turning 2x12v into 1x24v

Discussion in 'The Projects Forum' started by scampo77, Jul 23, 2011.

  1. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    can anyone reccomend diodes large enough to drive 500watt driving lamps

    i would like to take 24 volt from 2 12v batteries but only to drive a 1 lightbulb i was hoping to just steal a diode pack from a alternator but i have no idea if it will be big enough or if anyone has a suggestion asto a easier cheaper solution.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You can use a group of 1 amp diodes in parallel to increase the power levels they can handle.
     
  3. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    is that a good idea? if one fails all the rest would start falling over like dominos plus with a 12v system i would need around 40 of them
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    What are the diodes for? Are u sure you mean 500W :eek: driving lamps? Not something like 55W?

    If you want 24V from 2x12V batteries just put the batteries in series, no diodes needed
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    you did ask for a cheaper solution, and most people have lots of small 1 amp diodes, or can get them by the dozen for a dollar. Besides, if a diode fails because of too much power, it fails 'open', so no damage to your light would result. Figure out how many amps the light will require and use 50% more 1 amp diodes than that number.
     
  6. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Yes, a single diode has the same chance as 4 small diodes in parallel to fail so it doesn't really matter.

    If you want to drive 500W with 24V then the current necessary is about 21A.
    So a single diode rated at 30A should do. Or parallel three 10's or two 15's.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I too do not understand why everyone is talking about diodes.
    why can you not just put the batteries in series?
     
  8. praondevou

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    Jul 9, 2011
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    Thanks Strantor :), can somebody please explain?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Are you planning on using these driving lamps in a vehicle?
     
  10. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Diodes have been known to fail short-circuit. A massive over-current can blow a diode open, but a moderate one can just as well fuse it into a short. Diodes are also are not very good at sharing current, an effect known as current-hogging.

    On the whole, I would not recommend using diodes in parallel. That said, I would like to know why the OP needs diodes in the first place!
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    There's 3 for "why the diodes?" - I feel an answer coming....
     
  12. BrainFog

    Member

    Jan 24, 2011
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    I won't bother asking why the diodes.

    The fact that diodes can't be used in parallel is one of the first things I learned. I remember reading that all the current just goes through one, massively overheating it and leaving the others idle.
     
  13. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    i have 2 independent charging systems with 2 independent alternators. both are regular 12v charging systems and the rest of my car runs off of 12v like most cars. i was hoping that there is someway to take 12v from each system and add them together to get up to the 24 volt without a massive facelift to my already customized charging system.

    i figured if i could take voltage without charging the other this should be where i start looking so i thought diodes.

    yes these are 24 volt lamps and yes they are 500 watt each.

    http://www.normanlamps.com/product_info.php/cPath/386_594/products_id/9538
     
    Last edited: Jul 23, 2011
  14. praondevou

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    Jul 9, 2011
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    Are they completely independent, no connection whatsoever between the two systems? If the minus of each charging system is connected to the chassis, then this won't be possible with diodes.
    The two systems have to be in series.
     
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What is the intended use of these powerfull lamps?
    As you might know we do NOT allow automotive modifications.

    Bertus
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    Bertus,

    From reply #13:
     
  17. Jaguarjoe

    Active Member

    Apr 7, 2010
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    The frame on most of the common alternators is also the ground, or (-) connection. If both of your alts are mounted on the engine block then their (-)'s are connected together. This will not allow you to combine the two 12v outputs into a single 24 volt source.

    Diodes in parallel are like BJT's in parallel, the lowest Vbe gets the most current.
     
  18. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    if i insulate the alternator and completely isolate them from each other can i do it then? this truck is a service truck and i use the lamps for night time repairs. yes it is a car but its not insured or on the road.
     
  19. iONic

    AAC Fanatic!

    Nov 16, 2007
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    A question I asked myself, but should have asked the OP.
     
  20. scampo77

    Thread Starter New Member

    Jun 24, 2011
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    because the way that i pictured this working was if i took the first 12v battery on a alternator put a diode between the positive lead and then added another battery and connected the diode to the negative lead of my new battery i could get 24 v without disrupting the original charging system. from there i could charge 24v into second battery
     
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