Rising_Sun

iTrader: (2)

Tony, I've been down this road too many times. The last time was 4 months ago where I replaced my alternator 5 times in 8 days. I also had the exact same symptoms and had every alternator bench tested every time. I even drove my car to my alternator builder and they tested it in the car. After another thumbs up that day, left me stranded 50 miles away from home at a NELOC meet with a dead battery.

My own findings were most places bench test an alternator rotating faster than our 750 rpm idle. So they don't see the voltage drop. I guarantee I run wayy more accessories than the average Lexus owner and if you can measure voltage at the battery under 13.5 volts (under any circumstances) then it will drain the battery. The voltage regulator is ALWAYS the culprit. When you purchase a "remanufactured" Alternator, the windings maybe good. But it's the CHEAP regulator that keeps the battery from being charged. As proof, I have 3 Remanufactured alternators and only 1 with a good regulator!

SO I'M SORRY TO SUGGEST AS EVERYONE ELSE HAS..... Replace your alternator! Or bring it somewhere that uses authentic DENSO voltage regulators.

python

iTrader: (4)

its not always the regulator
http://www.labscopes.com/pg09.htm

RA40

iTrader: (6)

Interesting...good info.

trukn1, hope you can find the culprit.
Curiously, what alternators have been installed?

Though different, my experiences with aftermarket remanufactured parts has not been a bright spot. If this does funnel down to the alternator it wouldn't surprise me. Then looking at my Toyota remanufactured starters isn't a highlight either.

trukn1

Todd,, you never have to aplogize my friend. Sounds like you have mirrored my adventures almost to the tee. I really do think I may have to go online and order an alternator since it seems like I am having no luck with my local parts store. Gonna check Napa auto before doing so. I think, have to look at my receipt, that the re-maned alt I have is by Bosch (have used before with no problems). Voltage regulator has always been my culprit suspect as well, but I figured that so many just couldnt be bad. This is like my 5th alt in just over a year. Think I am gonna change my source. If anyone here can recommend a place, that would be helpful too.

Python,,you're right,,it's not always the problem, but considering the source of where I have been getting mine, primarily b/c I needed them NOW and that store had them in stock, my suspects are high.

Def gonna have to do some homework on this one. Sigh,,, back under the beast again. Good thing I got changing the alt down to about an hour now.

3UZFTE

The power from an alternator doesn't surge, as it fluctuates. The battery does nothing except absorb a small amount of energy once the vehicle is running. In the alternator, and on other vehicles it's outside of the alt, but the voltage regulator would be the buffer to make sure that your charging system doesn't overcharge or fry your electrical system, which isn't Ecm controlled. If the vehicle is started, the battery is no longer needed unless there is a heavy draw on the electrical components, I.e. Heat, radio, defrost, lights, radio, etc., which would drop the Alt below the 11.6 volts needed to operate computers and ecms, shutting the car of. The reason being that the voltage created is AC, which creates positive and negative current. However, because the electrical system can do anything with negative voltage, it rectifies it by sending it through a set diodes which than is inputted back into the alternator. The alternator pretty much skims off the top layer of voltage which is usually above 12.6 volts which is a fully charged battery. If your getting readings of the voltmeter being below 11.6 volts at any given time, there is likely an issue with the charging system, as opposed to the system storing the voltage. But, the fact that you've tested and pretty much replaced the things we thought it was, I think your going to have to go outside the box for this answer.

91LS400vgb

Sorry to disagree with you, but python and PD are correct. A battery should never be disconnected on a modern vehicle. A battery serves 3 functions: 1 - start the engine. 2 - supply current when a charging system is overworked, and 3 - act as a voltage stabilizer. Here's a quote from Tracy Martin's "How to Diagnose and Repair Automotive Electrical Systems." p.59

"The alternator needs something to "push" against to keep from producing excessive voltage. As a result, a battery should never be disconnected on a vehicle equipped with an alternator since the charging output voltage can increase to over 20 volts - enough electrical pressure to take out many (if not all) solid state components like ignition modules, computers, and stereos."

randal

Are you saying that the output of the ALT is a constant 14 v while the voltage at the battery fluctuates from 12.5 to 13.8v? That is a lot of voltage to be dropping (14-12.5 = 1.5V) across a wire that is supplying current for the entire car. That wire is normally a pretty hefty gauge and unless you are pulling a lot of current (> 50 A), I do not see how, electrically speaking, you can have that kind of disparity. Unless of course you are drawing lots of current and/or your supply harness wire is faulty.

With the given info so far, I would say that your ALT/regulator is doing its job but that you have faulty/intermittent wiring. I know it is puzzling and here is what I would do to get to the bottom of this. Since the "gremlins" seem to show up when driving and at seemingly random times:

Hook up some extra test lead wires for observation. One at the ALT and one at the battery + terminal. Bring them into the cabin for easy monitoring(I hope I don't have to say how important it is that these wires do not accidentally short to ground...oops, just did ;-) ) When the car starts acting up, use the voltmeter to check each. You should quickly have your answer as to whether ALT or wiring.

randal

Hmmm. This is an "interesting" view of operation. A battery in a modern car is a very integral part of regulating and distibuting power. As Python appropriately said, you can pull the battery out of a running 65 Mustang but don't try it on a new model. Why? The battery acts much like a large capacitor to store and filter the energy produced by the ALT. Without the battery, the control feedback loop(ie:regulation) is much less stable and large fluctuations in voltage can occur. Modern electronics such as computers (and your car has multiple "embedded" computers) do not like overvoltage or spiking voltage conditions. Tends to let the "smoke" out.

As concerns the operation of the ALT, there is a field coil and stator coil(that which rotates and is connected to the shaft). When more voltage is called for by the regulator (which is monitoring output voltage), the regulator allows more current to flow through the field coil winding which causes the magnetic field around it and the stator coil to increase. A larger magnetic field induces more current (di/dt) into the stator coils (given a constant shaft rotation) and produces more energy (higher voltage and/or current capability). If the output voltage is too high, the regulator backs off on the field current and brings the voltage back to where it should be. A set of diodes rectifies the 3 phase power of the stator and presents it to the output terminal which, in turn, feeds the battery and the rest of the system.

randal

I have to retract this statement about the charge voltage being >13V with full load at idle. This thread content got me to doing some experimenting with the charging system on my '02 LS430.

With a Fluke digital voltmeter on the battery, I got about 14v of charge. This was all with the engine idling at about 1k RPM, headlights and taillights on. Then I put the transmission in reverse which dropped the RPMs to about 700, and with brake lights on, reverse lights on, turned on every accessory I could find. This included rear defroster, 2 heated seats, high beam headlights, blower motor and stereo. Low and behold, the voltage started to drop and drop and drop until I was at about 11.70V. This was about the nominal voltage of the battery with headlight/taillight load when the engine was NOT running (my battery is 2 years old and the electrical system seems to be in good health...ie, no problems). Putting the transmission in park and revving the engine above 1200 RPM's brought the charge voltage up to around 13.5V. Not surprisingly, the rear defroster and seat warmers proved to be the biggest current hogs. The stereo (ML) seemed to be insignificant.

So, it seems that the battery charge is losing ground and the battery will not last forever with all accessories on and the engine idling around 700 RPM. That was a new revelation to me. Of course this condition is not the "norm" but could conceivably occur in a traffic jam I suppose. Apparently the ALT was not designed to deliver enough current at 700 RPM to supply the car's maximum accessory needs. I never get into this "deprived" charge condition because I do not sit in traffic idling with ALL accessories on for more than a few minutes. If I lived in Chicago in the dead of winter, I might be in trouble.

Again, just wanted to correct an earlier statement. I was wrrr...wrrrrr....wwwwrrrrr...it refuses to come out!

3UZFTE

It sounds like we have a bunch of electrical engineers. I won't continue to beat a dead horse but I would have to simply agree to disagree. I have tested quite a few cars by a quick disconnect of the battery, never once letting out the "magic smoke". I'm not going to sit here and say it's the best way to see if the alternator is creating enough voltage, but it's one of the most practical when all you have is a pliers or visegrips on the side of the road. The voltage regulator is what 'limits' voltage, the diodes rectify the negative AC voltage that the electrical system can't use. So it sends the -12v back through the alt to be turned into positive voltage. Electrical parts and systems aren't very hard to figure out, everything runs in a cycle. The battery is only a load on the charging system, anything that is than hooked into the charging system acts as a buffer from electrical surge, i.e. A light bulb. The thing is, from my experience, the computers are designed to handle a pretty wide variety of voltage, it's the amperage that tends to take computers out. Cars that I've tested, 93' Mustang Cobra, 00' Explorer, 92' LS400, 94' Ferrari 348 spider, 01' GS430, tons of Camrys, Corollas, 4runners, and other Toyotas when I worked at the Toyota dealership when customers came in for a new battery, but didn't want to reprogram their personal settings again, never once an issue, maybe I'm not doing it right, but from my experience, it's not going to take anything out.

Back to OP's problem, any luck? I remember you saying you were an OTR driver, just wondering if you've had any success or have solved your issue...

python

iTrader: (4)

u keep disconnecting battery cables on cars when they are running that have an ecm and all the electronics of todays cars...for the rest of u i suggest u do not do this...google the info if needed but im not going to sit here and argue something i know to be true.

trukn1

3UZ-- post 14 is my latest update, as I only get to work/drive my car on the weekends. Problem still exists and not solved yet. From what all I have been thru, in the elimination process, I am gonna pull the dash and start looking for anything burned out. Is strange that I was able to drive all the way home, with all the accessories on, and not have the lights dim, no CEL, nor did the car cut off with the warning lights I listed as being on. Am beginning to suspect I have a problem with the dash itself. Alternator is also another suspect for the regulator since it was a reman'ed and kinda an off brand. Need to get together a few dollars to grab a Denso alt, as I do seem to remember that I had no problems with those, however I killed it awhile back when my PS was still leaking (has long since been fixed BTW). Is frustrating period, and since I have limited tie to actually work on it, disappointing as well. May have to bite the bullet on this one and seem professional help if some of those other options are not resolving.

91LS400vgb

Thanks for that info, randal. I experience the same on my 91 LS, so I'm relieved to hear about your results. Btw, I keep a digital voltmeter in my cigarette lighter to help me monitor the system voltage so I'm aware of when the voltage dips. I've also noticed that the rear defroster is a big load so I'm in the habit of turning it off while sitting in traffic at low RPMs.

LiCelsior

iTrader: (32)

damn Tony, wish i can help you but u got a bunch of great people in here already.

skperformance

iTrader: (6)

Check the condition of the alt fuse , sounds like it might be getting heated under driving conditions and causing it to fail then but idle with the hood up or short drives is fine.