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  Topic Review (Newest First)
09-22-2010 08:55 PM
Originally Posted by nickmerc View Post
The irony of grounding a system to a metal frame that moves around on rubber wheels is not as ridiculous as it sounds. You are not really grounding anything on the car, you are connecting them to a reference voltage (negative battery post) so the potential will be the same at all devices.
Thank you, thank you, thank you.

I can hardly believe that I've been grounding things in cars for something like 25 years now and that simple truth escaped me all these years.

Makes total sense though, now that you say it.
09-22-2010 05:07 PM
nickmerc The irony of grounding a system to a metal frame that moves around on rubber wheels is not as ridiculous as it sounds. You are not really grounding anything on the car, you are connecting them to a reference voltage (negative battery post) so the potential will be the same at all devices.
Bubbler pipe
09-22-2010 11:16 AM
Sixpoint I love this forum.

Did I mention that I believe there's no such thing as too much knowledge?

Thanks for the input, all.
09-22-2010 10:39 AM
hellosailor Sixpoint, a boat's system IS very much like a car's.

There are some small but important differences, i.e.:
1-We expect to run things off the battery in a boat, at 11.6-12.6 volts. In a car we expect 14.3-14.4 from the alternator almost all the time.
2-In a car, the systems are disconnected from the alternator/starter when the car is started. In a boat they are not--so they can be spike damaged.
3-Tinned wiring is a must on a boat, to prevent corrosion.
4-Charging is different. A car's regulator is designed to "not overcharge" the battery during extended use. That won't charge the deep cycles on a boat properly, they need more power longer. And, the battery type will be different as well.
5-A $5.99/500 pieces crimping set might work on a car, but your boat deserves a $50 crimping tool and crimps that cost 50c each.

Still, there's an awful lot they have in common. And a lot of posts online, here and elsewhere, to cover most of it. Solar and wind add more layers or intricacy, partly because each needs a different regulation type (ideally MPPT versus dump, and both versus the engine's regulator) but the key trick is "Divide and Conquer". Break the problem down, look at each individual piece, then come back to see how they can or can't integrate.
09-22-2010 10:04 AM
eherlihy ... Oh yes - the BEST single reference that I have is Nigel Calder's Boat Owner's Mechanical and Electrical Manual. It cures insomnia too.
09-22-2010 10:01 AM
eherlihy .02 more -

Automotive and Marine electrical systems are VERY different. You can get away with things while working on a car, that will not last long on a boat. Butt splices, wire nuts, and no need to run a return line are three things that come to mind quickly. Also the ABYC has a wiring color code that will make your life easier (what does this wire do?) that is not used for automotive applications.
09-22-2010 09:30 AM
Sixpoint SD,

After some thought...if a particular boat's systems were kept strictly like those of a car, that is: 12VDC alternator charging a battery (or batteries) that run only 12VDC appliances, then I'd have it made.

I have a good bit of experience with automotive electrical systems.

However, throw in solar and/or wind charging, put a charge controller in there, plus the 12VDC alternator, then throw in the odd 110V AC appliance and the inverter(s) required, and my ignorance starts to show.

Still though - I think I'll take your advice about a 12VDC course; no such thing as too much knowledge. And one never knows when a new instructor will give you a new way of looking at things or share some golden tidbit that he/she has picked up from personal experience.

As an aside, it's always bothered me, when working with cars, that one can ground something to a metal frame...that's rolling around on rubber tires. Mystical, that is. :P
09-22-2010 05:22 AM
sailingdog Sixpoint—

Unless you're dealing with a really old car, the principles of the way the electrical system works is basically the same. The one major difference is that you can't use the frame of the boat as a ground, which is done on a lot of cars, since the frame of a car is usually metal—where it isn't on a boat. The alternator, battery, etc., are all basically the same though.

The wiring on car has some of the same problems faced by that on a boat, in that it is a vehicle that can often be used in a hostile environment. So, the wiring is generally stranded, but on a boat you should be using tinned marine grade stranded wire. If you think a car isn't a hostile environment, think about how much salt and such ends up flying around a car in a New England winter....they generally don't skimp on the salt around here. Terminations should be crimped with adhesive-lined heat-shrink tubing over them.
09-21-2010 09:59 PM
Sixpoint Sorry - for some reason I missed these replies until just now.

Thanks for the info mitiempo.

SD, are the systems that similar? I mean, I guess the basic principles would apply in either a car or a boat, so yeah...not a bad idea at all. Thanks
09-14-2010 05:10 AM
sailingdog Another option is to take a 12 VDC electrical course, like an automotive electrical system troubleshooting course at a local vocational school.
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