Question on LED's

[jibes138]

I installed a LED anchor light yesterday and had a question regarding operation and design. After wiring it up I tried to test continuity at the base of the mast and had no reading at all. I figured I hosed up the butt splices so I ripped it apart and re-crimped the butt connectors and re-shrank new tubing. Still no continuity. Then my neighbor in the boatyard had a battery powered tool so he attached the leads to the battery and it lit right up. How come you can't test continuity (using an ohmmeter) on an LED? Is there a switch that activates when it gets the right voltage?

On a related subject Stu recommends nothing less than 14AWG wire on a boat? I could not fit 14AWG wire through the hole at the top of my mast where the wires pass through, the wire I was replacing was more like 18AWG or smaller so I installed 16 AWG tinned wire, the max size that would fit through the mast. Unfortunately the very long lead molded into the LED was extremely small diameter wire, at most 22AWG or maybe smaller. This made the butt splicing a challenge. I used 22-16 butt connectors and a ratchet crimper and was able to bet a good splice so I will assume the wire was 22 AWG. Why do these manufacturers use such extremely small wire? Also the wire was not tinned although they had tinned just the stripped section that came with the unit. It is tiny and susceptible to damage IMHO and makes connections a real PITA. Even trying to get shrink fit tubing that will shrink around both 16 AWG and this tiny wire was a chore. I had to build up the small wire with small shrink tubes then a larger size that would fit over the 16AWG and the previously shrunk smaller tubing. Is it possible they do this on purpose just to get a good laugh?

 

[sesmith]

LED' s are not like bulbs. The wiring runs to a circuit board in the LED lamp, so a continuity test won't tell you anything.

The small wire gauge is because LED's draw very little current and don't need large wiring. You may be able to find step down butt connectors. Usually, what I do with small gauge wiring, is strip twice as much as I need to, then fold the bare wire up on itself. This gives the crimp more meat to grab, but the size of the crimp connector should match the wiring size.

 

[Stu Jackson]

Dave, my recommendation for minimum wire sizing was for a post where the skipper was replacing interior lights. I haven't even thought about anchor lgihts or wires up the mast. Smaller wires going that far, though, would lead me, again, to recommend larger wires, but perhaps not 14 ga.

 

[walt]

If you want some numbers, try a voltage drop calculator like this one http://www.calculator.net/voltage-drop-calculator.html

I plugged in 22 AWG, 12V DC, 0.4 amp (check your specs) and a 30 foot round trip.

Voltage drop is .39 volts or 3.25%. The best way (and probably most common) way to drive an LED is with constant current using a magnetic switching circuit so even through the voltage you supplied to the LED light at 12 volts is 3.25% lower than if you had used some big wires, the circuit still causes the current to be constant and the LED brightness is the same either way. However, it took you an extra 3.25% in power to get that brightness with the smaller wires. You generally know you have this type of LED light if the input voltage range is large such as 10 to 30 volts. In good designs, the switching does not need cause RF interference

Since most of these LED lights generally have a switching circuit now (best way for both constant current, high efficiency and wide input voltage range), this also explains why you didn’t see any resistance. The circuit probably doesn’t even start to turn on until at least a few volts are applied.

 

[MrUnix]

You can't easily test a LED for continuity.. a bare LED is an electrical one-way valve, allowing current to flow in one direction and not the other. LED bulb fixtures may or may not have additional circuitry which complicates things further. The best way to test is to simply apply voltage and see if it lights up. Pay close attention to polarity as unlike standard bulbs, it matters which way you hook it up.

Cheers,
Brad

 

[jibes138]

Stu, Not too many circuits on a boat will be longer than a masthead anchor light. I figure it is more than 120 feet round trip to the battery. My real beef is with these manufacturers that can't put decent size wires in their products. I would much rather have screw terminals to the device than cheap little 22 or smaller gauge wires to connect to. Also these wires are going to support the weight of all the wire in the mast in all kinds of horrific conditions like hurricanes.

 

[Stu Jackson]

Dave, I agree. For regular wiring down below, that's why I like 14 ga or bigger. Like I said, not doing any mastlight work myself, I covered that in my last post.

I completely agree about the Lilliput wiring on some of this stuff, including even stereos.

As Crazy Dave Condon and I also know, it happens with model RR stuff, too.

What's a dedicated hobbyist to do these days?!?

 

[sesmith]

Dave,

You need to provide strain relief up near the lamp to support the wire harness.

 

[jibes138]

sesmith, yeah I have a loop of wire at the masthead to keep any load off the potted device. I am thinking more of the butt connections and shrink tubing that is in a tube in the mast taking the load of the wire. The adhesive lined shrink tubing seems pretty rugged and I have a couple layers of it with each size overlapping the previous. I'll take another look tomorrow and see if I can beef it up a little more for support. Thanks.