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Old 12-08-2015, 13:50   #1
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Fried My Alternator :(

Through a series of stupid mistakes, I seem to have fried my alternator

The first one occurred when I was anchoring near the Holtenau Lock of the Kiel Canal, last May. I forgot that I had some heavy loads on the inverter. The mud was soft and it took two attempt to get the hook set. The windlass was used a lot, and even the bow thruster. Simultaneously with the heavy inverter load this was too much, and something flipped off and the alternator stopped producing output. It stank of burning electrical parts, and the "no alternator output" light was lit up on the instrument board. I was too tired to try to fix it and went to bed. In the morning, it was working normally (which seemed miraculous to me), and it worked normally the rest of the summer.

Fast forward to today. I was motor-sailing in the North Sea and noticed the "no alternator output" light was on. Sure enough, no charge voltage. Looked in the engine room, and it was hot -- no engine room fblowers. Damn. This time there was no load of any significance on the system.

I spent a lot of time reading the wiring diagrams and tracing circuits, and came to the conclusion that the problem was a bad contact in the crappy Yanmar ignition switch. This switches on power which closes a relay which powers up the alternator exciter wire and also the engine room blowers. It looked to me like I just needed to get power onto that wire and I would have charging and blowers. It seemed to me that the simplest way to do this on a temporary basis would be to put the power onto the field post of the alternator.

So I made a jumper and did so, after checking and rechecking and measuring the voltage (not to confuse 12v with 24v).

As soon as the contact was made, the engine lugged as it usually does when the big Leece-Neville 110 amp (x 24v) school bus alternator starts up. I thought -- well, I figured that one out all right. Went around to the other side to check the engine room blowers -- yep, blowing away. But then I notice a cloud of acrid smoke. Quickly took the jumper off. Damn, damn, damn.

The solution to the problem is obvious -- take off the alternator and take it to an auto electric shop for repair. I'll do that when I get back to the UK.

But -- what did I do wrong? I have thought and thought about it, consulted Nigel Calder's book, and just can't figure it out. I'm sure it was something stupid, but it would be nice to know what.
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Old 12-08-2015, 14:13   #2
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Re: Fried My Alternator :(

I would have to think about it a bit and DISCLAIMER I know just enough about alternators to be dangerous. But... my first guess is the jumper to the field caused the alternator to output max, full power and it overloaded?
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Old 12-08-2015, 14:32   #3
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Re: Fried My Alternator :(

i guess you could have assumed the alternator field blower circuit was blown for some reason and tracked it down from that angle .. but it sounds like the alternator could be toast.
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Old 12-08-2015, 14:38   #4
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Re: Fried My Alternator :(

The alternator should self excite once it takes up a load. I think Skipmac is on the right track. Depending on what is burned up you may be able to repair it, test it and then put it in the spares. Since you venture so far from home and have heavy electrical loads ( Gin tank circulation pumps, deep fat fryer, multiple coffee makers ect ect) you ought to carry a spare.

It could just be diode(s.) Blown ones out, new ones in. Off you go. Alternator will be stinky for a while but will live. If you melted any of the windings, its a different story.
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Old 12-08-2015, 14:50   #5
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Re: Fried My Alternator :(

Alternators have diode banks to make DC out of AC. Usually an overload will blow one or more diodes. Often the alternator will still function under light loads.
If you can get parts, there's plenty of info on the web about testing parts and replacing them.
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Old 12-08-2015, 16:03   #6
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Re: Fried My Alternator :(

I'm not sure what you are powering up but normaly to full field on alternator you ground the field wire? The rotor/field has power at all times to one of the two brushes the other is connected to the regulator which is a variable ground so to speak, the stator is where the output comes from
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Old 12-08-2015, 16:12   #7
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Re: Fried My Alternator :(

I think Skipmac is right. Full output for too long, everything gets hot, alternator, batteries etc. A good regulator often only allows that for 15-20 minutes max.
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Old 12-08-2015, 16:57   #8
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Re: Fried My Alternator :(

Quote:
Originally Posted by sartorst View Post
I'm not sure what you are powering up but normaly to full field on alternator you ground the field wire? The rotor/field has power at all times to one of the two brushes the other is connected to the regulator which is a variable ground so to speak, the stator is where the output comes from
Since he lost the blower at the same time, he probably correctly determined that he lost the B+ at the ignition switch at the same time (posts AC and 30). This B+ is the positive side of the circuit that allows current to flow through the slip rings to the rotor (rotating field), and is not a large current. Once this flow is established, the stator windings generate the 3 phase AC that the 6 diodes in the diode pack rectify into rippled DC. I think he is saying he went directly to the alternator and jumpered B+ (output) to the R terminal, which provided currently flow for the rotor, which re-established the rotating field. He did hear the alternator load up, but then, smoke.

I commend him for being out there, I'm not retired yet, and all his problems could easily become ours, later on. These Forums certainly have value.

The only thing I would have done differently (thinking from the comfort of home) would have been to reestablish the connection at the back of starter switch, which is between post 30 and post AC for my 4JH2-HTE, with an alligator clip lead. I noted that my manual has a connection table for that switch for off, on, glow plug, and start. His online one didn't, that I could see.

He full fielded the alternator, and that effectively bypasses the regulator, as full current is flowing through the rotor. That can be a usefull short term test. Depending on the regulator design (which is only controlling rotor current via voltage feeback, there are sometimes low resistance dropping resistors in series with the rotor circuit, to limit current flow through the brushes to a limited value, plus limit the current being rectified. It is possible with his set up that the alternator did have momentary output, was partially damaged the summer before, and now a diode bridge is open.
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Old 12-08-2015, 16:58   #9
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Re: Fried My Alternator :(

A Balmar regulator set for a max. 80% of alternator output would have saved the alternator. You will probably have to have the alternator rewound as well as new diodes.
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Old 13-08-2015, 01:03   #10
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Re: Fried My Alternator :(

I still don't understand why it blew up. I put power onto the terminal which is supposed to get power directly from the ignition switch. I still don't see how that could have cause this.

The alternator is regulated with an Adverc regulator. The diagram is below.

The original regulator (under a cap at the end of the alternator) remains in place with this type of regulator, so I was not bypassing it. As you can see, the Adverc brown lead is connected to the D+ terminal together with a lead from the ignition switch. This is where I applied power.

The fact that the blower started working seems to contradict any idea that I had the wrong terminal.

This really puzzles me. Power should have gone at the same time to the Adverc backwards through the circuit (as the case with the blower). However, I feel sure I am not understanding how this works.
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Old 13-08-2015, 01:10   #11
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Re: Fried My Alternator :(

Here is the wiring diagram:

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Old 13-08-2015, 01:18   #12
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Re: Fried My Alternator :(

I am guessing it was already very nearly "blown up" before you manually connected the power to the field activator. Sounds to me like the original overheating event partially melted or damaged insulation on the windings. Then you had the later hot engine bay event, and if I understand this correctly it might have been been brought about because excessive power draw from the field circuit blew the same circuit that fed the engine room blowers. Anyway, the damaged insulation led to excessive current draw on the field circuit, but this time it could get all the power it needed, no longer limited by the ignition circuit, hence full power generation for a brief period before the already started job of melting the insulation was completed at which point, phtt, lots of smoke, no power.

I had pretty well the same thing happen a few weeks ago when we bought a 50 year old car that had been sitting idle for a number of years. Test drove it the first day, power generation from the alternator was iffy at best, about 12 volts. The next day, after about ten minutes it started to put out full power, for about a minute, then melted itself into a puddle so badly I had to pull the battery lead to avoid a fire. Thankfully conventional car alternators are cheap items.

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Old 13-08-2015, 02:36   #13
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Re: Fried My Alternator :(

Quote:
Originally Posted by GILow View Post
I am guessing it was already very nearly "blown up" before you manually connected the power to the field activator. Sounds to me like the original overheating event partially melted or damaged insulation on the windings. Then you had the later hot engine bay event, and if I understand this correctly it might have been been brought about because excessive power draw from the field circuit blew the same circuit that fed the engine room blowers. Anyway, the damaged insulation led to excessive current draw on the field circuit, but this time it could get all the power it needed, no longer limited by the ignition circuit, hence full power generation for a brief period before the already started job of melting the insulation was completed at which point, phtt, lots of smoke, no power.

I had pretty well the same thing happen a few weeks ago when we bought a 50 year old car that had been sitting idle for a number of years. Test drove it the first day, power generation from the alternator was iffy at best, about 12 volts. The next day, after about ten minutes it started to put out full power, for about a minute, then melted itself into a puddle so badly I had to pull the battery lead to avoid a fire. Thankfully conventional car alternators are cheap items.

Matt
First plausible explanation. Thanks a lot for that.
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Old 13-08-2015, 05:23   #14
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Re: Fried My Alternator :(

Concerning the question of carrying a spare:

I am something of a fanatic about spares inventory, which results from having wasted a lot of time I could have otherwise spent having fun on cruises searching for parts.

However, alternators are so repairable in so many places -- since it's a common auto electric bit. And since this is one of two alternators on the main engine, and I have a heavy duty generator. So this alternator going out is not a cruise-stopper. I think I will carry a spares kit, but not a complete spare alternator. Otherwise with the starter of course.
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Old 13-08-2015, 05:30   #15
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Re: Fried My Alternator :(

On our delivery trip home the biggest single time waster was the alternator that stopped working just 36 hours into the trip. I fretted over avoiding this issue for a year before deciding to fit one good quality alternator with a spare basic (cheap) model carried on board in an air tight bag. The trick was to ensure they could be easily swapped. Got there in the end but the solution involved a bit of farting around with the welder to make a reasonably universal mounting bracket.


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