flickering charge light

[joss]

Our Hunter Horizon has two batteries and on alternator. The batteries go
through a 1,2,both switch. The problem is that the alternator/charge light
flashes (pulses). Some times it is very faintly, sometimes it is almost full
on, but always has a rhythmic pulse of about 80-100 per minute. This does
not change with engine speed, but the brightness of the light can change
over a period of minutes. There does not seem to be any pattern to it. We
have had the alternator checked and the batteries (service battery is new)
both have 13+ volts in them and full cells. Checked
all the wires and disconnected any equipment. My gut instinct suggests that
it is something to do with the alternator, but like I said, its been checked
and I have also changed the belt. Has anybody else experienced this problem?

thanks for any suggestions,
Jo


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[supermalc]

This has happened on a couple of old cars I had. The alternator light goes out when the alternator charges, so overcoming the battery voltage. Charging is ok, but leakage from damp? or some other source makes the light glow again.

An auto electrician will have a better answer, but this might start you on the right track.

<hr width=100% size=1>Malcolm. Just trying to be helpful.

 

[perlonious]

hhi
it sounds like the rectifyer is begining to break down... over a period of time the pulses will get faster when the enging is warm and slower when cold.....a normal alt test will only get you the output on a bench test.

how old is the alt?
how clean are the windings inside?
also check the earth if unsure then run another earth directly to the neg termial on the battery.

rgds brian

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[andyball]

Had this a few times & assuming you don't just mean at tickover, have found diodes within the alternator at fault. Several times this has gone for some time, then the alternator's stopped charging altogether (sorry).

On many alternators the charge light is turned off by a dc voltage rectified by 3 smaller diodes ( a "diode trio"), not the 6 main power diodes. In this case the field winding is fed from the same diodes, so if one is faulty the alternator output would probably not be as high as normal, although in a lot of cases you'd still see the "right" voltage at the battery.

here describes dismantling/testing them on a car alternator


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[joss]

thanks for responses. I appreciate the effort.

If it is a diode problem, would the frequency of hte pulses change with engine revs? Mine stays about the same.

Engine has done about 500hours. I would have thought that this is fine for an alternator if it is similar to one found on a car. There is a lot of black dust (possibly from belt or pully rubbing on engine insulation) maybe this is shorting it out inside?

Jo



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[andyball]

Alternators usually suprisingly resistant to dust/spray etc, but it's possible.

If the alternator's been spun on a bench test, with a charge lamp circuit.....and no flickering, prob. must be on your boat somewhere.

As mentioned by others, check or substitute temporarily the earth ( spare jump lead is quick), & also the warning lamp circuit, perhaps using a spare bulb if awkward to get to the panel light.

It it was me?: I'd run temporary circuits for w/l, + & - etc (if any doubt existed) , while still on the boat (assuming access not diabolical). If it still flickers with none of your existing wiring being used, it has to be the alternator.


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[[448]]

Joss, I had a similar problem on a car, and not being one to spend if it can be helped I checked the alternator brushes, and found one of them to be sticking. Once freed off the charging light went back to normal (and still is).
Cheers, Dave

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[joss]

Would it be OK to squirt a bit of WD40 in to the back of the alternator? (apologies if that's a really stupid idea)

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[Gunfleet]

Why don't you take it off the boat, then give it to an auto-electrician to test? It will cost very little to have tested and if necessary serviced. If he says it's okay you'll know it's something on the boat. For what it's worth I carry an entire alternator as a spare. I don't want it going wrong with a lot of mysterious problems in the middle of a cruise A good second hand alternator, bench tested, should cost way under £100 at an auto electrician's shop.

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[AndCur]

There are a number of causes of this.
1 Loose fan belt.
2 bad electrical connection
3 worn brushes/slip ring in the alternator.
If if you have rulled on number 1,2 a auto spark should be able to sort this with out any problems

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[Heckler]

classic symptom of worn exitation brushes
stu

<hr width=100% size=1>http://www.beneteau-owners-association.org.uk