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Alternator not charging.

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5 years 2 months ago - 5 years 2 months ago #25833 by Vlad1
Mazda MX-5 Miata 1993.
1.6L engine.

The car showed battery light, CEL and all other instrument cluster lights, I pulled over, turned the engine off and it would not start.
The battery was discharged. I took the car home and recharged the battery.
The battery is able to run high beams light for 30+ mins when fully charged. The voltage after overnight charging is 13.2V, after power load - 12.5V.

Now, when I start the engine, the voltage drops to 11.9V, so the alt is not charging.

Further tests. When the key is in On position - battery light is on, the light turns off after the engine is started.

Ground - checked PPF, all ground connections, some took apart, cleaned and put back together. Just to be sure, bypassed the ground altogether by connecting battery (-) to the engine block with jumper cable. That did not help.

Alternator - installed fully, tightened belt, the pulley is confirmed spinning when the engine is running.

Voltage.
  • When Off
  • White wire - 12.57V
  • White/black - 0V
  • White/green - 12.56
  • When key is in On, car not running
    • White wire - 12.24V
    • White/black - 0.68V
    • White/green - 12.25

    • When the car is running
    • White wire - 12.01V
    • White/black - 10.95V
    • White/green - 11.99V, then drops to 10.96V
    Something seems to seem odd with these numbers in red, why is 1V drop when running? It should match the battery voltage...
    I found this forum after watching this video
    , but my symptoms are a bit different. I do not have a full power loss in either of the regulator circuits.

    Another observation. If the car is running at the fully charged battery that has a battery charger attached to it and supplying 12V/5A, I can see the battery voltage start going up to 14.5V.

    Where can I get the wiring diagrams to run the diagnostics as it was shown on the video?

    BTW, the car has a non-working power antenna, also some other minor intermittent electric problems.

    Thank you
    Last edit: 5 years 2 months ago by Vlad1.

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    5 years 2 months ago #25838 by Desmond6004
    Is the positive at the alternator good? Your main positive cable might have a blown fuse in the circuit. Check it at the alternator.

    Getting involved in discussions because I have a lot to learn still.

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    5 years 2 months ago #25840 by Andy.MacFadyen
    I see 4 possible causes some simple checks with a voltmeter and tungsten test light first but I think you will end up with a rebuilt alternator. The early MX5/Miata/Enos was fitted with an alternator that is a bit undersized by modern standards however it is a very simple system.


    First test is unplug the 3 pin connector on the alternator and check for battery voltage at each of the three terminals in the plug. Both the White-Green and the White should be live with the ignition on ---- if not check the 80a and 30a fusse and for wiring damage or connector corrosion between the plug and the fuses. Next with it still unplugged and ignition on test for near battery voltage on the black-white wire --- I would also do this test with tungsten test light --- which should glow dimly.
    If these tests are okay reconnect the plug and put the voltmeter across the battery terminals , back probe the black and white wire at the alternator and supply it with battery voltage through the test light. With the engine running if the alternator is okay it should start charging

    " We're trying to plug a hole in the universe, what are you doing ?. "
    (Walter Bishop Fringe TV show)



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    5 years 2 months ago #25844 by Tyler
    Replied by Tyler on topic Alternator not charging.
    Sorry I misunderstood your intro post. :blush: You're clearly on top of things, as far as testing!

    At the risk of differing from Andy (who is a sharp cookie), I think you're done. :cheer: You need an alternator. It has everything it needs to do it's job, and still isn't. Your testing shows a working light circuit, a working regulator power circuit, and no opens in the main power or ground to the alternator.

    The only part that might suggest an issue is the change in voltage you saw on the white/green wire. A drop of 1V over a Main Relay circuit isn't great, obviously. But the 11V you saw should be enough to run the alternator regulator. It doesn't help that the alternator isn't charging during these readings. :silly: If you still have doubts, you can take a jumper from the white cable to the white/green wire and see if it makes any difference. If it does, we can dig deeper into the Main Relay circuit. If it doesn't, you still need an alternator.

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    5 years 2 months ago #25850 by Andy.MacFadyen
    :-) We ain;t differing Tyler ---- foobared alternator :-( is most likely cause. Not sure if these units are easy to fix some Denso units can have the regulator and brush box changed in about 10 minutes with alternator on still he car

    " We're trying to plug a hole in the universe, what are you doing ?. "
    (Walter Bishop Fringe TV show)



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    5 years 2 months ago #25853 by vinnyAudi
    As Andy said, I think the best course.of action if so checks out is to supply the alternstor with a signal. If it does not start charging, you likely need a new alternator. If it does, you have a circuit problem.

    Sent from my SM-N920V using Tapatalk

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    5 years 2 months ago - 5 years 2 months ago #25867 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    I did not test it today, came back home when it's already dark. But I remember testing it a month ago, with the connector unplugged. These measurements are on the terminals of the wire connector. It actually is a 2-wire connector, not 3-wire (G/W and B/W wires, the thick white wire has it's own lug nut attachment to the alternator, despite running in the same harness)


    So again, the voltages are taken at the terminal of 2-wire plug, (not the alternator coupling terminals). Also, the voltage on the solid wire was taken while it is attached to the alternator. The plug is disconnected from the alternator and measured, white wire is connected to the alternator while measured.

    With key switch off:
    • white wire -- 12.67V
    • white/black wire -- 0V
    • white/green wire -- approximately 12.68V

    With key switch on:
    • white wire -- 12.34V
    • white/black wire -- 11.97V
    • white/green wire -- 12.34V

    The number in red looks suspicious to me, my understanding it should be around 1V when the engine is not running, but I am not confident if this "around 1V" is obtained from the B/W wire while it is connected or disconnected.
    When the plug is connected, I get a bit less than 1V on the B/W wire (key "on", engine off), through the sewing needle with which I tapped the wire.
    In a day or two I should get a more solid connectors to tap into those wires. This is it for now...
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    Last edit: 5 years 2 months ago by Vlad1.

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    5 years 2 months ago #25870 by Andy.MacFadyen
    Those are okay readings you are going to need an alternator

    " We're trying to plug a hole in the universe, what are you doing ?. "
    (Walter Bishop Fringe TV show)



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    5 years 2 months ago #25873 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    That's my third one... Got one from acdelco, not charging. This one Mazda rebuilt, made by Mitsubishi. New in box from ebay. Not charging. Not to mention the one that died and started my whole journey. That one lastx for 2 years, but itself was a third replacement for the one that came with the car. My Miata seems to be eating them.
    You might be right though. I'll wait until testing with tungsten wire circuit tester and only then will give up on it.

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    5 years 2 months ago - 5 years 2 months ago #25874 by BobbyM
    Replied by BobbyM on topic Alternator not charging.
    Can you try the test that Paul does in this video at the 12 minute mark.

    Take a test light to battery positive and with a t-pin, back-probed on the white black wire, touch that wire with the engine running and see if you hear the alternator kick on.
    Last edit: 5 years 2 months ago by BobbyM.

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    5 years 2 months ago #25882 by Andy.MacFadyen
    It seems to be an issue on these early MX5 cars, probably the 60 or 70 amp alternator is supplying near its max output on a high revving engine. If it were mine I would check on the one make sites for an easy upgrade to say a 90 or 105 amp unit.
    It is a fairly standard 3 wire alternator complete with regulator, if you can find an alternator that will accept the v pulley and fit the mounting brackets it should work.

    " We're trying to plug a hole in the universe, what are you doing ?. "
    (Walter Bishop Fringe TV show)



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    5 years 2 months ago - 5 years 2 months ago #25883 by Andy.MacFadyen
    The brush pack and rectifier looks like an easy fit

    ebay link to rectifer and brush pack assembly

    " We're trying to plug a hole in the universe, what are you doing ?. "
    (Walter Bishop Fringe TV show)



    Last edit: 5 years 2 months ago by Andy.MacFadyen.

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    5 years 2 months ago #25884 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    Just did it. No change and the system voltage does not go up. So, you think alternator is dead?

    There was something else that helped (I was not able to monitor the alternator sounds since I had to go inside the car to start it so I'm not sure if this really is an alternator waking up. ut if not, then I have no explanation for what I am writing below).
    If the battery is fully charged (overnight on 5A current) and shows 13.2 volts,
    and also, if I put 30A input on the battery charger and keep it connected to the battery while the car is running,
    then the alternator seems to wake up and the voltage goes up to ~14.1-14.5V depends on revs (and this means yes, the voltage starts responding to the engine revs).
    If I unplug the charger, nothing changes immediately, but in around 3-5 mins the voltage goes down to 12.2-12.3V range and and does not elevate in response to engine revs.

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    5 years 2 months ago #25887 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.

    Andy.MacFadyen wrote: The brush pack and rectifier looks like an easy fit

    ebay link to rectifer and brush pack assembly


    Hey Andy,
    Thank you for the answer. So, this is what this alt needs, right?
    I've never done alternator overhaul. Do you think it's going to be like an easy swap?

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    5 years 1 month ago #26871 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    Taking the alternator apart was not hard.
    What would be the way to test the voage regulator and/or diodes? I want to understand what failed in my alternator and that I'm placing the working replacement.
    These are the pictures of the stator and electronics inside and new part that came in.
    Attachments:

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    5 years 1 month ago #26898 by juergen.scholl
    The rectifying diodes you can check with the diode function of your dvom. Put one meter probe on the positive outlet post (where your "thick" white cable was connected and the other lead to the diodes themselves, one at a time. There should be flow into one direction and no flow when you reverse the probes.
    Any diode that allows current to flow in both or no direction is at fault and you will have to replace the rectifier as a unit.

    Concerning the regulator there is no practical way I know of to "test" it easily on the bench, iout of the car.If the brushes and the spring tension/collector slip rings are fine then you just may want to put a new one in...

    With the rest of the alternator confirmed healthy you can check the regulator IN the car by applying varies voltage levels to the control wire. The alternators output should respond if it is sound.

    An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.

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    5 years 1 month ago #26916 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    I wasn't able to clearly find both poles of the diodes to test. One was obviously a soldered spot with the coil end. There were no other contact spots, other than the radiator into which they were pressed into.

    However, I think I found something that looks like potential culprit.
    On the new regulator, there's continuity of the top most brush to the metal contact seen on the low left side, see the picture below.
    In the non-working alternator, the same path shows no conductivity.
    Which way is it suppose to be?
    I am hesitating because 5he original voltage regulator looks more advanced than the replacement one (check the pictures in the previous post).
    And there are other soldering spots which purpose I cannot understand or guess.
    Should this circuit be conducting, like on the replacement part or is it going live when I supply the regulating current?
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    5 years 1 month ago #26925 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    I just replaced the voltage regulator. The hardest part was to unsolder it. I anyway had to cut the contacts to get the access and unsolder the remnants.
    Put everything together with a new voltage regulator.
    Applied 9V to the lower regulator contact (lower if looking as the alternator is installed on the car) and cranked the pulley to read the voltage on the B-post (negative attachment being the body in both of the cases).
    Initially it was giving jumps from 0V to 2-2.5v which should be normal I guess.
    Then after a minute or two me playing with it it started to show the battery voltage and stopped responding to the cranking.
    I disassembled and re-assembled again. No changes.
    The voltage does not go up between the B post and body no matter if I try to apply 3V or 9V.
    I'll try to put it on the car and check on the car tomorrow. But having doubts it will work.
    Not sure what killed that initially proper response...

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    5 years 1 month ago #26946 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    Confirmed dead by Autozone machine...
    Ordered a Denso unit. ETA is like 3 weeks.

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    5 years 1 month ago #26960 by Vlad1
    Replied by Vlad1 on topic Alternator not charging.
    I have a question.
    It looks like it is equally likely that I keep getting defective parts or units as well as I get undamaged units/parts, but destroy them by improper testing technique or some sort of undiagnosed failure at car's electrical system.
    One thing I know for sure - the ground path is checked by several more or less reliable ways and should be sufficient. The resistance of the car body measures around 0.03 -0.05 Ohms.
    Is there any way to diagnose the supplied voltage to the pigtail connector while the alternator is off car? Any particular sense to measure the voltage on B/W and B/G wires of the pigtail connector while the alternator is not installed?
    What would be theoretical way to damage the alternator by testing it?
    Can I damage the regulator by supplying 9V from the battery to the green/white connector while NOT supplying the 12V to the B post and just reading the voltage from that post while cranking the pulley? Must I supply the voltage on the b/w wire terminal as well to make sure I don't damage the electronics?

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