Alternator charging problems?

From the description you have more than one problem. First I would get the battery load tested to find out if it is still okay, they don't like going flat and being recharged repeatedly. Next you need to test the replacement alternator. From your description it sounds like it is either bad or the control circuitry has a problem. A few things to look at. First does the battery light come on with the bulb test function does it stay on with the engine running?
Next take a test light and unplug the alternator, turn the key on but don't start the engine. Use the test light and check all three of the pins in the harness connection for battery voltage. With the key on they should all show battery voltage because they are being fed power through the fuses and the ignition switch. If any do not show voltage that circuit is the problem. If they all test good then it is likely your alternator is the problem. It wouldn't be the first time a new part was bad out of the box and it has been getting more frequent.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

As for a higher output alternator, they put out higher amperage, not voltage. They are good if you have a big stereo or lots of electronics to power. Otherwise they are a waste of money because you don't need the extra amperage.

Had battery tested at AutoZone they said it was good and I just put a new alternator in it, I checked the plug at alternator an 2 of the wires were bright and the 3rd was really dim but had power. so if that wire is the problem and I have a hard time tracing it out can I bypass it and run a new one off the ignition switch some where, and what is the bulb test?
Thank you for your help.

Really dim isn't a good sign, what pin and wire color was it? The white wire is the sense control, it tells the alternator the battery voltage and controls the charge rate from that voltage. It feeds off the fusible link assembly directly from the battery. The red wire with blue stripe is the power feed to the regulator from the ignition switch, it comes out of a fuse, through the ignition switch and to the alternator. Both should be full brightness unless they have a problem. The yellow wire feeds the indicator light and does two things. If the alternator is working it will go out as the voltage from the alternator equals the voltage being fed to the bulb from the instrument cluster. It becomes a ground for that lamp if the alternator stops working. The bulb test is the lights on the dash like an oil, temperature, alternator, check engine and related ones that come on when you turn on the key then go out.

So it's the yellow wire that's dim and no lights on dash stay on only time battery light came on is after jumping it when I stop at a light everything would get dim and battery light would come on and that's at night with head lights on and A/C and radio.

It acted this way with the old alternator as well as the new one correct? Take a voltmeter and test the voltage output right at the alternators battery post, then at the battery. Engine running at about 1,500-2,000 rpm's. Are they the same number and what is it? Now do the same with the battery post from post to engine ground and post to alternator case. The number you posted suggests the alternator is not doing anything. Try doing the same voltage tests on the wires with the connector plugged in and the engine running, what does the voltage show now?

Okay, under load 13.3 at all and 13.6 at battery,11.75 to all case and block.
No load car and block 12.2,alt 12.7 battery 12.2 at idle , at 1,500 rpm's 13.30 at all and 13.20 at battery.
I didn't get the part that says with connector plug in, was I suppose to do the test with it unplugged and plugged in, the tests above are with it plugged in.

Okay, if I understand what you posted you have a wiring problem. Looks like a voltage drop between the alternator and the battery, likely from one of the grounds being corroded. The 11.75 volts suggests that. From the battery post to the case should read full battery voltage. As a test you could run a jumper wire from the case of the alternator to the negative battery post, that would bypass all the other grounds, Do that with the engine running at 1500 or so and measure the battery voltage itself, then shut it off and measure again. Any change? Being a 2001 it doesn't have the modern controls that throttle the alternator based on current usage, it should put out charging voltage all the way down to idle.

Okay, when I did the tests last my battery was almost dead. i had it charged and redid them.

12.52 at alternator,battery,block not running.
13.93 battery,14.00 alt running idle.
13.90 alternator case and block idle.
13.80 battery,13.83 alt 1,500 rpm's.
12.44 battery, alternator, idle under load.
13.60 battery,13.70 alt load 1,500 rpm's.
12.23 alternator case and block idle load.
13.50 case and block 1,500 rpm's load.
It just doesn't seem to charge at an idle.

From the numbers you have a bad connection. The alternator is charging as shown by the 13.93 and 14.00 volts in your second set. But when you apply a load as in the 12.44 idle under load, the voltage drops off. That is a classic sign of a poor connection, AKA voltage drop. For example say I take that meter and connect it to a single small strand of wire, with a 12 volt battery at one end, I will read 12 volts through that wire because the meter doesn't apply any load to the circuit. Now if I were to connect a 12 volt bulb in there and then measure it, I may see only 10 volts or so on that wire because that single strand cannot carry enough current to keep the voltage up. Same thing happens on a vehicle, a bad connection or corroded wire acts like a resistor and reduces the voltage but only once the load exceeds the ability of the connection to carry the voltage.
To test where the issue is, Take your meter set on volts. Now connect it between the positive battery terminal and the battery stud on the alternator with the engine running and the headlights on. Next take the meter and connect it between the negative battery terminal and the case of the alternator or a good bare spot on the engine. In both cases with very good wires and connections you in theory should see no voltage on the meter as all of the current should be in the heavy cables. In the real world you will see a tiny voltage like .10 or less because the cables do have some resistance. However if you see a voltage over one half a volt or higher, that cable or connection is bad. From the numbers you have posted I think you will see closer to a volt on one or the other which means a very bad connection. That drop would get higher the more of a load on the circuit as well. So say you are running the car and have the A/C on and the headlights with the interior blower on high, the voltage drop could easily be 3-4 volts which would drain the battery and cause your problem.
We will find it though.

Okay, so I'm taking positive cable off alternator and putting meter between cable and post of alt while car is running and test for volts. now I'm taking negative cable off battery and going from battery to case or block and look for volts there ?

Another thing I added the positive and negative cables but I left old cables on it still/ should I disconnect old ones and see what that does?

No, leave the cables connected while you test. The idea is to create two paths for the voltage to go. If the battery cables, connections and wires are good all of the power should go through the heavier cables with only a tiny voltage on the meter. However if a connection connector or cable is failing the meter will read a higher voltage as the power travels through it and not the main cable.
If you have new cables connected on top of the old ones, it is more likely to be a bad connection between the old cable and the parts. I would remove them, clean up the areas they connect then try it. You would be amazed how little it takes to stop a system from charging.

Did you mean to have the meter on amps not volts?
If so I'm pulling. 05 amps on negative side.
And .65 amps on positive side from all to battery.

Sorry I had a brain fart.
I'm getting .03.04 from alternator to battery positive.
And negative battery to block - is all I get .

No set it to volts. You are testing similar to this image except to the alternator instead of the starter. Say you have a fully charged battery at 12.6 volts. You start the engine and it now shows 13.6 volts, that is charging. With the meter connected as in the picture between the battery positive and alternator output posts and the cable connected with a load like the lights on, you should see a very low voltage, no higher than about .2 or so at the most if the cable and connections are good. If you them do the same on the negative side you should see a very low voltage. In a perfect world it would read zero, however nothing is perfect when it comes to cars. I think you will see a higher number on the positive side though as with the amp draw there should have also been a low like .05 that you had on the negative side if all of the current was going through the cable as it should.
If you want to see the idea just search for voltage drop testing, there are a lot of videos out there on it, from basic to explaining it down to electron flow.

Okay,. 03 is what I'm getting on positive nothing on new side.

Is that with a load on and idle? Try revving it up some. Then try the ground side. If it still reads low then it almost has to be on the sensing side of the system, or the feed into the vehicle. You can use the same testing method between the various connections as well. That is one advantage to voltage drop testing, you can do it with the circuits under power without removing a connection.

My friend had bought the car listed above for her daughter. Daughter does not drive yet so the car has been sitting naturally the battery went dead. I jumped it making sure positive was hooked to positive negative to negative etc., and it started just fine let it run it charged piece of cake. It is cold here so about two or three weeks later i was informed that it was dead again. I tried everything again except this time when it started the headlights were blinking dimly and it would not charge. It is a newer battery. Could it be a alternator or a sensor? i have never worked on a Lexus. what is up? please help. Thank you

Hello my name is Dave.

First thing I would do is test the battery, new or not it can still be faulty and keep the system from charging properly. I have attached a link to our tutorial to help you with this process.

https://www.2carpros.com/articles/car-battery-load-test

This can also keep the alternator from being able to provide enough amperage to fully energize the headlights. If the battery tests good I would suggest making sure it is fully charged and then test alternator. I have attached a tutorial to help you with this process.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

What should the alternator voltage output be at 800 RPM with all accessories turned on?
History of car: It previously had a problem of a no start, lights dim, starter clicking symptom seldomly.
Battery was replaced two years ago and I had the battery load tested recently, currently shows 12.8 volts. The car had a problem with wanting to shut off. I charged the battery and drove the car to AutoZone where it was tested on car as bad voltage regulator. I replaced the alternator with one from O'Reillys a rebuild Ultima Brand alternator. I drove the car for three weeks and the battery light came on, pulled car in parking lot and car would not start back up. Drove the car to O'Reillys and had them test it on the car and then bench tested. Bench test passed and test on car failed. All connections and cables have been checked. I went ahead and replaced it with a second alternator(same Ultima brand) and drove it home. I checked with a voltmeter and noticed that with all accessories turned on except for the air conditioning the voltage output of the alternator shows 13.5 volts at 800 RPM. When I turn the climate control on the voltage slowly drops down to 12.6 volts at idle.When I turn the A/C off and leave the accessories on the voltage picks back up to around 13.5 volts.
I have checked the A/C clutch coil with meter reads 5 ohms.
I have temporarily jumped the clutch coil with 12 volts and car running without climate control inside turned on and voltage does not drop down with accessories turned on.
I noticed when running the A/C the compressor does not cycle on/off. I hooked up R134A gauge set on a cool engine and pressures read 110PSI low and 110PSI high without car running and outside temperature 93 degrees. Do you think an overcharged A/C system would cause the problem? Or a faulty A/C pressure switch?
Or do you think the alternator will not handle the load the car has because it is cheap?
Any advice would help.
Thanks.

The charging system is not good if charging voltage drops drastically when electrical loads are applied. It could be the alternator or the crank pulley damaged harmonic damper, if equipped).

I do not believe the overcharging of the Freon is causing any problem to the charging circuit.

Hi Brandon, I have the same exact problem you described. Did you find the problem yet? The mechanic here does not know a whole lot. Did you try taking it to a shop who has a real charging system tester like Autozone used to have? I am curious if the new alternator is actually putting out any amperage at all at this point. The voltages are good without the AC running but I do not know if any real amperage is getting to the battery to charge it. I was thinking something is grounding out somewhere once the cooling circuit is engaged. Please reply with any suggestions. Thanks.

Hello CFOSTER2030,

Please post your question here:
https://www.2carpros.com/questions/new

Be sure to include as much information as possible about your vehicle.

Make sure you are logged into the site.

One of our experts will be happy to assist you.

Thank you for using 2CarPro.com.

Renee
Admin

It started with the surging of the headlights and blower fan motor. I then tested voltage at the battery while idling at 700 rpm voltage at 12.5. I then replaced the alternator because the battery was not very old. The new alternator did the exact same thing. At 1250 rpm with AC on and fan blowing on high voltage is at 14 volts. Same thing happens with rear window defroster (heavy load) at idle. Tested battery and was reading 10.5 volts. Replaced battery and continued to do the same thing. Without any load at idle it is at 14 volts. It seems under heavy electrical load at idle it cannot charge the battery. I replaced the ground wires and same thing still persists. The 100 amp fuse is good and the positive wire coming off the alternator is good as well. What could it be? Thanks.

Low charging like this is usually a engine block to chassis ground or negative battery to body ground that is missing. Can you locate and confirm there to major grounds are intact please?

Cheers, Ken

Hello, thank you for your reply. I have replaced the block to battery and chassy to battery ground connection. They all meet at the negative battery post.

Even at 1000 rpm with AC on my voltage is around 13 or so. Not until around 1,300 does it get back to 14 volts. Thought maybe it was also running to low on the rpm's. With AC on its sits at 700.

My other thought was I burned out two alternators because the battery failed on the first maxing out the original alternator. Then I stick a brand new alternator in with a bad battery ruining it. Is this possibly too? Thanks for your help.

Yes a bad battery can wipe out alternators no problem, I would replace the battery and the positive battery cable and get a warranty alternator. Is the alternator a Denso unit?


https://www.amazon.com/gp/product/B000C5UEA4/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=2carprcom-20&creative=9325&linkCode=as2&creativeASIN=B000C5UEA4&linkId=e515ea6539089ab8b97d1fe3a461b582

$117.00 on Amazon

I have same problem I was wondering in you ever solved it or not. I tried all the same things my battery will die if I run my AC too long. I have brand new alternator and battery and upgraded all wires to zero gauge.

I would check the ground from the battery to the engine and body, also did you use Denso? If not that can be the problem as well. Check out the link above.