Signs of Alternator Issues

[Hampton]

Guage on dash dropped from almost 14V to 12 and then bled down until I got a Battery Warning with the engine running. Belt was fine. I started the genny and charged the battery, but the alternator appeared to stop making electrons (STS).

Got back to dock, shut down, re-seated alt connections, restarted, and still not good. As I removed the alternator, I checked for current and the hot wire was just that - hot (12V). That was with the engine keys off, but batteries on. Is this normal? If the alt checks good, what is the next part to check (other than the connections at the other end).

If it checks good on the stand, I'll re-install it. If still not good, I'll swap alternators port to stbd after re-checking all connections - haven't checked at battery yet.

Any other ideas?

Rest of the story:

Spent night at island, went for walk, then prepared to return to dock.
Got alarm above and used genny for battery charging.
Cruised home to dock (2 miles).
Tried to fix, then removed alternator.
Tried to start truck - brand new battery is dead (obviously another issue - alternator? - no, something is staying hot with key off.)
Finally found someone with cables. Found someone else with car. Jumped truck. Almost out of gas - stopped and tried to refuel with engine on - idles too low and quit. Found another set of cables and got jumped again.
Dropped wife off at car.
Raced home.
Showered.
Shoveled in a breakfast burrito.
Got in car to airport. Got a block away. Turned back for cell phone.
Raced to airport.
Raced through security (lucky).
Arrived at gate with 18 mintues to go (bare minimum is 15).
Talked flight attendant into stowing bag in front closet (full plane).
Flew to Atlanta.
Signed in to work - now, I have a couple of hours to relax.

 

[BonBini]

Guage on dash dropped from almost 14V to 12 and then bled down until I got a Battery warning. Belt was fine. As I removed the alternator, I checked for current and the hot wire was just that - hot (12V). That was with the engine keys off, but batteries on. Is this normal? If the alt checks good, what is the next part to check (other than the connections at the other end).

If it checks good on the stand, I'll re-install it. If still not good, I'll swap alternators port to stbd after re-checking all connections - haven't checked at battery yet.

Any other ideas?

Sounds like your trouble shooting steps are spot on. I may have checked charging voltage at alt with engine running. And also felt alt to see if it was running hot (sighn of heavy loading)

 

[Hampton]

Sounds like your trouble shooting steps are spot on. I may have checked charging voltage at alt with engine running. And also felt alt to see if it was running hot (sighn of heavy loading)

Thanks. It wasn't long after shut down that I was down there trouble shooting. It didn't seem hot.

When I finally took it off, I unbolted it and held it in my hand, then, I disconnected the ground wire. With the Alt in one hand and the ground wire in the other, I got a small jolt. I checked it a couple of times. The body of the alt was Hot (12 V DC) with nothing but the Hot wire hooked up normally. This tells me that there is a short inside the alt between the hot wire and the body of the alt.

Does that sound about right?

 

[roadkingh1]

Thanks. It wasn't long after shut down that I was down there trouble shooting. It didn't seem hot.

When I finally took it off, I unbolted it and held it in my hand, then, I disconnected the ground wire. With the Alt in one hand and the ground wire in the other, I got a small jolt. I checked it a couple of times. The body of the alt was Hot (12 V DC) with nothing but the Hot wire hooked up normally. This tells me that there is a short inside the alt between the hot wire and the body of the alt.

Does that sound about right?

When the engine is on you should see about 13.5 to 14.5 volts at the battery, when off it should drop to 12.5. If you only have 12.5 at the battery when the engine is running, I would check at the alt. to ground to see if you have 13.5 to 14.5. If you do, you have a problem somewhere between alt and battery. If you have only 12.5 at the alt. you have a problem with alt. You use to be able to change the triode pack, I am not sure you can do that anymore.

 

[BonBini]

When I finally took it off, I unbolted it and held it in my hand, then, I disconnected the ground wire. With the Alt in one hand and the ground wire in the other, I got a small jolt. I checked it a couple of times. The body of the alt was Hot (12 V DC) with nothing but the Hot wire hooked up normally. This tells me that there is a short inside the alt between the hot wire and the body of the alt.

Does that sound about right?

The "jolt" does not sound right. Another way would be touch the wire back to it's original connection and watch for a small spark. Even another way would be install a amp meter in series to check for a draw. Most little DVOM testers have a built in amp meter these days...

If your still having trouble, I’d be glad to fly down to help, just cant get that old lear jet of mine fired up. I think I got the plug wires on wrong the last time I changed the sparkin pins...:huh:

Edit: actualy a jet engine may have at least one firing pin in there. hell I don't know. I'll have to get the service truck out here.

 

[flarepoman]

Take the alt to auto zone or any one of those places and have it checked for free.

Rick

 

[HUMPH]

Take the alt to auto zone or any one of those places and have it checked for free.

Rick

I tried that with mine, I actually took it to two different store and neither wouls test it because they could not cross reference the part number. I asked why they need a part number at the first place and the guy said that it will show a diagram for where to connect the wires. After I got my jaw back in place I took it and pointed saying "positive here, negative there" but they would not do it.

I bought a new alternator online and replaced it even though I was not 100% sure mine was bad. The "Z bracket" for this alternator was broken in half so I didn't know if that was the issue or if the unit was bad but I had a 2-week cruise coming and didn't want to deal with it.

Buy a new one for less than $200 and be done with it.

 

[Hampton]

My wife will be walking into our local alternator shop in a couple of hours. He'll be ordering one (MARINE) if that one is, in deed, bad.

Jet engines have ignitors - very powerful spark plugs - just like diesels.

 

[fwebster]

John,

The internals are most likely just a Delco type alternator. The alternator/starter shop should be able to repair or replace anything inside the case rather than replacing the entire alternator. This isn't the first marine alternator they have seen.

 

[flarepoman]

Hampton try this place I've had good luck and good on the $$$$$
http://www.arcomarine.com/

Rick

 

[fc3]

Trivial. Red wire is always hot. It's the "sense" wire for the internal regulator. The regulator senses the system voltage via the red wire to maintain the proper charging voltage. With the engine running, you should always see around 13.6 or so there. If there is no voltage there, the regulator will go "full field."

The purple wire is the exciter lead. There are no permanent magnets in the alternator. Thus there is no magnetic field to begin generating current. The exciter wire supplies some start-up current to the regulator so that the regulator can power up the field windings and generate power. Once the alternator is running, the bulk of the field current is supplied directly to the regulator via an internal connection to the rectifier set's output terminal.

Orange wire is the alternator output. The orange wire must never, ever be disconnected from the load while the alternator is running and the field coils have power. Without a connection to a load, the output voltage can easily spike to over 100 volts, far exceeding the PIV ratings on the rectifiers. Disconnect the output while the engine's running is a sure way to need either a new alternator or a rebuild with new rectifiers.

Black wire is ground. Proper operation requires a good ground connection. A poor ground might allow the alternator case's voltage to float above ground, causing the regulator to sense a lower voltage and kick up the output voltage.

Check that the ground on the alternator case is good. Should be nearly zero ohms. If there's battery voltage on sense, exciter, and possibly output with the ignition on and the engine not running, then the wiring is probably okay. If the voltage does not increase to over 13.6 with the engine running, there's a fault in the alternator. That's all there is to testing. If the boat's electrical system is equipped with a crossover charging system (battery isolator) then you will not see battery voltage on the output terminal when the engine is not running. This is normal. If the boat is equipped with an isolator, perform a diode test before testing the alternator. A bad (open) isolator can fault the alternator.

This is horribly bad physics, "the alternator appeared to stop making electrons." Makes my head hurt to read kiddie stuff like that.

 

[Hampton]

Good, I got to you. Thanks for all of the advice and excellent details. You must be an engineer, and, I must be a pilot.

The alternator is bad. New one on order for delivery early Wed. Lots of ways to save money, but, woke up on the boat Sunday, am flying a 4-day trip to Newark, West Palm, LaGuardia, Atlanta, Mexico City, Atlanta, Midway, and, you guessed it, Atlanta, then, I will install the new Alternator and head out on a 4-day boat cruise to the Apalachicola Sea Food Festival early Thurday morning.

Is there really a way to save $50 and still do this?

I'll update y'all when the trons are flowing again.

 

[fc3]

Not an engineer, but was a private pilot until my wife said, "You can have a boat or a plane, but you can't have both."

It's like landing a plane. Almost good isn't really good unless you're one of those who thinks, "Any landing you can walk away from is a good landing." I don't want to fly with those guys.

 

[Hampton]

Replaced alternator last Thurs AM. Spent Thurs, Fri, and Sat nights in Apalach tied up to my friend's new 60Da. Sun night, we spent out on the hook at Crooked Island with a Camp Fire.

 

[carterchapman]

John,

Did you end up rebuilding or buying a new one?