Fuse for an LED light

[NORO LIM]

I just bought a new sealed LED all-around white anchor/navigation light. It will replace the badly corroded non-LED light that came with the boat. I have a question about fusing a mix of LED and non-LED lights on the same circuit.

The all-around light is controlled by a rocker switch that also controls the two (starboard and port) navigation lights. "Up" turns on only the all-around light for anchoring, and "down" turns on all three lights for night navigation. The starboard and port navigation lights are not LEDs. All three lights are wired through a 15 amp fuse at the switch.

The instructions for the new LED light says to protect the light with a maximum 5 amp fuse.

Should I:
- change the 15 amp fuse to a 5? (Isn't a 5 amp fuse likely to be too small for the port and starboard navigation lights which are not LED?)
- place a 5 amp fuse inline where I'm connecting the new LED wiring to the existing wiring?
- ignore the instructions and leave the new LED wired through the 15 amp fuse?

Rewiring the new LED light to a new separate switch with it's own fuse is not practical.

Part of me (not the part that's on a budget) wants to replace the port and starboard navigation lights with LEDs also, but those lights are working perfectly and do not appear to be corroding at all. Also, I haven't investigated LED red and green navigation lights for fusing requirements. One might guess the requirements, at least from the same manufacturer, would be the same, i.e., 5 amps, but that seems to be the kind of information you only get after you open the package.

Any advice is welcome.

Bill

[Sneaks]

If it were me, Bill, I'd replace the present fuse with a 10 amp and wire a 5 amp inline fuse between the 10 amp fuse downstream side and the LED light. Easy to remove if you ever decide to go LED everywhere, unobtrusive, and effectively protects the light while keeping the running lights protected.



Don

[NORO LIM]

Thanks, Don. That certainly seems like a straightforward and simple solution.

Now I get a chance to display my ignorance, but I want to be sure about how to proceed. I was thinking of just putting the inline 5 amp fuse at the junction of the existing wire to my radar arch and the 24-inch wire that comes attached to the new LED. (This would put the fuse at an unobtrusive but accessible point, and would not require cutting, pulling or undoing any existing wiring.) Any need to worry about that placement?

[Sneaks]

[mmitchell]

I've changed out all the interior fixtures out to LED and the anchor fixture. Have left the running lights to incandescent as they only are on when we are under way so it is being charged by the motors. We have never camped out at the docks so have to be very frugal in how much power is being drawn on the batteries. We installed a class 37 for the house battery and it has been fine for about a day and a half. That is running the Wallas 24-7. So back to the fuses. I don't thing it's a real worry to be concerned about the 15 down to a 5 for the fuses.
The LED light only draw about a 5th of what the incandescents draw. They are much brighter too as we went from a 12 watt stock to a 42 watt.

[Almas Only]

I'm no electrical engineer, but I'd leave the fuses alone.

The purpose of a fuse is to prevent something "bad" from happening when a circuit shorts, or overloads. If all the nav lights have been getting power through a common fuse, the risk of an overload at one light knocking out the fuse, and thus the power to all nav lights, is apparently tolerable. If that possibility is not tolerable, separate the circuits now.

Otherwise, so what if the led shorts or overloads, and draws a little more power than it's fuse rating before blowing the existing fuse? It's not going to burn out the wires (they're supposedly sized for the higher amp fuse), it's not going to start a fire, and it's not as if we're dealing with an instrument which needs protection from a slight overload to save the whole unit. The led's are not cheap, but, in the end, they're still light bulbs.

If you do fuse the led separately, I recommend you don't install the fuse externally. If the fuse blows at night, on rough water, you don't want to go overboard changing it out. I prefer to keep the fuses where they're readily accessible, from the helm station.

[thataway]

We converted the 360 light to LED, and left the fuse the same. There is no protection for the light with the 5 amp fuse. You are basically protecting the wiring, if there is a short. There is a separate wire from the back of the switch which goes to the all around light--and you could put the separate fuse in that (behind the console)--but I don't think it is necessary, since the circuit is fused before the switch.

I have also converted some of the interior lights to LED--and left the same fuses in place.

[Sneaks]

Fuses are an interesting and in many ways misunderstood electronic/electrical component. They come in many flavors, the most common are general purpose, fast acting, and slow-blow. Usually the fuse is sized as a percentage of expected current flow. IE: if the expected draw is 10 amps, the fuse is sized to not only prevent wire damage but more often to prevent a fire or major damage within the device it's protecting. Lets say 50% greater or 15 amps. Anything close to 10 amps might cause an unwanted fuse failure, anything over 15 amps increases the risk of damage. A compromise.

Motors typically use "slow blow" fuses simply because the startup current is so high. It basically "holds off" blowing until it realizes the current has not dropped below the fuse current rating quickly enough, signifying serious trouble.

Some slow blows are incredibly tolerant of of overcurrent. One fuse in a radar I maintained kept blowing at the most inopportune time. Turns out the fuse was wrong. the proper fuse was rated at 600% overload for 3 full seconds!!!! Once the right fuse was installed, that puppy never blew again.

In something as simple as our C-22, general purpose fuses work just fine. My earlier recommendation to drop the 15 amp down to 10 amp was simply to keep the present current to fuse rating ratio the same. Bob's suggestion is just as valid. If a wire did short, either fuse will detonate before the wire even got warm. I do, however, still stick with the recommendation that the actual junction between the LED wire and the boat wiring be carefully made to prevent any water intrusion, and if you put a fuse in, put it where it's easy to replace - even at night at sea.

There's an old rule of thumb for hardware techies working for the government. I learned this from Charlie: If it blows fuses, get a bigger fuse....

Don

[Matt Gurnsey]

If you add a fuse, do it behind the console for two reasons-

Easy to get at.

Protects the wire from switch to light.

But I don't think I would worry. I'd leave the 15 in place and use it.

[thataway]

One other thing to remember is that the circuit has both the "anchor" in one position, and "navigation" in the other position. Be sure that you get the correct wire, if you do elect to put a fuse in line.

I have fused a number of circuits in the C Dories, and for the most part either added a second fuse block behind the console (in both the 25 and TC 255) as well as putting some in line fuses, for circuits which connected to the main battery switches or additional batteries. For all of these I used the blade type of fuse--used crimp fittings which had adhesive shrink wrap on the leads, and packed the rubber fuse holder with grease, so that there could not be any corrosion--even though all of these fuses are directly protected from the weather, they are still in high humidty environments. Also when adding fuses and working on the electrical system, be sure and label all of the wires and fuses. It makes it a lot easier if a fuse blows to find the right one! I use 1/4" wide plastic labels and wrap the label around the wire near a terminal. I put the label right along side of the fuse. Label both ends of a wire--for example if you add an additional battery--label the wire at the switch, and at the terminal of the battery--such as "house battery #2". Label both the plus and neg legs.

[NORO LIM]

Thank you all for the excellent suggestions and discussion.

I have been planning all along to solder and shrink wrap the new wire connections below the light. Both the old lamp itself and the old wire connections below it, showed considerable corrosion. With the new sealed LED lamp, corrosion in the lamp itself should not be an issue, but I do want to have a better wire to wire connection than the original. It actually took me a little while to figure out what was going on with the wiring until I got the old lamp and stalk disassembled. There were three wires from the lamp going into the top of the stalk, and only two wires coming out the other end. The original Perko lamp was a two bulb fore-and-aft affair designed for switching between one bulb for navigation and two bulbs for anchoring. Maybe it's common practice to convert these two-bulb lamps for all-around use on smaller boats? However, the hot leads from the two bulbs were joined to the hot wire from the switch in a not very well done three-way connection that finally came out of the stalk as a sticky wad of electrical tape, some kind of sprayed in foam, and loose butt-end connectors. I will see if I, a complete novice at this, can do better. I'm not taking bets, but I think I can.

I am leaning towards leaving well-enough alone and not adding an extra 5 amp fuse. I'm still uncertain about whether to leave the current fuse at 15 amps, or to drop it to 10amps. Any consensus on that?

[forrest]

Circuit breakers or fuses protect the wire that is feeding a load. The maximum size fuse is determined by the size of the wire. You can install smaller rated fuses if you want to protect a load more closely. Electronic devices that need a fast blow fuse are generally supplied with an internal fuse or a inline fuse directly ahead of the device. A good analogy to this would be a circuit in your house. No matter how many lamps, vacuum cleaner or TVs that you plug in, you don't go out and change the circuit breaker at the panel. If you have number 12 wire in your house you have a 20 amp breaker. If you have number 14 wire in your house you have a 15 amp breaker. Breakers (or fuses) are sized to protect the wire. If a bulb burns out so what, you replace it. If your hair dryer burns out, you buy a new one. If your stereo shorts out, a fuse inside the stereo blows. In each case the wiring in your house (or boat) remains intact (it doesn't burn up) because it is protected by the proper rating of the fuse or circuit breaker ahead of the wire. Another example would be when you pull your boat trailer. Just because you add a couple of tail lights and five clearance lights when you plug in your trailer, you don't increase the fuse size in your pickup for the extra load. The fuse that is in your distribution block is sized for the wire at the factory. If there is a short or load that exceeds the wire rating the fuse or circuit breaker trips. If you have a dedicated circuit such as for a pump, you can fuse the load according to the manufacturers recommendation as long as you don't exceed the rating of the wire.
Forrest

[NORO LIM]

forrest wrote:

[thataway]

The fuse does not protect the LED--it protects the wire. The fuse does not regulate voltage, it only limits maximum current. The current draw of the LED is inherient in the circuit--and cannot be limited by the fuse. You would have to measure the current draw of the two running lights (red and green) plus the LED light to see if a 10 amp fuse would be adequate--it probably would be.

Even though I have done a lot of soldering in electronics, I use crimp fittings and heat setting adhesive shrink sleeve protection on wires on boats. The only solder I use is the rare time that I have to wire a switch which a lug will not fit on. Incidently, invest in a good rachet crimper --this should be in every boater's tool kit, along with a digital volt/amp meter.

Solder joints are a bit more subject to cracking by vibration--but they can be done. If you solder, tape will not give adequate protection--use the adhesive shrink tubing. The best to do is to seal the bottom of the LED socket and any wire going there. This is not always easy, but silicone or specific self amlgimating tape can give a water tight seal around a socket.

Yes, some C Dories had a specific foreward steaming light, and separate stern light, with a second bulb in the "anchor light" to give the 360 degree coverage. This doubled the current draw of the anchor light over the steaming light. A 360 degree light is legal on this size boat, and is more effecient because of decreased current draw, and battery drain.

[NORO LIM]

Thanks, Bob. And here is what looks to a complete ignoramus like me to be a pretty good tutorial on crimping heat shrink connectors. Maybe others will find it useful, too.

http://www.pbase.com/mainecruising/wire_termination&page=1