Connecting devices to 12 V battery while charging

Discussion in 'The Projects Forum' started by RicksD, Oct 14, 2013.

  1. RicksD

    Thread Starter New Member

    Oct 14, 2013
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    0
    Hi,

    I'm working on a project for a course I am on. Basically we need to charge a 12 V battery while powering a light bulb and a fan - I know it's strange...

    We need to do this using renewable energy from our grounds, I am using hydro power from a fast flowing river. Is it as simple as the below:

    Connect alternator / generator to water wheel
    Connect alternator to battery
    Connect battery to two switches
    Connect switches to the fan and light bulb

    That seems too easy, do I not need any regulators or something to stop too much power going to the light bulb / fan, or fuses??

    If anyone could point me to a tutorial or something where someone is creating a similar project that would be awesome.

    Thanks for any help you can give!
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,126
    3,048
    Probably not. The battery itself is a big "regulator" holding the voltage in a narrow range by accepting or delivering charge. As long as the system is not over-powering the battery, it won't matter much to the loads. Battery-only might be 12V, and battery-at-full-charge might be 14V. The loads can accept this small variation.

    But this all raises the questions:
    1) Does your generator make DC, or do you need a rectifier? You may need a blocking diode if there is not one already present.
    2) What keeps the generator from over-charging your battery?
     
  3. RicksD

    Thread Starter New Member

    Oct 14, 2013
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    0
    To be honest I didn't think about the battery getting overcharged; would a charge controller do the trick do you think?

    I am planning on using multiple small generators, if of course it is possible to connect more than one to the battery in order to charge it, a permanent magnet DC motor 12v.

    Do you think these will even provide enough energy to charge the battery?

    So even with multiple devices attached to the batter that require different voltages, I wouldn't require a regulator as the battery would handle this?

    Also I am guessing I would need to convert the power to AC, especailly if we advance to the next course and are require to hook it up to a household item?
     
    Last edited: Oct 14, 2013
  4. wayneh

    Expert

    Sep 9, 2010
    12,126
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    Yes, that's exactly what they're designed for. But to buy one, you need to know the range of inputs it needs to handle.
    You can use multiple sources supplying one sink (the battery). This is called "OR"ing together power supplies. The simplest way is to use a blocking diode on each one. If it can contribute, it will. Otherwise, the diode prevents reverse current.

    It matters little what I think. It comes down to an energy balance. You can pull from the battery about half of what all the generators produce. The rest is lost in various inefficiencies.

    Not for lights or fans. Sensitive electronics may need better regulation though.

    Yes, that's what inverters are for. But don't forget that still more energy will be lost when converting to AC.
     
  5. cornishlad

    Member

    Jul 31, 2013
    196
    25
    Is a standard 3 phase automobile alternator bigger than you are considering ? Most of them have the charging regulator built in. Hook up the battery and the charging light that's all you need.

    If you can get it to turn fast enough that is. An Alternator is a far better bet than a dynamo
     
  6. RicksD

    Thread Starter New Member

    Oct 14, 2013
    3
    0
    Thanks for the help Weyneh, I do have one more question...

    Would I need to convert from DC if I was just powering fans/lights, or it is only electrical equipment that says it needs ac power? If I read this correctly my laptop charges using DC power, so I guess the black box on the wire is an inverter?
     
  7. wayneh

    Expert

    Sep 9, 2010
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    There are many fan and lighting choices for DC, so I would definitely choose those rather than convert to AC with an inverter.

    Most laptop power bricks are SMPS (switch mode power supplies) delivering something like 19V DC. You could indeed supply that same 19V DC in some other way. However, some computers mate their supply to the computer and they need to see a specific chip in the charger before they will initiate charging. That's a dirty trick, IMHO, and fortunately I think it's somewhat rare.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    For 12V DC household electronic items, might try a RV, recreational vehicle, store; even 12V refrigerators.
     
  9. pooter

    New Member

    Oct 23, 2012
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    I rebuild automotive alternators. Any questions you have I would be glad to help you with.
     
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