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Car Problem: Battery Discharge Light

Discussion in 'The Pub' started by termis, May 22, 2009.

  1. So for those of you who know how to tinker around a bit on your car...

    When the battery discharge light comes on in your car, is there anything other than the alternator that can be the culprit?

    Basically, while the wife was driving the car, the battery light would intermittently come on and off, and it stayed on until it eventually died on her in a carpark (it wouldn't start after turning it off).

    After jump starting the car, I knocked the alternator a bit, and that turned the battery light off, so at that point, I was pretty sure that brush in the alternator was going off. I went and replaced it with another alternator found in a junkyard, but after a couple days, the battery light came back on (though it much less frequency).

    Could it be just a bad alternator I got in replacement? Or is there anything else I should be checking?
  2. Regulators have been known to fail and these days they're built into the alt. The battery could have developed an internal short too.

    If its an older car +15 yrs my money is on the reg.
  3. Checked the belt tension?

    Also worth making sure the battery terminals are clean and tight.
  4. Yeah they can tend to fray a bit at the connections, and if it is touching wither the alternator housing, or the body anywhere, it can dead short and trigger that light as it fouls.
  5. Yeah, I checked the belts -- they seem fine, likewise for battery terminals.

    That voltage regulator sounds suspect, though I can't find it readily by googling around, (94 Toyota Corolla with a Bosch Alternator). In this case, I'd imagine it is indeed part of the alternator, and perhaps I just got a bad part? Hm... :?

    I'm just hoping that the light won't come on again & that it'll fix itself. [-o<
  6. The regulator should be a small black box screwed into the back of the alternator itself. The fact the light intermittently comes on would suggest perhaps the bushes in the alternator could be wearing out, I think u can test the regulator using a multimeter to check resistance which I think is stamped into the plastic.
  7. Chances are you'll have to replace the whole alternator.

    I was gunna mention the terminals, but someone already did. If there's a wee bit of corrosion on the terminals, boiled water and a wire brush help :)

    Also, might want to check the earthing strap. I'm not mechanic, but my brother is, and he mentioned this to me when we had to replace the alternator on my car.

    Also, on older cars (my 1991 Corolla is a bastard for this) it's quite common for the electrics to play up, so might want to check the wires for the light itself. As an example, the heat gauge on my car constantly sits at overheating. Can't be bothered to open up the dash to get to it :)
  8. This might sound a bit silly but ....... have you put the wrong sort of alternator on? ie. did the old one have an external reg and you've now put on one with a built in reg or vice versa?

    That will stuff things up.
  9. You're all wrong... :p

    94 Corolla, yeap, typical. Reg brushes go in them around now (their life span). Bugga going to a shit wreaker for a shit dud alternator they just pull of the wrecked car and bung on the shelf with no checking what so ever.

    Those alternators are very common, and we (I'm an Auto Electrician) tend to overhaul them for around $240. This includes new reg (which comes with brushes), new bearing, cleaned (or depending on the wear replaced) slip ring, cleaned and buffed (makes it shiny) brackets, and painted fan and pulley.

    Or if you're a tightass :p go down to Repco or something and get yourself a Bosch RE60 reg.
  10. thanks folks. I just drove to and from Ballarat and didn't see the light go off once.

    Last I checked, it was charging the battery at 13.5v, which seems fine. I'll keep an eye on the light. If it happens again (it'd be the third time since I put it on last Wednesday), I won't consider it a fluke anymore -- I'll go back to the junker and get my money back, since I got 90 days warranty on the part.
  11. Full charge should be up around 16v