Alternator not charging battery?

Discussion in 'Mech Tech' started by Stedlocks, Mar 15, 2016.

  1. this is doing my head in!
    Stupidly, I let my battery drain out....I took it off and charged it overnight, then left it another night, before testing it...it showed 12.5v after about 15 hours of sitting there....good, I thought, the battery isn't FUBARRED....now it's back on the van, it starts it fine, but the alternator light is on all the time.....the Volts when running are about 12.4, but when I increase the revs, they don't change. I've cleaned all the blimmin terminals I can think of, and still no change.
    My thinking is this.....is the battery knackered, so the alternator won't entertain charging it, therefore the little red git stays on?
    Any ideas?
     
  2. I'd start by changing your regulator. 13.5 - 14V is much better. If your battery's only showing 12.5V after a long charge, that's likely on the way out as well. Around 12.7V is fully charged.
     
  3. I've changed the regulator to a brand new one that I happened to have knocking about..I've got a feeling there's a loose connection somewhere..possibly dislodged when removing the battery to charge it. Does that sound feasible?
     
  4. There's a cable that goes from the positive connector to the alternator. Check that.
     
  5. Is it possible that the alternator is charging at all... i.e. it hasn't been triggered? I recently had the same problem on my Volksrod.

    Try bridging between the B+ & D+ connectors on the Alternator with a side light (5w) bulb (leaving the existing connections in place) after starting the engine. I jammed one lead into the trigger wire's spade connector and just touched the other lead against the screw post...

    If the Alternator has not initially been triggered into action, you will see the bulb flash briefly, the voltage across at the Alternator output should jump up to 13.5V (ish) and the dash warning light should go out.

    If this happens, it suggests that the battery cannot push enough current through the alternator trigger (through the warning bulb) to energise the windings inside the alternator.

    BTW, In my case, the problem wasn't the battery, but the warning bulb was too weedy - was 0.5w and needed 2w.

    P.
     
    Stedlocks likes this.
  6. Thanks for that....I don't know whether I understand properly, as I'm an electric numpty, but I will google!!
     
  7. Zed

    Zed Gradually getting grumpier

    There's a blue wire from the regulator that sends the cancelling 12v to the dash light. It's commonly broken into to set off various relays for split charge and the like. Might have been disturbed? It should disappear into the loom to the front, rhs of engine bay.
     
    AndyC and snotty like this.
  8. ^this...and check your other connections (again)

    If the wire to the alt light is missing/not connected, your alternator won't get any "tickler" current to get going.
     
  9. Thanks for the input, it's starting to make a bit of sense.....the previous owner liked a bit of electrickery, and has indeed spliced into the blue wire in lots of places....I can see the blue wire coming from the front, but it then turns into a snakes wedding.....seriously. There are about 4 different, non-original relays screwed to the engine bay, with all sorts of gubbins coming out of them.
    So, utilising Google, I managed to end up at ratwells page. I think I did this bit right.....I unplugged the 3-pin plug from the regulator, and with the ignition on, it was registering 4.55v on the D+ terminal. Does that mean the alternator is goosed? How could it be? It was fine the last time I ran it up ( about 2 months ago, hence the flat blimmin battery), with the little red git going out ....the alternator is brand new! Can they just stop working if you don't use em?
    I'm going to watch that video now, as I've had enough for today.....ive been poking and scraping in the cold for too long!
     
  10. To get to the B+ on the alternator, do I have to strip some tin away? I'm indoors in the warm now!
     
  11. Wizrod has already posted a good method for testing the diodes for the D+ circuit...the idiot light goes out when voltage at the D+ and B+ are the same...make sure the warning light is actually working
     
  12. Thanks...i just need to try to work out how to do it......
     
  13. Hi again, I really appreciate the help so far, but I'm still struggling...the bridging of the B+ and D+ , do I make that little circuit with the lamp on the rear of the alternator? Or somehow off the regulator? If someone could give me an idiots guide, I would be forever grateful!
     
  14. OK... so do yo have an alternator with an internal regulator (1 screw post and 1 spade terminal) or an external regulator (1 screw post and 3 spade terminals) ?

    For either: get a 5w side light bulb in a holder that has a couple of wire tails.

    For an internal regulator:
    1. wrap 1 tail to the screw terminal.
    2. measure the voltage across the screw terminal and a good earth - should be the same as the voltage across the Battery terminals
    3. turn the ignition on
    4. check that the alt warning bulb lights up!
    5. start the engine.
    6. measure the voltage across the screw terminal and a good earth again - if the alternator is working the voltage should now read 13.7V or more. If it hasn't changes, then the alternator has not kicked in.
    7. touch the other tail to the spade terminal (making sure to touch metal..not the insulation).
      1. If the Alternator is good, then the bulb should flash briefly.
    8. measure the voltage across the screw terminal and a good earth again - if the bulb flashed, the alternator should now be working and the voltage should now read 13.7V or more. If not - duff alternator or regulator.
    For an external regulator, the procedure is the same, except for 5. Instead, find the external regulator and locate the connector with a blue/greed (mainly blue with green stripes) wire attached. touch your other bulb-holder tail to this connection.

    What you are doing is this:
    The alternator need a kick to get it to start charging. The alt warning light, connected to +12v at the dash and using a 2w bulb causes enough of a current draw to wake the alt up. Too little current - wither due to a low battery or too small a bulb will not provide enough of a kick to get it going. Once the alternator starts, there 12v at the spade terminal too...so there is effectively 12v on either side of the warning lamp...so it goes out.

    By bridging the B+ & D+ posts with a 5W bulb we do 2 things: 1) we eliminate any voltage drop in the wiring between the battery, up to the warning light, and back to the engine - a tired battery will accentuate this. 2) a 5W bulb will draw more current than the 2W bulb in the dash, so will also help to compensate for a slightly week battery.

    So the procedure above should tell you have a good alternator/regulator combo. If so, then your issue may just be that the battery is a little tired and is not able to deliver enough current to wake the alternator up.

    Something else you could try: connect jump leads from a separate car with a running engine to your bus's battery and then start the bus's engine (as though you were trying to jump start it). The jump leads should be providing more than enough juice to kick the alternator into action. If the alternator starts charging and the warning warning lamp goes out now, it suggests that you battery needs replacing (or perhaps at least reconditioning).

    cheers

    P.
     
    alpha981, IZZYBAY, Zed and 4 others like this.
  15. Blimey mate, thank you so much for taking the time out to write that......it's spot on for an electrical moron like me!
    It's an external regulator.....it has a 3 pin block that pushes on the back. I'm going to try the jump lead thing first, as that seems easiest with what I have at hand.
    I'm kicking myself about this....the van was running beautifully before the battery went flat, and now I'm feeling some hate for it!
    I'm going out to try now, and I'll let you know how I get on....I'll take a couple of snaps too, to show you what a snakes wedding it is!
     
    Zed and vanorak like this.
  16. No probs :) I had the same problem recently with my Volksrod, so its all fresh in my mind!
     
    Stedlocks likes this.
  17. Also...after 15+ years of VW ownership, combined with a policy of not throwing stuff away, means I can lay my hands on most things...random side-light bulb holders, for example, without to much trouble ... I just have to move house every so often to a new place with a bigger garage!!!
     
  18. Without wanting to sound like a whinger, I can't get to any of the connectors on the back of the alternator...its tucked up tight, and there is a disc bolted to the back with three little bolts...the loom goes into a hole with a grommet there.
    I hooked the jump leads up to my kangoo and fired the van up....no change with the little bloody light.
    I'm at a loss....I can't believe the new alternator has just packed up. Could letting the battery run down do that?
     
  19. Ha! I've had loads of VW's over the years, but have never been any good with electrics....I can't see it, hear it or smell it, but it gives a nasty nip!
    I've just started cleaning things again (I'm good at that!), and have took the connections off the solenoid and cleaned em, I've also taken off the earth strap, and cleaned and scraped everything....the engine starts and runs perfectly, but the light is still there. I'm going to go talk to a bloke near me, who is pretty good....he might be able to come and have a go of the ideas that you have said......I can't get into the back of the alternator....1979, type 4 2.0litre, if that makes any difference.....I'm clutching at straws now!
     

Share This Page