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Car battery voltage drop

Discussion in 'Power Electronics' started by dontfeelcold, Feb 24, 2015.

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  1. dontfeelcold


    Feb 23, 2015
    I am in the process of setting up sensors in my car to monitor the engine so that I can tune it.

    One of the sensors is a thermocouple. The thermocouple signal gets boosted by an amplifier that needs 14.5v to 32v to get the maximum reading from the thermocouple. The other is an oxygen sensor whose controller runs from 10.5v to 19.5v. The combined maximum current draw is 3020ma but I would like some more headroom.

    My car while idling runs at 14.8v but it drops substantially for a split second when another component of the car is activated (hydraulically controlled 4WD). This keeps happening from time to time as the car needs to keep pressure in the 4WD hydraulics.

    So I will need something that can give a consistent output voltage that satisfies both devices despite what happens on the input.

    Is there a type of circuit that will do this? I am looking to do the circuit myself but need some help to understand what kind of circuit I will need.
  2. shrtrnd


    Jan 15, 2010
    I think what you're looking for is a 'voltage regulator' circuit.
    Your car voltage regulator circuit does fine for the car's electrical system requirements.
    You appear to need a separate voltage regulator circuit with tighter tolerances for your tuning tests.
    My only question would be, when the car is running normally and it experiences sudden intermittent voltage drops, would adjusting the car's tuning under steady-state voltage conditions, cause you problems when you've
    tuned your circuits, and then they see the intermittent voltage drops in normal driving conditions?
    I'm thinking it might be a better idea, to look at the possibility of compensating for the sudden voltage/current draw when your hydraulics kick-in during normal driving.
    I can't think of a device for that off the top of my head, maybe someone else here can. There used to be a lot of electronic devices made for suppression of electrical surges in automobile electrical systems, but with all
    the fancy advances in car electrical systems, the market seems to have dried-up. This might be something simple that you'd have to build yourself, to supress the sudden voltage drop of the hydraulic system start-up.
  3. Gryd3


    Jun 25, 2014
    Any car audio shop would tell you to use a Capacitor. And while I don't actually disagree, I do need to mention that it will only help for a tiny fraction, and they way most of the shops hook these things up, they back-feed into the car's electrical system... so.
    If I were you, I would run an auxiliary power line from the batter with a Fuse and a Diode in-line. From there, I would connect either a large Capacitor, or a small SLA battery. (Think mini car battery... from a motorcycle for example!).
    The additional battery should be fused as well. This will allow your capacitor or additional battery to charge with the vehicle, but if the vehicle voltage drops, the diode will prevent it from back feeding into the car, allowing you additional gear to run a little smoother. This is not a perfect solution, as there will be a slight dip in voltage, but nowhere near what you have been experiencing. Additionally, you can use a voltage regulator to make the output voltage that much more stable.

    *(Food for thought. You may be able to run the heating element from the O2 sensor separately... as a momentary voltage drop will not affect the temperature.)
  4. dontfeelcold


    Feb 23, 2015
    Since looking into things further, I am unsure if running a separate battery charged by the alternator but isolated to the rest of the car will smooth out the voltage drop when the hydraulics momentarily run. My understanding is that the the alternator runs the car when it's running, not the battery, so a second battery will still drop it's voltage but only down to its resting voltage.

    Will a boost converter be able to maintain a stable output despite the 2-3v drop? Do I need to be more specific on the actual voltage drop and the time it is low?
  5. Gryd3


    Jun 25, 2014
    Alternator typically runs things at 14.4V .. Momentary drops caused by the hydraulics regardless of how low it drops the voltage will allow the equipment to maintain a high 12V range at minimum. A capacitor will allow the higher voltage to be used... but at a much shorter time-frame.

    You can certainly use a boost converter for this application, there may be a slight dip, but it should not be noticeable.

    I guess the best thing to start would have been asking how stable you want it to be?
    The backup battery will prevent it from dropping below 12.2-12.6V, but it will still drop from 14.4. The Capacitor will do a better job at holding 14.4V but only for a very short time. The Boost converter is a more complicated item, but would provide the smoothest output.
  6. Kiwi


    Jan 28, 2013
    Try an ebay search for "150W-DC-DC-Boost-Converter-10-32V-to-12-35V-6A-Step-Up"

    Hopefully the drop in battery voltage during cranking won't cause it to drop out. Cheap enough to try.
    Last edited: Feb 27, 2015
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