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Thread: Inverters and Cranking

  1. #1
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    Inverters and Cranking

    I am aware that I can use a VIA EPIA board and get a power supply and something to regulate a 12v feed to it that will survive engine cranking. Will using an Inverter perform the same function or will it work differently?

    Fitting a fully fledged desktop pc appears to be cheaper to fit than a mini itx one, which is why I ask.

    Thanks

  2. #2
    Maximum Bitrate fantomas's Avatar
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    it depends what the input range of the regulator or inverter is and what the voltage drops to during crank. my inverter won't survive crank so i plan on going with an opus this summer when i buy a new car.
    rebuilding carpc... kinda..

  3. #3
    Variable Bitrate Osiris's Avatar
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    Seems to be with inverters, there can be a several factors to wieght in when deciding if it will suruvive crank or not. Im using a five gauge wire and a 400watt inverter and it survuves everytime.
    Osiris Networx

    --Tuning is all about price vs performance. You've got to find your own medium.--

  4. #4
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    So I could use an inverter, but theres no gaurentee it will survive cranking. Does anyone know what factors would affect this? Is there any way of powering a full pc of say 300w with a regulated 12v supply without using an inverter, as the Opus solutions and similar only go up to 90w as far as I know. Does the inverter out of interest supply a regulated supply?

  5. #5
    Variable Bitrate Osiris's Avatar
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    Opus goes up to 150watts...

    I would venture to say that if you have a healthy battery, (1)enough current going to the inverter (i.e. bigger power wires), (2)the inverter doesn't draw too much, (3)and you have enough voltage overhead, then you should be able to survive crank in theory. I am running 5 gauge wire to the inverter directly off the battery. The inverter is a Coleman 400watt inverter that would supply that rated number at max. My power supply is 200watts at max, therefore being that theres more than enough overhead for the inverter to supply to the computer.
    Osiris Networx

    --Tuning is all about price vs performance. You've got to find your own medium.--

  6. #6
    MySQL Error MatrixPC's Avatar
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    Quote Originally Posted by custardbomb
    So I could use an inverter, but theres no gaurentee it will survive cranking. Does anyone know what factors would affect this? Is there any way of powering a full pc of say 300w with a regulated 12v supply without using an inverter, as the Opus solutions and similar only go up to 90w as far as I know. Does the inverter out of interest supply a regulated supply?
    Another way to find out for sure is try it.
    There are couple things you should keep in mind.
    - Cable size. The bigger the better (4AG is better than 8AG) to connect from the battery to inverter and the shorter the cable is the better.
    - Car battery. The higher the Cranking amp is the better (1000+ CCA is better than 800CCA). And the battery must be in good condittion (NEW).
    - Car Starting system. The faster the car can start, the less power drain from the battery to the starting motor.
    - Last but not least. The inverter itself. More efficiency is better of course. The inverter LOWER working voltage or range. Working voltage from 10V - 18 Volt is better than 12V - 18V.

    Inverter wattage is depend. Sometime bigger is not always better. Get one that has continuous wattage at least 1.5 or 2 time the PSU require. If you use a 200W PSU, get an inverter that has at least 300W continuous.
    And in general, the GROUND wire to the inverter should be at least the same size as the hot wire or BIGGER and as SHORT as possible.
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  7. #7
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    Brilliant answers and just what I am looking for, looks like an inverter as opposed to an Opus style solution is what I am looking for. What sort of voltage drop could I expect during cranking?

  8. #8
    Stank Cheese n8scstm's Avatar
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    I was at Costco this weekend and they had a 1500 watt inverter for $85. It's the same one I have. It cant hurt to go bigger that way youll have room to grow. Or if you ever need to power a drill or something while doing your install.
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  9. #9
    FLAC
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    Car Cranking Equation

    Ok all. How big of a cranking cap do you need?

    That depends on
    A: The Load of your System.
    B: The Voltage of your Battery when you go to Crank
    C: The cutout voltage of whatever your powering.
    D: How long you think you'll be cranking for.

    Equation.

    Vout = Vin * e^(-t/(R*C))


    That means if you have a voltage at your battery of Vin, The cap C will discharge through the load R and reach a voltage Vout after time t.

    If you solve for C you get:

    C = -t/(R*ln(Vout/Vin))


    So, from above.
    A: if load of your system is 5 amps, 12v/5amps = 2.4 Ohms. R = 2.4 ohms
    B: voltage of your battery 12 volts when it is sitting there. Vin=12 volts
    C: cutout of my inverter is 10.5 volts, but my schottky diode is .5 volts so really it is 11 volts. Vout = 11 volts.
    D: I think it cranks for 1 second, so t = 1

    Plug it into the equation and you get 4.7 Farads.

    Maybe you only need .5 seconds of crank protection, thus 2.5 farads. Etc.

    Hope this helps UNDERSTANDING.

    -Jeff
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

  10. #10
    Variable Bitrate
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    You can use out Tank EZ circuit with a small battery to keep any pc running while cranking the car.

    KyferEz
    TheCarPCStore.com - Power Controllers (SDC), Inverters, Tank Circuit, GPS, OBDII, CarPCs, and more!
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