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Better reverse polarity protection?

Discussion in 'General Electronics Chat' started by jst3712, Oct 6, 2008.

  1. Leftyretro

    Leftyretro New Member

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    Well I like the suggestion that JimB made a few posting back. Have the main power route through the normally open contacts of the relay to the circuit to be powered. Put a diode in series with one of the coil contacts. The relay will only close with correct polarity is applied and will then transfer the high current to the load through it's contacts. The relay can be mounted externally or if the equipment is large and important enough, the relay and it's coil diode can be mounted internally.

    12vdc automotive relays can often be found at very reasonable prices as this example:

    12V SPDT 30 AMP AUTOMOTIVE RELAY | AllElectronics.com

    Lefty
     
  2. kchriste

    kchriste New Member Forum Supporter

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    And if you are really clever, you put the units power switch in series with the relay coil also. This will allow you to switch 25A with a small power switch and save on idle current when the unit is off.
     
    Last edited: Dec 17, 2008
  3. JOE--B

    JOE--B New Member

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    reversed Polarity P

    Thanks for all your replies I m really looking into these good ideas.
    however would A SSR. work? I guess it wouldn't be any different than using A diode in series, the ssr has A ≥ 1V drop that is what the data sheet says but when I tested it, only had a .4 voltage drop and it seems it has its own reverse polarity protection. thanks again guys.
     
  4. dave

    Dave New Member

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  5. Boncuk

    Boncuk New Member

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    You won't have to swap the drain-source connection - just use a MosFet without drain-source diode. There are plenty of them.
     
  6. Boncuk

    Boncuk New Member

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    Hi,

    mostly reversed battery protection is required for household stuff requiring little current flow.

    When powering an expensive current consuming device it should be double checked if the polarity is correct.

    Here is a cheap alternative to protect curcuits up to 40V and 1A, the Schottky-Barrier diode PMEG4010ER (NXP semiconductor).

    Here are some important data: VR=40V, VF (at IF=1A) 430mV (max 590mV), IR (at VR=40V) 10µA (max 50µA), part dimensions (body (SOD128)) 5X2.3X1mm (LXWXH)

    Hans
     
    Last edited: Dec 20, 2008
  7. flat5

    flat5 Member

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    "or does the diode die only when it wants to kind of thing? "

    Yes, only if it feels suicidal that day.
     

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