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Thread: Alternator going bad?

  1. #1
    ZOOOOOOOOOM ZOOOOOOOOOOOM mazdadude's Avatar

    '16.5 Mazda CX-5 Touring AWD, '05 PRIUS

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    Alternator going bad?

    The other day, the battery light came on when I started car, light went away after I warmed it up, and revved it a few times.

    Today, battery light came on, and would not go off after warmed up and revving like before, so I measured voltage and it was 12.3v engine off and 11.3 running.

    I charged battery to 12.5 volts and headed to store to get new alternator, when the voltage shot up to 13.3 on the way driving to the store. The battery light was then off.

    Alternator going bad?
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  2. #2
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    I would have a load test done on the battery first - any auto parts store will do it for free. If the battery checks out, replacing the alternator would be a safe bet.

  3. #3
    Registered Member Booski's Avatar

    2003 Mazdaspeed Protege

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    Does sound like a possible alternator issue,
    Always check for obvious first like loose cables and corrosion.

  4. #4
    Registered Member Indelibility's Avatar


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    Edit: Removed because I'm an idiot
    Last edited by Indelibility; 10-10-2013 at 11:58 AM.

  5. #5
    Yellow Jacket Keno1542's Avatar

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    The auto parts stores will also check the alternator for free as well, but it sounds like you may have a voltage regulator problem if the voltages are fluctuating like that.
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  6. #6
    Registered Member Silentnoise713's Avatar

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    Quote Originally Posted by JOE MAMA View Post
    I would have a load test done on the battery first - any auto parts store will do it for free. If the battery checks out, replacing the alternator would be a safe bet.
    +1

    How old is the battery?? Do you have any issues cranking? If the battery is old and it takes more cranks than usual for the engine to turn, I would lead towards battery. Luckily you can get that tested for free
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  7. #7
    ZOOOOOOOOOM ZOOOOOOOOOOOM mazdadude's Avatar

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    ok, did the full check for all connections, corrosion, etc., passed all visuals.

    Starter cranks over fine, no lag or slowness ever.

    The battery is a high end DRY CELL battery made by odyssey, and is only ~4 years old.

    I charged the battery at 1.5 amps for 5 hours, started and took for a 15 min drive and no battery light ever during test drive... hmmmm...
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  8. #8
    Yellow Jacket Keno1542's Avatar

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    Check the charging circuit
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  9. #9
    ZOOOOOOOOOM ZOOOOOOOOOOOM mazdadude's Avatar

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    I like how the internal voltage regulator/brush assembly is the same cost as a rebuilt alternator! ARGH!

    Ok, I found a new voltage reg and brush assembly for $65. I will be doing a rebuild.
    Last edited by mazdadude; 10-07-2013 at 02:35 PM.
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  10. #10
    ZOOOOOOOOOM ZOOOOOOOOOOOM mazdadude's Avatar

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    Replaced the brushes and regulator assembly.

    Bearing was still rolling perfect, and diodes/rectifier tested fine, soldered new regulator assembly in.

    Back charging 100% again! YAY!



    I might not have a warranty, but I saved $100-150 over a reman.





    Here is the video that I watched prior to the rebuild. http://youtu.be/qOo0iSnmwP4
    Last edited by mazdadude; 10-09-2013 at 10:24 PM.
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  11. #11
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    Quote Originally Posted by Indelibility View Post
    Easiest way. With the engine running remove the negative battery terminal. If the car still runs, it's the battery If the car dies, it's the alternator.

    The battery is really only there to start your car, unless you have some massive sound system or hydraulics.
    Never do this! This trick used to work in the old days before vehicles were controlled by computer. Your vehicle uses power from the battery because it's clean and consistent. Power from an alternator is not clean not consistent and an alternator is not designed to carry the full electrical load of the vehicle. When you pull a cable off of the battery with the vehicle running, you can fry the voltage regular and other electronic components such as the PCM/BCM/ECU, etc.

    Power from the battery is constantly used - not only when starting.

  12. #12
    Registered Member Indelibility's Avatar


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    Oops, worked fine last time lol.

  13. #13
    Mazda5 the Anti-Van thaxman's Avatar


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    SO a rebuild did it? How's your battery now? I've been through 3 in 4 years, and when I bought it after 3 years on the road, my car had already had the OEM battery replaced, so at least 4 in 7+ years.
    Is it possible that a f'd alternator could be killing the batteries prematurely?
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  14. #14
    ZOOOOOOOOOM ZOOOOOOOOOOOM mazdadude's Avatar

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    Quote Originally Posted by thaxman View Post
    SO a rebuild did it? How's your battery now? I've been through 3 in 4 years, and when I bought it after 3 years on the road, my car had already had the OEM battery replaced, so at least 4 in 7+ years.
    Is it possible that a f'd alternator could be killing the batteries prematurely?
    Yes I am back to 14.0 volts at idle!

    Battery is great, I LOVE my ODYSSEY Battery!

    2 Batteries in 1

    Odyssey batteries combine in one box the characteristics of two separate batteries. It can deep cycle (be recharged) as well as provide enormous cranking power.

    Military Grade

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    Superior cranking and fast charge capability

    The 5 second cranking power of Odyssey batteries is double to triple that of equally sized conventional batteries, even when the temperature is as low as - 40 C. Also, with simple constant voltage charging (alternator or independent charger), there is no limitation on the inrush current, so the user is assured of a fast charge.
    •Drycell Battery
    •Without Metal Jacket
    •12 Volt
    •55 Ah @ 10hr rate
    •850 CCA
    •950 MCA
    •1400 Cranking Amps for 5 Seconds
    •130 Minute Reserve Capacity
    •Cycle life @ 77 F 400 at 100% DOD
    •-40 F to 140 F Temperature Range
    •Made in the USA

    Features:
    •3 to 10 year service life, when properly maintained.
    •99.9% pure lead providing minimal plate corrosion
    •Explosion proof
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    •2 to 3 times the cranking power of equivalent size battery
    •Spill and leak proof
    •Superior vibration resistance
    •Fully Charged out of the box
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    •May be installed on its sides at any angle without sacrificing performance attributes
    •Military grade version of the Hawker Genesis
    •2 Year Full Powersports Warranty
    •Made in the USA


    These cars are very hard on batteries, after having 3 in 3 years I went with the ODYSSEY battery. The Mazda5, having the electric steering, doesn't help things either. As I monitor the voltages when driving and turning on different features like defroster, or high beams, etc. I notice that the voltage does drop for 2 seconds until the PCM reacts and readjusts the voltage regulator. So maybe the fact that the system is a bit lagging it puts additional stress on the battery.

    In my case, my alternator would work when engine was hot, but not work when it was cold. So if you had a failing alternator, and did a lot of short trips where the alt was not getting hot enough to charge, that would put a lot of stress on battery as well. However if it was not charging, you would/should have the "BATT" indicator light illuminated on the dash.

    After a week of certified repair, I will go ahead and perform an autopsy on the old reg/brush assembly and see if I can locate the failure.
    Last edited by mazdadude; 10-10-2013 at 04:48 PM.
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  15. #15
    Booga Booga? phunky.buddha's Avatar

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    Quote Originally Posted by mazdadude View Post
    Replaced the brushes and regulator assembly.

    Bearing was still rolling perfect, and diodes/rectifier tested fine, soldered new regulator assembly in.

    Back charging 100% again! YAY!

    Here is the video that I watched prior to the rebuild. http://youtu.be/qOo0iSnmwP4
    Haven't watched your linked video yet... but I don't know why I never thought to rebuild my own alternators- I do work in the electronics industry after all, I should have the skills to rebuild one. Where did you source your parts? Any thoughts on increasing the charge current on your alternator? I'd like to wind one to have more capacity...

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