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Reverse Current Protection

Discussion in 'General Electronics Discussion' started by dallypost, Jan 27, 2012.

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  1. dallypost

    dallypost

    5
    0
    Jan 3, 2012
    I am developing a 12 VDC version of an AC powered product that we currently sell. This system will be driven with a 12 volt automotive type battery. Connecting the battery backwards will fry a lot of components. I am considering a diode on the ground cable to prevent reverse current flow. However, this type of battery is capable of sourcing a lot of current. Therefore diode failure and heat are two considerations that I have. I am interested in how you might handle reverse current protection in a circuit such as this.

    Thanks
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,480
    2,828
    Jan 21, 2010
    Install a fuse, then a series diode, then a reverse biased diode (or even a Zener) across the supply rail.

    If the first diode fails and the input is reversed, the fuse will blow. A failure of the diode is likely to be to short circuit which will continue to blow fuses.

    You can also do some magic with mosfets, and their low Rds(on) means they may be under less stress.
     
  3. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi, converting an AC powered product to something automotive/embedded can require more than a reverse battery protection. You can have high transient and load dump (when cranking) this can burn you supply front end or leave your µC, if any, in unknown state due to small supply interruptions. Robust watchdog/brownout and firmware modifications can to be implemented. Also temperature range is wider for automotive products and you can face vibration, dust, grease... issues.
    Olivier
     
  4. dallypost

    dallypost

    5
    0
    Jan 3, 2012
    Thankfully, this is not going into a car. We will simply be using an automotive battery to power this portable device. The biggest current draw on the system will be a 1/3 HP DC motor that has a stall current of roughly 40 amps. I have placed a 22uf, 10uf and .1uf bypass cap at the power pin on the circuit board. Additionally, I have placed a .1uf cap at the power pin for all sensitive components, including an AVR processor, RF receiver, RF decoder, and an external EEPROM.

    Is there something more that you might suggest.

    Thanks
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,480
    2,828
    Jan 21, 2010
    The DC motor may put some pretty awesome noise on the power supply, so Olive2222's warnings still have merit.

    I'd be looking at some fairly significant protection of your circuit from spikes.

    Keeping the wiring to the motor separate from that to the electronics would be another thing.
     
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