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Discussion Starter #1 (Edited)
Here it is, my one and only full write-up on the Sentra charging system, all about it, and how you can diagnose and isolate your problems.

1. Why are my "charge" and "brake" warning lights both on at the same time?
2. How does the charge indicator light work?
3. How does the alternator and charging system work?
4. How come my alternator doesn't charge until I rev it to 3000 RPMs?
5. Why do my airbag and/or ABS warning lights come on with a bad alternator?


not finished, more to come. I'm just tired now.

1. Why are my "charge" and "brake" warning lights both on at the same time?

Answer: Actually, your charge indicator light is on, and the brake light slaves it. It's a flaw that nissan designed into the warning light system. Basically, there's a "bulb check relay" somewhere in the Sentra that is wired into the circuit that controls the alternator light. that relay connects the BRAKE light to ground. So any time the alternator light is on, that relay is activated and it turns on the BRAKE warning light too. WHY? Nissan thought it was a good bulb-check feature so that you know the brake light works when you start the car, even if the parking brake isn't set, since the alternator light is always on whenever the ignition is on and the engine isn't turning. They didn't stop and think about what would happen when a legitimate alternator defect while you're driving would kick the charge indicator light on. Most other car manufacturers have this bulb check feature built into the ignition switch. There's actually two contacts at the "start" position, one set activates the starter solenoid and the other set grounds the BRAKE (and temperature) warning lights whenever you are cranking the engine. Start any Chevy or older Ford and you'll see what I'm talking about.

2. How does the charge indicator light work?

Answer: It's just a simple light bulb in the cluster, behind a red lens that has a battery symbol printed on it. The positive side of this light bulb goes to the ignition switch, and receives +12 volts any time the ignition switch is turned on. The negative side of the light goes to the alternator through the "L" terminal on the connector.

When the ignition is turned on, but before the engine has been started, electricity is fed into the alternator to energize the field coil and produce the electromagnetism needed to generate electricity. That small amount of electrical power flows from the ignition switch, through the bulb for the alternator light, and into the alternator through the L terminal. Since that circuit is complete, the warning light is on (we call this the bulb check). Once the engine starts, the alternator begins to rotate and generate its own power. Once it's up to full RPM and is generating its own power, some of the power generated is tapped and re-directed, and now that is used to energize the field coil instead of the power coming in through the ignition and alternator light. Since the alternator is generating its own power, and power coming in through the warning light isn't used anymore, that warning light circuit is essentially "broken" or no longer connected to ground, and the bulb shuts off. This happens a second or two after the engine starts.

When the alternator isn't generating power, no power is re-directed back into the field coil any more, so it uses the power available from the alternator light circuit again. When this happens, current flows through the bulb filament, and the warning light turns on to warn the driver that the alternator isn't producing electricity.

It's VERY important to realize that this warning light won't always come on when the alternator goes bad. For instance, a bad voltage regulator (common problem here, too) would never complete the indicator light/filed circuit, and therefore power would never be generated. abroken field coil would do the same thing. When I bought my second 94 sentra, I knew before-hand there was an alternator problem, but it was confirmed when I turned the ignition on and the alternator light stayed off. Sure enough, I was right, because two minutes later the airbag light came on and the car died. When you turn the ignition on before you start the car, the warning light MUST be on -- that's your assurance that the field circuit is OK. if that light isn't on, you have a bad alternator.

Then, of course, it should go out when you start the engine.


3. How does the alternator and charging system work?

The battery, ignition switch, charge indicator light, AC generator (alternator), and wiring compose the charging system.

The alternator is composed of a rotor coil that spins with the engine, three stator coils that are fixed in place and never move, graphite brushes that transfer power to the rotor coil while it's spinning, copper slip rings on the rotor shaft that touch the brushes and make the connection, a voltage regulator, a rectifier, and a diode plate or diode trio. Bearings at the front and rear allow the rotor shaft to spin in place.

There are four electrical connections made to the alternator. The B terminal is the main output and provides the electricity generated. The S terminal is the "sense" terminal used by the voltage regulator, and is connected to the battery, and always has battery voltage. The L terminal (for "lamp") goes to the charge indicator light on the instrument cluster. And a ground connection is needed somewhere on the alternator's case.

Initially, the voltage regulator uses the battery voltage at the sense terminal as a reference point. This current isn't actually used for anything, the regulator just uses it to determine the battery's state of charge and the electrical load. Whenever the voltage at the S terminal hits a preset voltage (usually 14.4 volts), the regulator essentially "shuts off" the alternator until the voltage drops back down, then it "turns on" the alternator. This cycling of turning on and off the alternator happens several hundred times a second. The voltage sensing is done with a zener diode, which allows current flow at certain voltages. The regulator controls the alternator by turning on and off the -12 volts going to the field coil.

The +12 volts to the field coil is always there whenever the ignition is on, regardless of the regulator. So essentially, whenever the system voltage is below 14.4 volts, the field coil is energized and is producing electromagnetism.

Three fixed coils, called the stator coils, induce this electromagnetism when the alternator begins to spin. The power generated comes out in three legs of a three-phase AC power system. These three legs travel to the rectifier bridge, which converts this three-phase AC power to single-phase DC power. The "B" terminal on the back of the alternator comes straight from the rectifier.

Between the coils and the rectifier, there's a diode trio that taps into each leg and acts as a small rectifier to convert it to single-phase. This is the diode trio, or diode plate. Once the output power is tapped and converted, it's fed into the positive side of the field coil now, and that's how the alternator stays energized.

In order to get power from an alternator, you need to put power into the alternator. This is done through the "L" (lamp) terminal. There first needs to be a source of electricity to energize the field coil before the engine starts and spins the alternator. This is done through the L terminal which is connected to the ignition switch. When the ignition is on, current flows from the battery, through the alternator warning light bulb, and to the positive side of the field coil. Since the voltage is below 14.4 volts (remember, the engine isn't started yet), the voltage regulator turns the field coil "on" by connecting the negative side to ground. Now we have a complete circuit through the battey's positive terminal through the alternator light, through the coil, and to ground. We've got electromagnetism at the coil, and since the circuit is complete, the alternator warning light is ON. (bulb check.)

When the engine starts, the alternator RPMs get up to speed. Now the field coil is spinning inside the stator coils, and the stator coils begin to induce this electromagnetic field and three-phase AC power is generated. The power travels to the rectifier where it's converted to DC, and used to charge the battery. The three-phase power is also tapped and fed through the diode plate, converted to single-phase, and fed to the positive side of the field coil. Now, the alternator is generating its own power, and a very small fraction of that power generated is re-directed back to the field coil for the electromagnetism. Essentially, the alternator is now powering itself. When this happens, the initial current flowing through the alternator light is no longer needed to initially excite the coil (since the alternator is doing that for itself through the diode plate), so that circuit is no longer active. With the circuit not active, the light goes out. This is usually a few seconds after the engine starts. The B-terminal is connected via a thick 8-gauge wire straight to the positive battery terminal for charging.

Now the alternator is self-sustaining. If there's some problem where the alternator isn't producing electricity, there won't be any power generated at the stator coils. When this happens, the alternator won't be able to tap the power for the field coil, so it'll take it from the warning light circuit. Since the warning light circuit is now active again, the warning light comes on. The field coil will still be energized with the warning light on, even though the alternator isn't producing power, indicating battery discharge (the whole purpose of that light).

5. How come my airbag and/or ABS warning lights come on with a bad alternator?
 

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bulb check relay

Hi blackmaxima88,

I hope you will bear with me as English is my second language.

I have a 1994 Sentra 1.6 manual Limited EditionA year or so ago both lights (brake/charge) came on, I checked voltage at battery and alternator and measured around 11V with full load, replaced alternator and measured 14.5v which is rather high I think but left it at that. The alternator continues to put out normal charge since but every now and again both lights are flickering (frequency varies from 2 times per second to strobe like and faster). The flickering corresponds with clicking of the bulb check relay (which drives me nuts sometimes). When the two lights and the relay are not playing up the charge light is constantly on but very very weak, the light is only visible during night time driving. I have checked voltage at all stages and find that the system charges normal with the flickering/clicking showing very small variations in voltage (less than .5v). I have been driving the car without any problems despite the fore mentioned issues. Any ideas on this at least for me highly uncommon phenomena.

Thank you very much for your time.

Sincerely
Pekke
 

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where did you buy your alternator ???? i had the same problem with my sentra after changing my alternator wich i purchased at autozone (cheap i know) when i installed it about a week later my driving lights and dome lights would flicker constantly and i would get this ticking noise under my dash and my brake light and battery light woudl come one with this sound too after 6 months with this problem one day my car went crazy all lights came on really bright , the wipers went on like crazy and the tach went to 9k rpm and thein it died it started back up but the alternator was fried along with the tach and wiper motor so my guess would be the voltage regulator that is inside the alternator because after replacing the alternator again everything was fine no flickering no problems
 

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Simular problem

First. I'd like to thank GTRs_83 for a great detailed explanation about how charging system works. Thanks the other folks for good comment too. And I am also sorry for my English as it is not my first language.

Now with your help I have an idea what is going on with my car. I have Nissan
Sentra XE 1993 and it looks like I have a similar problem. I never replaced the alternator and probably it is still original one. For a last few month I started to hear a strange clicking (as I have just figured out today it was from bulb check relay) and seeing battery check light going on and off. But what you could expect from old car? I was not putting to much attention to this, my car was running pretty well and I never have a problem neither with starting nor running it. Never until it happened that two weeks ago I was not ably to start the car after a first cold night in the garage. I checked my fueling system, cleaned all the connection, recharged my battery and then was able to start the engine without a buster cable. But, after driving a mile with my headlights on my engine stopped. I charged a battery a little to be able to go back to my garage and then stated to study and test an electrical system.
Then I have goggled "Nissan bulb check relay" and have found this thread.

The summary of my testing is the following: my "Battery" check light is on when I turn the key to ON and then stays on after the engine starts. Then bulb check relay starts to flicker, but battery is not charging and after some time battery voltage goes down and engine stops. If I am increasing RPM to 2000 the relay stops to flicker.

So it looks like I have an alternator problem too. But to make sure before buying a new alternator I'd like to ask if somebody have another suggestion about possible source of the problem. Could it be the Bulb check relay itself?
How to check if alternator is charging a battery? Why my car was starting running well all that time even when the relay was flickering and "Battery" light was on?

Thanks,

Taras.
 

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just a thought

Since everyone here is talking about thier alternators going bad over "X" period of time.

1. Anytime you pass electricity through a circuit some of the electrons discharge their energy in the form of heat.
2. Excess heat IS damaging to electrical circuits.
3. Depending on how well your circuits are made the speed at which they degrade will vary.

Tl;dr? = don't buy a cheap alternator, it's cheap for a reason. look for a quality remanufactured unit with a warranty of at least 12mo/12000mi.
 

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So, where might I find the bulb check relay? I am having the same 'flickering' of the brake and battery lights, however I have a brand new battery and a fairly new (<1 year) alternator. I would like to check this relay to see if it might be the source of the flickering. I am also going to do an alternator test. Are there any other potential sources for this bulb flickering?

Thanks,

Kyle
 

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go grab the FSM (factory service manual) its in a sticky post at the top of this section.

you'll find pretty much everything you need to know in there.
 

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Hello, I read all this and thought I would add my question to the list.

My 93 Sentra has high mileage, but runs well. I noticed one day that the brake light came on. This seemed to coincide with my putting on the emergency brake? I do not remember now if it was so, or if the brake light just came on.

Anyway, I probably ignored it too long. Now I the brake lamp is not lit all the time, but clicks and buzzes, along with the charge indicator light.

So reading here and reading the manual, I dug underneath and found the bulb light relay because I noticed the clicking started on a very rainy day (suddenly) and I think my windshield might have allowed some moisture up there.

Well now that I have removed the relay, the clicking and buzzing is gone but the charge indicator is on, lightly, and brighter with the load on the system, I guess because the relay is out of the loop.

So I think the bulb light relay is fried, and I think also my alternator is bad now as well. But I get 14.6 volts at the battery terminals while the car is running, so doesn't that mean the alternator is working? I wonder if a new bulb lamp relay will make the charge light indicator turn off and also resolve the brake light issue?

Thanks for any help!
 

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Hello, I read all this and thought I would add my question to the list.

My 93 Sentra has high mileage, but runs well. I noticed one day that the brake light came on. This seemed to coincide with my putting on the emergency brake? I do not remember now if it was so, or if the brake light just came on.

Anyway, I probably ignored it too long. Now I the brake lamp is not lit all the time, but clicks and buzzes, along with the charge indicator light.

So reading here and reading the manual, I dug underneath and found the bulb light relay because I noticed the clicking started on a very rainy day (suddenly) and I think my windshield might have allowed some moisture up there.

Well now that I have removed the relay, the clicking and buzzing is gone but the charge indicator is on, lightly, and brighter with the load on the system, I guess because the relay is out of the loop.

So I think the bulb light relay is fried, and I think also my alternator is bad now as well. But I get 14.6 volts at the battery terminals while the car is running, so doesn't that mean the alternator is working? I wonder if a new bulb lamp relay will make the charge light indicator turn off and also resolve the brake light issue?

Thanks for any help!
it is the voltage regulator that is going bad these days you cannot just change the voltage regulator so you will need to replace the alternator since the regulator is inside it
 

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it is the voltage regulator that is going bad these days you cannot just change the voltage regulator so you will need to replace the alternator since the regulator is inside it
Thanks!

I am fixing my 93 sentra on a budget, and I have a voltmeter but am not so great at using it to its full potential for auto troubleshooting. I wanted to update my not-so-solved problem.

So according to your answer and others comments...

brake light = nissan design flaw when regulator (internal) fails. >>> Does this mean brake = bad regulator? That is what I am understanding.

buzzing/clicking = bulb check relay

Working on this idea and not wanting to blow anything or waste dollars (on flawed engineering and planned obsolescence) I found a 93 sentra at my local yard, looked nice on the inside, had been rear-ended badly but front end was all sealed up. anyway I took the alternator and the bulb-check-relay from that vehicle, hooked them up to mine, and found that I am back to square one: brightly lit brake light.

So I have spent 30 dollars, gotten a (perhaps bad) alternator which I'll take in to test at the parts store and see if I wasted my 25 bucks? Eh, even if so I would rather understand better how the system works. I know the old alternator did finally fail because it stopped putting out volts but new one produces 14 volts nicely.

So now I have a bad brake light, again. Which means simply that the alternator's regulator "is going" and soon this process will repeat. If I leave it, perhaps the bulb check relay will begin to buzz as it did before (junkyard one doesn't buzz).

So my question is: How did I get an alternator from the junkyard that also had a failing regulator? It seems unlikely if their car was rear ended and otherwise new, but maybe a collision causes bad electrical voltage? Hmm. Well the parts store has an $86 alternator. I guess the point is that if I get on, that the brake light will finally, turn off?

Thanks again for any help.
 

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So my question is: How did I get an alternator from the junkyard that also had a failing regulator? It seems unlikely if their car was rear ended and otherwise new, but maybe a collision causes bad electrical voltage? Hmm. Well the parts store has an $86 alternator. I guess the point is that if I get on, that the brake light will finally, turn off?

Thanks again for any help.
I wonder why this junkyard alternator/bulb-check-relay combo failed in the way it did, giving me the same symptom, a lit brake light?

This is due to Nissan's engineered flaw? I am a man trying to make a car work, not hot rod the thing. I guess the point here in this thread about the brake light is that Nissan engineers thought the regulator inside their unrepairable alternator, would never fail?

And if they thought it would fail, the regulator inside the alternator (unrepairable disposable crap) I mean, then why did they think that a light which says "brake" would be a good clue?

Forgive me if I am also sorting out the stupidity of engineers here as well. It is almost as illuminating as a brake light which has nothing to do with the brakes but everything to do with the vehicle being crashud and some new crap-box being purchased. I choose to make my 93 pos sentra run well, in spite of all this, so thanks to this forum and this thread. I do enjoy Nissan products, I put 200,000 miles on my Pathy and never had much problems. This one's a real gem, considering how damn painful it is to get the bulb check relay out. Buncha masochists who will never work on the vehicle are designing these things!
 

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Well no answers above.

So I will ask a different question: Can I repair the standard Nissan sealed unit at all? If the regulator fails, and the Nissan engineer has made it such that this can be observed by the BRAKE light being lit (???) and I cannot replace the regulator because all of today's units are sealed hunks of junk, then can I at least open the alternator and fix it? What about the auction below? Will this be enough to fix my now failed old alternator, and if the regulator in that alternator is fried, then I could fix the alternator so that it outs out 14 volts again but it would still give me a BRAKE light error because the regulator is fried? I know the experts here all say "duh, buy a new alternator" but you really aren't helping anyone with that answer. We need to work together more to make the old cars last. At the junkyard I go to, they told me they were crushing all these old cars, so I guess that's what we learn? Crush them and engineer even stupider crap?

Anyway, can I use this part below to fix my alternator? Thanks, I just want my brake light to turn off again.

STANDARD-MOTOR-PRODUCTS-JX-111-Alternator-Brush-Set
 

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I talked to my local motor rewinder, starter fix it guy (he does commercial motors, starters, alternators, generators, anything that has windings and spins) about this awhile back (that and he's a friend of mine from wayyyy back so I think I can trust him and he's not out just to get my $$$).
We priced out the pieces/parts to repair the Nissan alternators.
(full disclosure: I don't have a B13. I've got 2 B14's, but they've got the same brake light issues.)
A reman alternator from the local parts store ran something like $130, give or take.
Thru my 'contact guy', the regulator, diode pack, brushes, new bearings/bushings, etc. was going to total out to about $95 if I remember right, just for the parts alone.
The extra $35 was well worth the 'lifetime' warranty at the local parts store.
This comes to mind in this situation:
False economy - Wikipedia, the free encyclopedia

As far as fixing the brake light issue...ya, it's a bit of a pain and kind of annoying. I remember seeing a fix for it somewhere. Don't remember exactly what it was, but it involved doing a bit of rewiring in the instrument panel and soldering in a couple of extra diodes.
 

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I wonder why this junkyard alternator/bulb-check-relay combo failed in the way it did, giving me the same symptom, a lit brake light?

This is due to Nissan's engineered flaw? I am a man trying to make a car work, not hot rod the thing. I guess the point here in this thread about the brake light is that Nissan engineers thought the regulator inside their unrepairable alternator, would never fail?

And if they thought it would fail, the regulator inside the alternator (unrepairable disposable crap) I mean, then why did they think that a light which says "brake" would be a good clue?

Forgive me if I am also sorting out the stupidity of engineers here as well. It is almost as illuminating as a brake light which has nothing to do with the brakes but everything to do with the vehicle being crashud and some new crap-box being purchased. I choose to make my 93 pos sentra run well, in spite of all this, so thanks to this forum and this thread. I do enjoy Nissan products, I put 200,000 miles on my Pathy and never had much problems. This one's a real gem, considering how damn painful it is to get the bulb check relay out. Buncha masochists who will never work on the vehicle are designing these things!
have you had any problems burning fuses for the ''meter'' circuits?? like the tach fuel level and temperature?
 

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have you had any problems burning fuses for the ''meter'' circuits?? like the tach fuel level and temperature?
No, my fuses are fine.

I managed to get a bulb relay at a junkyard, and plugged it in, cursing these knuckle-destroying engineers all the way.

Once I got the relay in, the brake light took a couple days to go away, but it did, and worked fine for a few months.

Now I have red brake light again. Alternator is putting out 14 volts at the terminals, but I assume it is gonna die soon, as per this thread's explanation of how this circuit works. I do have a spare (new) alternator in the trunk but if this one is putting out 14 volts I assume I can still use it?

How do I know if the regulator within the alternator is gone, or if it is the bulb check relay?

I am going to go over to the junkyard and try and get another bulb relay, and see if that makes the light go away. I will update this here, I love my Sentra and want to keep it on the road.

Also I appreciate the poster who said there was a solution to get rid of this flaw, I would be happy to know more. I long for the days when I had a 60's chevy and was just able to replace the regulator every so often at a cost of 10 dollars. Why must "engineering" mean that humans and their tools go backwards? Seems very silly.

Anyway, thanks to those who've replied, I appreciate the help.

possentra93
 

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What brand of alternator have you purchase? I would like to know that and i have suggestion as well, the spare parts from Vile are just awesome. They tend to last longer and prove pretty reasonable.
 

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I have try autozone oreilley pep boys but when it first started alt lasted all most a year the replaced that lasted a month replace lasted a week replace lasted month replace lasted a week now it does not put out a charge at all when in the truck
 

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Sorry to bring up an old thread but I've got a question that relates.

On the first page he said, key on engine off the charge indicator light should be on.

First, is that the light with the battery or is there another?

Second, if it's not on, and I'm having a electrical issue, will the alternator still output 14 volts? Thanks

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