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

[blue thunder]

I just made it home tonight pulled into my spot and the car died. The headlights got dimmer and dimmer all the way home. I got out and checked the battery voltage and it read 12 with the engine off. I was starting to think I had a bad battery. I will have both tested at the auto parts store tommorrow to clear this up and take appropiate action. Thanks for all replies on this.


Mike

[subru92svx]

Its your alternator like trevor, and kwren have said. I had the exact same problem which was fixed with a new alternator. I think I paid around $200-$250 for my new one.

[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.

[ItsPeteReally]

Originally Posted by Trevor

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 may well be right Trevor, I'm just not brave enough to pin it down to an intermittent fault in the alternator's diode network. He certainly has a fault of some kind, and a voltage reading of just 12 volts on the battery is highly indicative of a fault in the charging circuit somewhere.

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.

You proposed nothing of the kind Trevor, I proposed that an effective test of the health of his charging system was to see if a voltage of over 14 volts appeared across his battery terminals with the engine running.

Whether or not an alternator with the kind of fault you propose could produce such a voltage and current is a moot point. I contend that such an occurrence is highly unlikely, there is certainly going to be a severe reduction in the generators DC output with the superposition of a large AC component. Given the fact that the internal resistance of the battery is very low, (until it reaches the point where it starts to starts outgassing, at about 14.4 volts) it might be interesting to determine whether it could generate enough current to raise the battery voltage sufficiently. I suppose that if you spun the alternator fast enough it might work ...... I dunno. I have no experience of trying to charge a battery with a defective alternator.

I am under no misapprehension about charging a battery, any voltage above the battery's own voltage will drive the electrochemistry involved in storing a charge on the plates, but to fully charge a battery, yes, you do need about 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.

What do you disagree with Trevor?

Is not a battery nearly flat at 12 volts?

Does a battery, fully charged, just after a run in the car, not show 13 volts or more, at least until the surface charge is dissipated?

Does it not read over 14 volts with the engine running?

These are facts that any reader of this thread can verify for themselves. Alternatively those with the initiative can look up many internet sites which show the same thing.

The point that I was trying to get across to the original poster was that a voltmeter is a powerful tool to diagnose his problems. Any idiot can go out and buy an alternator with very little evidence other than the anecdotes of other posters on this thread. He may well have a faulty alternator, I don't know, and neither does anybody else.

A simple test would have provided much useful information. The quote from Lord Kelvin in my signature is there for a reason.

[kwren]

And go on with your life. Another 150,000 to 160,000 miles and you might have to replace it again. Not worth messing with... Just replace the thing.

[Trevor]

Originally Posted by ItsPeteReally

The point that I was trying to get across to the original poster was that a voltmeter is a powerful tool to diagnose his problems. Any idiot can go out and buy an alternator with very little evidence other than the anecdotes of other posters on this thread. He may well have a faulty alternator, I don't know, and neither does anybody else.

A simple test would have provided much useful information. The quote from Lord Kelvin in my signature is there for a reason.

You can be sure that the other posters within this thread whom you decry, have much more than anecdotal evidence and the facts involved extend over years of proven experience. They do know what they are talking about.

The point is that operative text from your original post discounted/negated my diagnosis.:-

" Sounds like a bad connection somewhere to me.
Yes, still seems like a bad connection somewhere.
But you definitely seem to have a poor connection somewhere."

(Lord Kelvin) " I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."

The point of fact is that measurements taken using a DC voltmeter will NOT indicate the a fault I proposed, and which time and time again has been reported here as proven to be the result of a faulty alternator rectifier network. I have proven the facts using an oscilloscope and have suggested that the AC voltage range on a multi meter could very likely detect the problem, but no one has tried this latter idea to date.

The voltage figures you have suggested can not be used by way of practical testing for the fault in question; e.g. you state, " a fully charged battery is over 13 volts. " I have an SVX and an MX5, both fully operational, in my garage at the moment. The SVX was run an hour ago, the MX5 yesterday.

Using two high class digital, as well as one analogue instrument, all in parallel so as to confirm accuracy of calibration, connected directly across the battery terminals, no load; SVX 12.47 volts, MX5 12,27 volts. In practice published theory does not apply. Furthermore in the case in question here, tolerance must be allowed as consumer grade instruments are involved. Approximately 12 volts or better, would be an appropriate suggestion in respect of any testing.

[kwren]

then go buy yourself a new alternator and replace it It doesn't matter what is the problem with your alternator, you still have to replace it. Why waste your life messing with it. If you have a tire blow out would you call a taxi and go to a store and buy a tire gage and come back to check your pressure in the blown out tire?

[ItsPeteReally]

Trevor,
I do not want to take up arms in a variant of the solenoid wars

Let us go back to what the original poster said.

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.

Interesting, isn't it? His dash illumination is weak and/or intermittent.

I give it some thought, so apparently do you.

You post your response at 12:02, according to the site clock, as follows:

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.

A response, which you appear to have stored as 'boilerplate text' somewhere, which refers to a fault with the warning indicator lights - unfortunately not the dash illumination he was referring to. This is a response you post frequently.

Two minutes later at 12:04 I post my response, which actually addresses the fault he reports. Furthermore, when I post my response I am totally unaware of yours, because I have been composing and typing in the preceding few minutes. You subsequently appear to take umbrage with me because I seem to have discounted/negated your diagnosis.

I had no idea of your response at the time, and so could not pass any comment upon it.

But I will now: your diagnosis does not fit the symptoms as described by the original poster very well.

Trevor, I have no experience of alternators that have failed in the manner you so frequently post about. I am content to let you be the world authority on this matter.

With regard to the voltages across the battery, I posted the following questions:

Is not a battery nearly flat at 12 volts?

Does a battery, fully charged, just after a run in the car, not show 13 volts or more, at least until the surface charge is dissipated?

Does it not read over 14 volts with the engine running?

You post a couple of voltage readings, taken from batteries after the surface charge has dissipated, (i.e. not just after a run).

And finally, to the poor unfortunates who have had to read through all of this rubbish, think for yourselves. Anybody can be wrong, including me!