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Old 31-08-2010, 18:53   #1
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AC Reverse Polarity Indicator

Having to rewire my boat. I have Charlie Wing's book, Boatowner's Illustrated Handbook of Wiring. On page 288, his first project is the two lamp AC Reverse Polarity Indicator. He shows the "GREEN" part of the circuit as: Hot ->Resistor -> Lamp -> Neutral. His "RED" section is: Neutral -> Resistor -> Lamp -> Ground.

Wing's Diagram

But Technical Brief "Reverse Polarity Indicators" describes a one lamp system. It show the circuit as : Neutral -> Lamp -> Resistor -> Ground.

OBSERVATIONS: The lamp and the resistor's position are reverse on the two circuits.

Questions: 1. Does the position of the resistor make a difference?
2. Does having the LED vs. Neon Lamp make a difference?


p.s. Sorry I couldn't embed the Wing diagram, I couldn't get it to work that way. nb

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Old 31-08-2010, 19:07   #2
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1. Given its wired in series, it makes no difference where the resistor is located in relation to the LED. The lamp only knows the potential difference between its two contacts. I would though put the resistor first and then the LED for safety the LED's terminals are not at 120 volts just in case you accidentally touch it.

2. No, what matters is the voltage rating for whichever type of lamp you choose.

Nice diagram by the way.


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Old 31-08-2010, 19:18   #3
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Diagram should be came from Blue Seas. The other is from Charlie Wing's book.

Thanks again,
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Old 31-08-2010, 19:47   #4
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I 2nd put the resister first regardless. The led polarity doesn't matter because on ac it will be lit half the time, (flickers 30hz). If the resister is sized right for what you use it should be good.
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Old 31-08-2010, 19:49   #5
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It doesn't matter whether it comes before or after. It is in series. What matters is the total load (resistanc eon that circuit.
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Old 31-08-2010, 20:23   #6
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Thanks everyone. They are already soldered together. I just needed to know which way to install them. I think I like resistor first.

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Old 31-08-2010, 20:40   #7
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I don't the book with the ref of to two indicators but it is likely to have used a green indicator showing correct wiring (good) & red for reversal ( bad) with a further indication of both lights on indicating faulty earth. The cost of a green + red neon indicators is only a few cents & you can get for that the neon light, resistor built in & the lamp assembly. Works like this. green light means correct & power is on. red means reversed active & neutral don't use until fixed. both on don't use not earth fix. no light check for power outage.

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