Checking LED Anchor Light

[sailorboy1]

My mast was down the other day so I took the opportunity to replace the anchor bulb with a LED. Now that the mast is back up the light of course doesn't work.

- it worked before taking the mast down
- there's power at the terminal strip at the deck
- the wiring all looks good at the deck level with no indications of a break
- the bulb was an indexed type so only goes on 1 way
- testing conductivity indicates an open circuit
- tested the conductivity in both "directions" even though I don't think that matters

So indications are that either the bulb is bad, not installed correctly, or the wiring at the light itself has a problem.

But before I go get new bulbs and go up to find out I figured I would ask:

Is there anything special about an LED bulb as far as testing circuit conductivity through the loop?

[kmacdonald]

Originally Posted by sailorboy1

My mast was down the other day so I took the opportunity to replace the anchor bulb with a LED. Now that the mast is back up the light of course doesn't work.

- it worked before taking the mast down
- there's power at the terminal strip at the deck
- the wiring all looks good at the deck level with no indications of a break
- the bulb was an indexed type so only goes on 1 way
- testing conductivity indicates an open circuit
- tested the conductivity in both "directions" even though I don't think that matters

So indications are that either the bulb is bad, not installed correctly, or the wiring at the light itself has a problem.

But before I go get new bulbs and go up to find out I figured I would ask:

Is there anything special about an LED bulb as far as testing circuit conductivity through the loop?

Yes. It's a diode. Use the diode test function of you multimeter.

[kmacdonald]

It conducts in one direction and is an open circuit in the other. Polarity matters.

[John_Trusty]

I hate to give obvious advice to someone with many more miles under his keel, but here goes ... Did you try powering your bulb with reversed polarity to see if it will light? As noted above, diodes only work one way. I understand that some smart manufacturers are making embedded circuitry that automatically reverses if installed backwards. Assuming your bulb doesn't, it's worth a try before you (shudder!) go up 'there'.

[Lake-Effect]

Originally Posted by sailorboy1

Is there anything special about an LED bulb as far as testing circuit conductivity through the loop?

Testing with a meter is a first step; I like to test any mast lighting and wiring by using 12 volts (portable battery with a 10A circuit-breaker inline).



Isolate the mast lighting wiring from the boat, then apply 12 in one direction then the other; if it doesn't ever light, and you're getting no current flow, it's an open circuit: something broke or let go, or there's a mistake.

[Bleemus]

Reverse polarity.

[chris95040]

Probably obvious to you now, but next time "test the new gear before the sticks in the air"

[SteveSails]

What the meter 'sees' is not the LED diode but the input to the driver circuit. This may be a simple resistor in series with an LED to a complex constant current regulator. Without knowing the circuit hard to predict what reading a simple ohmmeter will give and if it will be meaningful for troubleshooting. But that meter can still be useful.

Try this:
Use the meter to measure the current draw of the connected anchor light, an LED anchor light will be about 250 - 400mA, if you have less than 100mA try reversing the polarity to the light. If you still have little or no current then either a bad connection (likely) or a bad anchor light. If the meter reading shows well over 1 amp then there is a short in the wiring or, again, a defective anchor light.

Hope that helps.

[Capt.Don]

As others have mentioned, it is probably the polarity -- just swap the + and - wires.

On another note, when I installed an LED anchor light, I "forgot" that it had a light sensor and would turn off during the daylight. Took me a while to figure that out.

Don

[sailorboy1]

Even though it's a LED (diode) which only allows current in 1 direction:

Wouldn't it still test as a complete circuit on conductivity (and I checked it both ways of hot/hot and hot/ground)? The diode should have passed conductance in one of those shouldn't it?

And I tried it at night even though I didn't one of those "auto" lights.

[skipmac]

Originally Posted by Capt.Don

As others have mentioned, it is probably the polarity -- just swap the + and - wires.

On another note, when I installed an LED anchor light, I "forgot" that it had a light sensor and would turn off during the daylight. Took me a while to figure that out.

Don

Yep. This is the quickest, easiest, cheapest check. Swap the leads at the base of the mast or switch or where ever you can access the power to the light and I'll give odds it works.

If that doesn't work then Don screwed it up.

[Lake-Effect]

Originally Posted by sailorboy1

Even though it's a LED (diode) which only allows current in 1 direction:

Wouldn't it still test as a complete circuit on conductivity (and I checked it both ways of hot/hot and hot/ground)? The diode should have passed conductance in one of those shouldn't it?

No, when any diode conducts there's a forward voltage drop; a single normal silicon diode has a forward drop of about 0.6v; LEDs have a forward drop of 2v or more (and even more if there are LEDs in series).



The forward voltage drop confounds most simple continuity checkers, and even many "diode checkers" can't read the higher drop across LEDs.


And the switching current regulator found in most LED assemblies or fixtures can't reliably be checked except by feeding them the right polarity of 12v.

[SteveSails]

YES, a diode conducts current in one direction only, BUT, your meter is not connected directly to the LED diode. There are other things in there that the diode that emits light needs to work and not burn out in a single flash of glory. See my previous post.

Capt. Don Good call on the light sensor, had the same issue once and it took awhile for the head slap to kick in.

[Montanan]

Is this the start of a new joke thread: How many people does it take to fix an LED bulb?

[flyingnut40]

I'll throw in my 2 cents worth.....
If you took out a "Normal" incandescent bulb, it was

a simple resitive load that had no care for polarity. If the
wires were reversed it would not care and still work.

The LED WILL care whether it is a simple diode and voltage
dropping resistor affair or a more sophisticated driver board

feeding an embedded LED. The price you paid will be your
best clue at this point.

If you have to climb the stick, turn on the power to the light
and take the original bulb with you. if you put the original
bulb in and it works, you know your wiring is O.K. albeit
possibly reversed. (But you have already reversed the leads
by now I'm sure)
That leaves you with a defective LED to replace (and bench
test) and have ready for next time!
Dennis