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  #26   IP: 206.125.176.3
Old 12-31-2009, 01:21 PM
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Quote:
Originally Posted by roadnsky View Post

Again, the DC experts could certainly give us better explanations...
I think you just did Jerry...nice work!
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  #27   IP: 142.68.244.115
Old 12-31-2009, 10:54 PM
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Quote:
Originally Posted by roadnsky View Post
Again, the DC experts could certainly give us better explanations...
I'm no expert, but when I rewired the boat last year I got rid of that ammeter in the cockpit ignition panel, eliminated that long alternator output wire, and replaced it with a very short cable to the starter solenoid and thence (big word alert) to the positive terminal on the engine start battery. http://www.moyermarine.com/forums/showthread.php?t=2727

So Jerry, I think you found the same kind of problem I had with that failing slave starter solenoid: bad connections in old circuits. Good work.
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  #28   IP: 142.68.253.106
Old 05-05-2010, 07:05 AM
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On re-reading this post, I've been pondering principles for this pesky jumpy tach thing. These are musings from an amateur boater who has lived through 3 used boats, not a professional marine engineer. I've only experienced it once on our first boat, but it was a nightmare. You can imagine my relief when I first fired up the engine after the big refit on this third boat and saw a nice, steady tach needle.

1. Draw complete schematics of a boat's wiring. Start with one based on the batteries and charging system (the heart of the system), and then branch out to include sub-schematics for the engine, ignition panel and house wiring. Those drawings take time to make, but they are essential for troubleshooting wiring. Take advantage of a rainy dockside day to work on the schematics with nice music going in the background. Put on work clothes, then get down and crawl into every nook and cranny, wearing glasses with little LED lights on the frames (but don't let anyone see you wearing them). Along the way, I suspect most owners of old boats discover wires, connections and parts that need updating.

2. Revising old wiring is a time-consuming but very worthy project on an older boat. Shorter and simpler appeals to me, but within sound marine electrical practices. Getting professional advice for best practices in marine electronics is not easy for average boaters.

3. A jumpy tach in an older boat can mean a mechanically faulty electrical connection in either a component or a wire. If in a component, then the easy way to identify it is to swap in a new component. Start with the cheapest ones , and the ones most likely from the schematics to be able to make the tach jumpy. Tachs are expensive, so just clean their terminals and check the cylinder number setting first, unless someone can loan you a reliable tach to swap in as a check. From the few stories I've heard, tachs can be the problem, but usually aren't.

4. The old-fashioned design for alternator wiring on our 70's vintage sailboats apparently was to run a long output wire from the alternator aft to an ammeter in the cockpit, and from there double-back forward to all other systems that draw from the alternator, including recharging the batteries. While that worked for decades in many boats when loads were lower, I get the sense that the modern style is to make the alternator output cable as short as possible, and then draw current for subsystems like the engine, ignition panel and house selectively in dedicated fused circuits. The modern approach seems to reduce opportunities for problems like the one described in this thread by eliminating the ammeter aft and replacing it with a voltmeter, and then running the alternator output directly to the battery via the starter solenoid. Electricity does not seem to like long runs, or at least it is harder to keep electricity flowing cleanly over long distances.

These are just early morning recreational musings of a hobbyist over coffee. Your mileage will vary.
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