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Alternator And Battery Issues And Alternator Upgrade Questions


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#1 datsa

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Posted 29 December 2012 - 08:43 AM

This is a long post.

THE PROBLEM: My (third) alternator and (possibly) the battery, are giving me problems. For the past several years my car has been getting the perplexing "battery discharge/brake warning" lights on my dashboard periodically during the drive. It was happening apparently randomly, sometimes at idle, sometimes driving city streets, other times on the highway. In each case, the battery discharge light and brake warning" light would come on for a few minutes and then go off. I read elsewhere that this is an indicator that the alternator or its voltage regulator were failing and need replacing. Whenever I would test the car, the problem would not occur and I got the nominal voltages of ~ 14.2 volts for the charging alternator and 12.5 volts for the battery.

A short time ago, I noticed the problem had changed a bit. When these warning lights would come on, they would coincide more with the idle speed dropping a bit. They were also starting to be more frequent and staying on longer (several minutes). If I a driving at night when this happens, the dash board illumination dims. Two weeks ago, I had trouble starting the car. And two days ago, at night, I left the lights on only for a few (~ 10 minutes) and then it would not turn over the engine when I tried to get it started. I had to get a jump start. So even though all the lights and instruments worked fine (at night) with little dimming when the engine was off, the engine would not turn over without a jump. The engine turned over on the first try with the jump.

Yesterday, I finally got the battery discharge light/brake warning light to go on while the car was curbside. I then metered out the voltage with a digital voltmeter and when the red dashboard warning lights came on the battery voltage dropped to 12.25 volts; when the battery discharge/brake warning lights went off, the battery voltage jumped to the charging voltage of 14.2 volts.

POSSIBLE DIAGNOSIS: So, I am assuming that either the voltage regulator is failing, or something else is wrong with the alternator. In either case, the battery is not being charged, and causing the battery discharge/brake warning lights to go on.

OPTIONS at this point are to:
1. Replace the voltage regulator only.
2. Replace the alternator, which comes with a voltage regulator.
and (maybe)
3. Replace the battery.


My car is on its third alternator, a 60 amp Bosch rebuild put in 7 years ago, but the previous (second) alternator lasted only 6 months. I know that over time, alternators can get glazing and other defects due to the heat and engine dirt and oil onto their windings, leading to premature failure.

I am assuming that replacing the alternator would be the best option given that if I choose the right vendor, I can get one that is a quality rebuild. So far, Denso and Toyota are two brands that I have in mind; maybe Bosch. I was told to avoid local parts store remanufactured ones as they fail too soon. Also, I read that a long warranty (year or more or lifetime).

Does anyone have suggestions about which alternators to get, where to get quality alternators and their warranties. My Corolla is an '88, which I know is old, but I like it enough that I'd like to keep it a while longer. It is also the best snow car that I've ever owned.

The battery (Diehard Gold model) was also replaced when the second alternator was put in, so it is even older. I know that over time, lead acid batteries can develop internal problems with their plates and chemicals, due to both charging issues and mechanical stress from driving that cause them to eventually fail.

Can anyone also suggest a brand of battery which to get?
Reliability and starting power are the most important factors for me, especially in cold/snow and hot weather. Some brands which I have been looking at are: Interstate, store brands ProStart, Diehard (again), etc.

ALTERNATOR UPGRADE? My car does not have any fancy electronics built in, save for an electric sunroof; everything else is manual. However, I do run chargers for a cell phone, GPS, and a laptop converter off the cigarette lighter. So, I was thinking that if I must replace the alternator, perhaps I could go with a higher amperage model, say 70 amps? I realize that 70 amps is max output and actual out is probably under 25 amps at idle. Some vendors sell doubled amp models, which offer twice the amperage output, and some local shops will upgrade/rebuild them that way. So if you brought to a local shop a 60 amp model, they return to you a 120 amp model that puts out 75 amps at idle. Of course, they are more expensive ~ $150-200 and come with only a year warranty.

Is it worth getting a higher amperage alternator or am I wasting my money?
How can I test the amperage requirements of my car (by metering out the amps under full load across the battery terminals?)


BATTERY UPGRADE? Should I look into an AGM battery such as the Optima Yellow Tops instead of a regular lead acid battery? Are the AGMs worth the expense? Are there problems with them in terms of long-term storage? Currently my car is a daily driver, but there is the possibility next year that I may be going overseas for a year and would put the car in storage during the time I am away,

Thanks for putting up with a long post.

#2 dom

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Posted 29 December 2012 - 10:56 AM

TYC are excellent, especially for the cost... New 70A alternator (no core charge) with lifetime warranty.

http://www.rockauto....2,parttype,2412

#3 friendly_jacek

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Posted 29 December 2012 - 12:24 PM

7 year old battery is pushing the limits. While the symptoms are pointing to alternator indeed, I would at least load test the battery before replacing the alternator, or replace both. Shorted battery can damage alternator.

The beat deal is AdvanceAuto battery with online coupon codes.

#4 datsa

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Posted 30 December 2012 - 03:09 PM

Another long post ahead.

Thanks for the suggestions. While I am going to go ahead and get another alternator and battery, I thought I'd do some more testing. I was curious about the inconsistency of the battery discharge/brake warning light, and I wanted to see what the actual numbers were, for voltage at least, coming from the battery. Here is my chronology:

0. I hooked up a DMM (digital multimeter) set to read DC volts to my car's battery.

1. With the engine off and all accessories disconnected, the DMM read 12.96 V from the battery. So the battery is putting out the right voltage, but for how long and at what current?

2. Turning on just the headlights alone (with all other accessories and lights off), the battery voltage quickly dropped to 11.50 V, then to 11.00 V, and then under 11.00 V. All this occurred within 30 seconds. Battery is not able to handle just the headlights alone.

3. With the headlights now off, and with the clutch in neutral and the parking brake on, I started up the car, which has not been run in 24 hours. The starter motor cranked several times before finally turning over, and its cadence upon trying to start was different than it has been in the past. The voltage from the battery dropped to 8.4 volts, and then to below 8. volts as the starter cranked; this low voltage coincided with the difficulty in starting. The DMM went from 12.96 V, to 12.66 V, and then to 12.25 V. Battery has a hard time handling the starter motor.

4. Once the engine entered its initial start up phase, the idle rose to ~ 1200 RPM, while the voltage from the battery charging voltage was as high as 14.48 V. In most cars, the engine computer controls the initial engine RPM to be higher than warm idle (~800 RPM) to give the engine more momentum to overcome a motor that had been at rest, to ensure proper priming and warming of the engine, etc. So, it makes sense that the initial volts would be higher than charging voltage. The dreaded "battery discharge/brake warning" light did NOT come on. So far, the voltage regulator and alternator are charging. And startup RPM seems normal.

5. As the engine warmed up, the idle dropped as expected to ~800 RPM. The DMM read between 14.10 V and 14.30 V more or less. Alternator is able to charge the battery.

6. With the headlights on, the battery charging voltage dropped to 14.05-14.09 V, and then to 13.95. When the charging voltage dropped to around 14.10 V, the "battery discharge/brake warning" light came on and stayed on. I tried this several times, with the headlights on, then off, then on, then off (see the next item in this list, #7 below). *Alternator cannot keep up with just the headlights on. Battery power had to kick in to help.*

7. With the headlights off, the battery charging voltage rose and then fluctuated between 14.17-14.25 V. Then "battery discharge/brake warning" light started flashing off and on, as it the voltage was at the threshold between normal and discharge.

8. If the pressed the accelerator and increased the RPM to 1500, little rise in voltage occurred. The battery discharge/brake warning light started fluctuating. At about 2000 RPM, the charging voltage jumped to between 14.4-14.5 V or so, and the battery discharge light went off. I repeated this several times, and sometimes the battery discharge/brake warning light would come on again or go off unexpectedly. At no point did the charging voltage go to 15 V or higher. This tells me that the voltage regulator was able to correctly limit excessively high voltage.

9. If I released the accelerator, allowed the engine to return to idle, and waited long enough, the "battery discharge/brake warning" light went off, even though the charging voltage had dropped to 13.8-13.95 V. The discharge/brake warning light did not come on despite the "low" voltage. *The cut-off voltage for when to engage the discharge light/brake warning light does not seem to be consistent; it seems to vary.)

10. I let the engine run for a while at idle, and the battery charging voltage was now reading 13.8-14.0 V, but the battery discharge/brake warning did not come on.

I wanted to test everything for current as well but my DMM does not test current above 15 A. I am going to buy or rent an ammeter that is able to handle high current and recheck the current. I am also going to drive the car for a while and then check the voltage and current, and then get the battery load tested before I buy a new battery.

Edited by datsa, 30 December 2012 - 11:09 PM.

#5 friendly_jacek

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Posted 30 December 2012 - 07:45 PM

Clearly the battery is bad. The volts with cranking shouldn't drop under 9-10V. Replace it ASAP and repeat the test. I assume there is no problem with battery cable or connection.

Edited by friendly_jacek, 30 December 2012 - 07:47 PM.

#6 tashirosgt

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Posted 31 December 2012 - 01:38 PM

THE PROBLEM: My (third) alternator and (possibly) the battery, are giving me problems. For the past several years my car has been getting the perplexing "battery discharge/brake warning" lights on my dashboard periodically during the drive.


My Corolla is an '88, which I know is old, but I like it enough that I'd like to keep it a while longer.



Are you saying you've replaced 2 or 3 alternators on the car from 1988 to 2012? That would be a normal amount. Or are you saying that you've replaced 3 alternators in a shorter period of time?

If replacing the battery fixes the problem with the battery light, you should still replace the alternator if it isn't charging adequately. A bad alternator can ruin a new battery.

It's worth checking your fuses to see that they are all the proper wattage. Sometimes people "fix" a problem with fuses by putting in a fuse with a bigger wattage instead of finding the problem in the circuit. Check that no wires are going bad on the 3-wire connector to the alternator. If you change alternators often, these wires tend to break near the connector.

Alternators go bad faster if they are overworked. It would be interesting to see the current draw from the battery when the car is shut off. I think you can do this by putting a resistor of known size between the negative terminal of the battery and the end of the negative cable. Measure the voltage across the resistor. It should be about zero with the car shut off. If it's not zero then V = IR tells you the current draw.

The belt tension on the alternator should be checked. Too tight or too loose are both bad.

#7 datsa

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Posted 01 January 2013 - 12:19 AM

The first alternator went bad in late 2004 but its replacement only lasted for six months. Then a third one was put in and it seemed to work fine until a few years ago, when it got the "battery discharge/brake warning" light error. As I mentioned above, that warning would only come a few times a day at low tach and stay lit for maybe 1-5 seconds, but about a month ago, it suddenly started coming on with much greater frequency, stay on longer, and do so at higher RPMs. Unfortunately, I never understood the meaning of it because both warning lights (battery and brake) and not just the battery. Now that I know more about it, I wish I had taken care of it earlier.

I replaced the battery yesterday after it failed two load tests, each reporting ~ 55% capacity on an 8 1/2 year old battery (The mechanic found the date code and showed it to me).
The car now starts up better, but -- as expected -- still gives the "battery discharge/brake warning" error.

I will check for proper fuses, serpentine belt tension, and measure the current draw. I assume I need to use a resistor that can handle high current without getting burned out by the batteries current before it can be measured. Is this correct?

As far as alternators, I plan on ordering one; I am trying to figure out if I can put in a slightly later model alternator (for the 1990-1992 Corollas with the same engine) that puts out slightly higher amps (70 amps vs. 60 amps for mine). All those new-fangled electronics consumes extra watts / draws extra current.

#8 datsa

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Posted 17 January 2013 - 08:24 PM

So, the new battery (Bosch 35-640B) is holding up well; it always starts up.

I finally got a new alternator today from RockAuto, a TYC which has a lifetime warranty. But I am curious about the specs and performance (I have not put it in yet).
Here is the test report:

8391240548_0bb3259a3b.jpg

It says that below 1200 alternator speed [RPM] there is no current.
Also, even the output at 1600 RPM seems low, ~ 15 amps!

Does this make sense, is it too low?

I thought these cars idled at 40% of their rating, so more like 28 amps for a 70A alternator.

Is there a difference between "alternator speed" and "engine speed"? I assume so, since the alternator is driven by a belt and because it has a smaller pulley diameter, should rotate at higher RPMs, right? I think in most small cars the ratio is between 2.1 and 3.1. I will measure the diameters to get a more precise ratio.

As far as fit, RockAuto, Amazon, and Toyota all say it should fit my car.


Edited by datsa, 18 January 2013 - 09:56 AM.

#9 dom

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Posted 18 January 2013 - 01:55 AM

Looks good... My 2004 Corolla crankshaft pulley (~130 mm) to alternator pulley (~55 mm) ratio is about 2.4:1, so the alternator is spinning at about 2400 rpm when engine is at 1000 rpm.

You'd be producing 70A at ~2900 alternator rpm with engine at ~1200 rpm, 80A at ~3500 alternator rpm with engine at ~1460 rpm, 40A at ~2000 alternator rpm with engine at ~833 rpm, and 35A at ~1800 alternator rpm with engine at ~750 rpm.

#10 Papa Bear

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Posted 18 January 2013 - 12:01 PM

The battery fixed the problem... return the new alternator


#11 datsa

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Posted 18 January 2013 - 12:45 PM

The battery fixed the problem... return the new alternator

I had more than one problem happening simultaneously.

1. The car was hard to start as the old battery was "on its last legs". Getting a new battery fixed that.

2. The alternator is having trouble charging the battery (both the old one and the new one). The alternator is not putting out sufficient DC current to keep the battery charged. This  happens mostly at low idle, such as when stopped and idling, but it also occurs randomly at higher idle speeds. At low idle, the charging voltage from the alternator is often less than 10-11 volts. The problem is especially acute when driving with lots of accessories on, such as at night with headlights, heater, taillights, etc. Then one gets the "battery discharge/brake" warning light problem, so common to Toyotas.tach-running.jpg


Edited by datsa, 18 January 2013 - 12:47 PM.

#12 jims99

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Posted 14 February 2013 - 11:54 AM

The battery fixed the problem... return the new alternator

I had more than one problem happening simultaneously.

1. The car was hard to start as the old battery was "on its last legs". Getting a new battery fixed that.

2. The alternator is having trouble charging the battery (both the old one and the new one). The alternator is not putting out sufficient DC current to keep the battery charged. This  happens mostly at low idle, such as when stopped and idling, but it also occurs randomly at higher idle speeds. At low idle, the charging voltage from the alternator is often less than 10-11 volts. The problem is especially acute when driving with lots of accessories on, such as at night with headlights, heater, taillights, etc. Then one gets the "battery discharge/brake" warning light problem, so common to Toyotas.tach-running.jpg

Hello, own a 1999 Corolla and have never had such a set of problems that you have.   The following questions pop into my aged mind.  First, what RPM do you idle at?    Second, Do you measure the charging voltage at the alternator or at the battery itself?  I looked at the Alternator chart and it sure shows that there is zero output below 1600 rpm BUT the actual rpm at 1000 rpm on mine seems to be about 2000 rpm (at idle speed of 900 rpm)  My 1999 corolla has never even shown a difference in the dash lights nor the headlights at idle or 60 mph so I'm quite confused at your discription of how your car operates.  I would be checking the Ground connection of the Alternator by measuring the voltage (while opperating at 1000 rpm) between the alternator frame/housing and the negative terminal of the battery...  let me know what you measure.  I would also measure the voltage from the negative battery post to the engine/frame points and see if the cable has excessive voltage drop while charging.    Good hunting,

Jims99