Volvo MD1 - ignition warning light (again)

penultimate

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Apologies for returning to the forum but I'm at my albeit limited wits end with a charging problem. On the advice of forumites I replaced the original 14v 2.5w lamp with a 12v 2.2w. The initial field current , as expected, was 0.2 amps and was insufficient to excite the alternator. If I short out the ignition warning light the field current is 4 amps and charging proceeds normally and regulation is fine.
I have tried replacing the 12v 2.2w lamp with 12v 5w, and the field current, as expected, was 0.4 amps; but still insufficient to excite the alternator.
The S.E.V. Marchal brushless alternator has been tested OK; and the original Bosch 3 pin regulator which was found to be defective replaced with new (£8).
The disadvantages of running with the ignition warning light permanently shorted out are that there is no warning of charging failure and that the ignition can be inadvertently left switched on after stopping the engine.
What can possibly be the problem?
 

VicS

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Puzzling. I would double check everything. That the new regulator is the right one and is fitted correctly. Not something that can be done easily but it would be nice to check that the current you measure is actually flowing through the field coil ie not being partly shorted out some where. I wonder if the field diodes are Ok but having said that being a S.E.V Marchal there may not be separate field diodes as the field current may be taken from the main rectifier ( with a blocking diode between there and the output). All of these thoughts though are ruled out if the machine has been properly tested and found to be ok.

I know the alternator but I have not worked on one. When my pals one packed up just took it to an auto electrician for him.

I think I would double check everything that you can and then take it somewhere else to be properly tested.

If you run it with the lamp shorted but then remove the shorting link (best done by fitting a switch perhaps) if every thing about the alternator is ok then it should continue to generate and regulate correctly on its own. May be worth a try unless any one can say why not. If it doesn't then the alternator is faulty I think but if it does then it is someting to do with the connection to the lamp maybe ??????
 

penultimate

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Thanks again for your patience and helpful reply. It's curious that when I remove the short across the lamp the alternator instantly ceases charging.
The alternator was removed from the boat for testing by a competent professional. He first demonstrated that the alternator was delivering full output, and then connected the new regulator to show that both were working.
I am now wondering whether the DF and D+ connections have become reversed when I re-installed. (The markings are very indistinct). Could this be the cause?
I have researched the internet but cannot find an internal wiring schematic for an alternator with an external regulator; and am reluctant to try reversing them for fear of doing some damage.
Any further thoughts?
 

VicS

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I have got a couple of diagrams but they show old fashioned eletro mechanical regulators but if you ignore the internals of the regulators then they may help. Interesting anyway perhaps. The connections are just the same as more modern electronic ones with which they are interchangeable. The Bosch regulators are also interchangeable with the SEV ones.

Alternatorwiring.jpg


On mine the regulator is connected by a wiring harness that plugs into the regulator and has the brush box (it's not a brushless alternator) attached to the other end so there is no scope for getting it connected wrongly. Also the warning lamp goes to the alternator (I don't know what the connection is marked but it is presumably connected internaly to "61") The wiring between the regulator and the alternator is colour coded: 61 to D+ either red or brown, F (or DF ) to DF either green or white and the earth connection is black.

One thing for sure is that if you have got D+ and DF mixed up it won't work but whether it fits with what you observe when you short the warning light I am not sure. I would look at those indistict markings very closely with a magnifier! I take it that its the ones on the regulator that you cannot ID. Those on the alternator will be easy to sort out.
I'd be prepared to bet you have got then muddled up as you know everything was working ok when tested, but other than identifying the markings I dont know what to suggest. You could go back with it disconnected and ask your electrician to ID the marks for you. He'll know which is which without being able to see them probably
 

VicS

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[ QUOTE ]
dirty slip rings

[/ QUOTE ] Explain to us all why a brushless alternator will have slip rings please before you go for your pint.

Then before you cry that it must have brushes and slip rings to connect to the field winding get hold of one, take it to bits and you'll see how it works!
 

MichaelHomsany

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Hi,
I don't know the system, but why not just use a transistor switch to turn the light on and off? The input to the base of the transistor is only on the order of a few ma.

Costs would be a current limiting resistor to the base of the transistor and the transistor itself, less than a € total. You could get even fancier and replace the incandescant with an led.

Best regards,
Michael
 

VicS

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[ QUOTE ]
but why not just use a transistor switch to turn the light on and off

[/ QUOTE ] Why make it so complicated? The system works because the current flowing through the waning light bulb is the current that provides the initial field current to get the thing to start generating An LED will not provide enough current on its own but a small bulb does. In effect the bulb is connected between the battery and the output from the field diodes and when there is little or no output from the field diodes (because the alternator is not generating) the bulb glows. As the volts output rises the bulb dims and eventually when the volts at the field diodes reaches the battery volts the bulb is extiguished. Ok an elecronic switch would achieve the latter functiion but not satisfy the need to supply the initial field current. No doubt it could be done, and may well be done these days, but the warning bulb on its own is so simple and effective.
 

VicS

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[ QUOTE ]
This will fix the problem, so why not?

[/ QUOTE ] You are obviously one step ahead of me. What is the problem with penultimate's alternator then. Or to be more precise what is causing his problem.
 

MichaelHomsany

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Good question.

With the understanding that, as said above, I've not aquainted with the system, and in addition, I'm in the middle of rural Vanua Levu, Fiji Islands, and thus can't personally inspect or test the device, (but would do so if penultimate would be willing to cover airfare /forums/images/graemlins/cool.gif), nor do I have any desire to argue...

First, the diagram you posted appears to be the regulator for a petrol engine, where the regulator is switched on via the ignition instead of the oil pressure switch. Not the end of the world, but a little harder to start as the field is energized as soon as the ignition is armed and the starter motor has to work harder (or arm, if hand-cranked).

Continuing with assumptions, if things are wired the way the diagram you posted indicate, and have said above, the sense logic is inverted to 'normal', i.e.; the bulb will be illuminated during charge and (apparent) off when fully charged -OR- if not charging (broken belt), which makes it pretty useless as an indicator.

If this is true (I don't know if it is) and if penultimate would like to maintain the system 'as was', I'd measure the voltage drops between the switch and the input to the regulator.

Personally, I would far prefer a charge indicator that is truely binary, not dependent on the integrety of a filiment, which when it fails, will remove not only the indicator, but will knock the entire charging system off line (current state-and yes, it is a poor pun!).

This is why I said it was 'broken' (besides not working /forums/images/graemlins/cool.gif)

BTW, the new avatar is a piccie of our boat at anchor at our home, Fawn Harbor, Vanua Levu.
 

penultimate

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I have checked for voltage drop between the switch and the regulator, as suggested by Michael in a later post; but I am now convinced (after reference to your schematics) that there is a failure within the alternator of the connection between D1/D2 and 61. That would account for the failure of the alternator to self excite; and would not have been revealed when the electrician tested the regulator and alternator because he simply applied 12v to the field. I'm still puzzled why the initial charging current fails to excite the alternator; but I'll PM you the results of further investigation.
When the opportunity permits I propose to disassemble the alternator and repair this connection.
 

VicS

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[ QUOTE ]
within the alternator of the connection between D1/D2 and 61

[/ QUOTE ] It sounds as though you are getting closer to the problem.

Thinking aloud:- If the small current from the bulb was getting through Ok it would just start to generate but I dont know what the output would be quite small I suppose and if the connection from the field diodes was broken it would not increase and the bulb would stay illuminated. When the bulb is shorted the full 12v would be applied to the D+ terminal of the regulator and it would then generate and regulate as normal. Yes that would explain it. Check that the connection from the field diodes is getting through to the D+ terminal of the regulator. If it does have a field diode trio it might be worth checking them. Some times they are a separate unit and sometimes they are integrated into the main rectifier assembly, BUT it is the SEV alternator in my diagrams that has an isolation diode in the main output rather than a field diode trio. If that applies then all you have to do is check the connection inside the alternator.

I am sorry that the diagrams are not clearer, I should have scanned them at a higher resolution. The labelling on the alternator terminals are, reading from the top, B1, 61, F, and E. the connections on the regulator are D+ DF and D-. There is going to be a bit of variation in the way different units are marked though.

It is pity your electrician did not set it up to run as it would do in service. His short cut in connecting 12v directly to the field connection may in the end be the factor that is causing you all the trouble you are having. You may still have to go back to him.

Good luck and do let us know how you get on. Or shout again if you think I can help any more.
 

VicS

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[ QUOTE ]
the diagram you posted appears to be the regulator for a petrol engine

[/ QUOTE ] It is in fact the diagram from a worshop manual for a Volvo petrol engine but it is quite normal for the same system to be used on small diesel engines. It certainly is on the Volvo MD11. I have a copy of the wiring diagram for that and it uses a similar alternator, but fitted with an intenal regulator. I do not really see where the extra load on the arm or starter is coming from. The bulb is powered from the battery and anyway the 0.2 amp is only equivalent to 0.003 of a horse power. The bigger load due to the alternator generating and supplying its own field current and recharging the battery does not materialise until the engine is running and is turning the alternator fast enough for the output rise to 12v. I don't really see why the requirements of a diesel engine in this respect are substantially different to those of a petrol engine.

I will however for my own education swot up on the logic behind the "rising oil pressure sytem"

[ QUOTE ]
Continuing with assumptions, if things are wired the way the diagram you posted indicate, and have said above, the sense logic is inverted to 'normal', i.e.; the bulb will be illuminated during charge and (apparent) off when fully charged -OR- if not charging (broken belt), which makes it pretty useless as an indicator

[/ QUOTE ] Sorry you have definitely misread the diagrams. I can assure you that the light comes on when the "ignition" is switched on and goes off once the engine is running and the alternator is generating. If the belt fails it will come on again. The state of charge of the battery does not come into it.

[ QUOTE ]
Personally, I would far prefer a charge indicator that is truely binary, not dependent on the integrety of a filiment

[/ QUOTE ] You are entitled to your own preferences but this system is one which has been in use in motor cars ever since they where first fitted with alternators. I have never such warning light fail and I think I would stick to the simpilicity of a filament bulb.
 
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