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  • Capacitor idea

    I'm not real familar with how a capacitor is suppose to work, but from what I understand, it holds a charge. And when the amp pulls more than the battery can supply, it capacitor supplys the power, so that there's less drain on the battery. What I'm wanting to know, would it be possible to use a capacitor with the Opus. It'd be like:

    battery<------>capacitor<------->Opus<-------->computer

    Would this let the system run longer when the car is off, without draining the battery, or at least not as quickly? Also, does a capacitor help 'clean' up the power, lessen the fluxuations(sp?)?

  • #2
    Re: Capacitor idea

    Originally posted by GezusK
    I'm not real familar with how a capacitor is suppose to work, but from what I understand, it holds a charge. And when the amp pulls more than the battery can supply, it capacitor supplys the power, so that there's less drain on the battery. What I'm wanting to know, would it be possible to use a capacitor with the Opus. It'd be like:

    battery<------>capacitor<------->Opus<-------->computer

    Would this let the system run longer when the car is off, without draining the battery, or at least not as quickly? Also, does a capacitor help 'clean' up the power, lessen the fluxuations(sp?)?
    Naw mon,
    those caps just "Assist" the 12 Volt power.
    they hold a charge but I dont think there would be any benefit for computer shutdown.
    America...
    just a nation of two hundred million used car salesmen with all the money we need to buy guns and no qualms about killing anybody else in the world who tries to make us uncomfortable.

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    • #3
      You would need an extremely large and expensive capacitor. People would use capacitors to start their car, if a battery wasn't so much smaller and cheaper. So the answer is that it's possible but not feasible.

      And yes, capacitors can be used to filter power supplies.

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      • #4
        For starters your diagram is incorrect, please try to use the search feature as this topic has been beaten to death already. I posted a diagram a little while ago with the correct setup.

        Code:
        battery ----- diode --------------opus--------computer
                                   |
                               capacitor
                                   |
                                   |---ground
        You have to place a diode in the circuit, and the capacitor goes between the +12V main and ground. If you don't use a diode then the capacitor will just discharge into the car's main electrical system which completely defeats the purpose. If you can manage to get a rather large capacitor (like soda-can sized, or around 45,000uF at a rating of at least 20V) then you can get about 1-2 seconds of computer use out of that before it discharges, which is basically long enough for your car to start without rebooting the computer, that's the extent to energy storage you'll get. The problem with this setup is that you need to use a diode which has a forward voltage bias on it (meaning it "looses" 0.5-0.7V in order to provide the one-way-only circuit), which means you loose a few watts of power, and the voltage input is lower. Your car rests at about 12.5V when fully charged, however after a little bit of use it will start to drop. Most power supplies have a build in low-voltage cutoff, so using a diode will drop the voltage by 0.7V, causing the cutoff to happen sooner than without.

        So to answer your question, using a capacitor will actually shorten the amount of time that you can use the computer with the car turned off.

        To answer your second question, capacitors are very effective at filtering out very low current AC voltages, however the problem with car automotive power systems is that they are very noisy and have a lot of DC spikes, a capacitor will only do minor smoothing out of those, but won't come close to eliminating them.

        check out www.howstuffworks.com it is a really good site and has a section on capacitors.
        IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

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