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Inceasing of current in a DC circuit.

  1. Jan 8, 2012 #1
    Given the scenario that there is only 1 DC voltage source is there a way/ circuitry that can increase the current. I know using a low resistor could induce a higher current in the circuit, but here is the trick, the resistance is fixed. Anyone who know how to do it, please do shed some light on this.
     
  2. jcsd
  3. Jan 8, 2012 #2

    vk6kro

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    It is possible, but you need some circuitry to do it.

    The circuit is a BOOST regulator. This starts as an oscillator and the AC voltage from this is stepped up to some required value and then rectified to give DC again, but at a higher voltage than you started with.

    Other types of BOOST circuit use an inductor which they develop a large voltage across (by changing the DC current flowing in it) and then this high voltage is rectified and filtered to produce a higher DC voltage.

    Being a higher voltage it will now put a higher current into the same resistor.

    Did you have an application for this, or was it just a casual query?
     
  4. Jan 8, 2012 #3
    @vk6kro
    Thanks for the reply,
    there is an application for it, to step up current enough to make a 12V motor run faster, because the source actually are solar panels and has a high dependency on sunlight.

    As for the boost regulator, i will require an AC voltage, and it is very not suitable with the new scenario where Solar Panels are use, efficiency alone is not that high, and AC conversion probably will drop the efficiency enough more..
    The other type, seems doable, but i will need more information on it..

    So the new scenario here is DC source comes from a low efficiency Solar Panel, and to drive a motor on wheels to push a load (ie Remote controlled car.)
     
  5. Jan 8, 2012 #4

    Bobbywhy

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    jungou93, you have confused the issue: you asked for a circuit to increase current, and
    vk6kr0 gave you a boost regulator. This, however, will NOT increase POWER delivered to the load. There is no free lunch! You cannot create energy!

    You say your solar panel does not output sufficient POWER to drive your motor load. If there is insufficient power output from the solar panel, no circuit can create more for you.
     
  6. Jan 8, 2012 #5

    vk6kro

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    Yes, the power source has to have spare current capability. However, a higher voltage will give more power into the resistor, provided the supply voltage can provide the extra current to the regulator.

    You can use either type of boost regulator with a DC source.. The first type is used where a large step-up in voltage is needed. The second is used when the required output voltage is not far from the voltage of the source.

    There are dozens of these regulators on Ebay and this is an example only:
    http://www.ebay.com.au/itm/DC-DC-Ad...Electrical_Test_Equipment&hash=item3cba522039
    This one is 86% efficient.

    However they do generate DC, which is what you asked for originally.

    Here is a higher powered version which can charge a 24 volt battery from a 12 volt battery. Again, the power source has to have excess current capability to provide the extra power supplied.
    http://www.ebay.com.au/itm/12-35V-D...Electrical_Test_Equipment&hash=item19c7a5f5ec
    $8 delivered isn't bad.
     
  7. Jan 8, 2012 #6
    Thank you guys for the explanation and help, my source do not have an spare current, it has too much dependency for sunlight.(sunlight determines the current and voltage, no light no power)
     
  8. Jan 9, 2012 #7
    Sorry, my panels are having a setting of 8V 2A, however producing about 1.4A, this having a spare of 0.6, is this enough for the inductive booster?
     
  9. Jan 9, 2012 #8

    sophiecentaur

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    If your spare panels have no spare capacity then you can't get any more power from them. This has already been mentioned but it may mean that your proposal is a non starter.

    But if you are prepared to have your motor run for less time, then you have a chance. One possible solution for doubling the volts to your motor would be to have two 6V batteries in series and switch your charging current alternately from one battery to the other. This would involve switching both positive and negative lines from the PV panel, which would be 'floating' in any case. This would be a relatively low tech solution and could involve a simple (double pole) relay and timing circuit. The only proviso would be that you would need to monitor the state of charge of both batteries and keep them more or less equal by adjusting the ratio of charging times. You wouldn't want one battery to become significantly more discharged than the other.
     
  10. Jan 9, 2012 #9
    Note - the movement in the solar industry is to use a boost circuit to maximize power draw from the panels AND provide a regulated DC Voltage ( usually for the AC Inverter).
    If you are looking to drive a motor - and the motor is not continuous, boost the DC, Charge a battery, then run the motor from the battery.

    If the motor is continuous and it needs say 20W - the solar panel you describe will not work. Also - the ratings on solar panels is under ideal conditions, (Light AND temperature) these nameplate values are almost never achieved in the real world - esp not continuously.
     
  11. Jan 14, 2012 #10
    This is pretty helpful. My school is actually making sure there won't be a battery on board the remote controlled solar car. And per its one big issue my team have encountered
     
  12. Jan 14, 2012 #11
    Hello junguo93: A car ( any car ) presents different challenges, more than just Voltage vs current, and nameplate ratings - weight being one of them. For an RC car I would at least consider a super cap then evaluate cost / physical size / weight / energy vs a battery - possibly a small LiIon battery is all you need.

    Also - you need to REALLY understand the characteristics of the motor in the application, full load current (steady state or rated ) is not the whole story. Use a battery and measure the current the motor needs to accelerate the car from a stop at it maximum weight. This current will probably exceed the capabilities of the solar panel, so you need to design around that (some form of energy storage ) or the car will never get moving. ALSO - probably not a concern due to the voltages you are using - but when the car is coasting - the motor will generate voltage - to properly engineer the system you need to know what the maximum V ( back EMF) the motor will generate - and make sure all of the components are rated to withstand that maximum voltage.

    Also - note, the solar panel will radiate energy back, so you need to make sure the panel has a blocking diode to prevent current from flowing back into the panel, from the energy storage. Many - panels have this incorporated, but if you are using raw components I would sat this is a necessity - typically this is a Schottky diode due to the low Vf ( which will rob you of power when current is flowing through it ) -- A small relay can also do the trick....
     
    Last edited: Jan 14, 2012
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