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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 06-10-2003
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Bad alternator???

When I attempted to start my in-board diesel recently, I cranked the engine a couple of times for 15 seconds or so, but it would not start. I went below to discover that the batteries -- 4 years old but still useable because I take good care of them -- were bubbling and emitting a foul odor. I then commenced to disconnect the battery cables, only to discover that both the positive and negative cables were very, very, VERY hot to the touch.

What gives? Bad alternator? Bad regulator? Or perhaps a bad starter? And is there any thing I can to check these out without taking them off and having them bench tested?

Once the batteries cooled, I removed them from the boat. Though they had been fully charged -- 12.6 volts or so -- one battery could not hold a load. So I''ll replace both and use the remaining good one as an emergency on-board spare.

But I''m also concerned that hooking up new batteries to a faulty charging/starting system will damage them.

Ideas?

Michael
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Old 06-10-2003
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Bad alternator???

Before you hook anything back up you want to make sure you have solved the problem which caused the cables to overheat. There is no way a bad battery would cause that to happen while the battery is being discharged (sounds like that was the case as you were cranking the engine). If the battery is being charged, then a shorted battery could cause the cables to overheat. But, as you were able to charge both batteries to 12.6 volts it appears that neither battery was shorted.

It appears that something is shorted out in your electrical system and that damaged one of your batteries.

I would try using an ohmmeter to find the short. You''ll probably need to disconnect wires to isolate it. You''ll probably find a very low resistance between the positive and negative battery cables with the batteries removed. Then, the trick is to disconnect things until it goes away. Then you''ve found your problem.

It shouldn''t be hard to find. If the cables were as hot as you indicated, there''s a very low resistance somewhere.
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Old 06-10-2003
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Bad alternator???

Some questions and then easier things to check first:
?1. Were the batteries at 12.6V immediately prior to cranking & fail to start?
?2. Selector was in "both" position when cranking?
?3. After removing batteries, you placed them on charge - one recharges, & other did not - have I got this right?
?4. Fuel valve was open, and decompression lever closed when cranking failed to start?
you would not be the first
INITIAL QUICK TESTS:
With battery switch off (batteries installed, but positive cable not connected), place ammeter between Battery positive (+ red meter lead) and Positive (Red) Battery Cable. Read no current - OK. Read any current, look to your starter wiring (short to ground).
Turn Battery Selector Switch to "Both", ensuring all DC Panel Breakers are Off, or Fuses removed.
Read current as above. No current - OK. Any current - look to panel feeder.
Regards,
Gord
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Old 06-10-2003
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Bad alternator???

Sounds like you may have a short in one of the cells.

Are they AGM or Gell? If not, have been monitoring the water level?

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Old 10-10-2006
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Crannking with flat battries will cause high amps to be drawn and if you were cranking for a while the cables will proberly heat up . This problem is not a fault in your alternator . Neil...
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Old 10-10-2006
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High currents!

I concure, batteries have the ability to produce thousands of amps for a very short time. In addition I would check connections to the battery and to the starter. A loose or corroded connection can cause the voltage at the engine to be too low to effectively start and high current from the battery.
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Old 10-10-2006
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I triy to use a dedicated starter battery, separate from the house battery. Starters are very hard on batteries..
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Old 10-10-2006
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Also if it cranked for 15 sec. or so and everything got very hot ,almost frozen engine could put high load on starter, also high resistance ie.coroded cables can generate quite a bit of heat.Art

Last edited by Artwerke; 10-10-2006 at 10:31 PM.
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Old 10-10-2006
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okkkkey, we have lots of marine experts on duty here. So many solutions!
So few real details.
It wouldn't start after prolonged cranking,,,,, but was it cranking fast enough? And was it now too cold to start without glow plugs,,,, that weren't needed and haven't been working all summer? Who knows?!!!!
But I love a mystery! Don't you? The answer may help one of us in the future.
The bad battery may be the answer but I doubt it. How long has it been since it last run? Did it crank normaly or slow? Did it try to start?
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Old 10-11-2006
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cardiacpaul is a jewel in the rough cardiacpaul is a jewel in the rough cardiacpaul is a jewel in the rough
considering the thread started in 2003, its either started by now, or he's been working on it a really long time.
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