Anchor Light drains battery before the night is over! - Page 2 - SailNet Community
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post #11 of 17 Old 11-10-2006
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I wonder whether the clue is in the "drains our battery" singular. If the anchor is a halogen then they will fail early if they are undervoltaged and if you only have one battery then by the time you go to beddy byes having run your cabin lights etc you probably don't have much left in the tank to begin with. If you also have a stereo and a fridge running off the same battery you were doomed before you began. On the other hand if it's an '83 model and has never had the wiring and anchor light upgraded since new I'd reckon your lampholder is shot or your wiring is simply not up to the job. Many boats from that era simply had cable up the mast that was too thin to carry the 12v current. Few people realise that 12v actually requires heavier wiring than mains voltage. If your nav lights are at deck level and are OK then that would support my theory. Get yourself a new anchor light, you'd be silly to not to go LED as even if your cable is not up to carrying 12v it should be happy with the amperage of LED which is bugger all.
Now, if your anchor light is part of your nav lights (i.e a tricolour with anchor and it's all at the top of the mast) I'd reckon the lampholder is shot.
By the way, if you are running your battery dead every time you go out then you have probably ruined the battery. It also takes a lot more than an hour or so to fully charge a battery that is completely flat.

Andrew B

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post #12 of 17 Old 11-10-2006
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If you had a short you wouldn't need to check insulation, you wouldn't have any! Shorts to ground can weld. Check your line for a high resistance, probably created by corrosive build up. Start in the socket (most likely place), work down to the switch. Disconnect power and check resistance. Good wire connections should show near 0.
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post #13 of 17 Old 11-10-2006
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It's not a short the fuse would blow. . A high resistance would decrease the amperage E=IxR or I=E/R. Low resistance (but above 0 ohlms) in the socket would produced heat and would cause premature failure of the bulb. However as that resistance is in series with the bulb it would reduce not increase the amperage. If however you are getting continuity with a low resistance to gound this could cause a higher than normal current in the circuit but less than the fuse rating. This could drain the batteries and would also produce additional heat. Premature death of light bulbs is always due to heat or vibration. In this case you can rule out vibration. If you are getting low resistance to ground from the positive side of the light circuit then the socket needs replacing. Water would also do this, if the socket was immersed in water and that is not a short circuit btw. Disconnect the battery. Check resistance in the circuit positive lead to negative lead (which is the ground) Use the above formula I=E/R and calculate your amperage it should be 1 or 2 amps.

Last edited by ebs001; 11-10-2006 at 06:26 PM.
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post #14 of 17 Old 11-10-2006
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Post Hope it helps!

A good place to start with any electrical education is a rudimentary understanding of Ohm's Law. It describes the relationship between Volts, Watts, Amps and Ohms. The website/link below has a pie chart diagram that will explain how the law works. Great information! Also the chart is on a website that is devoted to 12 volt circuits. It looks to be loaded with great information.

Good luck with solving the problem.

JC

http://www.the12volt.com/ohm/ohmslaw.asp#pie
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post #15 of 17 Old 11-10-2006
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ebs-

If the short isn't to a very well-grounded item...it could in fact allow enough amperage to drain the battery but not have enough to blow the fuse. If it is grounding out to the aluminum mast, there is no guarantee that the mast is even grounded electrically, especially if it is deck-stepped. Finally, aluminum oxide is a fairly good resistor...

Only a short to a well-grounded item would allow enough current for the fuse to blow. Especially, if it is a 15A fuse, which is often the case for navigation lights.

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post #16 of 17 Old 11-12-2006
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SD if it isn't well grounded it's not a short. A short is a circiut with no load (actually minimal resistance, even copper has resistance) and so will always blow the fuse especially something as small as 15A. If the mast is not grounded you will have an open circuit and no current can flow. If you have a poor ground ie resistance to ground you have a complete circuit which can allow enough current to flow to drain the battery without blowing the fuse.
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EBS-

If the short is caused by chafed/worn insulation and the wire is contacting the mast, and even it the mast isn't well grounded...most people would consider it an electrical short...since it is a completing the circuit in a place not designed into the circuit. It certainly is by my training as an electrical engineer...

If you check here, you will see that most of the definitions of an electrical short circuit are any inadvertent electrical connection. Whether the circuit has relatively low resistance or not is not necessary for it to be considered a short circuit.

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her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

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