Announcement

Collapse
No announcement yet.

Alternator or batteries - duff or not?

Collapse
This is a sticky topic.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Alternator or batteries - duff or not?

    A fairly common question asked here, and one that seemingly few people have a grasp of, opening up the likelihood of them being shafted by their local 'friendly' garage, so if I may, I'll try to remove some of the confusion.

    The charging system and batteries are very easy to check with a basic multimeter or voltmeter available cheaply from Maplin. This will do fine, for £8 you really should have one.

    So, basically, a quick and dirty check of your batteries. After the truck has stood for a while (overnight for instance) measure the volts at the battery terminals. It should be at or slightly above 12V. Stick your lights on, The voltage shouldn't drop significantly. This is a quick and dirty method. A specific load and a specific voltage drop is more accurate, but this will give you an idea.

    Right, your batteries are going flat overnight and the garage want to sell you an alternator for £300. It is FAR (really, far-far even!) more likely to be the batteries are shagged and wont hold charge. To check, start the engine and switch in 'idle up'. Check the voltage at the batteries. It should be approximately 14.4V. little bit over or under is OK. Stick your lights on. Once again, the voltage shouldn't change much. If this is so, your alternator is fine. You can also try switching on everything you can find step by step, and check your voltage holds up under maximum load.

    Another way of doing this for those more au-fait with electrical systems is to use a current clamp like this on your main battery +ve, start the engine and note the sign of the current flow (it will be +ve or -ve depending which way round the clamp is). Now start adding load, noting when (or if) the sign changes. This is the point at which you'll start to drain your battery, so keep the load under this amount, you power hungry maniac! Lots of huge spot lamps or enormous stereos can do this.

    Hope this is useful - it's certainly not hard, or expensive.
    Last edited by Apache; 24th December 2012, 22:39.
    Cutting steps in the roof of the world

  • #2
    Thanks for the post Apache.

    When I followed similar instructions I thought I was reading a faulty alternator as the reading only drained even with the engine running.

    I foolishly went to a garage I had never used before and although I wasn't ripped off financially, they did rip me off by saying the charging system was fine which ultimately lead to a very inconveinient fail to start.

    I would like to add that this test is very very very easy to do (I managed it) but if the readings show the alternator not to be working, don't panic until you have checked the belts.

    All my truck needed was for the belt tension to be adjusted (my mechanic guy did it for petrol/beer money) and now I have a fully working charging system, with some new belts planned for installation in January for a lot less than the £300+ the dubious garage may have wanted to rip you off for a new alternator.

    There are ways for testing the alternator directly but I havn't tried this.
    Leaky Surf

    Comment


    • #3
      Yeah, that's why you need to load up the system when checking, as a loose belt will probably look ok off load but will slip under load.

      Glad you got sorted at minimal cost.
      Cutting steps in the roof of the world

      Comment


      • #4
        I'll also throw earths into the discussion. Dirty, loose or corroded earth leads or connections can lead to a fairly significant voltage loss which might trick you into thinking your alternator or batteries are duff.

        Keep 'em clean and protected with a blob of grease

        Comment


        • #5
          Originally posted by Apache View Post
          Yeah, that's why you need to load up the system when checking, as a loose belt will probably look ok off load but will slip under load.

          Glad you got sorted at minimal cost.
          how do you adjust the tension of the belt and how tight should it be?

          Comment


          • #6
            There is a download available out on the net (bit like a Haynes Manual but not) and that gives the belt tension figures. I have it somewhere so when I get a chance I will post the figures.

            When my mate tightened my belts, he seemed to be adjusting something on the left side of the alternator. He should be round in the next couple of days so I'll get him to show me and I'll get a picture posted of the bit to fiddle with (unless someone gets there first.
            Leaky Surf

            Comment


            • #7
              Originally posted by Mark7081 View Post
              There is a download available out on the net (bit like a Haynes Manual but not) and that gives the belt tension figures. I have it somewhere so when I get a chance I will post the figures.

              When my mate tightened my belts, he seemed to be adjusting something on the left side of the alternator. He should be round in the next couple of days so I'll get him to show me and I'll get a picture posted of the bit to fiddle with (unless someone gets there first.
              on the 2.4 the adjuster is at the bottom of this pic under the AC compressor. hope thats of some use.
              A

              apologies for not rotating that, windows 8 is doing my head in!

              oh and there's a bolt through the bracket on the rod to loosen, not in the pic obviously.
              Attached Files
              Last edited by andyverran; 24th June 2013, 23:11.

              Comment


              • #8
                A good write-up. My batteries seem to be alright checking with a multimeter but I am getting a voltage drop when i drive with my lights on. Getting to as low as 8v sometimes. Worryingly it causes the temperature gauge to go up.

                I am going to get another alternator seen as it makes no difference running on one battery and it always starts in the morning even on just the one 580Ah.

                Comment


                • #9
                  I may be stating the obvious here but just to add........any amount of corrosion (oxidation) between the terminal posts & clamps will cause resistance & loss of electrical efficiency, particularly noticeable when most needed such as first thing in the morning during those cold winter months (as an analogy think; driving with the handbrake on) - now that I think about it, I doubt it's going to do the alternator much good either.

                  I've always protected my terminals with Vaseline (something that had been passed down from my Grandfather), however this will dissipate in time, particularly when hot.

                  local guys/friends at the dock absolutely swear by 'ASG Ultimate' on their batteries - that has to be good advice as they're working in a marine environment.

                  http://www.ebay.co.uk/itm/New-ASG-Ul...9#ht_550wt_932

                  .

                  Comment


                  • #10
                    Bit of a thread bump but what if things were going the other way - battery reading 15.2v at idle for instance ?

                    Comment


                    • #11
                      Originally posted by Paulpen View Post
                      Bit of a thread bump but what if things were going the other way - battery reading 15.2v at idle for instance ?
                      The voltage regulator on the back of the alternator is goosed!

                      Comment


                      • #12
                        Originally posted by BUSHWHACKER View Post
                        The voltage regulator on the back of the alternator is goosed!
                        Thats along the lines I was thinking but turned out my multimeter battery was goosed

                        Comment


                        • #13
                          puzzled

                          Any ideas on this would be very welcome.
                          I parked the left front in a pond overnight.
                          Once dragged out by the local farmer, the ecu was trashed.
                          Replaced it, and it starts fine, no flashing lights but the usual ones are on for a duff alternator.
                          Batteries are fine (one had discharged under the water, but is holding a charge fine), but only getting battery voltage at the terminals when running.
                          I changed the alternator, but the problem is still there.
                          There's the chance I've got a duff one, but can anyone think of what else it could be?
                          Thanks!

                          Comment


                          • #14
                            It turned out to be a big grey connection just in front of the fuse box. WD40, sorted.

                            Comment


                            • #15
                              Really useful info here - thanks.
                              Iíve just checked my battery and itís reading 12.36v with the vehicle off. Once the engines started it climbs up to 13.8. Itís about the same with the lights on. Is 13.8 too low for the alternator to be working correctly?

                              Im having a few electrical bugs such as the dash lights not illuminating (the backing lights on the dials, not the warning lights). The passengers electric window operates every now and then and the radio sometimes cuts out.

                              Is it likely the small difference between 13.8 and the recommended 14.4 is causing this?

                              Thanks

                              Comment

                              Working...
                              X