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Old 31-08-2011, 08:23   #16
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Re: Alternator Question

Assuming the OP is talking about the 6 main rectifier diodes and not a "bad diode in the voltage regulator", it would take 2 leaky diodes to cause a current drain and 1 would have to be in the positive array, and the other in the negative array. If they are truely shorted, they won't be for long! 1 shorted diode will not cause loss of output.

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Old 31-08-2011, 10:17   #17
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Re: Alternator Question

" it would take 2 leaky diodes to cause a current drain"
IIRC that depends on how the alternator is built, there are dozens of designs and at least three primary configurations for diode racks using different numbers of diodes.
I've HAD this kind of alternator failure, on a Japanese alternator (Hitachi or Denso) and traced it to one bad diode out of...might have been 6 on the frame.
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Old 01-09-2011, 05:14   #18
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Re: Alternator Question

I challenge you to provide a schematic/drawing in which one leaky/shorted diode in an alternator can cause current flow. Here is the "standard" simple diagram. I realize there's more to an alternator than this but this is how the 6 main rectifier diodes are wired.



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Old 01-09-2011, 09:57   #19
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Re: Alternator Question

"this is how the 6 main rectifier diodes are wired."
No, actually, that's one of many ways an alternator may be wired, and one of many diode configurations. That's a "wye" and there are still "delta" configurations, and variations in the number of diodes as well.

See illustrations 8/9 (Type P with isolating diode, and Type N with diode trio) in Edgar Beyn's The 12 Volt Doctor's Alternator Book for examples. If I'm reading those correctly, a single diode shorting out could cause a drain. In the many circuits there are also some with other devices tapped from the center point of the diodes, which would seem to allow for a drain through those devices if a blocking diode shorted.
And the many web citings from folks in the alternator or power business, that say a shorted diode can drain a battery--as a diagnostic. Surely, they're not all giving out bad information?

I know that there are literally HUNDREDS of alternator/regulator configuraitons on the market, implying that one common design "is" the way they are all made, just isn't so. Some of the differences are trivial, other's aren't.
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Old 01-09-2011, 10:33   #20
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Re: Alternator Question

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Originally Posted by hellosailor View Post
... See illustrations 8/9 (Type P with isolating diode, and Type N with diode trio) in Edgar Beyn's "The 12 Volt Doctor's Alternator Book" for examples ...
Here ➥ http://kb-kbh.dk/shipslib/el_ombord/...ndbook_ocr.pdf

Which page?
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Old 01-09-2011, 11:06   #21
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Re: Alternator Question

Pages 89/90 of the book. The PDF "page" numbers will differ.
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Old 01-09-2011, 18:08   #22
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Re: Alternator Question

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No, actually, that's one of many ways an alternator may be wired, and one of many diode configurations. That's a "wye" and there are still "delta" configurations, and variations in the number of diodes as well.
Wye and delta refer to the stator windings. I'm not talking about them, I'm refering to the main rectifier diode array. The drawings in the book on pages 89 and 90 are incomplete. They don't even show the negative bank of diodes.

Please show me one of the many other ways in which the main rectifier diodes are wired. I have a book with a couple dozen different alternator schematics all using the same "standard" diode array. Many alternators have what's known as a "diode trio" that comes off of the stator windings as well but one of them would have to be leaky/shorted as well to cause current drain. Just because you read something on the web, doesn't make it so. The web is rife with mis-information.

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Old 01-09-2011, 19:20   #23
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Re: Alternator Question

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Originally Posted by fairbank56 View Post
Wye and delta refer to the stator windings. I'm not talking about them, I'm refering to the main rectifier diode array. The drawings in the book on pages 89 and 90 are incomplete. They don't even show the negative bank of diodes.

Please show me one of the many other ways in which the main rectifier diodes are wired. I have a book with a couple dozen different alternator schematics all using the same "standard" diode array. Many alternators have what's known as a "diode trio" that comes off of the stator windings as well but one of them would have to be leaky/shorted as well to cause current drain. Just because you read something on the web, doesn't make it so. The web is rife with mis-information.

Eric
I've replaced/rebuilt a lot of alts with blown diodes and have yet to see one cause an errant draw on the bank. I'll still keep an eye out though cause I've learned to rarely say "never"...
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Old 01-09-2011, 20:09   #24
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Re: Alternator Question

Where a single component can easily cause a drain is in the field wire. So, depends on how this alternator is wired. If the field current comes through the ignition switch then there shouldn't be a drain with the system off. On the other hand, a lot of small alternators with internal regulators take the field as a tap (inside the alternator) off the main battery connection. In that case the failure of a single component in the regulator can cause a drain of several amps which can lead to a dead battery. I've seen this many times.

Easiest diagnosis with no tools is to simply disconnect the charging wire from the alternator and letting it sit overnight. If the drain does not occur then it is a drain through the main charging connection. If the alternator does have a separate field wire you can disconnect that the next night just to make sure.
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Old 02-09-2011, 04:31   #25
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Re: Alternator Question

Certainly if you leave your ignition switch on and there is a failure in your regulator, you could have a drain. As far as the main diode configuration, there is only one as far as I know and it is universal. Iv'e seen some Bosch and Yanmar alternators with 2 extra diodes wired off the central connection of a wye stator but the basic configuration is the same. This is how we convert the AC produced by the stator to DC. It's a basic design used universally in alternators as well as DC power supplies. One leaky/shorted diode cannot cause current flow. I'm still waiting to see one of the other "many diode configurations".

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Old 02-09-2011, 05:38   #26
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Re: Alternator Question

Thanks, hellosailor.
Pages 89/90, in the book, is PDF page 48.
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Old 02-09-2011, 10:33   #27
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Re: Alternator Question

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I just finished installing a new sea water pump. The instructions tell you to tighten the bolts while the engine is running, being careful of the fan belt!
Murder. Must be a bad translation.
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Old 02-09-2011, 11:19   #28
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Re: Alternator Question

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Originally Posted by fairbank56 View Post
I challenge you to provide a schematic/drawing in which one leaky/shorted diode in an alternator can cause current flow. Here is the "standard" simple diagram. I realize there's more to an alternator than this but this is how the 6 main rectifier diodes are wired.



Eric
Your drawing is not complete; you have to show what feed the regulator, brushes. Normally 3 diodes connected to the extremity of the star before the 6 main rectifier diodes, any positive diode leaking will feed the regulator, brushes and may produce a drain depending how the regulator behave.
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Old 02-09-2011, 11:27   #29
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Re: Alternator Question

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I agree with the previous. But the alternator on old Yanmar don’t give much current. I hade a Yanmar YSB8 and the alternator rotated at the same speed as the engine. The engine work best at 2500 rpm and at that speed the alternator gives between 25 - 30 A. I made my own pulley and that way doubled the speed on the alternator. On the picture I have also change the alternator.
Nice picture, what is the melting temperature of the synthetic (“plastic”) pulley.
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Old 02-09-2011, 12:13   #30
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Re: Alternator Question

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Your drawing is not complete; you have to show what feed the regulator, brushes. Normally 3 diodes connected to the extremity of the star before the 6 main rectifier diodes, any positive diode leaking will feed the regulator, brushes and may produce a drain depending how the regulator behave.
The 3 diodes you refer to are the diode trio which I also refered to before and stated that one of them would also have to be leaking/shorted in addition to one of the main rectifier diodes in order for current to flow.



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