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battery light

Discussion in 'Ford Trucks' started by s. donato, Dec 14, 2011.

  1. s. donato

    s. donato Senior Member
    Messages: 314

    hey guys since it has gotten colder when ever i start my truck from a cold start the bettery light comes on. My SG2 says voltage is in the 11-12 range until the truck gets up to full running temp which is after about 30 mins of run time.

    i just replaced both batteries b/c it thought one was going. but now i am thinking the alternator that i put in right before i replaced the batteries may be the problem. :realmad: i already told my mechanic to get a replacement b/c i feel that its not working right.

    anyone else experience this before? a couple friends of mine said it more then likely is the warm up process(they have ford diesels too) but they agree its taking a bit long to get back to 14 volts on the meter.
     
  2. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,957

    Anytime the batt light comes on,,,its the alt. the diodes in the alt are bad/going bad an that causes the light to come on, just replace the alt and you'll be fine
     
  3. abbottfarm

    abbottfarm Senior Member
    from Maine
    Messages: 108

    Yeah, probably your ALT. Make sure when you buy a new replacement you have it bench tested before you pay for it. You would be surprised how many are junk right out of the box.
     
  4. s. donato

    s. donato Senior Member
    Messages: 314

    yeah the one i got was rebuilt from a very reputable guy. it took one call and he said bring it in for a replacement free of charge(no charge for install). i thinking of getting a NEW one and then keeping his rebuilt that they put in tomorrow as a back up. as i drove home tonite from work it according to my SG2 it was only at 13.1 after 30 mins of city driving.
     
  5. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    So it does eventually get to 14+ volts?

    Does that mean worn brushes or a shorted stator field won't cause the light to come on? What about an open armature?
     
  6. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Should be 14.5 volts with the truck running. If it's not, the alternator is toast or soon to be.
     
  7. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,957

    The Batt light on means that the diodes are going bad/are bad internally. You could replace them, but why? Take the alt apart find the diode pack and then try and out it back together? Nah new one
     
  8. GL&M

    GL&M Senior Member
    from PA
    Messages: 223


    I just replaced one that wasn't charging at idle. When running and the RPMs were up it charged. If you let it sit at idle for a while and shut it off, it wouldn't start. New alternator and the problem went away.
     
  9. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    I guess I'm confused. The only thing that makes the light come on is a diode failure? Other failures wont make the light come on? And what's the difference between an internal and external diode failure?

    Maybe you know this also. Someone told me once that automotive alternators produce three phase power. Is that true?
     
    Last edited: Dec 17, 2011
  10. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    The thing with replacing just the diodes is the rest of the alternator is also tired. You have the bearings, voltage regulator, windings and brushes that are tried. A plow truck alternator gets spanked every time you work the truck for a while. It has a huge heat load each time! Just replace it or upgrade the alternator output and the wire to the battery / batteries. Make sure the belt is good and the belt tensioner is good.
     
  11. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    Where did dieselss go? I was hoping he would answer those questions....
     
  12. s. donato

    s. donato Senior Member
    Messages: 314

    seems like it was the alt. its weird the guy bench tested it after it was removed from the truck and it was charging fine. i think it was pretty much doing that from time to time b/c the day it got removed my voltage was in the 13's but the whole week it was 12's and low 13s. but new rebuilt is now in and i haven't seen it go below 13.6 so far. i need to drive the truck a bit more before i can say for certain.
     
  13. TerraScraper

    TerraScraper Member
    Messages: 40

    Keep us posted, my light is flickering as well in my 6.0. how many miles on your truck?
     
  14. s. donato

    s. donato Senior Member
    Messages: 314

    70k but just bought the truck so not sure if it was original alt.
     
  15. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,957

    I'm back donato lol Scheech can't a guy take a break lol. J.k. the alt does produce 3 phase electricty, thats the diodes job to convert it to single phase. And yes to the light q? Thats the only reason the light will come on. Or when you just turn the key on. No a days alts only have "internal" parts so theres nothing external to "play" with. If the its now putting out 14+ with a load on it it bad. Dont always go by what the factory gauge is telling you when you cking it. Get a meter on it.
     
  16. s. donato

    s. donato Senior Member
    Messages: 314

    I have a scan gauge and when i checked it against the meter directly conectted to the alt we had a .1-.3 difference so that's why i know 13.8 isn't that bad b/c when we checked it against the meter - the meter had 14.1.

    anxious to hook up my plow and move it around a bit and see what happens ;-)
     
  17. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,957

    It'd prob gunna be ok, now. Not gunna be ok when you need it the most. I would disregard the bench test, and just replace it.
     
  18. s. donato

    s. donato Senior Member
    Messages: 314

    no i agree dieselss. i had them give me a new one which is why i know this one is alot better already. had the heated seats going while driving around this morning with the SG2 saying 14.1 the whole time - it did bounce around a bit from 13.8-14.2 but that's a much smaller window then the 11.2-13.8 from the one i had them take back.
     
  19. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,957

    Oh yea. 11v it was toast. Did you get an upgrated one? Upgrade your output wire? Add a gnd wire to the alt?
     
  20. dieselss

    dieselss PlowSite Fanatic
    Messages: 10,957

    Did forget to ask. What truck and motor?