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3rd Alternator Failing

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Tofasttoocare View Drop Down
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    Posted: July-14-2019 at 5:11pm
I am working on a persisting issue with my 1996 Ski Nautique. It has the 5.7L ProSki EFI chevy motor. It seems to keep burning out alternators. I have had mine rebuilt 2 times and am about to need a 3rd. I have had a place that has been in business for over 30 years do it each time so I think they know what they are doing. My only concern with the rebuild is that the alternator needs marine parts and they are not using them.

I have had my battery tested and it has always tested good. I have had to recharge it a number of times when the alternator has failed. Voltage drop between the alternator positive is negligible and the alternator case is has a negligible drop. The only concern i can find is there is a 0.3 V drop between the battery and the green wire (exciter) when the key is on. I have looked for where the drop is coming from and it seem to be a lot of small drops that add up. For example there is 0.06V drop across my ignition switch.

I have looked for wiring diagrams and tried to trace the green wire back but it has not been successful.

My main concern is weather or not the 0.3V drop is enough to cause the alternator to be over work. If that is not a concern I am going to attribute it to the alternator itself and purchase a new one from Skidim,
1996 SNOB

350 Chevy Pro Ski TBI

PCM 1.23:1
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8122pbrainard View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: July-14-2019 at 5:33pm
Jay,
Have you ever disconnected the battery with the engine running? Do you have a "Perko" switch or similar and if so have you ever switched it with the engine running? Have you ever jumped the boat? Are you battery/cable terminals clean and tight?

What is the shop saying has been the problem? If diodes, then one of the above could be the problem.

I wouldn't worry about that .3 voltage drop. You are reading through the rectification diodes.

Internal parts are the same as automotive. It's the case that makes it "marine"


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77 Tique

64 X55 Dunphy

Keep it original, Pete
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gt40KS View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gt40KS Quote  Post ReplyReply Direct Link To This Post Posted: July-15-2019 at 1:21am
Provided your shop has been building them correctly and bench testing before handing them over, sure sounds like an issue I had with my Camaro back in the day ( ok, several decades ago). There was a short in the charging cable that was feeding back to the alternator. It was a very minor break in the insulation running next to the block before getting back to the battery. Small enough not to severely damage the battery, though I suspect it didn't do it any good, but large enough that long term exposure would fry the alt. We had a heck of a time tracking it down because on the VOM it was a very negligible difference and of course the crack in the insulation was on the underside of cable out of eyeshot. Anyway, replaced the cable & problem solved. Hope it turns out to be something as simple with yours ... if there's one thing I hate it's chasing down electrical issues   
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1995 Ski Nautique GT40
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-15-2019 at 9:48am
If you click on the link below, you'll no longer be able to say you don't have a diagram. Page MT17

If you want to find where the green wire taps into the purple wire from the ignition switch, you'll have to do some untaping of the harness.

Like Pete said, the 0.3 volt drop is nothing to worry about

Why do you think "it's about need a 3rd rebuild"?





link

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Tofasttoocare View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tofasttoocare Quote  Post ReplyReply Direct Link To This Post Posted: July-16-2019 at 11:05pm
Pete,
I have not disconnected the battery at the posts or with a Perko switch (don't have one) while the boat is running. This tests if the alternator has failed I believe. We have jump started the boat using a jumper pack several times because of the discharged battery. The terminals are clean and tight. They are cleaned each time the battery goes back in for the season.

The shop has replaced the diodes each time. I think the brushes were done the first time as well. The last time it was replaced the post that the exciter wire attaches to was loose. I may have over-tightened it when installing it and partially broke it free causing the failure.

If I am on the exciter post and the negative battery terminal with the wire connected and the key on I don't think I am reading through the diodes. I am not sure about that though.

gt40KS,
Sounds like a huge headache. Wiring is definitely not my favorite. I'll keep an eye out for that. Most of the wiring is wrapped and I haven't seen any chaffing marks though.

KENO,
Thank you for the link that is very nice to have. I saved a copy for future reference. The alternator started off the season charging at about 14V. We have put about 20 hrs on it so far and it has been declining steadily. It is now down to about 12V when reading at the battery or on the posts of the alternator. I have been aware of the problem since the season started but have been hoping to be able to find the route cause before I buy a new one. I don't want to burn out a brand new one.

Thank you all for the replies,
Jay
1996 SNOB

350 Chevy Pro Ski TBI

PCM 1.23:1
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: July-17-2019 at 8:15am
Originally posted by Tofasttoocare Tofasttoocare wrote:

If I am on the exciter post and the negative battery terminal with the wire connected and the key on I don't think I am reading through the diodes. I am not sure about that though.


I think you're right provided all the diodes are good.

I also think the alternator is dead now, since you're reading essentially battery voltage when you check it and the battery is needing to be jumped.

This must be a Motorola or Mando alternator you're dealing with?
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Tofasttoocare View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tofasttoocare Quote  Post ReplyReply Direct Link To This Post Posted: July-17-2019 at 8:40am
We've still been using the boat and it has been starting for us. I was referring to jump starting the boat last year when we had this same issue. So it is currently charging, but probably only at right around battery voltage.

Yes, it's a Mando, or at least that is what skidim recommended to me as a replacement when I sent them pictures of what I have.
1996 SNOB

350 Chevy Pro Ski TBI

PCM 1.23:1
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