12Volt DC and 9 V battery for LED strip

Discussion in 'The Projects Forum' started by lone.vaas, Mar 14, 2016.

  1. lone.vaas

    Thread Starter New Member

    Mar 14, 2016
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    Hello,

    I am working on a home project and I am a noobie at electronic circuits.

    I want to power 1m of 12V LED lights (light strip).
    I want to be able to connect it straight to a 12V DC , and when i disconnect it, the LED strip needs to get powered by a 9 V battery.

    The circuit is below, am i correct in understanding that the diodes will make the selection for the higher voltage for me?
    please help...
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    with the circuit drawn, the 9v supply will be disconnected when the 12v is on, and reconnected when the 12v is removed.

    D1 can be ommited
     
    Last edited: Mar 14, 2016
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Steering diodes are often used to select the higher of two voltages, as you show, but do you think the LED strip will light with only 9V?
    Welcome to AAC!
     
  4. #12

    Expert

    Nov 30, 2010
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    Yep. It'll work...if the 9 volt battery has enough quality.
    The little rectangular 9V batteries are fairly weak. They struggle to provide a tenth of an amp.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    1. What kind of 12V led strip, and spec or links?
    2. What kind of 9V battery, and how many ( mA)?
    3. 12V and how many current (mA)?
     
  6. Alec_t

    AAC Fanatic!

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    Perhaps I should have asked "Will it work with only 8.3V?". I forgot to allow for the diode drop ;).
     
  7. #12

    Expert

    Nov 30, 2010
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    Wise guy.:p
     
  8. lone.vaas

    Thread Starter New Member

    Mar 14, 2016
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    Hi guys, thanks a lot for the help!
    First off i didnt expect anyone to reply so fast!

    @Dodgydave thanks for the info! That really helpful, i did not know that!
    @Alec_t Thanks for the greetings!
    @#12 I am using a Duracell 9 V battery that powers it for quite some time. Pretty strong stuff.
    @ScottWang 1) all i know is that it is a 1meter strip with 12 V written on it
    2) 1 x 9V Alkaline duracell battery, not sure abt the mA.
    3) output 12V = 5 A , thats whats written on it.

    Sorry if i dont know most of the answers to the question but I'm eager to learn anything you'll think may be useful.

    Thanks guys!
     
  9. #12

    Expert

    Nov 30, 2010
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    That's mostly up to you. We deal with ginormous amounts of people with all kinds of skills to no skills at all...even dangerous to themselves!:eek:
    You start with a question, we figure out how to do it, but it's really hard to guess what you need next.
    That's mostly up to you.:p
     
  10. lone.vaas

    Thread Starter New Member

    Mar 14, 2016
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    @#12 Yes, that's quite true!

    Do you think there will be a trickle of current into the 9V battery? I'm worried that the battery may explode or something!
     
  11. #12

    Expert

    Nov 30, 2010
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    forget about it. Something like microamps on a bad day.
    Bottom of page 1. Reverse leakage.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    I checked the info about the current of Duracell 9V battery is 580 mAh, 12V led strip probably won't work for less 11V.
    Have you ever using 12V to light it up?
    Is it a RGB led strip? (can you take any photo?)
    Does it has remote control?
    If your led strip as this one then its I = P/E = 14.4W/12V = 1.2A
    So if the led strip can power by 9V, but the current will not light up too long, since the current only has 580 mA.
    If you have adjustable power supply then you can power the led strip from 8V.
     
  13. lone.vaas

    Thread Starter New Member

    Mar 14, 2016
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    @#12 thanks for the info!
    @ScottWang Yes i managed to light it up with a 9 V battery but anything less (like a 6V ) doesnt do a thing. of course it doesnt light up as much.
    It isnt an RGB one. Photo attached. could you elborate on what you mean by an "adjustable power supply" ? would that be a DC current?

    I managed to make the circuit as mentioned by @Dodgydave and it works great!

    Any idea on what kind of circuit i would need to build one with a rechargeable 9V battery?

    20160315_230211_1024x576.jpg
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Just the same circuit with a resistor in parallel with the 9v diode, this will charge the nicad/nimhi up, try a 68 to 100ohms.
     
  15. ScottWang

    Moderator

    Aug 23, 2012
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    Adjustable power supply -- the meaning at here is that any kind of power supply the output voltage can be adjust as 0~15V or 0~30V, and with dc current, etc...

    Does the led in series with a resistor and in parallel?
    Could you measure the value of resistor without power up?
    Could you measure the total current when you power up the led strip? (the A meter set on 10A range)
    Measuring the current:
    +V → (+) Ameter (-) → (+) Led strip (-) → Gnd(or 0V)
     
  16. lone.vaas

    Thread Starter New Member

    Mar 14, 2016
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    @Dodgydave is this the kind of circuit you're talking about?

    Could you explain to me how the resistor is able to charge the battery?

    Also, if the switch is off, in the attached circuit diagram, will the battery still charge?
     
  17. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yes it will still charge, the resistor drops the remaining voltage above 9v so approx 3.6v for a rechargeable battery at 68ohms will give 52mA charge current and will decrease as the battery charges up, 100ohms will give 36mA and decrease as charging up.
     
  18. #12

    Expert

    Nov 30, 2010
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    The resistor doesn't charge the battery. The 12 volt supply charges the battery by pushing current through the resistor.
    This is the same as reverse leakage through the diode, but massively increased.
    I also want you to notice that alkaline batteries are not rechargable. If you persist in this, the alkaline battery will probably puke on your desk.
    You are much better off with a NiCad battery if you want to charge it.
    Then again, a NiCad 9V battery is designed with a little less voltage than an alkaline battery and you might get into trouble with not having enough voltage for your LEDs. Just as the 6 volt battery doesn't work at all, the NiCad will be delivering about 7.8 volts to the LED strip. That might cause a problem.
     
  19. lone.vaas

    Thread Starter New Member

    Mar 14, 2016
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    @Dodgydave @#12 Thanks for the help guys, I'll do a little research on the 9V rechargeable, so far I can only find a 300mah battery, no idea if that will be enough to light the strip.
    @ScottWang I have very little experience with a multi meter and have no idea if i was doing the right thing, i tried to measure the charge across the LED strip and I got a reading of 1.3 (?) when it was powered up and then i heard a high pitched noise ( no idea where it came from) then i lost my nerve.:confused:
     
  20. ScottWang

    Moderator

    Aug 23, 2012
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    Show me what is your multi-meter, the brand and ID number, a front photo or the links for the multi-meter.
     
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