Dash Lights coming on and off

[blue thunder]

I'm having the same issue as Idaho biker girl a few posts back. Two nights ago i got in my car to go home and noticed the illumination light on the dash seemed weaker than usual. I drove home with no problem. Today on the way to work the dash lights came on and stayed intermittedly. I tried a test someone said to try. I started the car and then disconnected the negative battery cable and the engine stalled immediately. I was told this means the alternator is bad. Then I drove home tonight with the dash lights coming on and off the whole way. I then got my multimeter and checked the voltage and it read around 12 amps non-running which means the battery is fully charged right? Could my alternator be flaking out and still be charging my battery? I have one ordered for thurs. although I haven't paid yet. Any advice or experience appreciated. Thanks.


Mike

[Trevor]

Originally Posted by blue thunder

I'm having the same issue as Idaho biker girl a few posts back. Two nights ago i got in my car to go home and noticed the illumination light on the dash seemed weaker than usual. I drove home with no problem. Today on the way to work the dash lights came on and stayed intermittedly. I tried a test someone said to try. I started the car and then disconnected the negative battery cable and the engine stalled immediately. I was told this means the alternator is bad. Then I drove home tonight with the dash lights coming on and off the whole way. I then got my multimeter and checked the voltage and it read around 12 amps non-running which means the battery is fully charged right? Could my alternator be flaking out and still be charging my battery? I have one ordered for thurs. although I haven't paid yet. Any advice or experience appreciated. Thanks.


Mike

You state that the battery measured around 12 amps. I guess that you mean 12 volts. The alternator is very likely to be faulty. However it could be charging, but only on half cycles via the rectifier network, which may keep the battery charged if the load has been light.

The dash indicator lights test circuit, incorporates blocking diodes to eliminate a sneak circuit which would otherwise exist. In an event involving faults within the alternator rectifier network, alternating current is induced on line. The result is pulses of reverse voltage, which pass the blocking diodes in the test circuit and energise the indicator lights.

N. B. Running the car with the battery disconnected is bad news and can cause damage, particularly if the alternator is faulty and there is an over voltage run away. Protection included in the electronic circuits has in your case saved the day, and the alternator voltage regulator is probably OK, but count yourself lucky.

[ItsPeteReally]

Originally Posted by blue thunder

I'm having the same issue as Idaho biker girl a few posts back. Two nights ago i got in my car to go home and noticed the illumination light on the dash seemed weaker than usual. I drove home with no problem. Today on the way to work the dash lights came on and stayed intermittedly.

Sounds like a bad connection somewhere to me.

I tried a test someone said to try. I started the car and then disconnected the negative battery cable and the engine stalled immediately.

Whew! You were lucky! You should never do this. The battery acts as the voltage regulator for the charging system, but thankfully, your car stalled, things could have got much worse if the car had continued to run.

Then I drove home tonight with the dash lights coming on and off the whole way.

Yes, still seems like a bad connection somewhere.

I then got my multimeter and checked the voltage and it read around 12 amps non-running which means the battery is fully charged right?

Errr..... don't you mean 12 volts? If you had put an ammeter across the battery you would surely blow its internal fuse.

Actually 12 volts is pretty much fully discharged, a fully charged battery is over 13 volts, and with the engine running you should see over 14 volts.

Measure again with the engine running, if you see over 14 volts everything would seem to be fine.

But you definitely seem to have a poor connection somewhere.

[blue thunder]

Yes sorry I meant 12 volts. I will certainly check the connections and check voltage when the engine is running. Thanks for the quick reply.

Mike

[Trevor]

[QUOTE=blue thunder]Yes sorry I meant 12 volts. I will certainly check the connections and check voltage when the engine is running. Thanks for the quick reply.

Mike[/QUOTE

Attention Mike,

As you have acknowledged only one reply, it would appear that you have not read my prior advice. Please do so, as the diagnosis is carefully detailed.

It is unlikely that your problem involves poor connections. Everything indicates an alternator fault as I have described.

[ItsPeteReally]

Originally Posted by Trevor

Attention Mike,

As you have acknowledged only one reply, it would appear that you have not read my prior advice. Please do so, as the diagnosis is carefully detailed.

It is unlikely that your problem involves poor connections. Everything indicates an alternator fault as I have described.

Trevor, your diagnosis does not fit Mike's problem very well. The fault he describes is an itermittent one, with the lights coming on and off, as he puts it.

He undoubtedly has a problem somewhere, but I am not brave enough to definitively state where it is. If you can have an intermittently bad diode in the alternator then you may well be right.

The possibility of an alternator with a damaged diode network being able to raise the voltage measured across a lead acid battery to over 14 volts might be a good topic for future discussion.

Pete

[kwren]

it's life is over as you have known it!!
Take care,
Keith

[Trevor]

Originally Posted by ItsPeteReally

Trevor, your diagnosis does not fit Mike's problem very well. The fault he describes is an itermittent one, with the lights coming on and off, as he puts it.

He undoubtedly has a problem somewhere, but I am not brave enough to definitively state where it is. If you can have an intermittently bad diode in the alternator then you may well be right.

The possibility of an alternator with a damaged diode network being able to raise the voltage measured across a lead acid battery to over 14 volts might be a good topic for future discussion.

Pete

Pete,

My diagnosis exactly fits the fault described. You will notice that I have stated that a fault within the rectifier network/alternator rectifier network, would cause the problem, not a “bad diode”. The problem within these units/networks often is the result of faulty soldered diode connections brought about by excessive heat. This can and often does, constitute an intermittent fault.

You state :- “The possibility of an alternator with a damaged diode network being able to raise the voltage measured across a lead acid battery to over 14 volts might be a good topic for future discussion.”

Just how and where did I propose that anything along these lines could take place? I can only assume that you are under the misapprehension, that unless an applied voltage of in excess of 14 volts is applied, no battery charging will take place. Even so part wave rectification could in point of fact, deliver reduced current at 14 volts.

The accuracy of your statement:- “Actually 12 volts is pretty much fully discharged, a fully charged battery is over 13 volts, and with the engine running you should see over 14 volts.”, certainly requires discussion and correction.

[Trevor]

Originally Posted by blue thunder

I'm having the same issue as Idaho biker girl a few posts back. Two nights ago i got in my car to go home and noticed the illumination light on the dash seemed weaker than usual. I drove home with no problem. Today on the way to work the dash lights came on and stayed intermittedly. I tried a test someone said to try. I started the car and then disconnected the negative battery cable and the engine stalled immediately. I was told this means the alternator is bad. Then I drove home tonight with the dash lights coming on and off the whole way. I then got my multimeter and checked the voltage and it read around 12 amps non-running which means the battery is fully charged right? Could my alternator be flaking out and still be charging my battery? I have one ordered for thurs. although I haven't paid yet. Any advice or experience appreciated. Thanks.

Mike

Pete,

The first sentence in the thread which you have omitted and which tells all, regardless of the rather confused description which follows, reads:-

"I'm having the same issue as Idaho biker girl a few posts back."

Also note:-

"Today on the way to work the dash lights came on and stayed intermittedly."

" Then I drove home tonight with the dash lights coming on and off the whole way."

N.B. The lights came on, i.e. were not switched on.

I and obviously others here, have been able to interpret the description, having become used to some having problems when describing faults.

My object has been to prevent the enquirer becoming involved in fruitless testing, based on irrelevant voltage figures. It is most unfortunate that matters have become controversial as a result of misunderstandings and in this context touches of sarcasm are not helpful.

Unlike another thread, no one is in fact wrong here and all have simply been misunderstood.

Cheers, Trevor.

[ItsPeteReally]

Ah! a truce

The sad part of it all is that we may have driven the original poster away.

We may never know whether or not his alternator charging warning light was ever illuminated, or what voltage was developed across the battery terminals.

It may well have been that he had a defective alternator, but he could possibly have had a circuit continuity problem elsewhere.

I will certainly be very careful about what (and how) I post in the future, my only concern was to try and prevent him from spending over $100 on a new alternator if he didn't need one.

Pete

[kwren]

Originally Posted by blue thunder

I'm having the same issue as Idaho biker girl a few posts back. Two nights ago i got in my car to go home and noticed the illumination light on the dash seemed weaker than usual. I drove home with no problem. Today on the way to work the dash lights came on and stayed intermittently. I tried a test someone said to try. I started the car and then disconnected the negative battery cable and the engine stalled immediately. I was told this means the alternator is bad. Then I drove home tonight with the dash lights coming on and off the whole way. I then got my multimeter and checked the voltage and it read around 12 amps non-running which means the battery is fully charged right? Could my alternator be flaking out and still be charging my battery? I have one ordered for thurs. although I haven't paid yet. Any advice or experience appreciated. Thanks.


Mike

A battery will read 12 volts when fully charged. When working properly, it will have the cranking power it was designed to have. It can also read 12 volts when it is not fully charged because of the construction of the battery cells. under a load it will not read 12 volts when it is not fully charged, again because of the construction of the cells in the battery.In reality the best way to check out this intermittent problem is with a volt meter. When the goofy red lites all come on, open the hood with the motor running, of course and check the voltage at the battery terminals. you should get 12 volts. if you are lucky enough to have all those red lites go off while you are driving, stop the car, but leave the motor running. raise the hood and check the voltage at your battery terminals. You will see about 14 volts which is the output of the alternator at this time. Congrats! you have found the problem. Since all the voltage and regulator controls are in the alternator itself, the alternator has to be replaced! Why?? because you want the alternator to work all the time not just intermittently. It is on the way out and will not work at all soon! You can also trust some of us that have gone through this and just replace the alternator to start with, but it is a bunch of fun to work it out yourself!
Good luck with your SVX. (Don't we just love these cars!!!!)
Keith (77 year old shade tree mechanic)

[Trevor]

Firstly please be sure that I am not trying to extend an argument, but do wish to amplify the detail in respect of that which has proven a never ending problem having considerable technical interest.

The suggestions made here is that a faulty alternator can be detected using a DC voltmeter, because the output measured across the battery, will not be close to 14 volts, if the machine is defective.

It is fact that members here have had an alternator checked by professionals after experiencing the flashing trouble lights problem, then have been advised that the alternator is OK. One would expect that the output voltage has been measured under load by way of a test, but one must presume that the procedure has not detected an AC component in the output, due to only DC test gear being employed.

My contention is that the alternator could produce adequate voltage, albeit at reduced current, even though a faulty diode may exist, but at the same time produce an alternating current component within the output. N.B. --- Hence my reason to dispute the validity of a simple DC voltage test.

The alternator is in effect a three phase device, incorporating nine diodes in rectifier bridge networks, so that the failure of a single diode may only somewhat reduce output current, and the voltage regulator could compensate in respect of voltage.

We need someone who has an alternator with the fault in question, able to carry out proper tests and experiments, in order to be able to exactly confirm the several factors which apply. The understanding required, will likely be above the head of the average auto electrician.

[kwren]

Originally Posted by Trevor

The suggestions made here is that a faulty alternator can be detected using a DC voltmeter, because the output measured across the battery, will not be close to 14 volts, if the machine is defective.

It is fact that members here have had an alternator checked by professionals after experiencing the flashing trouble lights problem, then have been advised that the alternator is OK. One would expect that the output voltage has been measured under load by way of a test, but one must presume that the procedure has not detected an AC component in the output, due to only DC test gear being employed.

My contention is that the alternator could produce adequate voltage, albeit at reduced current, even though a faulty diode may exist, but at the same time produce an alternating current component within the output. N.B. --- Hence my reason to dispute the validity of a simple DC voltage test.

The alternator is in effect a three phase device, incorporating nine diodes in rectifier bridge networks, so that the failure of a single diode may only somewhat reduce output current, and the voltage regulator could compensate in respect of voltage.

We need someone who has an alternator with the fault in question, able to carry out proper tests and experiments, in order to be able to exactly confirm the several factors which apply. The understanding required, will likely be above the head of the average auto electrician.

One of us is able to use a simple test to check an alternator with a DC voltmeter.
None of the people here care about how a diode works. If an alternator doesn’t charge the battery, the alternator has to be replaced. . I have a lot of education and years of experience including one electronics school that began with basics including how every part of an alternator is made, the composition of batteries, and eventually getting to electrical schematics that you couldn’t put on a a sheet of paper as big as a double page of a newspaper. Just one school was 8 hours a day for a full year. I would be void of logic if I couldn’t tell that the alternator was bad if all my red lights came on and I put a voltmeter on it and only got the 12 volts from the battery. When I drove it again and the red lights went off, checked it with the lights off and the output was 14 volts. When 14 volts are put into a 12-volt battery, it charges the battery, period. More logic! I do not need all my education and experience to find out why my alternator doesn’t work.I only need to know to set the meter for dc volts, put the red lead on the positive battery terminal and the black lead on the negative terminal. I don’t even care why the alternator doesn’t work. Why, because to replace the parts in our old alternator would cost at the least $2,000.00 at the Subaru dealer. Several of the parts cost more each than replacing the whole alternator! More logic, just pay the $200 and get a whole new alternator at the same Subaru dealer!
You might be amazed at how little electrical expertise these auto “mechanics” actually have!
KISS Keep It Simple, St----
Keith

[cdvs]

Originally Posted by kwren

...None of the people here care about how a diode works...Keith

You are clearly not speaking for yourself (or me) and there is no need to speak for others. Especially, if you are going to disparage their intelligence and/or curiosity.

A generator produces direct current (DC) which has a fixed polarity, + and - are always on the same side (wire). An alternator is more efficient than a generator, but produces alternating current where the polarity (+/-) switches as the armature is turned. A diode is like a one way street sign, or a turnstile. It allows current to flow in one direction only. By placing a diode on both sides of the output an alternator can be polarized to supply a DC system.

A diode can fail in 2 ways.

It can stop passing current in either direction. If only one fails, this will result in only half of the output being supplied to the system. Because there will still be voltage of the correct polarity, this condition is difficult to test and is the reason why so many bad alternators are tested and proclaimed good.

A diode can also fail by allowing current to pass in both directions. Diodes are designed to resist a certain amount of reverse current flow. This is called the reverse breakdown voltage. If it's capasity to resist this flow is diminished, things will not be well. The symtoms of this are difficult to predict, except that the greater the load, the greater the symtoms will become. This condition will diminish a battery's ability to accept and deliver a charge and eventually render it useless. Note that such a battery might provide acceptable voltage readings if not under load.

What Trevor is suggesting is that this condition can be discovered by using a voltmeter set to A/C to find what he refers to as 'alternating current component'. Prior to reading his repeated suggestion in this forum, I was unaware of any test for this condition. I have not had the opportunity to perform this test, but it does make sense. Historically, a repair would envolve replacing both the battery and the alternator. Usually one, then when that didn't work, the other.

Charl

Edit:corrected spellings.

[kwren]

Charl, you are right to say, “You are clearly not speaking for yourself (or me) and there is no need to speak for others.” But not right to say “Especially, if you are going to disparage their inteligence (Intelligence) and/or curiousity. (Curiosity)…. I was certainly not intending to disparage anyone here but was trying to make it simple for maybe the one or two SVX owners that are nor predisposed with the workings of the internal components of their alternator.. Offending anyone was certainly not my intent and I apologize to anyone that I inadvertently offended. I misspoke and I am sorry
Take care
Keith