AC boat

Discussion in 'General Electronics Chat' started by sdowney717, Jun 30, 2013.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
    Title is AC reverse polarity phase detect circuit for boat power

    I have a boat
    The boat has a reverse phase polarity circuit using an alarm and light.

    The new rule is a 25000 ohm impedance resistance must be maintained between neutral and ground wires.

    The current old alarm has 0.5k resistance.

    I also want to power a SPDT 12 vdc relay to turn my 4 pole 35 amp main disconnect relay off and on. So that power to the boat is turned off and the alarm sounds if power exists between neutral and the ground wires due to reversed polarity phase condition.

    I can do it all myself using a relay etc... BUT the circuit will have a low resistance like 300 ohms not anywhere near the 25,000 ohm rule.

    So what can I do? Can anyone show a circuit that can maintain that high 25,000 ohm impedance and still allow switching a relay and turning on the alarm?

    Here is pic of alarm.
    Pic of relays before being wired up

    and more info on what I am talking about here

    I have a functional light as described in article. The other problem with joining neutral to ground on a boat is power may flow from ground wire through your body back to the source. Especially if the ground wire at the shore plug breaks.

    Last edited: Jun 30, 2013
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    First off, your app skirts into our TOS by violating the "no line connected device" rule... Here's the best answer I have keeping that term in mind.

    Put an opto isolator & resistor between neutral and ground. 25K across the peak line voltage (call it 155 V on the low side) gives 6mA, good enough to fire an opto isolator. That gives your 12V system isolation from the AC, and a signal to detect when "neutral" is swapped with "hot."

    The output of the opto is not powerful enough to pull in your (so far unknown) (to me anyway) relay. It should be simple enough to add a transistor and such to boost the current level and filter out the line pulses.

    If this thread survives I'm sure others will present the whole circuit (don't use any that have a 555 or any IC, that is just unnecessary). I'll have some time later on to pound something out.
  3. sdowney717

    Thread Starter Member

    Jul 18, 2012
    Hi thanks, I hope it does survive as I need some practical help.

    I have some opto isolators from an inverter I repaired that I ordered and they sent me way too many.

    They are EL 817
    Last edited: Jun 30, 2013