Intermittent alternator charge

[jonjo]

A week ago during a routine service an engineer pronounced that my alternator was faulty and would require a trip to a service centre.

After seeking a second opinion a bad live circuit to the engine ignition panel light was diagnosed and when replaced the alternator generated a charge. I measured 13.6V across the battery after this repair.

Over the next couple of days I tested the engine and each time the ignition light went from a bright light to completely out when the engine fired up.

Then however during a 6 hour trip I noticed the ignition light had started to glow faintly and the engine control panel ammeter showed no charge. Now when starting the engine the ignition light dims to a faint orange colour and the battery voltage is low 12v while the engine is running in gear.

What should I investigate next?


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[LadyInBed]

You don't say how old the rig is, but if you extract your alternator and take it into your local Lucas repair shop and ask them to test it. They will soon tell if it's ok or not.

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[andyball]

Is it an internal voltage regulator type of alternator? (some have a separate one mounted nowhere near the alternator).

If internal...remove alternator for test/repair, external?? cd be problem with wiring or the regulator

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[vyv_cox]

My experience of a faintly glowing charge light has been that one of the internal diodes had failed, so the alternator was producing a partly AC output. This may also cause your batteries to become very hot but not to achieve a full charge. Follow the other advice - take it to a good auto electric shop for testing and repair. These people are in a very competitive market, so prices are usually rock bottom and the quality of work is high. Don't use a general truck or automotive garage, they often don't have the equipment or skills to do the job properly.

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[jonjo]

The problem is the yacht is part way home on a delivery trip and the winds look really good this weekend for the Flushing to Dover leg. Maybe I should charge the batteries up on the marina mains and hope the service battery is sufficient to power the Tricolour during a night sail?

Given the risk of an a/c output charge from this alternator, can I electrically disconnect the alternator for the delivery trip?

Would an alternator service centre turn-around the job in 4 days?

Before departing the local yard estimated an alternator service would cost 90 to 400 euros plus the cost of tracking down the problem with the input voltage, so I was really happy to hand over 30 euros to the second mechanic who got the alternator pumping in a charge having fixed the ignition light circuit.

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[jonjo]

The yacht/engine is 30 years old but the alternator is non standard, in fact the yard mechanic pointed out to me that the alternator pulley is not vertically aligned with the two on the engine.

I removed the wind generator last week but left a complex lump of voltage regulator in place, this has a large heat sink on it. There is a Victron 450 mains charger/inverter on board but I do not think there is any other smart voltage regulator plumbed in.

The whole setup warrants a week-end circuit tracing but I just want to get back to UK waters first.

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[vyv_cox]

No problem running the engine without the alternator, provided that the belt doesn't drive anything else as well. I suspect that a full charge should be enough to get you across that trip in the forecast winds of this weekend. Depends a bit on what battery bank you have. I guess the voyage time will not be a lot more than 14 hours so you shouldn't need lighting for too long.

Good luck!

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[andyball]

Many electrical specialists keep new or recon alternators on the shelf, so much less than 4 days.... repairing yours is not a long job,depends on how busy they are I s'pose.

You can electrically disconnect the alternator w/o problem, very,very carefully remove & insulate/tie back the large output wire & the smaller ones too ........disconnect the battery while you do this (in case a wire or tool touches earth) & be sure to mark the wires/make a sketch if it's not absolutely obvious where they came from.

If you do that you should get no w/lamp at all.



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[chriscallender]

You could also buy a portable 12v emergency power pack which could either be used to start the engine or power nav lights in case the main batteries are competely dead. I don't think these things are too expensive (30 or 40 pounds at a guess).

Chris

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[jonjo]

What is a typical masthead TriColour wattage? 25W .. 40W?

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[oldharry]

In my experience the cheaper portable battery packs dont actually have much power in them. They can give enough for a starter for around 10 -15 seconds, but have very little reserve for use as a service battery. Add up the total wattage of your lights and anything else you are going to use, divide by nominal battery voltage, to get a total amps per hour demand. The battery will normally be marked with an Amp hour rating - divide that by the amp hour demand of your lights and knock off about 30% to find out how long a fully charged battery will last. Remember too that once you drop below around 60% charge, there may be insufficient power to start the engine, and unless they are deep cycle batteries they will be damaged (i.e. start losing their re-charge capacity) if they are discharged below about 50% of the total.

You may be able to get a straight service exchange unit for your alternator. That way you know everything is good - mechanics (bearings, brushes etc) and electronics. This is usually the best thing to do for ongoing trouble free service.

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[david_bagshaw]

Usually a standard navagation bulb is 10 or 25 W


Disconnecting Alternators

Remove all the small wires , leave the thick one/s connected.

Then there will be no charge, but also no damage to the remaining good diodes if there is any residual magnitism left in the core.

residual glow of charge lights is as others have suggested, diode failure, or wiring failure, excessive resistance in the big conductor to the batt, earth fault.

Many moons ago when we were in deepest france, having charge troubles a quick fix was a set of short wires & charge light & reg box set up near the alternator. & direct alt to battery, missing out the trip to the consol & ampmeter. Like all things simplest is best.



<hr width=100% size=1>David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[colvic]

Just got back from Spain and saw this:

We had a very similar situation a few years ago with every component being brand new...Adverc were even offering to replace what they had supplied...when chap in the chandlers asked if I'd checked the belt tension. Anything more than 13mm deflection and there is every posibility that the alternator won't give pout a charge EXCEPT for the last few seconds after you switch off the engine and the revs drop away.

400 Euro's is daylight robbery for an alternator when you can pick up a new Lucas/CAV 70amp job for under a £100. Gert back to UK and sort it out here.


Phil

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[jonjo]

> missing out the trip to the consol & ampmeter

Sounds a bit like my current cold start routine. Open engine access panel, hold wire against live battery and fuel heater terminal, count to 10 then nip back to ignition key.

I had to replace the live feed to the ignition light to get the past original dead-light no charge problem so maybe the general quality of engine control console circuits is suspect.

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[jonjo]

> new Lucas/CAV 70amp job for under a £100.

This is good news. I have never purchased one before, do I need a marinized version?

The plan is to start a 1 year refit in August this year so I would prefer not to purchase a new alternator without first planning the whole new electrical system. Would such a high capacity alternator create too much side force on the two engine pulleys it is connected to and would I have to simultaneously invest in a smart charger to stop my batteries from boiling?

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[tr7v8]

No the new alternator loadings would not cause problems, although you may struggle to get enough belt wrap to drive the altrnator pulley and the regulator will take care of battery levels, although to make full use of it a smart charger would be better, also depends on how big a battery(ies) its charging.

Jim
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<hr width=100% size=1>Jim

Draco 2500

 

[colvic]

I've sent you a PM

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[tristan]

Assuming that the electrical system on the engine is not too complicated, then it is a field or charge diode failure.

Also, i suspect that your ammeter is wired in directly using large guage cables - please tell me i'm wrong and that it is wired from a shunt! The practice of using analogue ammeters and excess wiring about 10 - 20 years ago is starting to show it's shortfalls in longevity.

As long as the alternator does not appear to be discharging the batteries (short to ground) then it will not damage the charge circuit in your trip at the weekend, but the whole charge/monitoring system sounds like it needs attention and renovation.

Good luck.

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