Intermittent alternator?

[ld50]

My alternator crapped out yesterday.
I checked to see if it was putting out by pulling the neg cable off my battery and it died. I checked the wires and they all looked okay, so I went and got a new one from the auto store.

I started it up a while ago and damned if the alternator isn`t working again.
Can they go like that? I always experienced that when they go, they go. I`ll see if it keeps crappin out I guess.

 

[ld50]

Hmm, this morning, no alternator current. Hit the train tracks halfway to work and it came back. Turned off engine at work and then restarted and it crapped out again.

I`m going to go over the wiring after work and see if that does anything.

 

[ianonhercules]

Bad alternator

My understanding is that you should never dis-connect the battery while the engine is running as the diodes get overloaded and fry. The way to determine if the alt. is working is to read the voltage across the battery terminals with the engine running. If all is well with the alt. then the voltage should be about 14 Volts, if 12 volts or under it is possible that the alt. is faulty, but it could also be the voltage regulator.

Ian

 

[ld50]

My understanding is that you should never dis-connect the battery while the engine is running as the diodes get overloaded and fry

If you left the battery out of the loop for a long time, it would not be good for the alternator/voltage regulator. The battery acts as a filter, to absorb harmful voltage spikes caused by the alternator. (we went over this in another thread)
To do it for what amounts to a couple seconds can cause no harm, and the only reason you would do this is with the suspicion of a fried alt. anyway.
If it was so detrimental, then our alternators would fry everytime a battery terminal came loose.

 

[YBNormL]

My alternator suddenly died last year. I looked at the gauges, and noticed that the voltmeter was at the bottom of 'Normal'.

Limped the vehicle home, with the voltmeter getting lower and lower. Took the alternator off the engine, and then the brush hood off the back of the alternator. One brush was shattered, and the comutator (the brass rings that the brushes ride on) were gouged through to the ceramic insulator.

No warning, just "poof"! Dead alternator. So yes alternators can go just like that.

James

 

[ianonhercules]

Fried Alternator

ID 50

Yes, you may be right, on the neg. terminal. On reflection, the cautions that I have heard are for the positive terminal at the battery. On my boat, I have a "1-2-both-off" switch for the batteries. There is a jumper between "1-2-both", that maintains connection while switching from one position to another, so that the switch can be used when the engine is running. In addition to the above there is a device on the alternator called a Zap-Stop that does stop the positive leaking to ground in the event that the switch is turned to off.
Surely, if you dis-connect the neg. terminal you cut off all current to the alternator and it will stop producing current, as the alternator requires some field current to work? Your regulator varies the amount of current/voltage to the alternator as the needs of the battery are satisfied.
I maintain, that the only safe way to check the alternator is with a voltmeter, either at the battery or directly at the terminals of the alternator.
It is unlikely that a battery terminal will fall off completely so there will always be some current passing...maybe not enough to start the engine but usually enough to run the lights etc.
I surely don't have all the answers but the above, in my experience, I believe to be essentially true.

Good luck,

Ian

 

[88vert]

Sounds like your wires are crap

 

[ld50]

Surely, if you dis-connect the neg. terminal you cut off all current to the alternator and it will stop producing current, as the alternator requires some field current to work? Your regulator varies the amount of current/voltage to the alternator as the needs of the battery are satisfied.

It`s a trick I learnerd in grade ten auto class, the engine will run off alternator power only, the battery is in the circuit, but does not have to be connected to complete it. When your engine runs with the battery and alternator working well, the battery is always being asked to take more charge, once the battery is charged you sort of run off what power is available from the battery AND alternator, with practically all the current flowing past the battery from the alt..
Guys who run more lights and sound will use higher amperage alternators and maybe even another battery, without them, you could theoretically suck the current right out of a battery with too much drain, then the car could stall and your battery wouldn`t even be able to start ya.


I SHOULD ADD:
Maybe some sort of system is being used in newer vehicles to shut the engine off when the battery comes out of the circuit? (after 93 at least)

The test is quick and the result is instantaneous. No alt=stall. bad alt=drop in idle speed.
Easy way to see if it will work tho`

Anyway

I have checked the wiring and it`s gotta be the alternator. I can get it to work if I hit it with a big hammer, so something inside is buggered up.

 

[ld50]

How long will my batteries run my truck?

I found out today, dying within feet of where I work, luckily I pulled off to the side and only had a short walk!

I got a TWO battery setup ( I flicked the switch to bring my reserve battery into the circuit the last time the alt was working, to get them both nice and charged)

I estimate I got about an hour of night driving with headlights/heater/radio/windshield wipers on. Basically home from work then back to work with no charging.
That was a lot of draw, I could probably get two hours easily, of daytime driving, with no accessories running.

I first noticed my my wipers getting slower, so I shut off the heat and radio, and dimmed my dash lights immediately. Then at the next light my abs light came on. When I started off, the truck chugged like it was running out of gas for a sec, the check engine light came on briefly.
Half a block later the light came on again and she stalled.

Why didn`t I change it out before work tonight?
Just overconfident I guess. And lazy. Not to mention it is so nice to work on my truck at my work.

 

[ld50]

Well that`s that

All back to normal now.

`twas a biotch getting the old pulley off the old alt though, the nut would have none of it.

 

[ld50]

WTheck!

Now my new alt is goin down. It works when the truck is cold, for about two minutes, then stops putting out current. I checked and double checked all connections, followed the manual for checking the system and found everything is good up to the point where the alternator is supposed to be charging but isn`t.
The manual says if everything checks out, to buy a new alternator.

I am having a hard time believing that it would just be a faulty alternator and not a wiring problem, but it did work for a couple weeks right?

Is there a circuit breaker somewhere that is tripping? I`m confused, it`s kind of like the old problem, but not exactly....

 

[ld50]

I wanna be more specific.

there is power and continuity everywhere there should be.

By the book, with the ignition on(engine not running), I should have 12 volts at the B+ and A terminals, with 1 volt at the I terminal.
-I have this-
With engine runing at 2000rpm, I should now have14 to 14.7 volts at the B+ and A terminals, and 13 to 14 volts at the I terminal
-I don`t have that, it gives the same reading as with the ignition on and engine off.
(and of course, the engine will die if the neg battery terminal is removed )


The thing the book doesn`t outright say is wether some problem with the wiring system would stop the alternator from putting out any current.

All I can arrive at is the conclusion that the alt is faulty, which I`ve never heard of before...

 

[ld50]

Well I returned the alt for another one, and just went for a little drive. Everything is...

All back to normal now.

Sure hope it holds up...

 

[spta97]

Originally posted by ld50
Well I returned the alt for another one, and just went for a little drive. Everything is...


Sure hope it holds up...

Well, when I've looked for alty's in the past most of the ones sold were refurbished. Perhaps the 1st one you got was just a bad-refurb?

I had an alty go on my buddies '68 cadillaic and the battery lasted from NY to NJ (about 1.5 hours each way). I would charge the battery at night so it was truly a battery powered car. Eventually it had to be replace though.

Let us know how the new-new alt is working for you.

 

[ld50]

Put about an hour on it today, still workin..


THE BRAND I HAVE BEEN USING IS BOSCHE, BTW.

 

[ld50]

Still working as it should, I guess I bought a bad one after all, thanks for the input guys.

 

[spta97]

Originally posted by spta97
Well, when I've looked for alty's in the past most of the ones sold were refurbished. Perhaps the 1st one you got was just a bad-refurb?

I had an alty go on my buddies '68 cadillaic and the battery lasted from NY to NJ (about 1.5 hours each way). I would charge the battery at night so it was truly a battery powered car. Eventually it had to be replace though.

Let us know how the new-new alt is working for you.

Hey - This post wasn't me! Can someone tell me the best way to contact the moderators to find out if this is an error??

Thanks..
the "real" spta97

 

[mhn3773]

thats freaky...just PM rick he will know what to do about it

 

[Rick]

I've never seen that happen before. Since you've changed your password I wouldn't worry about it.

 

[spta97]

Ok, thanks.