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Better reverse polarity protection?

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hi! I'm looking for a reverse polarity protection circuit diagram can any body help? it needs to be able to handle at leas 25 amps at 12 volts DC. any suggestions please.

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
 
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.
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.
 
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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.
 
It won't.

Under reversed supply polarity, the MOSFET is not biased ON but the internal parasitic drain-source diode would conduct and power/destroy the load.

However, if we swap the drain-source connection, then it will work.

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