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Overheating alternator symptoms?


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I hope you folk will forgive me raising something that might have been at least partially answered in the past - I've little experience in boat ownership and none at all in engine electrics!

The symptoms I noted (yesterday) are these:

  • engine battery warning light comes on (strongly, not flickering); this is at gentle cruising speed, say 1,000 - 1,300 rpm.
  • the meter showing the charge rate for the engine battery is way off the (max) scale
  • after a while, the rev counter drops to zero and at the same moment the warning light goes off;  then both come back; then both disappear.
  • charging still seems to be max
  • engine battery volts are c 12.7/13 as reported by the Merlin Smart gauge

No obvious signs of loose connections on the back of the alternator, no change in behaviour with a bit of amateur jiggling.  I have not yet managed to understand the wiring fully and do proper continuity testing (gonna wait for everything to cool down a bit first!)

Belts to both alternators seem good (i.e. physically), no screaming sounds.  Possibly the belt on the domestic bank alternator is a bit tight...

It was an exceptionally hot day.  At one point we had rev counter working and the battery light went out.  However any time the battery light was on, the rev counter was working.

 

I guess there could be more than one problem here simultaneously e.g. there is genuinely a charging issue, and there is also an unrelated intermittent connection issue that affects the warning light and the rev counter.  Just a coincidence that they appeared at exactly the same time....

 

If the battery light comes on from time to time, what's the worst thing that can occur if we keep moving until we reach a boatyard with a competent electrician?  Flat battery, or something worse - cooked and ruined components....?

 

Thanks in advance for any thoughts.

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If the taco is working, the alternator is energised despite the charge warning light being on.

 

The likely cause is that the warning light wire to the alternator D+ terminal is shorting to ground which will stop the charge rate right down to nil. Could be a wire short or inside the alternator.

 

The regulator in the alternator could be in an overheat situation.

Has it gone back to normal when it has all cooled down?

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Would you have solar charging? If so, in this weather, the solar voltage might be causing the alternator to shut down later in the day. What happens if you put a heavy load on the electrics.

 

Rev counter probably driven from the engine alternator while the warning lamp could be from both or either depending on how professionally it was wired.

 

I would also like to see the voltage reading from BOTH battery banks when it does this to try to decide which alternator is playing up.

 

I wonder what any multi-plug in the engine wring harness is like.

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There is solar charging - I turned this off at the isolator to see if it would make a difference, but it didn't seem to.  I'm guessing there is split-charging across the domestic and starter batteries, but don't know how that works.  There are two battery warning lights - I am pretty sure it is the starter battery light that is coming on.  Oddly enough, last summer on bright days the domestic battery bank light would flash on and off steadily, generally only when the engine was idling, but I have not seen that recently.

Do I understand it correctly that, somehow, there is (or should be) a system that measures the charging (voltage? current?) and if this exceeds some threshold, acts in some way to limit it?  And if the limit takes effect by dumping the alternator output, this would cause the battery warning light to come on?  Given that the alternator is still spinning, what happens to the unwanted power output?  (You can see that I don't know anything about these kind of systems - recommendations of links for on-line study very gratefully received!)

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12 minutes ago, Andy Spiceley said:

There is solar charging - I turned this off at the isolator to see if it would make a difference, but it didn't seem to.  I'm guessing there is split-charging across the domestic and starter batteries, but don't know how that works.  There are two battery warning lights - I am pretty sure it is the starter battery light that is coming on.  Oddly enough, last summer on bright days the domestic battery bank light would flash on and off steadily, generally only when the engine was idling, but I have not seen that recently.

Do I understand it correctly that, somehow, there is (or should be) a system that measures the charging (voltage? current?) and if this exceeds some threshold, acts in some way to limit it?  And if the limit takes effect by dumping the alternator output, this would cause the battery warning light to come on?  Given that the alternator is still spinning, what happens to the unwanted power output?  (You can see that I don't know anything about these kind of systems - recommendations of links for on-line study very gratefully received!)

 

Something odd here. In your first post, you talked about the engine alternator and later the domestic alternator. That sounds like a twin alternator engine and it is NOT standard to link the two systems, but some do. Either simply or complexly with expensive kit. Now you talk about split charging but split charging uses one warning lamp, you also have just said you have two.

 

Start with electrical notes on my website tb-training.co.uk, but there are several other resources that will be pointed to in a little while.

 

No load dumping takes place. Unless you have added extra gizmos the alternators each have a voltage regulator that control the current going to the spinning electromagnet. When the voltage gets to a set point the current to the rotor is reduced, so the magnet is weaker and in turn it can't "make as much voltage" (simple non-technical explanation).

 

The regulators may or may not be temperature compensated to reduce the output at high temperatures, and may or may not have a default setting if it sees overvoltage. The ones I am used to go high enough to volt wise damage batteries.

 

I get a feeling this may be worn brushes, epically in the alternator is very old, but the symptoms do not seem to quite fit that.

 

 

Edited by Tony Brooks
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Hi Tony, thanks for the swift response and apologies if my ignorant use of terms confuses things!.   It's a twin alternator engine, (betamarine 38) two warning lamps, (17 years old, 5200 hours on the tachometer).  Solar panels with MPPT controller were added in 2015 but I have not worked out from the documentation we acquired with the boat (no updated wiring diagrams!) whether they are charging just the domestics or both sides (the latter would seem to imply some kind of splitting so perhaps it is more likely it is just on the domestic bank?)

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1 minute ago, Andy Spiceley said:

Hi Tony, thanks for the swift response and apologies if my ignorant use of terms confuses things!.   It's a twin alternator engine, (betamarine 38) two warning lamps, (17 years old, 5200 hours on the tachometer).  Solar panels with MPPT controller were added in 2015 but I have not worked out from the documentation we acquired with the boat (no updated wiring diagrams!) whether they are charging just the domestics or both sides (the latter would seem to imply some kind of splitting so perhaps it is more likely it is just on the domestic bank?)

Beta idiot plug in the loom in good order? Not sat in an oily puddle?

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1 hour ago, Tracy D'arth said:

If the taco is working, the alternator is energised despite the charge warning light being on.

 

The likely cause is that the warning light wire to the alternator D+ terminal is shorting to ground which will stop the charge rate right down to nil. Could be a wire short or inside the alternator.

 

The regulator in the alternator could be in an overheat situation.

Has it gone back to normal when it has all cooled down?

This is based on the assumption that we are dealing with a 3rd generation 9 diode machine.  I suspect it may be a 4th generation 6 diode unit. Prefer not to advise until I know. 

37 minutes ago, Andy Spiceley said:

There is solar charging - I turned this off at the isolator to see if it would make a difference, but it didn't seem to.  I'm guessing there is split-charging across the domestic and starter batteries, but don't know how that works.  There are two battery warning lights - I am pretty sure it is the starter battery light that is coming on.  Oddly enough, last summer on bright days the domestic battery bank light would flash on and off steadily, generally only when the engine was idling, but I have not seen that recently.

Do I understand it correctly that, somehow, there is (or should be) a system that measures the charging (voltage? current?) and if this exceeds some threshold, acts in some way to limit it?  And if the limit takes effect by dumping the alternator output, this would cause the battery warning light to come on?  Given that the alternator is still spinning, what happens to the unwanted power output?  (You can see that I don't know anything about these kind of systems - recommendations of links for on-line study very gratefully received!)

Next time it happens, try wiggling the ignition switch. 

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17 minutes ago, Andy Spiceley said:

Hi Tony, thanks for the swift response and apologies if my ignorant use of terms confuses things!.   It's a twin alternator engine, (betamarine 38) two warning lamps, (17 years old, 5200 hours on the tachometer).  Solar panels with MPPT controller were added in 2015 but I have not worked out from the documentation we acquired with the boat (no updated wiring diagrams!) whether they are charging just the domestics or both sides (the latter would seem to imply some kind of splitting so perhaps it is more likely it is just on the domestic bank?)

 

As start batteries spend all but a few minutes a day fully charged, typically solar will only charge the domestic bank unless it's a twin output controller or extra components have been added like a Voltage Sensitive Relay. I doubt you have one of those.

 

I think Sir N is probably onto something. I think a six diode alternator would shut down and put the ignition light on with certain ignition switches if one output termnal plays up.

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1 hour ago, Tracy D'arth said:

Beta idiot plug in the loom in good order? Not sat in an oily puddle?

What @Tracy D'arth says. Any weird intermittent mismatch between engine and control panel with a Beta engine, the first thing to check is the multi pin plug and socket in the engine wiring loom between the engine and control panel. This can disconnect itself with vibration, or one, or more pins can go bad from corrosion. Usually covered with a black rubber boot. Pull it apart, with the engine off. Check none of the terminals are a horrible green corroded colour and push back together. There are various tricks to stopping it coming apart again in the future. Now see what the engine and control panel do. If the problem hasn't been fixed, then it is on with the fault finding, but this plug/socket is a weak point in the otherwise excellent Beta marine set up.

Jen

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7 minutes ago, Andy Spiceley said:

Thanks very much to you all for your advice - when I get back to the boat, will check out the multi-pin connection as advised first, and then work through the other suggestions.

 

There might be two depending on cable length between engine and control panel, one might be to be hidden below the control panel

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A much cooler couple of days boating, and we still have the symptoms, so I guess we can rule out the weather!  I can report the following:

  • the multi-way plug looks nice and clean, no muck or gunge, everything seems firm and no amount of jiggling seems to make any difference.
  • we cruised for around 3 hours on two days and the rev counter and battery warning light were out for all of that time.  However, we carried out some more organised measurements whilst moored up and during that the rev counter & battery warning light re-appeared.  When the rev counter is off and there is no warning light, the starter alternator appears to be outputting 12.7v.  When the rev counter is on and the battery warning light is lit, the alternator output was measured at 13.5.  Both measurements tallied with the battery monitor voltage reading at that point. On the back of the tacho I measured 12.9v on the +ve and 6.55v on the signal wire when the rev counter was registering, but I didn't get the chance to take any readings at the tacho when it was not registering (at that point it stayed on until we had to leave the boat!)

I am wondering if there are two faults (intermittent connection somewhere on the signal wire) and an under-performing alternator?  Of course, the bad connection could be within or on the alternator itself. so the two things could both be associated with a failing alternator....  Does that make any sense?

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There is little point in measuring the voltage on the rev counter signal wire, its not DC but variable frequency AC dependant on the alternator speed.

The charging voltages are too low. 

I think it is time for you to get a professional to look at your system.

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I'm a bit puzzled by the thread title. I've not noticed any mention of overheating of the alternator in the body of discussion.

 

But then I only scanned quickly through....

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The thread title is probably bogus - I wrote overheating because all these symptoms became apparent on a very hot day so I wondered if it was an overheating problem.  Since the problem persists after everything cooled down and on much cooler days, this is probably an irrelevant co-incidence.  So should probably re-title the thread, if that is possible.

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The person who can give you the best help asked for a photo of the alternator so he can identify it. He also suggested that when the problem occurred that you turn the ignition  switch on and off a few times. Have you done either?

 

He suspects that you have a six diode alternator, rather than the more usual nine diode model found in canal boats, so if he is correct you may get a lot of well intended but useless answers.

 

A nine diode alternator would normally have the warning lamp on when the rev counter stops, but yours does the opposite. I have very little, experience of modern size diode alternators but I think that if they lost the feed from the ignition switch (not the warning lamp wire) I think the alternator will lose the magnetic field in the rotor. That would stop the rev counter, but with no supply to the warning lamp (because of a faulty ignition switch) the warning lamp would be off. I am only about 50% sure of this, so you really need Sir Nibble.

 

With no reference voltage from the ignition switch, I am not surprised the charging voltage is all over the place, so I can't condemn the alternator at this time and with the present information.

 

Please post a photo so Sir N can see what you have got and advise accordingly.

 

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Firstly, when you say the alternator is “outputting 12.7v” what is really happening is that the alternator isn’t outputting anything, the starter battery is holding the voltage up at 12.7v. The alternator is turned off.

 

If it’s anything like our Beta 43, the starter alternator is a 6 diode unit. Fundamentally different from a 9 diode unit in the way the warning light works etc. The 6 diode unit has 3 wires going to the control panel, the tacho  the warning light and another wire going to the ignition switch which is the off on command. Current flowing through the warning light has nothing to do with the alternator field current, initial excitation etc.

 

So in this case what is happening is a bad connection between the battery, via the ignition switch, to the “on off command” connection on the alternator. On our boat this is a brown wire but I guess a Beta of different age might have different wiring colour scheme.

 

When 12v is lost on the “on off command” terminal, the alternator internal circuitry shuts off, the warning light is disabled and since there is no field current the tacho output stops working.

 

The only thing not explained by this is your initial comment about the “charge rate” which i take to be the voltmeter. This is simply connected across the battery via ign switch so it’s hard to understand why it should be reading much more than battery voltage. Does it return to zero when the engine is stopped /ign off?

 

So in summary check the back of the ignition switch for poor connections, the multi-plug in the cables to the  engine, the brown wire on the alternator and check for any chafing/cable damage in the path between panel and engine. I suppose it could be the actual ignition switch but I would have thought that would have an impact on other things - but then again, maybe not - so do as SN says and when the symptoms reappear, cycle the ignition switch on and off a few times.

 

If the problem persists, use a multimeter to check the voltage on the brown wire at the back of the alternator with engine running when the problem is happening - but only if you can do so safely, spinning belts with loose clothing or dangly bits is a recipe for disaster! If the voltage is 0 there is a wiring problem. If it is 12v or so, it is an alternator problem.

Edited by nicknorman
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Don't some marinisers tuck an inline fuse away close to the starter that feeds the ignition switch. If so, that is another potential problem area. Vetus seem to sometimes seem to mount it near the relay box.

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Oh and another thing, there is a cable-mounted 40A fuse somewhere on or near the engine. This provides power to the whole panel from the starter battery (via starter battery + connection stud on the engine) so locate and check that for corrosion / reseat it etc. If that is intermittent it would affect everything to do with the panel including engine stop function, so probably not implicated but best to check anyway.

Tony you beat me to it by 100mS!

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