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Author Topic: Burnt alternator excite wire  (Read 301 times)

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ChrisW

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Burnt alternator excite wire
« on: August 25, 2019, 01:46:03 PM »

I was running my engine at the dock today and started smelling and seeing smoke.  I cut the engine off and went down to take a look and noticed that the plastic around the alternator excite wire was melted.  It was also melted up to the key switch.  I am hoping that one of you guys might have a clue as to what is going on.

Let me tell you what happened.  I was testing my engine today because it overheated yesterday at the dock before I was about to take it out for a sail.  I did just recently install a new heat exchanger.  However, I ran the engine for hours a week before with no problems.  Right now I am not worried about the engine overheating, but I thought I should just mention that.

So I add coolant to the reservoir because the coolant all came out after overheating, and then I started the engine.  Everything seems OK.  Engine temperature is normal.  Runs for about 15 minutes.  But, I noticed the alternator was not working.  And the tachometer was not working.  The voltmeter on the instrument panel read 12 V.  I checked at the batteries and was reading about 12.6 volts.  The tach was at zero.

I gave it the thought that maybe I inadvertently turned the battery switch to off when the engine was running, but that did not seem likely to me.  I noticed the vbelt was too loose, so I stopped the engine, tightened the belt, and restarted the engine.  Alternator and tach still not working.  But then about five minutes later the alternator and tach kick in.  I keep running it for about five minutes and decide to increase the throttle a bit.  Just a little bit from idle, which I had been running it at until then.  I had my eye on the instrument panel while doing this.  The tach jumped very high, over 2500 rpm, which it obviously was not doing, then dropped back down to about 1400 rpm, which is probably correct.  The voltmeter went to zero.

It was very shortly after that that I saw the smoke coming from behind instrument panel.  I will add that after the alternator kicked in, the voltmeter looked like it was running too high, but it has always done this.  It was somewhere above 15 V, almost 16V.  Maybe the voltage regulator is to blame?

Anyway, it looks like I am going to have to pull that purple alt excite wire and replace it.  One other thing that I must mention is that there isn't a fuse between battery and key switch.  I know, it's something I've been putting off but will do so very soon.

Thanks
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KWKloeber

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Re: Burnt alternator excite wire
« Reply #1 on: August 25, 2019, 03:28:03 PM »

I canít say what exactly caused the over current on the excite wire, maybe diodes? RC will be the answer guy for that.

But, JFYI the excite wire and the fuel pump feed are redundant (if itís a non B engine) ie, you can use one wire to supply both.
Thereís both there because the excite is part of the OEM engine harness from universal and CTY ran the fuel pump feed wire.
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
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ChrisW

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Re: Burnt alternator excite wire
« Reply #2 on: August 31, 2019, 09:10:16 AM »

I am going to go with the answer that it's a bad alternator.  I was wanting to get a new one eventually anyway,  one that puts out more amps and has a smart voltage regulator.  Anybody have any recommendations?
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Stu Jackson

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Re: Burnt alternator excite wire
« Reply #3 on: August 31, 2019, 10:30:43 AM »

I am going to go with the answer that it's a bad alternator.  I was wanting to get a new one eventually anyway,  one that puts out more amps and has a smart voltage regulator.  Anybody have any recommendations?

Regulator:  Balmar MC-614 (and read Electrical Systems 101 for management with Amp Manager and Small Engine Mode)

Don't spend unnecessary $$ on a Balmar alternator, do a lot of research, check Maine Sail's offerings
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Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

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ChrisW

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Re: Burnt alternator excite wire
« Reply #4 on: September 01, 2019, 01:21:10 PM »

I am going to go with the answer that it's a bad alternator.  I was wanting to get a new one eventually anyway,  one that puts out more amps and has a smart voltage regulator.  Anybody have any recommendations?

Regulator:  Balmar MC-614 (and read Electrical Systems 101 for management with Amp Manager and Small Engine Mode)

Don't spend unnecessary $$ on a Balmar alternator, do a lot of research, check Maine Sail's offerings

Thanks.  Would you happen to know what suitable alternators would fit a Universal M-25XP?

I've been researching alternators on this site, but the problem I am having is that I don't know if any of the alternators being discussed will actually fit in the same spot as the old one.  I read where one person said that it's not as simple as just bolting it on.  He had to have something custom fabricated.  That sounds expensive, especially since my marina charges a fortune per hour for anybody doing any work (more than the average doctor charges).

I don't know the model number of the old alternator but it's a Prestolite. The model number is faded away.   The boat is a '94 model.
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Stu Jackson

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Re: Burnt alternator excite wire
« Reply #5 on: September 01, 2019, 01:54:56 PM »

Chris, the reason I suggested looking at Maine Sail's site is that he explains small case alternators quite well.  He also used to have a Catalina 36, so he knows Universal M25 series engines.  Some of his photo layouts have pictures of M25 series engines.

He speaks quite a bit of Leece Neville alternators.  We've discussed it here, too, and a search on LN as well as looking at the Elec Sys 101 will show you more.

I also have referred folks to http://www.ase-supply.com/category_s/561.htm, ASE.  You can call them and speak to Bob, they actually have two guys named Bob, but they know alternators and, I think, our engines.

You're right, you need to put yourself in a position to just give the right parts to your yard dogs to save $$.  A better way is to learn to do it yourself.  "None of us was born an electrician."  :D

Good luck.  Happy Hunting.
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Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

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ChrisW

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Re: Burnt alternator excite wire
« Reply #6 on: September 01, 2019, 03:22:01 PM »

Chris, the reason I suggested looking at Maine Sail's site is that he explains small case alternators quite well.  He also used to have a Catalina 36, so he knows Universal M25 series engines.  Some of his photo layouts have pictures of M25 series engines.

He speaks quite a bit of Leece Neville alternators.  We've discussed it here, too, and a search on LN as well as looking at the Elec Sys 101 will show you more.

I also have referred folks to http://www.ase-supply.com/category_s/561.htm, ASE.  You can call them and speak to Bob, they actually have two guys named Bob, but they know alternators and, I think, our engines.

You're right, you need to put yourself in a position to just give the right parts to your yard dogs to save $$.  A better way is to learn to do it yourself.  "None of us was born an electrician."  :D

Good luck.  Happy Hunting.

Is this Maine Sail's site?  marinehowto.com
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Stu Jackson

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Re: Burnt alternator excite wire
« Reply #7 on: September 01, 2019, 06:47:11 PM »


Is this Maine Sail's site?  marinehowto.com

Yes it is.
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Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

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mainesail

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Re: Burnt alternator excite wire
« Reply #8 on: September 02, 2019, 12:32:32 PM »



Is this Maine Sail's site?  marinehowto.com

We are currently custom building a number of direct replacements for the most common Leece-Neville alternators found on Universal diesel engines, including the CMI-72-IR (internally regulated/ignition excite - choose your voltage set point) the CMI-72-ER (externally regulated 72A) and the CMI-105-ER. The CMI-72-IR/ER is a direct replacement for the old 51A 8MR-2049 series which has been discontinued by Leece-Neville. We also build a Delco based 90A Motorola/Prestolite frame externally regulated alternator called the CMI-90-ERM

https://shop.marinehowto.com/t/alternators--regulators
« Last Edit: September 02, 2019, 12:32:58 PM by mainesail »
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ChrisW

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Re: Burnt alternator excite wire
« Reply #9 on: September 02, 2019, 02:06:03 PM »

Thanks, mainesail.  I checked out your site and found it helpful.  For now I came to the conclusion that the proper alternator upgrade with external regulator would put my bank account at a dangerously low level.  So I decided to just replace what I had with something similar.  I ordered a LN 110-686 so I can go day sailing and marina hopping.  When I do decide to do the proper upgrade, probably next year, I will keep your store in mind.
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mainesail

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Re: Burnt alternator excite wire
« Reply #10 on: September 02, 2019, 02:55:22 PM »

Just be sure what you're getting is genuine LN. The benefit of the CMI-72-IR, over the LN, is that you can choose your internal regulators voltage set point and you can't do this with the LN.

The real benefit is that if you decide to upgrade to external regulation, in the future, we have the components to convert the CMI-72-IR to external regulation. You're also getting more amps...
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Sdsailor

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Re: Burnt alternator excite wire
« Reply #11 on: September 16, 2019, 12:46:15 AM »

Chris W. I literally had these symptoms when one of my negative battery connections was loose. The alternator current had to find its way through the instrument panel. Voltage was reading 15+v. It destroyed my depth sounder display, thankfully that and the chart table lamp were the only casualties. While your alternator may have been damaged, maybe there was a culprit?
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KWKloeber

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Re: Burnt alternator excite wire
« Reply #12 on: Yesterday at 08:08:05 PM »

Chris

Did you check the cost of rebuilding the stock Moto alt?  It's usually pretty reasonable and you'd have a genuine.
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Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain
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