'92 Volvo 240 sedan 190k

Been having having this problem on and off for a while and its occurring more often (but not always). Sometimes I get dim dash warning lights. Perhaps happens more when its damp or maybe that's my imagination. The lights tend to go out if I raise the RPM. However, and this is what confuses me - it doesn't seem to be voltage related - I have a cigarette lighter voltage meter and it doesn't vary much between when the dash lights are on vs off. The car seems to charge fine and the voltage is 13.8-14.1V on the cigarette lighter voltage meter. When I start the car I see 12.5V at low revs until I rev it slightly and the voltage then rises - I think this is a characteristic of the alternator and exciter wire set up.

I've previously done a lot of research/diagnosis and reading the miriad of posts here but still can't figure this out. Replaced the alternator brushes, checked grounds,checker batter cables etc for voltage drops connections etc, re-soldered the cluster, checked the exciter wire and connections, and nothing helps. I thought the last time I changed the voltage regulator (1000 miles ago) had fixed it but the problem has re-occured and the brushes still look almost new. Really out of ideas at this point. Try an new alternator?

So > 1 year later and I now have this problem again. The problem went away by itself for a year and is now back - I have dim dash lights. The battery seems to charge fine (14.2V while running). Measuring the voltage between exciter connector on alternator and ground/battery -ve = 1.8V which I believe is the cause of the dim lights. Last year we concluded that the problem was the alternator but since I've been driving the car with no problems seems a waste to replace what seems to be a functioning alternator... I connected the excitor wire connector to battery positive and the lights went out - maybe that should be my fix since it cures what seems to be the cosmetic nuisance of the dime dash lights!!?

When I had an intermittent dim battery warning lamp the problem was poor tension in the connector pins of the wiring harness attaching to the instrument cluster. Took the connector apart and bent the pins to get a better contact with the cluster and this solved the problem.

Hi,

Boy, this has been a long thread in the making ... since June of last year!

When I first broke into the thread I thought you were talking about dim dash lights of the instrument cluster. Those that light up the whole from from the top down.
After Winking and Blinking a little, I thought you meant in like the rheostat dims those bulbs. I read on to pick up on that maybe you are talking about the battery (idiot light) glowing dimly. At last, it then made sense but I still see " and other dash lights" above information the title bar?

Dan followed up your post today and that places you back into Art's posts. While browsing through those I noticed he has it all covered for faults with an alternator.
I didn't see that he told you what the exciter wire does so your later conclusion is that 1.8 Volts must be the problem.

He is talking about bad connections and alike internal and external.
I will have to say that you are wrong zeroing in on that exciter wire voltage.
That would be a normal voltage drop from battery voltage.
You are reading whats left of the current and voltage that is allowed to come through a small bulb that's the red idiot light. It's bright when it has a good path to ground so it "theoretically" burned up the difference. If that light burns out, you "theoretically" get nothing out of the alternator upon start up. Sometimes residual magnetism slaps a theoretician's face too!

The exciter circuit uses a working bulb to limit current coming into windings to create a small amount of magnetism to be generated.
This is for initial start purpose only.
It does this by going to ground through the alternator itself.
This causes the light to burn bright until the alternator's windings start moving. The magnetism then starts cutting through other winding wires and starts bumping out other electrons from inside the wires.
As this process keeps building more electrons with more and more revolutions. This build up is fed back around and around by the regulator through the carbon brushes until the battery light starts to notice a push back. This opposition to power flow to its original ground flow causes "The light" to grow dimmer.
This is where the "idiot light" gets its name as it "does not know" how much opposing voltage is coming out of the alternator's "B+" side.

This is where a dash mounted voltage meter can inform the owner of any other more important problem going on with the charging system.
A wavering needle on a voltmeter can mean loose belts, short carbon brushes that excite the rotor windings. If you see your headlights occasionally flicker while stopped in front of your garage wall, a voltmeter will wiggle more often in the day time. So, it's a better heads up for the other twelve hours a person can drive and the red light gets even dimmer with sunglasses on!

A Bad bearing or bad slip rings can make the brushes stop working properly.
Bouncing and arcings from them while in a worn slip ring groove is hard on the brushes. If worn short enough the springs can no longer hold them down onto the slip rings.

If this can go on long enough the solid state regulators become not so solid state.
They like smooth DC current flow and any arcing are not continuous flows to be nice enough for fast switching transistors. These transistors work on very small amount of current flow change hold voltage limits to within a few tenths of a volt of feed back range. They are also temperature affected that move that limited range more. On and on it goes!

Now, that we are understanding the positive side of the inner working of an alternator, we still have understand, that the WHOLE OTHER HALF, the ground or minus side "B-" has to work!
If you don't you will get a lot more negative results!
The alternator's housing, for whatever Volvos reasoning, it is rubber mounted!
This is why you need a ground wire in good ... No, Excellent condition!
Remember, the regulator needs that feed back voltage!
It's watching that tenths of a volt range on the battery and the entire cars system.
You turn on a fan or signal blinkers it's in there adjusting amperage output!

On my voltmeters, in all my cars, I can see a few tenths wiggle and in that signal notification it has told me when and what is the amount of loading.
I then can figure out what turn off to slow the drainage.
With a battery light being totally out ... say to lunch and when it works, dimly or brightly, your car has already had bad breath for awhile!
How long before you get to go to lunch, with a tow truck driver, is how lucky do you feel!
As Dirty Harry said to the punk, "Have I fired five or six times?"

GET A VOLTMETER and put it on full time duty!

Phil

Maybe you should re-read Art's posts! If not I would start with a new Bosch voltage regulator.
Dan

Of course I should!. I spent a lot of time diagnosing this previously with Art's and others help - I'm just in denial that its the alternator since the battery charges fine even when the dash lights are dimly on. Also, I've replaced the regulator twice. I'm going to do the various diagnostics I did before again and I'm sure it will be the same conclusion. My post was really just in jest/frustration.

Are you using Bosch regulators?
You can take the car or alternator to Autozone or similar and they will test it for you.

Dan

"When I start the car I see 12.5V at low revs until I rev it slightly and the voltage then rises..."

Yes, this is normal behavior when the pre-excitation circuit in the regulator is not being delivered battery through the D+ wire. It occurs because of residual magnetism in the core of the rotor, but we can't rely on it in every alternator.

The lamps light at whatever brightness according to the difference in voltage between B+ and D+. You can see the light dimly when the difference is just a volt or two, which may be the case if there's a bit of corrosion in a broken wire or connector.

Next time the lights are on dim, or before you rev it up to get it charging, measure at the D+ and B+ terminals and make sure you check the housing of the alternator. With the car running you should find ~13.5-14.5 on both terminals, and 0V on the alloy case with reference to battery negative. Try to be sure your probing doesn't "correct" the condition by checking the lights are still dim, if you don't see a problem. Your digital voltmeter will be adequate to sort this.
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Art Benstein near Baltimore

Artificial intelligence is no match for natural stupidity.

So here's something that will likely help a diagnosis..

Battery voltage engine off 12.9V
Battery voltage engine running with dim dash lights (battery positive to negative) = 14.15V
B+ 14.2V (to the fuel rail ground)
D+ 12.3V (to the fuel rail ground)
Battery light comes on nice and bright when the ignition is turned

Bad regulator? I replaced the voltage regulator 1000 miles ago. I think I bought a Bosch.

Voltage between fuel rail ground and alternator case?
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Art Benstein near Baltimore

He had a photographic memory that was never developed.

0V (well maybe 30mv)

What are the voltages before it begins to charge? You said you have to rev it up to get it to charge, right?
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Art Benstein near Baltimore

A boiled egg in the morning is hard to beat.

Its hard to tell because its only a couple of seconds before the alternator is 'excited' or 'excites itself' but before the alternator starts to charge B+ is 12.6V and D+ is about 10.6V. When I turn the ignition to just before start B+ is 2V. So seems to be a consist 2v between D+ and B+. So what's causing this voltage drop?

Oh, I thought you had to rev it to get it started. Where did I read that. That's what is consistent with normal behavior when there is no pre-excitation.

We just need now to divide the problem between the alternator and the car.

The warning light's brightness is proportional to the difference between B+ and D+. I assume that's just a typo in your post "When I turn the ignition to just before start B+ is 2V" and you meant to write "D+" because that's the normal voltage you would expect at D+ with ignition on motor stalled. It is close enough to zero to give you bright lamp test indications, but not 2V from B+ at that moment.

Next test you need to do is measure the voltage at the red exciter wire disconnected from the alt, and also at the D+ terminal on the alt while it is turning. Be careful, especially for the hot manifold and rotating parts. What you expect is the exciter wire will be the same or close to B+ voltage, and if the alternator is already charging, the D+ terminal on the alt should also be at B+ voltage.

The behavior with an open circuit to the field (brushes, slip rings, and rotor winding) is slightly different between some aftermarket regulators and Bosch EL series. The Bosch will give you a dim bulb through a 68-ohm resistor even if the field is open circuited, where the aftermarket, without that resistor won't warn you - the bulb will be dark.

Somewhere on this board there's a post of mine where I put these pics. Let me know if you've already been there. I've had to swap a battery in front of the Baltimore Basilica early one Sunday morning because the field coil wire severed from the slip ring. The third picture shows what the battery light would indicate with that open circuit.













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Art Benstein near Baltimore

When electricians get sent to hell, they have to wire whole houses in UF.

Thanks Art, yes I inverted my B+ and D+ !

So, with engine running and exciter wire disconnected I get:

B+ = 14.1V
D+ terminal = 11.6V
End of disconnected exciter wire = 13.6V
Obviously all dash lights are out

Good! You've assured yourself the problem is in the alternator and verified the exciter wiring through the dash and all the uses for D+ in ABS, SRS, etc. are not loading it.

Now, if you can't see a problem with the brushes, slip rings, or the installation of the regulator, such as poor connections to its case ground or spring terminal, I think you're in for a replacement alternator. It is tough to analyze any further than that unless you have a means to play with it on the workbench.

If you have an auto electrician in town you're better off than gambling on the lifetime warranty rebuilds being sold by the local parts places.


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Art Benstein near Baltimore

A lot of money is tainted. 'Taint yours and 'taint mine.

Thanks again Art. Before this thread and since I was out of ideas I was erring towards a replacement alternator so great that with your expert help that's confirmed.

I may remove the regulator one last time. I'm pretty sure the brushes and the regulator are OK but I wonder about the ground/spring terminal. I don't recall the internal regulator connections. What should I be looking for to confirm everything from that perspective is OK.

If I do end up getting/installing a new regulator - agree with your assessment of parts from local parts places. Never had luck with them. In the past I've searched for local auto electricians but never came up with anyone - cost of living and hence labor cost too high in my area and probably to high for that type of place to be able to survive. Given that what would be an alternate source for a new/refurbed alternator ie a reliable brand/source? Also, I see discussions about different amperage alternators - 80amp vs 100amp. Is 80amp what a stock '92 240 needs?

DIY mechanics is detail work; that's where the devil lives. When I miss something, it is invariably because I was lazy. Too lazy to get the proper light and magnification on the work, making up for what I no longer have in youthful eyesight.

Given you don't recall whether you replaced the regulator with a Bosch or other, I suggest you pull the alt out of the car. Do the detailed inspection of the ground wire: pull it too - its troubles hide under the insulation at the terminals.

When you have the alt out, inspect the slip rings closely through the regulator opening. Get a meter on them too, to measure the rotor winding resistance. Check the bearing feel. Note the metal-to-metal connections made at the regulator and ensure they are bright and shiny. Try to figure out why it seemed to work when you first replaced the brush pack. Could be thermally sensitive. Is it warm yet in ND?

Short of disassembling the unit, that's about all you can do. I cannot give a recommendation on a supplier, as I've always gone to the junkyard for them. If you do that, one mistake I can help you avoid. That's the one I refer to as my magpie mistake. You see one sitting high and shiny in a 740 -- easy to pull, and almost looking new. It turned out to be the reason the car was in the PNP, most likely. The spray-and-pray rebuild was one of the worst I've ever seen. Go for the greasy one, maybe.
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Art Benstein near Baltimore

When a clock is hungry, it goes back four seconds.

Thanks Art

As luck would have it the car has been running fine on my last two commutes to and fro from work (about 10 miles each way) - such is the nature of intermittent problems. The night before these two days I did clean all on my fuse connections but straight after that the dim dash lights were still there so I thought that hadn't helped so I assume the lack of recent problems is purely coincidental. It has been less wet/humid right recently though so perhaps...

In any case, most likely this weekend I'll remove my Bosch regulator again and verify that one last time but then I'm going to keep an eye out for a decent quality replacement alternator at an OK price. Luckily since the car is running really well and seems to charge OK there's no real hurry.

Thanks Art. I did try this is my prior troubleshooting a while ago but will try again

That's a pretty quick answer. Could maybe help you if your response provided some quantitative information. Basically there are two ways to troubleshoot electrics.

The first way requires no test lights, meters, or any other means of measuring cause and effect. You just ask around to see if you can match symptoms to what others say is the cure. Like diagnosing your illnesses on Web-MD. Then you replace parts until you get the right web page.

The second way asks that you measure what is happening and understand why your meter or test light responds the way it does. This can be more difficult, if you've not done those same tests and measurements to a working system. We can help with that, but you have to be our eyes and ears with detailed and accurate observations.

First way: guessing.

Second way: science.

So when you try again, report the readings you get with the motor idling, and the warning lights on or partially on. Readings at D+, B+, and at the case. Take the readings directly on the terminal studs.

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Art Benstein near Baltimore

A plateau is a high form of flattery.

Hi,

Some of the diodes in the alternator may be open / shorted, but without an oscilloscope to view the output you’d never know, aside from some RF noise. You’d still get voltage output, but there would be ‘‘gaps’’ in the output as the field rotated through the defective diode controlled segment. This would not be visible on a ‘‘slow’’ multimeter.

Goatman

Thanks for the responses

Since I don't have an oscilloscope I guess there would be no way to know this (other than replacing the alternator)?

Could there be a problem with the 90 degree and/or half moon connectors on the back of the guages? While I have re-soldered the board etc it occurred to me that I haven't checked them (other than having undone and inserted them a few times)so maybe there's a poor/intermittent connection. I may pull the gauges with the car running and wiggle to see if that makes a difference. As you can tell since I've done so much trouble-shooting previously with non success I'm rather grasping at straws