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  Montauk wiring - Help me destroy the rats nest!

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Author Topic:   Montauk wiring - Help me destroy the rats nest!
newt posted 07-23-2002 05:20 PM ET (US)   Profile for newt   Send Email to newt  
I am working my way through my newly aquired '84 montauk, and would like to organize the wiring.

The mess that is there now, consists of twisted splices, and inline fuses, and I can not imagine trouble shooting this mess, and would also like to free up some storage in the console.

Did the factory wiring include a fuse box or bus bar?

How many circuits are recomended? For example, should I have 1. for the lights another for radio, another for the gps, another for the engine guages, etc, or just a main breaker/fuse?

Also, there is switch on the front panel with a 30A label. Is this a main on/off, or a breaker?

I am interested in how the factory wiring was installed and also what others have done.

If it matters, presently there are dual batteries with a 1,2,both,off switch. They are located in the console (I know this is a matter for debate, but I am planning on leaving them there as I like the free space in the back)

Final question, with dual batteries, should all the electronics and lights be wired to one battery, with the second battery isolated by the 1,2,both switch so that I will always have backup power?

Thanks.

jimh posted 07-23-2002 06:43 PM ET (US)     Profile for jimh  Send Email to jimh     
At a minimum, your Whaler probably came wired with a small, AG-fuse holder, distribution panel and three pull switches.

The first switch was likely wired at the factory for the Navigation lamps. It would have been a three position switch, OFF-ANCHOR-RUNNING style configuration. The second and third switch were probably labeled ACCY 1 and ACCY 2 and were not wired at the factory.

On a small boat there are just not that many circuits needed.

You can wire your instruments right to the +12Vdc buss since they all have their own ON-OFF switches. They probably have inline fuses, which you can retain, or you can wired them to use some of the other fused circuits in the distribution panel. It has about 5-6 fuses available.

I'd wire my instrument lights and the compass light to the NAV light switch, since you will likely need the instruments illuminated about the same time you'll need the running lights.

That leaves two switches for perhaps a bait well pump, cockpit lights, or something else.

newt posted 07-23-2002 09:04 PM ET (US)     Profile for newt  Send Email to newt     
Thank Jim. It sounds like I need to identify the distribution panel. I didnt think to look for one because the existing electronics seam to all be pigtailed together - not to any panel. I will investigate further.
DJS posted 07-25-2002 12:15 PM ET (US)     Profile for DJS  Send Email to DJS     
Newt,

I have an older Model Lowrance GPS/Sonar unit. In the owner's manual the following is said about power connections:

"The LMS-350A works from a twelve-volt battery system. For the best results, attach the power cable directly to the battery. You can attach the power cable to an accessory or power buss, however you may have problems with electrical interference. Therefore, it's safer to go ahead and attach the power cable directly to the battery."

Also, my VHF radio is also attached directly to the battery. I assume this is also because of interference. Of course an in-line fuse holder should be placed in the line from the plus side of your battery, as close to the power source as possible.

Hope this helps,

David

jimh posted 07-25-2002 12:52 PM ET (US)     Profile for jimh  Send Email to jimh     
Probably every manufacturer of an electronic device for onboard use would like you to connect it "directly to the battery."

If one followed all those recommendations they would have a dozen wires running to the positive post of the battery, and an equal number to the negative post as well. That is not an approach to wiring that is very extensible.

It seems perfectly acceptable practice to bring the battery leads to a distribution block and from there to wire all accessories. If the current load drawn by any individual accessories is small in proportion to the current carrying capability of the wiring used to connect the battery to the distribution block, then the potential for significant common mode currents is minimized.

To explain this technically, the wire between the battery and the distribution block has a small but finite resistance. Any current flow in this wiring results in a slight voltage drop. If instrument-A draws current, it creates a voltage drop that affects the operation of instrument-B.

If a particular instrument is highly sensitive to small variations in the supply voltage, these tiny variations may affect its operation. In the real world, designers of instruments should anticipate this and take measures to avoid the problem.

By using a large gauge wire to connect the battery to the distribution panel, you will minimize the voltage variations.

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