value:
    (Vsupply - Vleds) / Iwanted = (11.1 - 4X2.2) / 0.02 = 2.3 / 0.02 = 115 Ohms
    The nearest E12 value will be 120 Ohms.
    You can make 7 strings like that to have 28 leds connected.
    The other 2 leds can be connected with a seperate resistor of:
    (11.1 - 4.4) /0.02 = 6.7 / 0.02 = 335 Ohms.
    The nearest E12 value will be 390 Ohms.

    Bertus
     
    SgtWookie likes this.
  3. Medowin

    Thread Starter New Member

    Jun 23, 2010
    16
    0
    Forgive my noob-ness, but what exactly is a "counter connection"? And where could I get them?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    By "counter connection" Bertus actually means "mating connector" or "mating connectors"; plugs that will fit the jacks or vice versa.

    balance connector type: JST-XH
    connector type: 4.0mm Banana Connector

    You need to find a datasheet for the battery you are considering purchasing.

    Rather than the Yahoo! buy, you might look here:
    http://www.hobbypartz.com/83p-2650mah-3s1p-111-20c.html
    $19.70 vs your $22.95 price.

    You might read a review on BlueLipo batteries here:
    http://www.rccrawler.com/forum/showthread.php?t=226987

    You might read some threads on RC forums, such as this one:
    http://www.rcgroups.com/forums/showthread.php?t=1159506

    Googling "BlueLipo batteries" will give you lots of hits.

    Keep in mind that LiPo batteries occasionally burst into flames when charging. :eek: You should charge the pack outside in a suitable safety container designed for that purpose, using a charger that's set up for your battery.
     
  5. Medowin

    Thread Starter New Member

    Jun 23, 2010
    16
    0
    So what I should do is just buy a banana connector, plug it in to the other one, strip the wires to the new connector and solder that to the circuit? And I guess just leave the balance connector alone?
     
  6. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Whatever you do, DO NOT be tempted to think you can connect strings of five "2.2V" LEDs in series across the 11V battery without a resistor. This would result in the current being unstable, with unpredictable brightness and a high risk of the LEDs being destroyed.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It looks like the banana connectors on the large wires are sockets, but I can't be certain by the photo, and there is no datasheet available that I can find.

    The balance connector is where your charger monitors whether the individual cells in the pack are charged/discharged equally; if one of the cells has a much lower charge than the others, you could wind up overcharging the other cells and have a fire.

    I am really not very familiar with these high-power LiPo packs that RC hobbyists use. I DO know that they can catch fire during charging - or even afterwards; you need to take appropriate safety precautions such as charging them outdoors in a safe container.

    You really should poke around on one or more of those RC forums, do a good bit of reading, and ask some questions about the care and feeding of those types of batteries. Please don't just connect it up to some arbitrary charger (ESPECIALLY not an automotive battery charger) or you will likely wind up having a fire and/or explosion.
     
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