Need a little help with a dc system

Discussion in 'General Electronics Chat' started by Sbarton, Nov 19, 2009.

  1. Sbarton

    Thread Starter New Member

    Nov 19, 2009
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    I need to know how to wire 6- 6 volt batteries to achieve 36 volts and at the same time how to get 12 volts across all six batteries. Or where to get a large amp transformer, I need to install a large power inverter which requires 100 amp at 12 volt dc.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You cannot simultaneously get 12 and 36V; by doing a series/parallel connection you can get either 12V (three sets of (two batteries in series) in parallel, or 36V (all six in series); but you can not do both at the same time.
     
  3. Sbarton

    Thread Starter New Member

    Nov 19, 2009
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    That's what I was thinking but I was not sure. Where could I get a 36 volt transformer that would bring it down to 12-14 volt dc and give me roughly 100 amps?
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What is the input for the transformer? If it is the 36V DC battery bank, then you will need a 36VDC to 12VDC "buck" dc-dc switching converter. These are relatively complicated, and utilize some hard to get parts, so buying one is usually the path of least resistance.
     
  5. Sbarton

    Thread Starter New Member

    Nov 19, 2009
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    Sorry I should have gave a little more info, I need to run 110 volt for power tools. The power inverter was bought already with out much thought:( the inverter requirers 12 volts at 100 amp when used at full compacity. I would like to pull power from all 6 batteries, and not just 2 of them.
     
  6. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    What is the battery rating?
     
  7. Sbarton

    Thread Starter New Member

    Nov 19, 2009
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    6 Volt, 232Ah per battery, they are Interstate workhorse 2200 deep cycle.
     
  8. zgozvrm

    Member

    Oct 24, 2009
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    You could, however, hook all 6 batteries in series to get 36 volts, then tap off any 2 of those batteries to get 12 volts. This would only give you 1/3 the power at 12 volts than if you were to parallel 3 series pairs.

    So, you could use 2 larger batteries (in series) to get the 12 volts, and 4 smaller batteries (in series with the 2 large ones) for 36 volts.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    What is the requirement of 36 volts? Is it a vehicle of some kind with a 36 volt system? If you have an engine, could you put a 12 volt alternator on it to charge your batteries?
     
  10. MikeML

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    Oct 2, 2009
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    Practically, this is a really bad idea, unless you are willing to build 6 chargers; one for each battery. Tapping a load off a subset of the batteries will make it such that you cannot charge them in series without overcharging some of the batteries in the string...
     
  11. Sbarton

    Thread Starter New Member

    Nov 19, 2009
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    It's our cushman tool cart aka golf cart with a box on the back.
     
  12. BMorse

    Senior Member

    Sep 26, 2009
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    How would you just "tap" off of those batteries wired for 36 to get 12? They are still all connected in series, so your "12" volt output "tap" would still have 36 volts:confused:....
     
  13. Sbarton

    Thread Starter New Member

    Nov 19, 2009
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    I can get 12 volts from any pair of batteries, however I want a way to pull from all six at once.
     
  14. zgozvrm

    Member

    Oct 24, 2009
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    Agreed. But I wasn't aware that he was trying to charge the batteries in place. In most applications, you remove the batteries and charge them separately.
     
  15. zgozvrm

    Member

    Oct 24, 2009
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    If you put six 6 volt batteries in series so that the negative terminal of battery #1 is in contact with the positve of battery #2, negative of #2 in contact with positive of #3, etc., you would measure 36 volts across the entire bank of batteries (positive of #1 to negative of #6). However, if you tap off any 2 batteries, you will have 12 volts (positive of #1 and negative of #2, positive of #2 and negative of #3, etc.)
     
  16. MikeML

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    Oct 2, 2009
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    Tapping isn't the problem, charging is.

    I would get a very big multi-pole switch or relay, and wire it to go from three groups in parallel, to all six in series. The switch/relay would need to be rated at ~20A. Configure for series for driving the cart, and then switch to parallel for running your power tools... You probably dont need to be running your tools while running the cart...:D
     
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