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Old 08-06-2007, 06:58 PM   #1
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Any alternator experts out there ?

I run two alternators on entirely seperate systems, one for the house battery bank and one, a Delco, for the starter/windlass battery 120 amp hr, 1 year old. The Delco alternator is probably the same age as the yacht 17 years.

After I had a mechanic on board to fix a broken belt tensionin arm, the Delco sarted to give problems. First, I had to rev the enbgine to about 2500 rpm to get it to start charging, after a few weeks, it stopped charging all together. Concurrently, the rev counter played up, and now shows about a sixh of true revs. I have had the alternator checked and it is said to be OK, but I am not totally sure of this - there are some indiffrent elecricians around here, Turkey.

The alternator has main positive and earth connections, plus three small spade connections but the wires disappear into a harness and emege Who knows where.. One of them is purple and there is a purple lead into the rev counter.

Any advice wuld be gratefully received

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Old 08-06-2007, 10:34 PM   #2
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Quote:
Originally Posted by steelfan View Post
The Delco alternator is probably the same age as the yacht 17 years.

After I had a mechanic on board to fix a broken belt tensionin arm, the Delco sarted to give problems. First, I had to rev the enbgine to about 2500 rpm to get it to start charging, after a few weeks, it stopped charging all together.

Any advice wuld be gratefully received

Check the belt, first for slippage , then check it to see if it is correct in terms of it fitting the alternator pulley ( depress the belt in the centre of longest unsupported point, re-tension until you get max depress of about 12mm.

Run engine at normal RPM - if problem remains - come back for low voltage boffins.

Richard
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Old 08-07-2007, 03:36 AM   #3
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I know slightly less about alternators than I do about combine harvesters....but, my main alternator was acting in a similar way. A local samaritan suggested it was an 'exciter wire'. So he had a gander at it, deduced that it had come adrift, re-anchored it and it has been fine ever since.

David.
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Old 08-08-2007, 01:12 PM   #4
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Hi Steelfan

As a backyard mechanic my first piece of advice is to take this advice with caution.

In an alternator there is a spinning magnetic field (field/rotor/exciter coil) used to generate electricity in a stationary winding (stator). (the exciter coil uses less current and wears the brushes less. That is why it is the moving part.)

So a small amount of electricity from the battery is fed to the field coil to make it a powerful but light magnet.

The amount of electricity fed to the field coil is varied to keep the alternator output stable over all RPM ranges. A regulator controls this, on modern alternators this is integrated in the alternator often in the brush holder and has 3 connections input, earth and output to coil. On old alternators this could also be a small box mounted on the engine somewhere.

The stator generates 3 phase electricity which is recified by diodes integrated in the alternator and charges the battery.

The recified a/c has a dc votage with a ripple on it (imagine it like a 10meter deep ocean with a swell running over it, the water height varies above and below 10meters as the waves roll over). Many tacho's use the frequency of this voltage ripple to indicate revs. (should be the purple wire) The fact that your revs are about 1/6 of nomal can indicate at least 2 blown diodes inside the alternator. The other two small wires should be your field coil. One should be to earth, the other will be a switched 12V which may be via an external regulator. Some alternators also have a wire that indicates alternator failure.

Good luck!!
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Old 08-08-2007, 01:22 PM   #5
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@sirlespat



Thank you!
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Old 08-13-2007, 01:26 PM   #6
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Thank you for the ideas. I had already checked the belt tension and it is fine, but you are right to mention it - no point in getting into the clever stuff if there is an easy solution.

There is 12v on the green wire with the key turned to first position, no voltage on the purple or brown wires.

I've had the alternator apart but it is a bit of a mystery to me, though I did find a high reistance between one of the brushes and the spade terminal where the green wire is normally attached, so I bypassed that. It still does not work.

The lettering stamped on the side of the alternator seems to read 1103116 61a 1k9 12v NEG

The green wire leads to the brush nearest the front (pulley end) of the alternator

The brown wire leads to te brush nearest the back of the alternator

The purple wire leads to the top of one of the three diodes which can be seen when the casing is split

I thought six diode were needed, not three - am I wrong ?

There is a capacitor inside the alternator, and also a small black box about 2 cm x 1 cm

I could no test the diodes without further dismantling the alternator

Any further ideas, please ?

John
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Old 08-15-2007, 11:23 PM   #7
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Hi John

Thanks for the detail in your reply. From what you tell me I think your system runs like this.

"12v on the green wire with the key turned to first position" - this is the supply to the field coil.

"small black box about 2 cm x 1 cm" this could be the regulator, can you see any wiring to it?

The 12v should come in on the green wire, go through the regulator to the brush. This is possibly why there was high resistance between the terminal and the brush (could be normal). Shorting it out should have removed the regulator as a cause, you would have seen hi charging amps even at low rpm

"no voltage on the brown wire" this is the earth or 0V of the exciter coil.

If you have reassembled the alternator try measuring the current flowing through the green or brown wire with the key on but motor not running. Perhaps your field coil is open circuit.

Also were the brushes in good condition and did you clean the fine gap on the commutator (where the brushes run with a matchstick) and polish the commutaor with vey fine wetndry sanpapper you should find continuity between opposed sections of the commutator

i would expect 6 diodes too but sometimes they are stacked so only the top ones are visable. Auzee also had your problem and in his case it was the field coil. Thinking about it the field coil would retain a small ammount of magnetism with the power off so some output would be possible at high rpm.

Do you have a voltmeter capable of checking diodes? ( Will have a symbol that looks like this -|>|- squashed together )

No wonder you guys love sailing. (Most work above deck, problems easily diagnosed visually etc)

Good Luck!
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Old 08-18-2007, 11:44 AM   #8
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THANK YOU FOR THE VERY DETAILED AND EASY TO FOLLOW REPLY.

I STRIPPED THE ALTERNAOR AGAIN AND IN FIDDLING ABUT WITH THE BRUSHES DISCOVERED THE PROBLEM BY ACCIDENT - A CRACKED BRUSH HOLDER THAT WAS ALLOWING THE BRUSH A LITTLE MOVEMENT, ENOUGH TO STOP THE CURRENT WHEN IT WAS IN MOTION. I EXPECT LL THE GROVELLING AROUND IN THE ENGINE SPACE WAS GOOD FOR MY SOUL, IF NOT FOR MY BACK

John
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Old 08-18-2007, 11:55 AM   #9
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Very happy for you that you found the problem. Whatever it took for you to find the problem you can bank to the "learning curve".
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Old 08-19-2007, 12:43 AM   #10
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Hi John

Thanks for posting news of your successful repair. Another victory for calm and considered approach. Having fixed your alternator, now you will be designated an electrical system specialist by many of the boat owners around you who will share their challenges and solutions with you. (A much more relaxed way to acquire knowledge and easier on the back) I can tell you now that my sum total of experience came from replacing worn brushes in my wife's car one time. Auzee's original post about the exciter coil was right on the money,.... I wonder when he is running his next combine harvester maintenance course and where we can sign up!!!

Happy Sailing
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