Another alternator question

[Stu Jackson]

Umm, it's the regulator AND the alternator

Mick nailed it.It's your boat, your choice, rebuild the alternator, and make it work, but if you still have automotive regulation you're basically screwed.Rebuild the old one and add external regulation.Or buy a new(er) alternator, and a new regulator.The single belt limits you to 100 amps, but that's MORE than enough with a new regulator. Without a new regulator NOTHING will work properly.Try this, too: C34 Projects page --http://www.c34.org/projects/projects-electrical-system-upgrade-2.htmlHey, Fred, welcome back!

 

[Bill Roosa]

Jvass, what does rotor current have

to do with the output current? The regulator just turns it on and off real fast to give a magnetic field. Once you have the 2-3 amp current going in the rotor making a magnetic field the motor turning the field is where the work comes from.I see your are from west point. You are not one of those "ring knockers" are you?

 

[jviss]

Replace alternator

If you attempt to charge a 400AH bank with a 40 Amp alternator and an external regualtor, you will probably fry the alternator.

 

[jviss]

to Bill

Bill, (it's Westport, not Westpoint - I'm actually a Manhattan College grad (NY)).What you describe is not how an alternator works. It is what is referred to as an induction machine. Stator current is proportional to field current according to: Ir-s=Ir*Nr/Ns, where Ir-s is stator current, Ir is field current, Nr is rotor turns, and Ns is stator turns.The DC current in the rotor (field) is "chopped" by old-fashioned relay-style regulators in order to regulate output. But it's the DC current that provides the magnetism, not the the chopping. The output power comes from converting the rotating magnetic field into a current in the stator, so in answer to your first question, "what does what does rotor current have to do with the output current?" the answer is everything! Or more precisely, the output current is directly proportional to the rotor current, according to the turns ration of the rotor and stator.

 

[Phil]

Yes to the bat wire

I had 2-4d on one bank and a extra battery on the secdond bank with a 50 amp, not good. The alt would never get them charged. The system had an exterior regulator. Replaced it with a 105amp selfexciting alt and by past the exterior regulator, KISS. The starter wire had to be increased substantialy for that start up draw but the wirers to the batteries stayed the same. Everything is much happier now. The batteries charge without a problem and the alt ramps down the way its suppose to. Nothing has burned, melted, exploded, boiled, knock no wood.

 

[Fred Ficarra]

Perhaps I detect a miss-conception JVISS.

The regulator regulates the amount of current to the rotor. That current is DC. That creates a magnetic field. That field VARIES in strength. That's how alternator output is controlled by the regulator. THE ROTOR CURRENT IS NEVER PROPORTIONAL TO STATOR SIZE. That is simply not a requirement of an alternator. Maybe you are thinking of some kind of fixed output device.Stu, Thank you. Good to be back. We took the dogs you know.

 

[jviss]

To Fred.

Fred, you don't read my notes carefully, and then say I'm laboring with a misconception. You simply didn't get what I wrote. First, you simply re-stated what I did, which is that the DC current causes the magnetism, in the rotor. Perhaps you don't know that many regulators modulate this field using switching rather than linear operation, which would be less efficient (hence the term "switching regulator). In fact, the earliest voltage regualtors used with alternators were electromagnetic switchers, like a relay, very similar to the voltage regulators of the automotive generator era.I never said that "THE ROTOR CURRENT IS NEVER PROPORTIONAL TO STATOR SIZE," as you shouted. I did say that stator current is proportional to rotor current. The proportionality is governed by the turns ratio of rotor to stator. I don't know what you mean by saying I must be thinking of "some fixed output device." The basics on the operation of alternators, the fundamental mechanism, can be found by searching for the topic induction machines.

 

[Fred Ficarra]

To jviss

Huh?I don't see the need to make a simple device complex. What's the point of all this?

 

[ClownPilot]

Ye ol' standby replacement

When it comes to alternator swaps, nothing but nothing beats a Delcotron by GM automotive. They are cheap, abundant, easy to service with readily available brush kits, bearings et cetra.I am referring to the alternators used in pre-ninety vehicles. Those commonly referred to as single wire alternators. Easily adaptable to most other vehicles ... even Jaguar! But then, I love to cut and grind and MIG weld bracketry together. But seriously, the standard Delcotron is a 50 amp model, but also has a 90 amp model available. Both internally regulated. Both regulator pins can be tied together and set at 12 volts. Simply jumpered from the BAT+ (Battery) lug on the alternator makes for the 1 wire interface that completes the charge system!The function of the two pin regulator is,1) FIELD connection (requires 12 volts)2) RELAY connection. This is used to turn the alternator on and off. 12 volts turns the alternator on. Normally, it is wired to the ignition switch. Some cars wire it to the oil pressure switch so that the alternator doesn't load down the battery when the starter motor is turning the engine over.My advice is this ... Go to the junkyard and buy a delco alternator. Size it up and determine what physical installation changes may have to be done. If it looks doable to you ... go for it. Install it, then lay the standard charging harness aside. Tape it off safely so that it won't spark on grounded metal surfaces. Run a 10 AWG wire (no more the distance of six feet if possible) to plus terminal your 12 volt bank of batteries. The other end to the BAT terminal of the alternator. Run a ground wire of the same size to the ground bus of your battery systems. Go to the local parts store like Auto Zone and purchase a two lead GM alternator regulator pigtail connector. Tie the two leads together on the pigtail and connect the pigtail to the 12 volt BAT terminal.Start up the engine and measure the output from the BAT terminal. Goose the engine to approx 1000 rpm. This will kick the alternator on. You should see a clean 14 volts on your meter!GM has a very intuitive regulator. The best there is in IMHO. Never needed to replace one, but getting one for a spare costs less than 20 bucks.works for me ... but then, if it don't for you, just return the altenator and because you didn't change your wiring, just untape your old alternator harness and your back to business.Tom