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Old 15-10-2018, 08:37   #1
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Most common alternator issues in the field

After a few informative back and forths on this forum, I'm taking an automotive electrical class at my local community college. (After this class I take diesel maintenance and trouble shooting)

Right now we're going over charging systems/alternators. We're covering:
output tests and needed repairs
charging system circuit voltage drop tests
regulator tests and repairs
testing and replacing diodes and/or rectifier bridges
inspecting and replacing brushes
etc

I'm curious, what are the most common charging issues you have on a boat while far afloat? Do many people do that many repairs? or just carry spares?

Again, thanks in advance.
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Old 15-10-2018, 18:17   #2
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Re: Most common alternator issues in the field

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Originally Posted by fschaefer4 View Post
After a few informative back and forths on this forum, I'm taking an automotive electrical class at my local community college. (After this class I take diesel maintenance and trouble shooting)

Right now we're going over charging systems/alternators. We're covering:
output tests and needed repairs
charging system circuit voltage drop tests
regulator tests and repairs
testing and replacing diodes and/or rectifier bridges
inspecting and replacing brushes
etc

I'm curious, what are the most common charging issues you have on a boat while far afloat? Do many people do that many repairs? or just carry spares?

Again, thanks in advance.
Very few people will carry a full set of diodes and regulator parts for their alternators. When an alternator craps out, most people take it to a rebuild shop. It is easy and inexpensive.

Smart sailors have either spare alternators, or other ways of charging their batteries. Even for those with the knowledge and skills to rebuild an alternator onboard, a spare unit takes away the time pressure to get the job done while on a crossing.
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Old 15-10-2018, 18:25   #3
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Re: Most common alternator issues in the field

Loose connections. New wiring from an external regulator factory crimps all failed. Intermittent tach readings almost always result in: check the connections.


Anything electrical that is intermittent is almost always a bad connection. May "look" good, but ya gotta PULL on it.


Good luck, good question.
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Old 15-10-2018, 18:30   #4
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Re: Most common alternator issues in the field

We carry a complete spare alternator (never used in 14 years) and a Ford external alternator regulator to back up the Xantrex (Balmar) regulator (used once).

We had the crescent alternator adjusting bracket break in half once, but spliced it with a bolt and fender washers until we could have it welded back together. Later, we replaced it and kept the welded one as a spare.

We have broken alternator belts several times. We drive a 105A alternator with a 1/2" v-belt over a 62mm pulley. We carry spare belts.

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Old 16-10-2018, 07:02   #5
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Re: Most common alternator issues in the field

All that makes sense. Thanks guys.

@billknny- Full replacement means quickly being up and running without having to diagnose and repair in the field. Then the old unit can be diagnosed and repaired without critical time pressure. I'm sure there are shops all over the world that can rebuild an alternator- even in the most out of the way places. Having a replacement regulator makes a lot of sense too. Two is one and one is none!

@ Stu Jackson- One thing the teacher in my class keeps repeating is that corrosion or bad connections are the number one electrical problem in vehicles. That's my experience with overland motorcycle trips. Clean, dialectic grease where appropriate, reconnect and protect (if possible) will solve a huge number of electrical problems.
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Old 16-10-2018, 08:41   #6
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Re: Most common alternator issues in the field

I would go as far as to say that dielectric grease is appropriate everywhere, excess can be wiped off if necessary.
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Old 16-10-2018, 09:18   #7
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Re: Most common alternator issues in the field

Connection issues aside, I think there are 3 main faults

Diodes, which will blow if you attempt to hot swap batteries while the engine is running

Regulators, voltage out of range

Stator connectivity, check the brushes and connection between slip rings suggesting the stator is ok

Outside of faults your problem is to source parts, and sometimes Alts can be difficult to identify
My Westerbeke has a Motorola Prestolite alternator for which I need a regulator, but I cant ID the model
makes it hard to find the part ...
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Old 16-10-2018, 11:02   #8
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Re: Most common alternator issues in the field

The only problem I have ever had with several boats was broken/ slipping belts.
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Old 16-10-2018, 13:40   #9
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Re: Most common alternator issues in the field

... and here I was thinking the question had to do with alternator Field windings... a potential source of problems, or a bad pun.
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Old 16-10-2018, 14:17   #10
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Re: Most common alternator issues in the field

I have had 2 alternators die. One attached to the engine that got submerged... No they don't survive contact with seawater! The other when some idiot who should have known better swapped the start battery and forgot to tighten the terminals. These days with solar so common a lit of the rational for carrying a spare alternator goes away as long as you have enough solar to run under emergency conditions. Much of our higher electrical consumption tend to be luxuries not essential navigation etc.
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Old 16-10-2018, 14:39   #11
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Re: Most common alternator issues in the field

Quote:
Originally Posted by ZULU40 View Post
Connection issues aside, I think there are 3 main faults

Diodes, which will blow if you attempt to hot swap batteries while the engine is running

Regulators, voltage out of range

Stator connectivity, check the brushes and connection between slip rings suggesting the stator is ok

Outside of faults your problem is to source parts, and sometimes Alts can be difficult to identify
My Westerbeke has a Motorola Prestolite alternator for which I need a regulator, but I cant ID the model
makes it hard to find the part ...
I think you mean rotor rather than stator.

The slip rings / brushes makes the connection to the rotor windings (i.e. field winding). The stator windings as their name suggests are stationary.
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Old 16-10-2018, 14:39   #12
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Re: Most common alternator issues in the field

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I have had 2 alternators die. One attached to the engine that got submerged... No they don't survive contact with seawater! The other when some idiot who should have known better swapped the start battery and forgot to tighten the terminals. These days with solar so common a lit of the rational for carrying a spare alternator goes away as long as you have enough solar to run under emergency conditions. Much of our higher electrical consumption tend to be luxuries not essential navigation etc.
This is a good point. I almost never use my alternator for charging (solar does that). Also, my alternator is on its own pulleys and belt, so if I had to remove it for some reason, the water pump">raw water pump wouldn't be affected. Still, I suspect it helps to balance the side forces of the raw water pump. Otherwise, I could live without it until I found a place to repair or replace it.
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Old 16-10-2018, 15:52   #13
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Re: Most common alternator issues in the field

#1 Failure I see is blown diodes - #1 Cause usually an owner or guest rotating the battery switch through OFF with the alt producing power. #2 Cause of blown diodes is a bad or loose connection that open circuits the alt output circuit.. Even saw a engine panel mounted ammeter melt the internal shunt and cause an open circuit when an owner installed a 120A alternator and kept the 0-30A ammeter in the circuit path..

#2 Failure I see is brushes - This is usually due to age or just cheap carbon brushes being used.

#3 Failure I see is overheating death - #1 cause is the bank is too big and alternator too small or too light a duty for the task.

#4 Failure I see is a failed regulator. #1 Cause corrosion. #2 Cause most likely heat. #3 Cause short circuit.

#5 Failure of front bearing - #1 cause belt slippage creating excess frictional heat resulting from trying to extract too much HP from too small a belt. Often melts the seal right out of the bearing and then, once exposed, it soon fails..
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Old 16-10-2018, 16:24   #14
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Re: Most common alternator issues in the field

Many people upgrade the stock alternator with a higher output. So the original ends up being a spare. But I have not had an alternator fail in ~40 years. Batteries fail though.
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Old 16-10-2018, 16:55   #15
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Re: Most common alternator issues in the field

Nobody mentioned the strength and critical alignment of the alternator bracket.... I have the old original set up on my boat... Should I be scared as they say?


https://www.catalinadirect.com/index...t-retrofit.cfm
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