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Thread: Power Inverter left plugged in?

  1. #1
    Maximum Bitrate KyleYankan's Avatar
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    Power Inverter left plugged in?

    Hi everyone. I have a quick question. If I leave my power inverter plugged into my battery, and my PC plugged in the power converter, does it drain my battery? Like, even If I turn off my PC and nothing is running o nthe inverter? Does it still contain a small amount of drain?

  2. #2
    Low Bitrate cavramair's Avatar
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    If the inverter is running, then yes, its draining your battery. They way I worked around this is I installed a relay between the power lead of the power inverter. That way if the car is on, the inverter will run, but will shut off when I turn off the car. Saves draining your battery, which my inverter does real quick if let run while the car is off or on accesory.
    -Drew Taylor
    2000 Grand Am GT PC

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    MySQL Error Scouse Monkey's Avatar
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    Oh good greif! this has been asked many times! Did you even try to search? I doubt it!

    Of course it will use some power. Only way it won't is if you turn it off.

    You can make a simple circuit laike cavramair describes about or if you add a second relay powered by the PSU 12V line (off a molex) then the Inverter will stay on until the PC shuts down (handy for when you are in a rush to get out of the car).

    Or you can buy a startup/shutdown controller to fully automate it. for how these work (you can buy them from the mp3car.com store)

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    Maximum Bitrate KyleYankan's Avatar
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    I did search for it, however I didn't find anything. I admit, I only spent a minute searching though. I'm thinking about a double-relay now.

    2 Relays in parallel, so if either turns on, the inverter powers up.
    I'm thinking about using a DPDT relay hooked up to my ignition. One pole hooked up to the inverter, the other to my power button/circuit to hit power button. That way, when I turn my car off, the comptuer gets the power-off signal. Then a relay on the signal line of the parallel port, which will turn off when the PC turns off. So then both relays will be off, and the inverter will shut off. this has probably been done before, but I've been tinkering with designs in my tiny little mind.

    Does anyone have a circuit to "pulse" the power button, when a relay is thrown? Like, kind of turning a rocker switch into a momentary switch? :-P
    I'm gonna search now.

  5. #5
    Maximum Bitrate KyleYankan's Avatar
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    Here's another quick question:
    I have a 400watt inverter. I have a 750 amp battery.

    Now, I wanted to know how many amps my inverter drew from my battery, so I would:

    400 watts / 12 volts = 33.3 amps?

    It seems to me that 33.3 amps is way below the 750 provided by my battery. Is it still enough to tank my 'puter though?

    Or is my math here completely wrong? I never really got watts too much. :-/

  6. #6
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    You're right. You don't get watts properly. From the Wikipedia: "It is the rate in joules per second at which energy is being converted, used, or dissipated." To derive that, you need to know a couple of things:
    1) What is the voltage (the electrical "pressure" in the system)
    2) What is the amperage (roughly, what is the "volume" of electricity being moved)

    What you calculated was the theoretical volume of electricy your inverter COULD draw from your battery. Your battery CAN supply a very large number of amps, for example, when cranking your car as starter motors need a large "volume" of electricity, measured in amps, to start.

    That does not mean your battery will send 750 amps to every device that you hook up to it. Imagine if this was true for your house. When you plugged in your vacuum cleaner to the wall, hundreds of thousands of amps would flow into it from the power grid. *Poof*.

    The "pressure" in the electrical system is voltage, NOT amperage. Imagine drilling a hole in the side of a very high pressure water pipe. The force of the water would be tremendous, however the volume that comes out would vary depending on the size of the hole. In really simple terms, your electrical device determines the size of that hole when you switch it on. If you switch it off, the hole is closed. (Yes, I know this is a tortured analogy. Apologies.)

    Voltage can and does fluctuate in the car, ranging from 10 - 15 volts roughly in normal operation, this is why people use voltage regulators to prevent their components from getting zapped when this happens.

    Second, if you search on "power calculators" you will find information on ways to find out how much your full up system will draw, which is probably of more immediate importance to you.

    Third, get a startup/shutdown controller (available at mp3car.com store), also known as DSSC (digital startup/shutdown controller) instead of messing with your own. You'll save loads of time and frustration.
    Quote Originally Posted by ghettocruzer View Post
    I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
    Want to:
    -Find out about the new iBug iPad install?
    -Find out about carPC's in just 5 minutes? View the Car PC 101 video

  7. #7
    Maximum Bitrate KyleYankan's Avatar
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    BugByte:
    I thought Watts = Volts * Amps.
    I calculated what my 'puter would use, 33 amps. So, if I used 33 amps out of 750, I have 712 amps left over for powering my starter/car?

    Also, I don't ahve $60 to blow on a startup/shutdown controller. I'd rather build a simple one myself, even if it menas running a momentary switch under my seat/in the dash to turn it on/off.

  8. #8
    ddn
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    New hobby time.

  9. #9
    Low Bitrate 273BeLow's Avatar
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    most invertors I've seen (and the one I have) shuts off when your battery drops >10v

  10. #10
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    Watts does = Volts X Amps. How many volts does your system draw? Let's say 12. How many amps does your system draw? YOU DON'T KNOW. If it's 5, you'll consume 60 watts. If it's 10, you'll consume 120 watts.

    I calculated what my 'puter would use, 33 amps. So, if I used 33 amps out of 750, I have 712 amps left over for powering my starter/car?
    No, you calculated how many amps your inverter could draw at maximum power. That has absolutely nothing to do with your computer.

    You need to know how many amps each component in your system draws. Or use one of the POWER CALCULATORS to figure it out.
    Quote Originally Posted by ghettocruzer View Post
    I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
    Want to:
    -Find out about the new iBug iPad install?
    -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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