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Flickering/flashing charge/ignition light


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My charge arning light keeps flashing at me irrespective of the number of revs the engine is giving. I did some tests with a multimeter and these follow. Any ideas what the fault might be?

1) Fan belt is not loose and batteries do not need water.

2) Battery voltage after standing for a week: Domestic bank 11.5 volts. Starter battery 12. 5 volts.

3) Output from alternator at about 1000/1500 revs = 13.8 volts (measured direct from alternator)

4) Charge at battery terminal – circa 13.6 volts.

5) Battery readings after about 20 minutes charging = 13.5/13.7 volts, domestic and starter.

6) Battery readings after being left to stand for about 20 minutes; Starter 13.2 volts. Domestic bank 12.6 volts.

7) Light continued to flicker throughout the charging process and at different rev levels. Taking the domestic batteries off-line (turn-off at isolation switch) made no difference.

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It is possible that there is a voltage regulator in line somewhere, either accross the rear of the alternator or integrated into a split charger.

Just to negate a few other things try this

1. Disconnect the rear of the alternator - if it is a plug in type just pull the plug, if a terminal just disconnect the positive feed.

2. Start the engine - the charge light should now illuminate fully - this will prove the circuit to the light. If it continues to flicker the problem will be further down the line.Stop the engine and continue to diagnose

3. I would then start from the panel end checking the circuit as you go. Try finding the feed to this light and power it directly - again, should glow correctly - if not, then you know the problem is there (Just use a small power source, just in case)

4. trace the wiring back, remembering to disconnect it from the split charger, or voltage regulator first and then check again... this will prove the wiring back - DO NOT REVERSE DC FEED either the regulator or split charger otherwise there may be rev erse polarity protection diodes inside that may blow

5. work your way through the system back toward the alternator testing as you go and you should locate the problem..

6. Ironically it may just be the connection to the alternator.. if so at least you will know your charging system back to fron when you have finished!!!

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If you're going to run the motor with the alternator disconnected then make sure you remove the fan belt as you should never have an alternator spinning whilst disconnected or you can cause internal damage. As you will only need to do it for a few seconds then the fact that the water pump will also most likely not be working will not matter.

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Hi Soundings

I think my reply may just be an eleboration on Gav's post above, but this is from personal experience when I rebuilt the dash of my old boat.

I'm not sure what sort of boat you have, but if an ex-hire craft they often used to be wired thus: the ignition light is wired directly to the ignition-on position of the ignition switch. The wire then leaves the light and goes to the back of the alternator. When the ignition switch is on but the engine not running, current flows from the switch, through the light, and to the alternator where it is grounded and hence the light glows. This is done to provide the necessary "excitation voltage" for the alternator coils. When the engines is started, this excitation voltage is used to create the magnetic field in the alternator, and then electricity can be produced. Once the alternator starts generating power, it is effectively fed back up the same wire to the light. As there is now positive voltage on both sides of the light, it goes out.

If the bulb is flickering, it could be a bad connection/broken wire from either your ignition switch to the bulb, or from the bulb to the alternator. When I had the problem with my dash, it turned out to be a broken wire 6 inches from the back of the alternator.

Sorry if I am either teaching you to suck eggs, or indeed have got the technical side a bit wrong, but I am only a layman at this electrical stuff, but that's how I understand it.

Happy hunting ....!

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If you're going to run the motor with the alternator disconnected then make sure you remove the fan belt as you should never have an alternator spinning whilst disconnected or you can cause internal damage. As you will only need to do it for a few seconds then the fact that the water pump will also most likely not be working will not matter.

Running an alternator unconnected will indeed damage if it is run up on load - in other words the engine is turning it into its peak charging zone - ie higher revs.. however, this is caused by prolonged use and just for literally a 10 second start i will say that there should be no risk of damage. But as said, if you really want to be sure, just drop the belt off as it literally only needs a few seconds running to check

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If you drop the belt off then what exactly are you testing.

Not the alternator output that's for sure, but the output is already proven as per the OP (at least as far as voltage is concerned) regardeless of anything else I merely made the point that it is unwise to spin the alternator unless it has the battery as a buffer.

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If the lamp is correctly connected this removes the charging device from the circuit, there should be, within the circuit, a 'gate' either electronic or mechanicaly electrical via a relay that says no charge is being produced. This is why, when the engine isn't turning, and the ignition is switched on, that the light illuminates. This will just show very quickly if there is a problem with the circuit per se and will just confirm that the light operates correctly - if it does at this point you will know that it is likely to be an alternator problem, either not correctly terminated or, in the case of the 'multiplug' type a problem with the circuitry within the alternator. This is unlikely to be the case with an alternator with screw gate terminals - especially if you can test the voltage output directly, but will be an easy starting point.... you are then into the methodical fault finding from that point forward....

I agree that there shouldnt be any difference between this and NOT running the engine as the results should be the same, but it sometimes may be all that is required to 're-make' the connection with the alternator ... its an odd thing I know!!

Im just transposing vehicle mechanics to boat engines but if anyone knows differently feel free to correct me.. I know our VM's are still taught to disconnect the alternator to check charging issues in this manner

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Thanks eveybody. I am no electrician, or mechanic for that matter, so moving on from here is difficult for me. It there a reliable and not too expensive boat elengineer around who could have a look-see for me. The boat is in the Stalham area and so am I

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Thanks eveybody. I am no electrician, or mechanic for that matter, so moving on from here is difficult for me. It there a reliable and not too expensive boat elengineer around who could have a look-see for me. The boat is in the Stalham area and so am I

Best man is to PM Dan on the forum as he will probably be able to point you in the right direction

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That'll be a dynamo then mark

No Gav, it was definately a Lucas alternator.

I found this web page very useful http://www.tb-training.co.uk/MarineE08.html#CHARGING SYSTEM – ALTERNATOR and the part I found to be the reason behind my charging issue was

"In theory, the majority of alternators fitted on small craft will not start to charge unless they get a little extra magnetism in their rotors – in practice, given a sound engine and a strong nerve, they may well, as long as the engine is revved high enough. I do not condone this practice, but it can get you out of trouble.Normally the extra magnetism is provided by the current flowing through the warning lamp when the ignition is switched on."

My old boat was originally fitted with a rising oil pressure switch, but this had been bypassed at some point with the ignition lamp to provide the extra voltage. Until I found the broken wire, I used to have to rev the engine to about 2000rpm to get the ignition light to extinguish.

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Regrettably, the visit to Rickos did not fix the problem - the only advice we got from the electrician was disconnect the lamp. That certainly works in that the alternator continues to charge ok. Advice/background info from Chris was more helpful but at the end of the day nothing has really changed - other than the lamp and buzzer are now disconnected.

What I have learned is that I have an old AC alternator. This could be pos or neg earth but as the boat was built in 1981 I would have thought this was well in the negative earth era. So:

1) Is there a modern alternator that can be dropped in in place of the old AC without needing to mod the brackets.

2) Is there any kit that sits between the alternator and the battery that will need upgrading if I change the alternator.

3) When I mentioned changing the alternator I was quoted a rough price of £600 to £1000, which sems extortionate to me.

4) How do I know for certain if a boat is wired pos or neg earth.

Thanks

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Why not just fit a shunt and ammeter to give you a real indication of the situation re charge – discharge when running, it will be relatively inexpensive and far more of a real indicator of the health of the charging system than the ubiquitous cheaper alternative of a volt meter. DC circuits have no earth; you have simply feed from and return to the battery. The wiring colours should be a clue to if it is + or – return but are not proof positive.

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All sounds a bit over complicated for a lamp flickering on & off to me.

The lamp is usually in series with the (exciter) wire (12v) to the alternator. If its intermittent, then as said earlier, it is likely be a poor connection on that line.

E.g. A Connection before lamp, The lamp itself, A break at the soldered connection terminal in the alternator or even a fracture in the lead itself.

I had a similar problem on my Kit Car where the lead had fractured approx 2 inches back from the alternator & was caused by the vibration / movement of the engine.

Hope this helps

Grant

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That all makes sense to me but I am no electrician and for some reason there was a reluctance to get involved (in a hands on sort of way) at the yard today. No testing equipment was even brought aboard!

The fact remains however that the AC is an aged alternator and will need to be changed at sometime. Newer unitts are far less complicated so it does make sense to update sooner rather than later.

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All sounds a bit over complicated for a lamp flickering on & off to me.

The lamp is usually in series with the (exciter) wire (12v) to the alternator. If its intermittent, then as said earlier, it is likely be a poor connection on that line.

E.g. A Connection before lamp, The lamp itself, A break at the soldered connection terminal in the alternator or even a fracture in the lead itself.

I had a similar problem on my Kit Car where the lead had fractured approx 2 inches back from the alternator & was caused by the vibration / movement of the engine

But in this case, the light was disconnected when the engine had stopped and the igition was off. After a restart the alternator kicked in straight away at13.8 volts.

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Yes, I know what you mean. It sounds easy to somebody that has some experience, but if you have none, then it doesn't matter how well you explain something, it will not help, because when you are at the boat actually looking at it all, its difficult to carry out the actual fault finding.

MBird did an excellent description of how it works and was spot on. To be honest though, if you can get somebody with electronic / electrical skills to come to your boat, it should be straight forward to trace, although it could be time consuming, but certainly not complicated.

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Hi GrantS,

You are so right and it is the checking that I had hoped Rickos engineer would do!

I actually know my way around a standard alternator ok with its two wires (charging and light/tickler). This is an old AC though and several of the components that are built into a modern unit are in fact separate on an AC. Thus when you look at it there are more that two wires coming out the back! Confuses the hell out of me so, yes, I need an electrician but who? Alo, I probably do ned to upgrade the AC as it is obsolete kit - but at up to £1k to fit.........

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