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A few days ago was running the engine when the revs went up unexpectedly. At the same time the alternator light came on. Had a look and the stud for the connection to the battery had snapped.

That all makes sense.

So took alt off and took it to a shop. They replaced stud and a rectifier they said was shot 340$ later nice shiny new looking alt

Reinstalled as before.now the warning light stays on. Grrrrrr

Assuming the alt is good what else could cause the light to stay on?

 

I need to put a tester on the back of alt when running just to be sure it going, but wont get to that till tomorrow morning. In the meantime.........

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To go, the alternator needs three connections. The main battery lead, an ignition wire connection to excite the alt, and a sense wire to detect batt voltage. The fourth wire is the warning light, not essential.

If its externally regulated (iirc yours is) it needs only the main batt + and the field connection to the reg, plus the warning light.

Have you connected everything properly?

If the light is on, the alternator is likely not switching on.

Does the voltage increase?

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Just had time to do this. Started engine and watched battery voltage on the solar panel controller. It went from 8 to 14 and back down when engine off. Also noticed tacho not functioning. I think it reads from the alternator as well

So is there a shitty connection between the alternator and instrument panel?

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Put a meter on the heavy black cable on the back of the alternator that I believe goes to battery and the other pin on engine and got exactly 12v. Does that mean I am charging batteries?

 

I think that means you are measuring your battery voltage?  

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Are you internally regulated or ext?

If ext three stage, will be ramping up to 14V+, with max Amps until it achieves absorbtion V, then stay at that voltage with

decreasing current until absorb time is up.

Check for volt drop in battery cable to alt as that could provide delta V for light not to go out. (hi resist joint)

Also could be balance diode.

 

How do I do that?

External smart reg.

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Back on board.

 

I triple checked the wiring is as it was. 12.4v off the back which is batteries. Alternator as new. Rev counter cuts in at half throttle. Also this morning while running the revs suddenly dropped for a number of seconds which sounded like the alternator kicking in but I was below and couldn't see if the light went off.

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Also be aware that some of the "smart" chargers don't always start at the beginning of the charging cycle when you kick them off.  They may take just a little while to work out what they need to do.

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After a weekend of work I'm back trying to diagnose this thing.

Queston: does the regulator make the alternator stop producing charge or does it just stop the charge reaching the batteries?

 

There is also a small (2cm) black cube that looks like some kind of switching device sitting above the alt with minor wires coming and going , maybe to reg maybe to ignition.any ideas what it is?

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After a weekend of work I'm back trying to diagnose this thing.

Queston: does the regulator make the alternator stop producing charge or does it just stop the charge reaching the batteries?

 

There is also a small (2cm) black cube that looks like some kind of switching device sitting above the alt with minor wires coming and going , maybe to reg maybe to ignition.any ideas what it is?

 

That could be a voltage regulator, or something.

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Queston: does the regulator make the alternator stop producing charge or does it just stop the charge reaching the batteries?

 

Smart charger / regulator stops the alternator producing current by controlling / reducing the field current.

Field current is a small current that effectively creates a magnet, so that the spinning coils of the alternator can produce the power. Without the field current, the alternator can't produce power. 

Field current is often controlled by a small, mysterious and un-important looking single wire....

 

If you didn't fully inform your supplier of your exact alternator set up, you might have the wrong bits (that I note cost you a far amount of money). It's also very easy to alter an alternator after market. We turned ours from a regulated alternator to being run by the smart charger, by taking it to an autoelectician, he took a key part out (replaced it with a dummy holding part) and all we were left with was a single wire sticking out. That wen't into the smart charger, and everything worked like a NASA mission.

 

The is about the extent of my alternator knowledge, other than having enough knowledge to know when its time to get someone else to fix it.

 

The small black box is likely very important. It may be a detonator, touch the wires and everything goes boom. But seriously, the old law of fixing Holdens applies. If you have bolts left over, you've missed something. With alternators, if you have wires left over, you've missed something...

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How did they know the rectifier was shot?

 

Broken studs aren't normally related to rectifiers. Broken studs are related to cyclic loading, vibration and metal fatigue.

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Yep, the reg switches on/off the alternator.

The little square box sounds like a relay. Likely it turns on the freezer compressor when the ignition is on. But it could be something completely different.

Pics?

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Smart charger / regulator stops the alternator producing current by controlling / reducing the field current.

Field current is a small current that effectively creates a magnet, so that the spinning coils of the alternator can produce the power. Without the field current, the alternator can't produce power. 

Field current is often controlled by a small, mysterious and un-important looking single wire....

 

If you didn't fully inform your supplier of your exact alternator set up, you might have the wrong bits (that I note cost you a far amount of money). It's also very easy to alter an alternator after market. We turned ours from a regulated alternator to being run by the smart charger, by taking it to an autoelectician, he took a key part out (replaced it with a dummy holding part) and all we were left with was a single wire sticking out. That wen't into the smart charger, and everything worked like a NASA mission.

 

The is about the extent of my alternator knowledge, other than having enough knowledge to know when its time to get someone else to fix it.

 

The small black box is likely very important. It may be a detonator, touch the wires and everything goes boom. But seriously, the old law of fixing Holdens applies. If you have bolts left over, you've missed something. With alternators, if you have wires left over, you've missed something...

Of interest, you actually have to short out the field on a alternator to neutral in order to stop induced current as the simple passing of the windings through the energised stator will still produce a potential which in turn creates potential in the stator and current flow. Your alternator is still working otherwise!

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All you guys are supposing that this is an "N" type alternator. It may well be a P type....

 

An N type alt regulates the alternator on the N (-) side, and a P type (+) on the positive side. Field control is then different of course, and the regulator is normally either an N or P type and MUST match the alt. Some fancy regs can  be switched, one to the other, but not many.

 

Basically all you do to convert an internal reg alternator to external, is remove the connection from the brush to the internal reg, and lead it outside to the external reg. This is not too hard on most alts.

 

Alts need volts to start - also known as exciting the alt. Some alts are self exciting, but most are not. Thats why an alt wont switch on, for example, when you try to crash start a car with a dead flat battery - the alternator doesn't have the volts required to switch it on... Most battery charges also require a min voltage to be present before they will go as well.

 

So, the result of this thread at this point may highlight this for some. Either spend the time and effort to learn about this stuff, or employ someone to do it for you.  Its worth getting right - the correct charging voltage for a specific battery is the target - being out by as little as 0.2v when charging can increase your charge time by as much as 30%. Running a battery at its bulk charge voltage long term will significantly decrease its life.

 

There are lots of variations in alt types and setups in boats. Diags remotely are very difficult.

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