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Mike the Boilerman

Curious alternator problem...

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Its a basic ACR clone alternator, and the red light stays on. 

 

The curious thing is it is poking out 40+Amps, while the red light shines as bright as before the engine starts. 

 

Any ideas, anyone?

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8 minutes ago, TheBiscuits said:

Bad wiring?

 

Yep, I'd agree with that!

 

I'll tell it to shape up and be good. 

 

 

Actually I was thinking more along the lines of 'there is a fault'....

 

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3 minutes ago, Mike the Boilerman said:

Yep, I'd agree with that!

I'm pleased to have been helpful.  MrsBiscuit thinks it makes a pleasant change! :D

 

5 minutes ago, Mike the Boilerman said:

Actually I was thinking more along the lines of 'there is a fault'....

Me too ... prolly with the wires.

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Just now, TheBiscuits said:

I'm pleased to have been helpful.  MrsBiscuit thinks it makes a pleasant change! :D

 

Me too ... prolly with the wires.

 

Thanks. You and Mrs Biscuits have been a great help!

 

 

  • Haha 2

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6 hours ago, Mike the Boilerman said:

Its a basic ACR clone alternator, and the red light stays on. 

 

The curious thing is it is poking out 40+Amps, while the red light shines as bright as before the engine starts. 

 

Any ideas, anyone?

So, not that I know much about alternators: -

 

  • The field is being energised by something or you wouldn't be getting a decent charge
  • But it's still drawing a lot of juice as the light stays on

So

  • There is a short to earth between lamp and alternator (but unlikely as it probably wouldn't self excite)
  • The auxiliary diodes are shot so it's only the warning lamp feedin the field (would that give 40A? I said I don't know much about alternators?)

 

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Not shining brightly, but I did have a case where the warning lamp was about half normal brightness yet the alternator was still putting out a good charge.

A day or two later the diode pack completely packed up and no charge.

So could it be a flaky diode?

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7 hours ago, Mike the Boilerman said:

Its a basic ACR clone alternator, and the red light stays on. 

 

The curious thing is it is poking out 40+Amps, while the red light shines as bright as before the engine starts. 

 

Any ideas, anyone?

What does the lamp do as the engine starts and the alternator energises?

 

It is not unknown for a wiring, fusing fault, or faulty ignition switch to cause the field diodes to try to supply the auxiliaries but far less likely on a boat where the auxiliaries are a few warning lamps and gauges. If this is the problem then the lamp would dim and brighten again as the alternator energised.

 

Could also be a blown positive diodes or two so the main output voltage is low but the D+ (field diode) voltage is correct. This causes the field diode to try to charge the batteries vis the warning lamp.

 

All assuming its a 9 diode machine. If its a six diode one then all bets are off.

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Is this a new issue Mike or something you've lived with and decided to sort out? If the former, my money would be on the diode issue.  Boater Sam is usually pretty helpful on alternators... ;)

 

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Ours did this on boat purchase, never went out in spite of ammeter proving input. Seller was clueless on electrics.

Eventually it failed completely. Replacing like for like with acr clone fixed it with no alteration to wiring. Assumed diode.

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8 hours ago, Mike the Boilerman said:

Its a basic ACR clone alternator, and the red light stays on. 

 

Get another (cheap clone) swap them over, if the light stays on you now have a spare, if the light goes out - problem solved.

 

At least for a few £s you will know where the fault is (alternator or wiring).

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2 hours ago, Sea Dog said:

Is this a new issue Mike or something you've lived with and decided to sort out? If the former, my money would be on the diode issue.  Boater Sam is usually pretty helpful on alternators... ;)

 

 

It's a new issue with a brand new alternator, fitted to the Gleniffer during the rebuild. The identical alternator on the Kingfisher engine removed, worked fine. Or rather, the issue has existed ever since the gleniffer was re-installed last summer.

 

I'm sure someone will suggest getting Richard back to fix it but it strikes me as a trivial fault I can fix myself, but on thinking about it I've fallen at the first hurdle.

 

(The first step in fault tracing being imagine a fault that could cause the observed symptoms. The second step is to think of a way to test to see if your idea is right.) 

 

 

Edited by Mike the Boilerman

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4 minutes ago, Mike the Boilerman said:

The identical alternator on the Kingfisher engine removed, worked fine.

So at least you know it is not the alternator at fault.

 

Now to explore your wiring ………………………...

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2 hours ago, Tony Brooks said:

What does the lamp do as the engine starts and the alternator energises?

 

I thi k it continues to glow at exactly the same intensity. Sometimes I think I notice a fleeting slight reduction in intensity for a brief fraction of a second but can't remember clearly. I'll start the engine again in a sec and check. 

4 minutes ago, Alan de Enfield said:

So at least you know it is not the alternator at fault.

 

Now to explore your wiring ………………………...

 

How so? Different instance of same model of alternator, altered wiring. Could be either, I reckon!

 

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If its the ACR series with the big "pudding basin"  plastic cover you are welcome to come round next time you are in Reading so we can check the diodes. If you want to then switch to PMs s I do not broadcast to the world when I will not be at home.

 

I am fairly confident its a diode or two that have failed and you will still get amps out of the machine, even with two diodes down, but it will be at a reduced voltage so charging is compromised.

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29 minutes ago, Mike the Boilerman said:

 

I thi k it continues to glow at exactly the same intensity. Sometimes I think I notice a fleeting slight reduction in intensity for a brief fraction of a second but can't remember clearly. I'll start the engine again in a sec and check. 

 

How so? Different instance of same model of alternator, altered wiring. Could be either, I reckon!

 

 

Maybe you need a 3rd alternator just to check the other two...………..

 

Remind you of anything ?

  • Haha 4

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30 minutes ago, Tony Brooks said:

If its the ACR series with the big "pudding basin"  plastic cover you are welcome to come round next time you are in Reading so we can check the diodes. If you want to then switch to PMs s I do not broadcast to the world when I will not be at home.

 

I am fairly confident its a diode or two that have failed and you will still get amps out of the machine, even with two diodes down, but it will be at a reduced voltage so charging is compromised.

 

Oops sorry, its an A127 type, not an ACR. I get the two confused. Will post a photo in a sec. 

 

Anyway I just started the engine to observe exactly what it does. As follows:

 

1) Ignition ON. Light glows brightly.

2) Turn engine over to start. Light dims to perhaps 3/4 brightness while starter spins engine.

3) Clamp meter on alternator output rises to 20A or so during starter operation

4) Disengage starter operation and engine ticks over (at starter turn-over speed), light returns to full brightness. Charge current remaisn at about 20A

5) Increase engine revs and charge current rises to 67A and light stays at full brightness, with no change.

 

Do you still think this might be an alternator problem Tony? Will PM you if you think so. Thanks for your offer.

 

 

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Seeing as how clean everything is - could that 'soot' on the 'white potted' thing be relevant ?

Edited by Alan de Enfield

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1 hour ago, Mike the Boilerman said:

It's a new issue with a brand new alternator, fitted to the Gleniffer during the rebuild. The identical alternator on the Kingfisher engine removed, worked fine.

Ah, then I'm inclined to think installation issue or manufacturing defect. The reasoning behind my question, as I'm sure you understood, was that installation faults tend to be there immediately on commissioning whereas developing faults are likely to be equipment/component failure or wiring mishaps.

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6 minutes ago, Sea Dog said:

Ah, then I'm inclined to think installation issue or manufacturing defect. The reasoning behind my question, as I'm sure you understood, was that installation faults tend to be there immediately on commissioning whereas developing faults are likely to be equipment/component failure or wiring mishaps.

 

Yes should have made it clear this problem has existed from the get-go, but has not been high on the list as it actually charges fine. 

 

One day though, it might stop charging and I'll have no way of knowing until the lights go out.

 

 

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I seem to remember a similar problem in a car years ago before clever electronics

Alternator was goosed.

Take the alternator  off and take it to an auto electrical place to get it checked, easy and simple.

That will eliminate the alternator being at fault.

ETA 

You say its charging but at what voltage? 13.9v would still give a charge into your old batteries.

Edited by Loddon

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Right, having thought about it, I think a possible, likely even, cause of these symptoms is a wiring error, the light is powered up other than via the alternator. 

 

Unfortunately I cant check this for a few days as had to go out and earn a living.

 

 

1 hour ago, Loddon said:

You say its charging but at what voltage? 13.9v

 

14.4v

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Maybe the wire has fell off the field connection on the alternator and is now resting on the earthed casing and the alternator is self exciting

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