Chonic Alternator Failure

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ntsqd said:
Curious as to why you think this. Not claiming anything either direction, just curious.
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Many modern alternators seem to have a real problem with duty cycle and any sort of 'self protection.' The alternator on my POS 95 Olds handily failed after a battery discharged, (twice) which turned out to be the brake light switch sticking intermittently. The damn thing does not have 50K on the clock.

When you jump a rig using a running car, that alternator is suddenly subjected to the extreme charging load of a dead battery, and then you get in there and cause what amounts to a dead short on the output, IE cranking the starter.

There is absolutely nothing to limit current flow other than the impedance / resistance of the conjugate system you have just created, which, practically, is a dead short.
 
So it's more a technique thing that an outright parts problem. Granted it's partly a parts problem too. I always insist on letting the running car sit there connected to the dead car for at least several minutes while on a high idle if not off idle before even trying to start the dead car. By first trying to charge the dead battery I've successfully jump-started with a pair of 10ga. wires. The running alt keeps the voltage up while the cranking current comes from the surface charge on the 'dead' battery.
 
66plyValiant said:
have battery tested, check main battery wire at alternator for voltage, check ammeter in dash for failure
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Had a nice sunny day today, carpe diem, so as I was leaving for work I popped the hood and placed my DCOM probes in the batter clamps, rested the hood down and set the meter on it.

After sitting all night, battery read 12.6 Volts
During cranking ~10.5 Volts
After start up ~15.4 Volts
At alternator battery stud 15.75 Volts

After work I picked up a jug of distilled water now that I know I need it. Also it appears this current alternator has dropped another feild and I'm down to one.

I think what I am going to do is go ahead and get in to AutoZone at my soonest convience and pull the alt and VR so they can go ahead and test them bad and replace them. I'll recheck these readings on the fresh parts and see what I get.

Tommorrow I'm gonna pop the caps before work and top off the battery which I'm now almost 99% has probably had the water boiling out of it for awhile now.:violent1:

Should I proceed with this gameplan guys^^^

Keep in mind, I have a lifetime warranty on the alt and I'm only several months into the 1 year warranty on the VR so they are free to replace.
 
Well if it's charging at 15.75 (this is warm?) there might not be anything wrong with the alternator field, but this could very well be the usual voltage drop problem
 
67Dart273 said:
Well if it's charging at 15.75 (this is warm?) there might not be anything wrong with the alternator field, but this could very well be the usual voltage drop problem
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The 15.75 is cold 1 minute after startup. I feel like its dropped a field or two. At hot idle in gear any load dips the ammeter slightly torwards discharge, just the brake lights will do so.

Before you ask, I dont know what my idle is at.
 
When cold, the alternator will put out a higher voltage but even cold, 15.75v is too high; something is messing with the regulation system. The battery seems to be Ok if it is at 12.6v after sitting, so focus on the alternator and VR.

What is the battery voltage with the system cold and running, measured with the VM leads direct on the battery terminals? Also, what is the direct alternator output at a very high idle (like 1500 rpm), and cold? It is important to measure and share that information.

BTW, you're not losing fields, you are blowing diodes in these alternators. The described symptoms are classic for that.

It sounds like you have 2 problems:
1) Lack of voltage regulation since the alternator output is too high
2) It is very likely that there is some heavy, or spiking load in the car that blows diodes one by one, and that is not showing up on the ammeter. There are a number of circuits that take a feed direct from the alternator output and don't get fed via the ammeter when the car is running; they only show a stready ammeter draw when the car is not running. Examples: horn, headlights, some of the turn signal stuff, etc. Any spiking shorts in these or the associated wiring and switches will load the alternator and you won't necessarily see it spike on the ammeter.

You need to run this down rather than just swapping the parts. It is nice that the lights and such don't dim, but this is likley overcharging the battery which will eventually fail, and it could be a precourser to worse. Some light dimming with a correctly running system at low engine speeds is better than a chronic or worse problem.

And, just IMO, so take it as just that, dump the Duralast stuff and go with something better. You at least got your money's worth in replacement parts!
 
I've seen bad batteries show 12 volts. Turn the key and it drops like a hammer, 2 or 3 volts. Bad battery. A battery that properly stores cranking amps , at 70 degrees, no less than 9.5 volts after 20 seconds. Yes you would need to pull the coil wire to run this test. 20 seconds continuous run isn't going to hurt a good OEM starter. I don't know if 20 seconds or longer would damage a modern mini starter.
Since you've seen your battery drop to the 10s in a short period, I suspect it's going bad.
The general term "bad battery" covers a few different symptoms/conditions and creates different charging system conditions.
 
With a weak battery and high internal resistance, it could be doing that but a cranking drop to 10.5V as reported is not all that bad; most are spec'd to 10V or less under cranking loads as you noted. The symptoms as orignally stated points to diodes blowing, and with the overvoltage output when cold, I would focus on the regulation issues 1st. If the car has been run like that for months (as it seems), that has not done the battery any favors...
 
Yes the Duralast are JUNK.I quit buying electrical parts from Autozone back in the 90's and Advance Auto electrical parts around 2001.The electrical parts batterys,alternators,starters,etc are just garbage from these places.My Dad bought a alternator from there about a year ago took it home installed it and it was no good.He took the new alternator back to Autozone.I told him to tell them to bench test the new one they replace it with.They tested 5 different new Duralast alternators before they found a good one.He laughed asked for his money back and went to NAPA.
I just put a new starter on for a neighbor who is disabled Tuesday.Got the new on reconnected the battery and the starter started turning the motor over as soon as I toched the cable to the battery.I told the neighbor his new starter was junk.I took the starter back off and told him to goand get a different one.He goes into the house to get the box the starter came in and you guessed it Duralast.I told him take it back go buy a starter at NAPA.
 
I worked as a service writer for a dealership for a couple of years out of college. Many times we would get older cars (say 5 or so years old) that would have a bad alternator. After pricing the dealer item, then the better aftermarket rebuild, many would INSIST that we install an AUTOZONE alternator. All the mechanics would cringe and we had a policy to explain that even though they had a free replacement at AZ, that we would not honor any sort of labor warranty. We knew from past experience that you could go through 4 or 5 alternators (or starters) before you found one that would work more than a couple of days. There reputation for electrical items was really really bad. It was always the local NAPA or CAR QUEST that we used for aftermarket rebuilds. It made a big difference. On the same note, I was reading through this discussion and didn't see any note about what type, age, and size of the battery you use. Also, are there any accessories installed (amplifiers, A/C, lighting upgrades) that would really stress the factory system? Have you looked at your alternator and battery ground or you battery cable conditions? How about coil condition? How is your main feed at the firewall bulkhead? Burnt connections or poor conductivity? What type/brand of voltage regulator are you using? Switch brands? I would agree that a weak or bad battery could really put a hurting on your system. Having discharge at idle with the lights on is common and almost considered normal especially if you have replaced your headlamps with halogen or any other sort of higher wattage bulb. That is why you see many converting over to relay systems. Personally, I went through my entire charging system by using a PowerMaster alternator, relay added for the run circuit, additional heavy charging wire from alternator to to starter relay, headlight relay system with heavier feeds to headlights, and a decent heavier capacity battery that is kept on a maintainer when not in use. Even with all that, a lot of stop and go driving with the stereo going, headlamps on, and/or the heater/AC fan running will give a discharge condition at idle since more power is being required than that charging system can provide at the lower rpm. Also, avoid the "blue" race-only voltage regulators. They are designed for short term use and create an overcharging condition that can fry a battery or old wiring in a heartbeat. Hope some of this helps.
 
I don't even buy mine at NAPA but my Dad has had good luck with them.There is a little Mom and Pop shop here locally that rebuild them and that is where I get all my alternators and starters from.
 
^^ Amen on that. We try to only get alternator/starters and associated parts from NAPA or a local rebuilder.

Just a bit more on this problem: Blowing alternator diodes can be caused by increased resistance in the wiring to the battery. Whenever you have any sort of surge load (like turning on headlights, which have low resistance until the filaments are glowing, or the heater blower motor), the surge of current has to come from 1 of 2 sources: the battery or the alternator. If the wiring to the battery through the ammeter has higher resistance than normal, like corroded connections to the ammeter, the battery, through the firewall, or a fusible link that is getting marginal, then the surge will have to come almost solely from the alternator. In a properly functioning system, the surge will be shared by the battery.

With the excess voltage in this case, the turn-on surges will be even higher, and with the marginal parts put in the Duralast units, the didoes will blow just that more easily. So, I suspect this system needs to be gone through thorougly to:
1) find the reason for the improper regulation (high alternator voltage)
2) check the whole wiring from battery to alternator to find any high resistance points

This may be happening without any high surge parts with the voltage regulation problem. Case in point: I have raced 2 rally cars that blew diodes in good GM internal-regulator type alternators; it would ususally happen in night racing when I would be turning on the 6 high powered halogen racing lights. I finally figured out that the remote mounted battery in the back with the cut-off switch had enough added resistance (even with a 00 ga battery cable) in the battery circuit that the racing turn-on surge of the racing lights would 99% be sourced from the alternator rather than being shared with the battery. BTW I never fixed the battery resistance in either car; I just kept a lot of alternators on hand! Using 135A didoes helped some.
 
I recall saying early-on to find the local rebuilder and get the parts from them and not any of the "Low Price" type chain stores. Nice to see others with the same experience and response. The problem is that now what he has for core is junk and they may not want it. I always keep the original anything and eat any core charge.

I was also thinking the 15.75VDC charge voltage was too high, but not being well versed in diagnosing charging systems I wasn't sure. 13.6VDC to 14.7VDC is what I'm used to seeing with deep cycle batteries.

At first what 67Dart said about voltage drop wasn't making any sense to me, but now I think that I see it. Measure the voltage between the alternator's case and the VR's case while the engine is running. It should be zero, as in 0.0 and not 0. something. If it is not zero then the difference in grounds will be skewing the VR to cause a higher alt output voltage than is correct.

FWIW with trunk mounted batteries I insist on a ground cable of the same size as the hot cable, and run it to a boss on the engine block. Over the years I've found that relying on the chassis from a high current ground isn't a good plan. Every weld in the chassis that the current has to cross is a resistor.
 
RedFish said:
I've seen bad batteries show 12 volts. Turn the key and it drops like a hammer, 2 or 3 volts. Bad battery. A battery that properly stores cranking amps , at 70 degrees, no less than 9.5 volts after 20 seconds. Yes you would need to pull the coil wire to run this test. 20 seconds continuous run isn't going to hurt a good OEM starter. I don't know if 20 seconds or longer would damage a modern mini starter.
Since you've seen your battery drop to the 10s in a short period, I suspect it's going bad.
The general term "bad battery" covers a few different symptoms/conditions and creates different charging system conditions.
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Last few conventional batteries I had fit this description....would show 12 volts no matter how long it sat...put a load on it and down to 3-4 volts.....would suggest a load test, either as described above or by a tester....I am hooked on AGM batteries. Sure, they are a bit pricey. But if you give it good, clean cables/ends/lugs and have a functioning charging system they will last quite a while....with no need to clean the posts or add fluid....and no more staining concrete whenever you park...
 
I "thought" Matt had done some testing on this. The main causes of troubles IN NO particular order...........

Voltage drop in the ground circuit

Voltage drop in the ignition circuit

Regulator out of spec

Battery problems

Resistance in the charge wire, USUALLY the age old bulkhead connector / ammeter problem

I think this "blown diode" thing is being overstated. If there's enough resistance in the charge wire to cause diode problems, you are going to have smell and smoke from bad connections at the bulkhead ammeter.
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CHECK

VOLTAGE DROP IN GROUND CIRCUIT

Make these checks with engine running fast, warm, and with battery "as normal" as you can get. Check first with all accessories off, and again with lights, heater, etc on.

Stab one probe of the meter onto the battery NEG post. Stab the other into the regulator mounting flange. There should be very little voltage, zero is perfect. More than a couple of tenths of a volt means the grounding is poor.

Clean and re--mount the regulator with star locks, and consider adding a ground (no10 or larger) from regulator and ECU to block. On a V8, there are holes in the driver side rear head (look at the front of the pass side!!) to add a "starter" (ring to ring) cable to the firewall

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VOLTAGE DROP IN IGNITION CIRCUIT

This ALSO involves poor connections in the regulator connector (70/later)

The path is battery----starter relay--fuse link--bulkhead connector--ignition switch connector--through the switch--out the switch connector--out the bulkhead connector-- to underhood loads (ignition, regulator, alternator field, idle solenoid, choke, etc)

Key on, engine not running. Find switched ignition under the hood, either alternator blue field wire, (70/later) or the "key" side of the ballast. Hook one meter probe to that, hook the other meter probe to battery positive. More than .3V (three tenths) means you need to improve the voltage drop. ANY VOLTAGE DROP in BOTH the ground and ignition circuit ADDS to regulator sense point.

The easy way to repair this is to break the output of the ignition switch coming through the bulkhead, use that to fire a relay, and fuse the relay off the starter relay. Then supply underhood loads off that relay

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REGULATOR OUT OF SPEC

AFTER you check voltage drop, try a different battery, if charge voltage is too high (optimum 13.8--14.2 warm) and not below 13.5 nor above 14.5, replace the regulator

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BATTERY PROBLEMS

BEST way is to swap in a known good battery

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RESISTANCE IN CHARGE LINE

This, in old mopars is a large part of why I always preach the MAD electrical page:

http://www.madelectrical.com/electrical-tech.shtml

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

Now, even Ma knew this was a problem, look up "fleet wiring" sometime, which essentially beefs up the wiring through the firewall and BYPASSES the bulkhead connector

The path from alternator to battery is...........

The eyelet at the alternator stud..........through the bulkhead..........through the ammeter...........back out through the bulkhead..........through the fuse link..........to starter relay...........to battery

This is easy to check. With the engine running fast, and charging "hard"

(to simulate this, crank and kill the engine several times to run the battery down a bit, then test with lights, heater, etc, on)

Hook one probe of your meter to the alternator output stud. Hook the other to battery POS post. Now "THIS OPINION" can vary. This voltage will vary. That's because there can be a LOT of current. On a STOCK harness which might have a 50-60 amp alternator, I'd say as much as 1 volt is OK. This is under HEAVY charging.

Along with this last, you can "wiggle test" the bulkhead connector, and stick your (careful!!) hand up in the dash and feel "for heat" at the back of the ammeter.
 
"I think this "blown diode" thing is being overstated. If there's enough resistance in the charge wire to cause diode problems, you are going to have smell and smoke from bad connections at the bulkhead ammeter." Actually, they go hand-in-hand; with turn-on surges and high battery charging circuit resistance, you can have the didoes go but not readily see the issues anywhere else because things are not too awful bad in a steady state mode; you see some dimmer headlights and taillights and such. Battery charging wil not look excessive since any added resistance in the charging lines will slow charging rates. Add in the marginal diodes with a cheap alternator.....I know you know the schematics by heart; just imagine some resistance in the charging circuit lines, like a poor fusible link, and where the current will come from for a sudden heavy load in the headlights. He is blowing diodes for a reason; the alternator symptoms fit it to a tee.

Regardless, he has bad regulation. The above detailed troubleshooting is pretty darned goo should be followed and the results reported. It is hard to help more without good data. Good lukc! It IS all fixable.
 
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