6 Volts from 12 Volt System!?!?

[Katapult Mike]

I recently bought a 47 year old boat (Islander 36) which has had a lot of work done to it over the years, some good, some bad. One of the prior owners apparently hired Mickey Mouse as a boat electrician..... and Mickey apprently liked to drink on the job. So I am tracking down some mysteries. There are a lot of wires that have ben cut and left dangling, and lots of squirelly splices.

I am trying to get running lights working. Found no power getting to the stern light, so strating following the wire back. Quickly discovered a dangling tail where someone had decided they needed a cigerette lighter plug worse than the needed a stern light. Don't understand the reasoning there, but whatever. Didn't trust the reading I was getting on my voltmeter at the cigerette lighter plug, so traced back one more splice and cut wire upstream. Same reading. 6 volts. Batteries were fully charged and places where things were working properly showed 12.5+ volts.

What I don't know about electriciity would fill volumes. But I can think of two possibilities. Maybe it's just that the wiring has multiple crummy splices nad corroded connections, and the imperfections just happened to cause a voltage drop of exactly 50%. In that case I just need to perform the boat yoga and run new wiring back to the circuit breakers.

But another possibility occured to me. Maybe 6 volts was intentional? Is there such a thing as a splitter, that converts a 12 volt current into two 6 volts? Were six volt lights or accessories that plugged into cigerette lighters ever a thing? I was doing this stuff 40 years ago (not 47) but I don't remember such a thing.

Any ideas?

[thinwater]

Bad wiring. No such thing as a splitter. Technically, it is possible to step down, o course, but that is not the issue. A cig lighter and a transom light both require 12 V (40 years ago there would not have been a 6 V option that was USCG approved).



I suggest getting a book on 12 V wiring and reading it a lot. Some people will suggest ripping it all out, which is possible, but I may be smarter for a semi-beginner or very rusty pro to work on just a few circuits at a time. Then see what you find and what you think. Most likely there is some bad and some good. As for nav lights, you probably want to switch to LED fixtures for the amps they save (you will at least double battery capacity). Don't try to retofit bulbs; the fixtures are almost certainly faded and corroded, and the bulbs don't save that much money over new sealed fixtures.


If you decide to re-wire, look at whether the switches are where you want them and remote wireless switching options; some are just $25.

[Kettlewell]

As for nav lights, you probably want to switch to LED fixtures for the amps they save (you will at least double battery capacity). Don't try to retofit bulbs; the fixtures are almost certainly faded and corroded, and the bulbs don't save that much money over new sealed fixtures.

I guess it depends on the boat and the fixtures. I found that switching to LED bulbs worked great in most cases, and saved a ton of work.I did purchase a sealed masthead tri-color LED light which is the first masthead light I have ever used that didn't require fiddling with to keep going at least several times a year. Having a sealed light up there is great.

[kayakerChuck]

Having recently been through this, I'm in the "tear it out" camp.

Start by tracing the wires from the fixtures back to the breaker panel. If the circuit makes sense and is safe & sound, label it and move on.

If it does not make sense, or is not safe, cut it out. Make a list, and carefully re-wire.

I cut about 300' of wire out of my 30'er. Most was dead, some was in use, some was scary, and one shore power hot lead ended in bare wire just laying in the bilge. (Even better- my shore power breakers physically moved, but did not actually break the circuit when switched "off".)

[Katapult Mike]

Thanks guys.

LED's are a no-brainer. I plan to replace the exterior fxtures as well. I noticed Perko still sells exactly the same running lights as I have mounted, apparetnly available wth ether LED or incandescent bulbs, but I am not impressed. They don't seem very well sealed. What do you guys recommend for bow and stern lights and where is the best place to buy them online?

I would think modern technology could produce something very well sealed that should last a long tme.

As far as rewirng, I am in the "do a bt at a time" camp. I want to sail ths boat this summer, not work on it every weekend.

[boatpoker]

When I bought my current boat I removed one full green garbage bag (the giant leaf type bag) of wire from the boat and started over ... I feel your pain.

If you PM me an email address I'll send you a pdf of the ABYC Electrical Standards.

[GILow]

A few diodes in series would produce that voltage drop. Maybe they did actually NEED six volts for something and did it that way.

But yep, rip it all out and start again.

I’ve done this now for more boats than I can count and it has been, by far, the most valuable job I’ve done on any of them.

[GILow]

Originally Posted by Katapult Mike

Thanks guys.

….What do you guys recommend for bow and stern lights and where is the best place to buy them online?.

Hella are my favourite lighting brand.

[Pete7]

Couple of years ago the Hella 25 stern light finally bit the dust when the lens broke from years in the sun. Given it was 3 decades old not bad.

I replaced it with a much bigger Aqua Signal 40 series off e bay for a fraction of the new price and in mint condition. Fitted with an LED bulb its far brighter for the fraction of the current the previous filament bulb used.

However, you should be aware that the lenses for the 40 and 41 series are becoming very rare to find because they stopped production.

I think when the time comes to replace our bow bi-colour I will switch to the 34 series with an LED. Haven't looked at them, but suspect these are sealed for life units.

[JBP]

6 volt systems did exist, but disappeared after 1950 or so.

[wsmurdoch]

I ripped out two 5 gal buckets of unused wiring from my boat. At the scrap yard I got enough money for two cases of beer.

Because digital voltmeters have a high internal resistance in 12V DC circuits they can find odd voltages especially when the circuit itself has a high resistance. I have a 12V taillight bulb with longish wire leads and alligator clips that I use to put a 1A load on the circuit while I measure the voltage. It's handy for finding bad connections in a circuit.
.

[RaymondR]

The series resistance from poor connections problem is overcome in industrial instrumentation services by using a 4-20 mA varying current transmission circuit instead of a varying voltage circuit. The 4-20 mA transmitter puts a varying current between 4 and 20 mA through the wiring circuit and at the receiving end through a precision resistor and the voltage drop across the resistor is used to derive the display or control output.

If one wanted 6 volts for some purpose one might wire two 6 volt batteries in series, giving 12 volts, and tap off the earth side 6 volt positive for six volts supply from earth to first positive.

There are numerous portable battery powered devices for which one might need 6 volt supply.