At the end of the day after letting my Yanmar 18 on my Hunter 29.5 cool down for ten minutes, I went to pull the stop wire and awaited the beeping of the ignition. It turned out a well-intentioned crew member had turned the key off but the engine kept running anyway. I've always heard this will ruin the alternator. Later I was able to start up the engine without any problem and shut it down the usual way. But I'm worried that my alternator may be shot and don't know how to tell. I'd appreciate any help. Bill O'Donovan Williamsburg VA
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Paul Akers
Easiest way is...
...if your electrical panel has a voltage guage for your battery bank(s). Or if you don't have a guage, a multimeter check on the alternator will tell. In both cases, besure the engine is revving when you check. On the control panel, the voltage meter should read about 14.1 volts when the alternator is outputting. If you use a multimeter, the red lead should be touching the red pole on the back of the alternator. The black lead should be touching any ground. It too, should read 14.1 If it reads less than that, then the alternator is not outputting. Also check it on a friend's engine to ensure that the multumeter is working correctly, also.
...if your electrical panel has a voltage guage for your battery bank(s). Or if you don't have a guage, a multimeter check on the alternator will tell. In both cases, besure the engine is revving when you check. On the control panel, the voltage meter should read about 14.1 volts when the alternator is outputting. If you use a multimeter, the red lead should be touching the red pole on the back of the alternator. The black lead should be touching any ground. It too, should read 14.1 If it reads less than that, then the alternator is not outputting. Also check it on a friend's engine to ensure that the multumeter is working correctly, also.
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Tim Leighton
WRONG SWITCH
Bill: There was quite a bit of discussion on this subject about a year ago and you can probably find it in the archives section. Before I continue, I want to warn you that I'M NOT AN ELECTRICAL EXPERT!!! As I recall, there is no danger of frying your alternator simply by turning the ignition off and then pulling the stop cable. I've been doing so for 15 years on my 1985 H31 just east of you in Norfolk. (In fact, I relocated my stop cable to the cabin so I can leave it out to provide an extra measure of security against thieft.) Have experienced no ill effects at all. I think the problem you are referring to is switching the master battery switch to "OFF" while the engine is running. That will potentially fry your alternator. Hope this helps. Again, check the archives. That's where I'm headed now! Smooth sailing. Tim (S/V "TIDE")
Bill: There was quite a bit of discussion on this subject about a year ago and you can probably find it in the archives section. Before I continue, I want to warn you that I'M NOT AN ELECTRICAL EXPERT!!! As I recall, there is no danger of frying your alternator simply by turning the ignition off and then pulling the stop cable. I've been doing so for 15 years on my 1985 H31 just east of you in Norfolk. (In fact, I relocated my stop cable to the cabin so I can leave it out to provide an extra measure of security against thieft.) Have experienced no ill effects at all. I think the problem you are referring to is switching the master battery switch to "OFF" while the engine is running. That will potentially fry your alternator. Hope this helps. Again, check the archives. That's where I'm headed now! Smooth sailing. Tim (S/V "TIDE")
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Aldo Lozano
Tim is correct, Bill...
...the electrical switch (key) merelly give power to the starting system (starting solenoid en the starter itself) and also feed the thermic and pressure switches and the lightc and horn(buzzer for the alarm. The voltage for thefield of the alternator is supplied through the regulator, which in turn take it directly from the battery. An alternative method of mesuring if you have output from the alternator is jus with a voltmeter on the battery as suggested on the previous post. Before starting, you should read around 12 volts, dropping to 11, 10.5 when you are cranking and then 13.8 to 14.1 as Tim mention. Electrical systems on ours boats are the simplicity itself, very elementary. Good luck... Aldo alozano@monmouth.com
...the electrical switch (key) merelly give power to the starting system (starting solenoid en the starter itself) and also feed the thermic and pressure switches and the lightc and horn(buzzer for the alarm. The voltage for thefield of the alternator is supplied through the regulator, which in turn take it directly from the battery. An alternative method of mesuring if you have output from the alternator is jus with a voltmeter on the battery as suggested on the previous post. Before starting, you should read around 12 volts, dropping to 11, 10.5 when you are cranking and then 13.8 to 14.1 as Tim mention. Electrical systems on ours boats are the simplicity itself, very elementary. Good luck... Aldo alozano@monmouth.com
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Larry Baker
Fried Alternator
Do not start the engine with the BATTERY SWITCH set to "off." This, will indeed fry the diodes in the alternator. Larry Baker Flat Broker Grapevine, TX
Do not start the engine with the BATTERY SWITCH set to "off." This, will indeed fry the diodes in the alternator. Larry Baker Flat Broker Grapevine, TX
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Aldo Lozano
Switch of?
Larry, I am curious... You mind start it by hand? If the battery switch is off, how you get the power to activate the starting solenoid and, eventually, the starter. In a normal installation, switching off the battery, also cut off the power to the regulator,and, in doing so, to the field of the alternator. No current in the field, no output from the alternator. Diodes have nothing to rectify, no heat. I am sure I am missing something...Please, can you let me know? Aldo S/V Isabel alozano@monmouth.com
Larry, I am curious... You mind start it by hand? If the battery switch is off, how you get the power to activate the starting solenoid and, eventually, the starter. In a normal installation, switching off the battery, also cut off the power to the regulator,and, in doing so, to the field of the alternator. No current in the field, no output from the alternator. Diodes have nothing to rectify, no heat. I am sure I am missing something...Please, can you let me know? Aldo S/V Isabel alozano@monmouth.com
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Bryan C.
Issue is disconnecting batts while engine running
If you alternator is wired thru your battery switch, and you switch to off (disconnecting batt) the power produced by alternator has nowhere to go and will fry alternator. Can avoid this by connecting alternator output to house or installing a batt switch with a field disconnect or installing zap-stop.
If you alternator is wired thru your battery switch, and you switch to off (disconnecting batt) the power produced by alternator has nowhere to go and will fry alternator. Can avoid this by connecting alternator output to house or installing a batt switch with a field disconnect or installing zap-stop.
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