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  • Low alternator voltage in hot weather

    Hi Guys

    I searched the forums but couldn't find anything relating to experiencing low alternator voltage during hot weather.

    The background is that I had trouble with my fridge over Christmas/New Year. After a couple of days I got the voltage drop light & it wouldn't run properly. I discovered the second battery (deep cycle charged via Redarc isolator) wasn't charging properly.

    In order to keep any eye on what was going on I fitted two voltmeters in the cabin with an LED off the isolator so I know when it was connecting the batteries (or not!). I also got one of the voltage boosting diodes.

    Generally the alternator outputs enough to trigger the isolator to join the batteries although I think the output is a bit low. Often around 13.6-13.8V with a hot engine during 'normal' weather.

    Over the last patch of hot weather, ie 35-39DegC, I found that the voltage would drop considerably. Down to 12.5-12.9 when running around town. This is with the extra 0.5V voltage boost. This is too low to kick the isolator into joining the batteries & was undoubtedly the cause of my fridge woes - just not getting enough voltage to trigger the isolator keep the second battery properly charged.

    I've read lots about the low charging voltage of the Prado alternators but don't know if my issue is consistent with what to expect or whether my alternator is crook.

    I spoke to two auto-sparkies today, one said I may need a new alternator (something like $700!), the other didn't have much of an idea & said he'd need to run some tests to find out what's going on.

    Is there anything I can do to maintain a higher voltage during hot weather?
    Is it likely that my alternator is crook & will a new one fix the problem?

    All ideas & assistance appreciated.

    Cheers

    Craig
    ______________________________________________________________________
    August 2008 D4D Auto, Grey, Uniden UH-013 UHF, custom cargo shelf, colour-coded ARB Sahara bar, Hella Rallye 4000 Compact 55W HID driving lights, dual batteries, LOUD Stebel air-horn, in-betweeny roof racks

  • #2
    Hi Craig,

    If your alternator voltage is getting down to 12.5V with the booster fitted I'd say
    you have an issue with your alternator. Assuming you have checked the batteries out
    and their ok try turning on your headlights, aircon & rear screen demister when the
    engine is cold. If the alternator can maintain around 14.0V volts then it is most likely
    a thermal fault with the voltage regulator.

    If the alternator can't hold the voltage with cold engine bay then again could be the regulator,
    brushes or faulty rectify diode/s in the alternator etc.

    Cheers
    Leigh
    HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

    Comment


    • #3
      Have not experienced it with a Prado but earlier Corollas we had to uprate the alternators as on really hot days they would just stop charging altogether, you could have them under load with everything on and they would charge fine then after about 5 mins you could watch the voltmeter suddenly flick as the alternator shut dowm and then the car would run only on the battery until the whole show just stopped. IIRK the originals were Bosch but only 60 amp and when we fitted the 80 amp off another model all was fixed permentantly.

      I must admit I was surprised when I found the Prado only comes fitted with an 80 amp Alt.

      Cheers Rick

      Comment


      • #4
        what condition are your batteries in, your main battery may have a problem?
        Also because its relative easy to check, make sure you have good earth connections on battery and alternator.
        stepped up the a 200 LC for towing,
        but had a 2012 and 2010 150 Prado GXL auto diesel in Graphite with Bridgestone D697 A/T. Dobinson C59-300/325 and Bilsteins. Accessories : two baby seats. Sidewinder`s Dual Battery isolator and rear power outlet kit. Pirana Battery tray, Hayman Reese towbar with Toyota wiring kit and Brains`s guard.

        Comment


        • #5
          Hi guys

          Thanks for the replies.

          I checked the earths of both batteries & appear good to me.

          The main battery is the original jobbie (October 2008 D4D). Second battery is a deep cycle which would be maybe 2-2.5 years old.

          I charged both batteries fully last weekend (using my nice new CTek MXS15!) & ran some voltage measurements before going out this morning. Here are the results.

          Stone cold engine before starting the car this morning - air temp about 29DegC, measured with multimeter across batteries
          Main: 12.18V
          Aux: 12.31V


          Engine start - no accessories on, 1500rpm, Isolator had joined batteries & measurement from internal voltmeters fitted to dash
          Main: 14.0V
          Aux: 13.7V

          Cold engine - headlights; a/c; rear a/c; rear demister all on, engine 1500rpm, internal voltmeter again (isolator had dropped out)
          Main: 12.3V. Then after less than a minute dropped to 12.1V then steady at 12.0 V
          Aux: 12.5V

          After a minute or so the main rose to 13.1V. Don't know why.

          At idle with all accessories on main dropped to 11.9V then to 11.5V

          Driving around with only the front a/c on the main battery was reading about 13.5V & the isolator was linked.

          Hot engine with all accessories on, 1500prm, isolator was still connected
          Main: 13.0
          Aux 12.8V

          So, IMO certainly looks like the alternator isn't charging properly.

          Does it look like I need a new alternator?

          If so, is the genuine one the best or are there aftermarket options?

          Cheers & thanks

          Craig
          ______________________________________________________________________
          August 2008 D4D Auto, Grey, Uniden UH-013 UHF, custom cargo shelf, colour-coded ARB Sahara bar, Hella Rallye 4000 Compact 55W HID driving lights, dual batteries, LOUD Stebel air-horn, in-betweeny roof racks

          Comment


          • #6
            The rise after a minute could be attributed to the glow plugs turning off though
            they usually don't stay on for that long.

            I looks like the voltage regulator in the alternator is faulty, you could change the regulator
            if you can get one for a reasonable price. If car has done a lot of K's or you can't get a
            cheap regulator would probably be best to fit a new alternator or get a reco unit from
            Toyota.

            Cheers
            Leigh
            HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

            Comment


            • #7
              Has anybody fitted a higher A alternator to a D4D? I did this with my GQ but there wasn't much electrickery in the old TB42.
              [url=http://www.myswag.org/index.php?topic=12264]My Prado[/url]

              Comment


              • #8
                Thanks Leigh

                It was probably less than a minute & likely to be the glow plugs turning off as you mentioned.

                I'll search for a voltage regulator & see how that goes.

                Cheers

                Craig
                ______________________________________________________________________
                August 2008 D4D Auto, Grey, Uniden UH-013 UHF, custom cargo shelf, colour-coded ARB Sahara bar, Hella Rallye 4000 Compact 55W HID driving lights, dual batteries, LOUD Stebel air-horn, in-betweeny roof racks

                Comment

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