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Old 22-06-2013, 07:21   #1
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Reverse Polarity LED

Hello,

Helping my mate that just picked up a 38 foot Island gypsy to restore...

There is not a reverse polarity light on the current panel. We would need to order a reverse polarity indicator/alarm from a supplier here in Hong Kong, taking 2 to 3 weeks.

Should be easy enough to make one tomorrow for the panel we started making today, from the parts I have on hand !!!

If memory serves me... As we are in a 230v 50Hz area, I think I need a 50k resistor to allow the LED to be below 5mV as a breaker will trip at 5mV.

230 / 50,000 = .0046

Anyone used a different sized resistor in Europe, Asia, or Australia ???

Alan
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Old 22-06-2013, 08:00   #2
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It's late here but I hope this link might help you.

http://led.linear1.org/1led.wiz

Also remember your dealing with ac so every time the current alternate you light will come on if you don't build a bridge rectifier with diodes. Also if you don't use diodes you may just blow you led.

I'm sure your an electrician so you understand the dangers of 230v

Please let me know how it goes
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Old 22-06-2013, 08:02   #3
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Re: Reverse polarity LED

Quote:
Originally Posted by Hkalan View Post
Hello,

Helping my mate that just picked up a 38 foot Island gypsy to restore...

There is not a reverse polarity light on the current panel. We would need to order a reverse polarity indicator/alarm from a supplier here in Hong Kong, taking 2 to 3 weeks.

Should be easy enough to make one tomorrow for the panel we started making today, from the parts I have on hand !!!

If memory serves me... As we are in a 230v 50Hz area, I think I need a 50k resistor to allow the LED to be below 5mV as a breaker will trip at 5mV.

230 / 50,000 = .0046

Anyone used a different sized resistor in Europe, Asia, or Australia ???

Alan
4.6ma doesn't sound like enough to run a LED. You need to check to specs on the LED, but I would guess you need more in the range of 20-30ma (8000-10000 ohm resistor?)

I don't understand:
Quote:
I think I need a 50k resistor to allow the LED to be below 5mV as a breaker will trip at 5mV
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Old 22-06-2013, 08:07   #4
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Also I'm not sure what you mean by tripping circuit breaker? It should be measured in amps not volts. Are you trying to protect your new indicator circuit?
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Old 22-06-2013, 08:17   #5
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Re: Reverse polarity LED

Hello,

I have DC LED's as well as 230v AC LED's... This situation would work with the AC LED's.

If I have voltage above 5mV on the neutral, the RCD will trip. I would require the draw to be less then that to the LED.

Here is a diagram for North America...

The wife found the AC LED's... it has a resister inside... I will bust one open to see what we have... I may not need one...

Will keep you posted !

Alan
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Old 22-06-2013, 08:44   #6
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Re: Reverse polarity LED

(I think the OP is referring to the 5 mA trip current of a GFI breaker. But such polarity indicators are usually right at the AC input, and marina ground-fault trips where they exist (eg Europe) trip at 30 mA)

The best choice would be a premade indicator light that's been designed and certified for the AC power in the boat's home jurisdiction. Any appliance repair store should have them (incandescent, neon or LED) for around $5 or less.

Yes, one could be hand-made from raw parts, but such assemblies attached to AC are probably against most codes.
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Old 22-06-2013, 08:53   #7
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5 ma (amps) will trip some rcd's (not 5mv) you need to work out the resistance of your finished design and then.

volts 230 divided by your resistance = your amps.

This is the first time I have seen the diagram so thanks for sharing it.
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Old 22-06-2013, 09:43   #8
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Re: Reverse polarity LED

A simple resistor limited, half wave will work but remember that the reverse breakdown voltage of LEDs is quite low so you will need a diode conducting in the opposite direction to limit the reverse voltage on the LED.
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Old 22-06-2013, 09:53   #9
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Re: Reverse polarity LED

Hello,

My mistake... mA not mV.

I just tried the 50K resistor that I have. Worked perfect !

Thank you gentlemen !

Alan
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Old 22-06-2013, 10:09   #10
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Re: Reverse polarity LED

The Original question....I have led's on all my AC C/B's as indicators.

They are wired across the AC out, with a 10Kohm resistor on EACH leg of the LED.
(10K 5w 10%)
50Hz is so fast you wont see the flicker. It does not trip the GFI.

The LED your wife found is perfect BTW>
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Old 22-06-2013, 12:38   #11
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Re: Reverse polarity LED

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Originally Posted by sy_gilana View Post
The Original question....I have led's on all my AC C/B's as indicators.

They are wired across the AC out, with a 10Kohm resistor on EACH leg of the LED.
(10K 5w 10%)
50Hz is so fast you wont see the flicker. It does not trip the GFI.

The LED your wife found is perfect BTW>
The OP is wiring the LED from neutral to ground, hence the question is when neutral is hot, will there be enough current flow in the LED to trip an up-line RCD?

Your description sounds like yours are wired across neutral and hot. I would not expect them to trip an RCD.
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Old 22-06-2013, 23:26   #12
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I would wonder why they design the reverse polarity led to earth instead of active using diodes?

If the electrician got the active and neutral wrong on the dock then there is a chance that there is no earth, so you could be using a reversed polarity and no earth with no indicating led working (testing rcd would let you know something is wrong and is a goo idea)
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Old 22-06-2013, 23:51   #13
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Re: Reverse polarity LED

having the reverse light led trip the GFI is almost a cool feature... automatic disconnect if the shore polarity is backwards...

it won't have any effect if the polarity is correct.
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Old 23-06-2013, 01:57   #14
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Hey smac999 that was my first thought and i agree but the light will not work.
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Old 23-06-2013, 10:02   #15
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Re: Reverse polarity LED

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having the reverse light led trip the GFI is almost a cool feature... automatic disconnect if the shore polarity is backwards...

it won't have any effect if the polarity is correct.
... then you wouldn't need a light, it could just be a resistor that would pull ... 20 to 40mA?

Not a good idea actually. You want clear indication of reverse polarity, not some mysterious trip that might have been caused by it. Also, you want the dock's GFI trip because there's a real ground fault, not because a deliberately added resistor caused it.
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