Basic electical

[bradmc]

I don't know much about the elctrical systems of a boat.
I have a few questions
On a 18 ft bowrider I want to put in a electrical system that can put out enough juice to play a sterio 200 (watt) ,depth sounder and the average doodads assciated ith a small craft IE appropriate lights.

I need to know what I am supposed to look for.
Can somebody tell me the bare bones approach to an electrical system
a (the anckle bone is connected to the leg bone) sort of deal.

I know ill need an alternator (are there other choices?)
then where does the power go (to a battery?)
WHat do I hook my electronics directly up too?
(a power bar???)

excuse my ignorance and I DONT plan on doing this myself, I just want to price the equipment I will need and the basic concepts. I will stick to fibre glassing and painting.

thanks

[mattotoole]

The best thing you can do is buy a good book on the subject. There are dozens of books on marine electrics, as well as general restoration and repair guides. Fifty bucks worth of books is well worth it before committing far more money and a bunch of time to such projects.

I notice you're from Vancouver. All the bookstores there seem to have great marine sections. I imagine the public libraries do too. When I'm in town, I spend a lot of time in the marine bookstore on Granville Island.

[gonzo]

Does this mean the engine doesn't charge a battery?

[Tim B]

There are a thousand ways to wire a boat. In terms of connections, the best is a soldered joint with heat-shrink tubing over it.

The centre of all electrical systems on a small craft is the battery. Normal marine batteries are 12 volts. for 24 volts, use two batteries and connect the positive terminal of one to the negative terminal of the other. The other two terminals have 24 volts across them (12+12). The battery has a capacity, rated in Amp-Hours. a 4AH battery will supply 4 amps for 1 hour, 2 amps for 2 hours etc. The required capacity is dependant on the load applied and the time for which it is applied. The load is usually taken as the emergency case. Lighting + Nav gear for 10 hours,then just Nav gear for 6 hours. The latter is often supplied by an emergency back-up battery.

From the battery, there is usually a selector switch (main/backup) and then a switched distribution (distro) panel. Permanantly connected to the battery/ies (or sometimes with an isolator) is the charge controller, running from the alternator/wind turbine/solar panels.

Distribution panels are as various as the ways to build them. At thier simplest, they are just a bank of switches. The two main power cables will come in at one side and the negative (black sheath) will go into a straight bus-bar. the positive lead will come in and either be soldered directly to the switches or clamped to a bus-bar that goes onto the switches. The load is then connected between the switch (positive) and the bus-bar(negative).

Rating the system is just a case of adding up the maximum current required by each component. This will give the required wire-rating at the battery. The wire-rating from the distro panel is dependant on the current drawn by the equipment it is supplying. The wire does not have to remain the same size through the whole circuit, but it is good practice for it to remain the same size along each run.

Despite the fact that this system is only 12 or 24 volts it is good practice to put fuses in the supply line and distro panel. This prevents damage to the rest of the system if one part fails.

I'lll post some diagrams,

Tim B.

[Tim B]

Here are a few examples off the top of my head.

Wiring electrics is really quite easy, just take the time to plan it.

Hope this helps,

Tim B.

[gonzo]

Soldered joints have been found to create a hard spot leading to broken wires. Aerospace industry uses all crimps now. I suppose that if the solder joint has shrink tube or is well secured it wouldn't be a problem.

[Tim B]

I've never had a problem with a soldered joint. obviously it is detrimental to flex any connection too much, but you can't get a more reliable metal-metal joint than soldering (welding is not applicable here (except for aluminium cable which isn't used on small boats)). The major problems are corrosion and negative-lead-rot (a type of corrosion that affects the whole negative lead). Soldering also softens/melts the sheath next to the joint, giving better immunity to water ingress into the cable itself.

I might point out that aircraft electronics are not designed for use near water!!!!

Tim B.