× Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

Alternator not charging.

More
31 Dec 2018 16:54 - 31 Dec 2018 16:57 #25833 by Vlad1
Alternator not charging. was created 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: 31 Dec 2018 16:57 by Vlad1.

    Please Log in or Create an account to join the conversation.

    More
    31 Dec 2018 23:09 #25838 by Desmond6004
    Replied by Desmond6004 on topic Alternator not charging.
    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.

    Please Log in or Create an account to join the conversation.

    More
    01 Jan 2019 06:50 #25840 by Andy.MacFadyen
    Replied by Andy.MacFadyen on topic Alternator not charging.
    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

    "Through the grease streaked windows
    Of an all night cafe

    We watched the arrested get taken away"

    ( Bernie Taupin )

    Attachments:

    Please Log in or Create an account to join the conversation.

    • Tyler
    • Tyler's Avatar
    • Offline
    • Moderator
    • Moderator
    • Letting the magic smoke out since 2011
    More
    01 Jan 2019 10:24 #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.

    Please Log in or Create an account to join the conversation.

    More
    01 Jan 2019 11:20 #25850 by Andy.MacFadyen
    Replied by Andy.MacFadyen on topic Alternator not charging.
    :-) 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

    "Through the grease streaked windows
    Of an all night cafe

    We watched the arrested get taken away"

    ( Bernie Taupin )

    Please Log in or Create an account to join the conversation.

    More
    01 Jan 2019 13:13 #25853 by vinnyAudi
    Replied by vinnyAudi on topic Alternator not charging.
    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

    Please Log in or Create an account to join the conversation.

    More
    01 Jan 2019 21:17 - 01 Jan 2019 21:19 #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...
    Attachments:
    Last edit: 01 Jan 2019 21:19 by Vlad1.

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 03:33 #25870 by Andy.MacFadyen
    Replied by Andy.MacFadyen on topic Alternator not charging.
    Those are okay readings you are going to need an alternator

    "Through the grease streaked windows
    Of an all night cafe

    We watched the arrested get taken away"

    ( Bernie Taupin )

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 09:08 #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.

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 10:36 - 02 Jan 2019 10:36 #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: 02 Jan 2019 10:36 by BobbyM.

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 14:43 #25882 by Andy.MacFadyen
    Replied by Andy.MacFadyen on topic Alternator not charging.
    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.

    "Through the grease streaked windows
    Of an all night cafe

    We watched the arrested get taken away"

    ( Bernie Taupin )

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 15:16 - 02 Jan 2019 15:28 #25883 by Andy.MacFadyen
    Replied by Andy.MacFadyen on topic Alternator not charging.
    The brush pack and rectifier looks like an easy fit

    ebay link to rectifer and brush pack assembly

    "Through the grease streaked windows
    Of an all night cafe

    We watched the arrested get taken away"

    ( Bernie Taupin )

    Last edit: 02 Jan 2019 15:28 by Andy.MacFadyen.

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 16:29 #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.

    Please Log in or Create an account to join the conversation.

    More
    02 Jan 2019 18:13 #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?

    Please Log in or Create an account to join the conversation.

    More
    07 Feb 2019 23:04 #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:

    Please Log in or Create an account to join the conversation.

    More
    09 Feb 2019 08:02 #26898 by juergen.scholl
    Replied by juergen.scholl on topic Alternator not charging.
    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.

    Please Log in or Create an account to join the conversation.

    More
    09 Feb 2019 13:30 #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?
    Attachments:

    Please Log in or Create an account to join the conversation.

    • Not Allowed: to create new topic.
    • Not Allowed: to reply.
    • Not Allowed: to add attachements.
    • Not Allowed: to edit your message.
    Time to create page: 1.102 seconds