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Alternator Ind light question


Martin Megson
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Hi,

 

Looking for advice on a problem with my engine alternator. When I started up this morning I noticed the red indicator lamp didn't light. The bulb seems ok and while checking it I found that slight movement of the bulb holder made it come on (with ignition switched on but engine not running). Thought I had solved it but now when engine is running the lamp is flickering on and off quickly. I've checked the voltage across the battery which is just over 12 when engine stopped and just below 14 when running so I think the alternator is charging the battery ok.

 

I'm no expert but I seem to remember that the Alternator lamp negative is earthed through the alternator and when the alternator is working the output puts the light out. I'm thinking that the negative lead to the lamp might be an intermittent connection which is causing the bulb to flicker when running and sometimes not come on when ignition is on but engine not running.

 

Please could any electrical experts tell if this is a likely fault before I do anything further.

 

Thanks

Edited by Meggers
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The D+ terminal that the indicator bulb is connected to on the alternator should be at (very near) same voltage as on the B+ battery output terminal where you presumably measured the 14 volts. This should place the bulb with 14 volts at both sides of the exciter circuit it provides, so no current should flow through bulb.

 

I would solve the intermittent bulb connection problem first (dodgy exciter wire?) with engine not running, then look towards an alternator problem if it doesn't stay out when engine running and charging.

Edited by by'eck
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If the batteries are fully charged, it doesn't take much effort to bring the volts up to 14 point something, but with the alternator having to work hard it might be a different matter and you might find its not working very well. Yes, brushes could be a reason. I'm also thinking about a blown diode, but I think that tends to cause the light to glow dimly rather than flicker. Anyway, fix the bad connection then try loading the alternator up to see if its working OK

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Thanks for the helpful replies. I seem to have cured the initial fault as the ind light now comes on when ignition turned on. However,it stays on when engine is running. It is now dim rather than blinking and gets brighter if the engine speed is increased. Still seems to be charging the battery ok. Also checked the brushes which are in good condition with plenty of length. As it is the starter battery there is not much I can do to increase load on the alternator.

 

The boat has an adverc battery manager but this is only connected to the second alternator charging the leisure bank. There is a green overcharge warning light which s connected to the ind light. This should also Coe on when he ignition is on and go out when it's charging and now this one has stopped coming on. Picture shows the wiring between the two lamps. The alternator ind lamp had a resistor wired between the terminals, could this have blown.

 

Nicnorman mentioned a blown diode as a possibility. Where is this located and is it easy to test with a multimeter.

 

Photo

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Check if the volts on the D+ terminal (that connects to the bulb) are the same as battery volts on B+ terminal. They should both be around 14 volts with charged battery when measuring against batt negative/ground and engine running of course.

 

If not maybe blown diode(s) (there are six feeding the battery) or faulty voltage regulator.

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Thanks for the helpful replies. I seem to have cured the initial fault as the ind light now comes on when ignition turned on. However,it stays on when engine is running. It is now dim rather than blinking and gets brighter if the engine speed is increased. Still seems to be charging the battery ok. Also checked the brushes which are in good condition with plenty of length. As it is the starter battery there is not much I can do to increase load on the alternator.

 

The boat has an adverc battery manager but this is only connected to the second alternator charging the leisure bank. There is a green overcharge warning light which s connected to the ind light. This should also Coe on when he ignition is on and go out when it's charging and now this one has stopped coming on. Picture shows the wiring between the two lamps. The alternator ind lamp had a resistor wired between the terminals, could this have blown.

 

Nicnorman mentioned a blown diode as a possibility. Where is this located and is it easy to test with a multimeter.

 

Photo

The diodes are integral to the alternator. I am no expert in the practicalities of alternators and it probably depends on the make, but I suspect a degree of disassembly would be required to test the diodes. Someone else would be able to advise better.

 

If a diode has blown, the alternators max current will be significantly reduced so it might be easier to check the charge current having depleted the batteries somewhat, if you have a clamp meter. (And if not, get one because they are cheap on eBay and very useful!)

 

Found this:

 

Indicator lamp is dim after starting, and gets brighter as engine RPM increases.

 

Battery lead to alternator loose or bad

Ground connections are bad

Battery is bad

Alternator is bad due to open diode failure

Edited by nicknorman
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Now I'm even more confused. I checked the voltage at each side of the bulb. It is reading just over 12 on the battery side but over 16 on the alternator side. Seems the alternator is over charging which would explain why the battery is still charged. I'm now thinking it could be a faulty regulator and I happen to have a spare so I'll swap it over later and see if that cures it. Failing that can anyone recommend a good electrician on the south Oxford. I'm currently stuck on the Thames at Eynsham and plan to head up the Oxford as soon as I can get off the river.

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Now I'm even more confused. I checked the voltage at each side of the bulb. It is reading just over 12 on the battery side but over 16 on the alternator side. Seems the alternator is over charging which would explain why the battery is still charged. I'm now thinking it could be a faulty regulator and I happen to have a spare so I'll swap it over later and see if that cures it. Failing that can anyone recommend a good electrician on the south Oxford. I'm currently stuck on the Thames at Eynsham and plan to head up the Oxford as soon as I can get off the river.

 

Apologies for not suggesting this before, but it seems highly likely you have a bad connection in the main cable from the B+ output terminal of the alternator to the batteries themselves. This high resistance allows the alternator output volts to rise even beyond the voltage regulated limit (over 100 volts is possible with open circuit alternator) since there is little or no load on it.

 

The warning light then has battery volts on one side but the higher 16 volts you measured on the other so the lamp glows as reverse current is fed through it, and gets brighter as the engine revs are increased and the unloaded alternator gives even more volts.

 

First disconnect the batteries, then clean and re-make connections at both battery and alternator end. Check also for anything in between like charge splitting relay etc. and re-make those connections as well.

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If there is a 4-volt difference in the way you describe, then I don't see how it could be the regulator's fault.

 

Depending on how things are wired up, the two possibilities I can see are:

 

1. A poor connection between the alternator and the battery (as suggested by Richard); this could be the alternator output terminal (is it a screw-on or blade terminal?), the cable and/or its termnations (the crimp terminal at the alternator end is a defnite possibility). However I'm not convinced that this would cause a high voltage such as you describe, unless the alternator is battery-sensed or has an external controller.

 

2. A blown rectifier diode in the alternator itself. You can replace these yourself but it is a bit more difficult than replacing a regulator as it involves more dismantling and usually some soldering. The output from the faulty phase is no longer clamped by the battery voltage, so its voltage rises and is also seen on the D+ terminal

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If there is a 4-volt difference in the way you describe, then I don't see how it could be the regulator's fault.

 

Depending on how things are wired up, the two possibilities I can see are:

 

1. A poor connection between the alternator and the battery (as suggested by Richard); this could be the alternator output terminal (is it a screw-on or blade terminal?), the cable and/or its termnations (the crimp terminal at the alternator end is a defnite possibility). However I'm not convinced that this would cause a high voltage such as you describe, unless the alternator is battery-sensed or has an external controller.

 

2. A blown rectifier diode in the alternator itself. You can replace these yourself but it is a bit more difficult than replacing a regulator as it involves more dismantling and usually some soldering. The output from the faulty phase is no longer clamped by the battery voltage, so its voltage rises and is also seen on the D+ terminal

 

Hi Allan, yes you would think that a built in regulator would limit the voltage, but with a near open circuit it doesn't take much rotor field current to allow the volts to creep up.

 

Whilst a blown output diode would create the higher voltage at the D+ terminal, as you say because of the unloaded phase winding fed through the diode trio, surely it would be lower rather than higher on the main B+ output terminal?

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Thanks once again for the advice. The alternator has a single connector onto spades so I'll check that is clean and tight and also the connections to the battery as you suggest. There is no external controller on this alternator. The only other wire is the rev counter feed. I'll go and check all the connections as suggested and then change the regulator as I have a spare.

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Thanks once again for the advice. The alternator has a single connector onto spades so I'll check that is clean and tight and also the connections to the battery as you suggest. There is no external controller on this alternator. The only other wire is the rev counter feed. I'll go and check all the connections as suggested and then change the regulator as I have a spare.

Also check the battery isolator switch

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Hi Allan, yes you would think that a built in regulator would limit the voltage, but with a near open circuit it doesn't take much rotor field current to allow the volts to creep up. True

 

Whilst a blown output diode would create the higher voltage at the D+ terminal, as you say because of the unloaded phase winding fed through the diode trio, surely it would be lower rather than higher on the main B+ output terminal? Which if I read it right is exactly what the OP is reporting ("only just over 12")

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He actually says in post #8 - 12 volts on the battery side and over 16 volts on the alternator side. Although he doesn't specifically mention the voltage on the D+ terminal it must be something similar to provide the potential difference to illuminate the warning lamp.

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He actually says in post #8 - 12 volts on the battery side and over 16 volts on the alternator side. Although he doesn't specifically mention the voltage on the D+ terminal it must be something similar to provide the potential difference to illuminate the warning lamp.

 

 

As I interpret his post, by the "alternator side" of the bulb I infer that to be D+, so that's 16v on D+

 

The "Battery side" presumably comes from the battery itself, so only 12v on the battery but an unknown voltage on B+ depending on the wiring.

 

It could still be either explanation. I reckon if B+ is around 12v, it's an alternator fault, but if B+ is around 16 it's a poor connection to the battery.

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Almost sorted.

Cleaned and tightened all the big cables between alternator and battery, including isolation switch. Seems to have sorted the charging level which is now showing 14.13 volts at the B+ terminal with engine running. However, the ind light is still on when running and gets brighter as revs increase.

I think that the system is now charging ok but will get an electrician to check it out properly, have a feeling there is a fault in the alternator.

 

Thanks for all your help

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Almost sorted.

Cleaned and tightened all the big cables between alternator and battery, including isolation switch. Seems to have sorted the charging level which is now showing 14.13 volts at the B+ terminal with engine running. However, the ind light is still on when running and gets brighter as revs increase.

I think that the system is now charging ok but will get an electrician to check it out properly, have a feeling there is a fault in the alternator.

 

Thanks for all your help

 

so now what's the voltage reading at the IND terminal?

 

(and the B+ taken at the same time)

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Almost sorted.

Cleaned and tightened all the big cables between alternator and battery, including isolation switch. Seems to have sorted the charging level which is now showing 14.13 volts at the B+ terminal with engine running. However, the ind light is still on when running and gets brighter as revs increase.

I think that the system is now charging ok but will get an electrician to check it out properly, have a feeling there is a fault in the alternator.

 

Thanks for all your help

 

But what is the all important battery voltage when there is 14.13 volts at B+ on alternator?

 

Anything less than 14 volts suggests a problem still, or under-engineered cabling. It would also explain why the light glows brighter as revs are increased.

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Think I've almost worked it out. Got very confused as both D & B terminals are showing same voltage usually around 14 v but I'm still getting 16 v at the actual bulb. As you can see from the wiring diagram in the link the warning lights for the engine and leisure alternators are connected. Having checked the leisure alternator the B+ terminal is at 14.25v but the D+ is over 16 and climbs to 18 as engine speed is increased. This is the source of the high voltage at the bulb. It would seem tat iris actually the leisure alternator that is faulty. If I've read your replies correctly it seems likely that a diode as gone in that alternator.

 

Wiring

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Think I've almost worked it out. Got very confused as both D & B terminals are showing same voltage usually around 14 v but I'm still getting 16 v at the actual bulb. As you can see from the wiring diagram in the link the warning lights for the engine and leisure alternators are connected. Having checked the leisure alternator the B+ terminal is at 14.25v but the D+ is over 16 and climbs to 18 as engine speed is increased. This is the source of the high voltage at the bulb. It would seem tat iris actually the leisure alternator that is faulty. If I've read your replies correctly it seems likely that a diode as gone in that alternator.

 

Wiring

 

Sorry can't see on your diagram how the warning lights for starter and leisure alternators are connected. I see only one alternator with Adverc connected, and only one alt warning light plus the Adverc one.

 

Assuming this is the leisure alternator though, it seems like a main output diode may have blown giving rise to high volts on D+ terminal from unloaded phase as per Keeping Up's post #10.

 

Apologies if I have missed it but can you confirm that leisure batteries are at the same 14.25 volts as leisure alternator B+ terminal (or nearly so). This should help confirm above.

Edited by by'eck
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Sorry can't see on your diagram how the warning lights for starter and leisure alternators are connected. I see only one alternator with Adverc connected, and only one alt warning light plus the Adverc one.

 

Assuming this is the leisure alternator though, it seems like a main output diode may have blown giving rise to high volts on D+ terminal from unloaded phase as per Keeping Up's post #10.

 

Apologies if I have missed it but can you confirm that leisure batteries are at the same 14.25 volts as leisure alternator B+ terminal (or nearly so). This should help confirm above.

 

Hi thanks for the quick reply. The wiring diagram only shows the domestic circuit but the d+ terminal of the engine alternator is also connected to the red ignition light shown in the diagram. The leisure batteries are at the same voltage as the B+ terminal. When I get off the flooded Thames I'll get it tested but it looks very much as you and Keeping up suggest.

 

Thanks again for all your help. Wiggly amps aren't my strong point.

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Hi thanks for the quick reply. The wiring diagram only shows the domestic circuit but the d+ terminal of the engine alternator is also connected to the red ignition light shown in the diagram. The leisure batteries are at the same voltage as the B+ terminal. When I get off the flooded Thames I'll get it tested but it looks very much as you and Keeping up suggest.

 

Thanks again for all your help. Wiggly amps aren't my strong point.

 

Can you draw us a diagram of that?

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