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Hino EH700TiAC sudden charging issue. Drops to 12 v or less during cruising. What is happening

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    Hino EH700TiAC sudden charging issue. Drops to 12 v or less during cruising. What is happening

    Hi, all of a sudden the voltmeter started to drop on the SB engine and fell to 12v during cruising speed. The port engine have had the same issue earlier. It starts at 13.8 volt when adding speed but drops in 3-4 min to 12 v = not charging. I tightened the alternator belts but with no real difference.
    What could be the reason as I cannot find info in the user manual? Where to start looking? The engines have less than 1000 hours on them. On shore power (of course) all works great.
    All help appreciated

    #2
    Do you have the original Denso alternators? I had my stbd alternator cook a voltage regulator, then I put the Golden Wrench trying to install a new voltage regulator. Soooo, I bought a new Delco 140 amp unit and installed it, along with #4 wire, on the port engine because that’s the one that charges the house batteries then installed the former port alternator on the stbd engine. There’s a shop in Everett, Washington that is very familiar with the Denso alternators.
    P/C Pete
    Edmonds Yacht Club (Commodore 1993)
    1988 3818 "GLAUBEN”
    Hino EH700 175 Onan MDKD Genset
    1980 Encounter Sunbridge "Misty Blue" (Sold)
    MMSI 367770440
    1972 Chevrolet Nova Frame off Resto-mod in the garage
    Boating on the Salish Sea since 1948

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    • brad4550
      brad4550 commented
      Editing a comment
      PC....Mag is located in Finland...however they should have an alternator repair shop.

    #3
    Thanks! Yep, got all original. How do I check if this is the reason? Looks like both engines got the same issue now. Could it be loose wires, fround or similar?

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      #4
      Ground...

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        #5
        Strange things... When looking at the voltmeter above the circuit board, it shows that both engines are charging, 14,6-8 volt. But on the dash not at all the same reading. Any ideas. I also found this in the engine room, one of the 2 alternator belts was busted, but as these are two per engine it should not affect the readings, right?

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          #6
          My gauges vary between the lower and upper helm. They are relatively close, but the lower helm will give a low reading, usually the temp, but the upper will be reading much closer to the actual as measured with a laser sensor. After nearly three years of owning this boat, I view it as the expected reading at each station and accept that they are different.
          P/C Pete
          Edmonds Yacht Club (Commodore 1993)
          1988 3818 "GLAUBEN”
          Hino EH700 175 Onan MDKD Genset
          1980 Encounter Sunbridge "Misty Blue" (Sold)
          MMSI 367770440
          1972 Chevrolet Nova Frame off Resto-mod in the garage
          Boating on the Salish Sea since 1948

          Comment


            #7
            One thing to check is there is a oil pressure switch that closes with oil pressure that is on the exciter circuit. If this switch is defective the alternator will not charge. Switch could be failing as the temperature of oil comes up thus the start and stop action of charging.
            Ron O'Blenis
            B 38 175 Hinos 1989
            Completed Great Loop
            https://ronandfaye.blogspot.com/

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              #8
              Ron, sorry, stupid question but what/where is the exciter circuit. Could really be this as it first shows that it charges but slowly drops to 12 v on the dash meter. But still, why does the voltmeter on the circuit bosr still give right charging readings?

              Comment


                #9
                The generator field voltage is derived from the actual battery voltage; lower the battery voltage, more exciting of the generator field is needed to boost the generator output. Some generators have an internal connection for this, you can't do anything about that. Many genberators have a separate terminal where a cable is connected to represent the battery voltage. In many cases boaters take a short cut by taking the output post of the generator and using a short cable feed that to the sense input of the generator. It is assumed that since the output post is connected directly to the battery positive post this is the right thing to do. Well, it is not! Corrosion, poor connection, long cable run and heavy charging current flowing through that cable causes a voltage drop at the battery end but the alternator sees some value above that.

                It is possible that
                a) the battery is nearing its end of life so its output drops when not being charged, and
                (b) due to voltage drop alonng the charging cable the battery is not being properly charged.

                Check if you can spot a short wire going from the generator output to the sense input on tge alternator. If it is there, remove its end from the alternator's output post and using a longer cable connect the sense post directly to the battery positive post.

                Good luck
                Retired, computer expert / executive
                Bayliner 285 Cruiser / Mercruiser QSD 4.2L 320 HP Diesel
                Live in the Bay Area, CA, USA, boat in Turkey
                D-Marin @ Turgutreis in Bodrum/Turkey
                bdervisoglu8@gmail.com
                bulent@pacbell.net

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                  #10
                  I checked the alternators on both engines and both deliver abt 14volts staedily. So why does the dash cauges on both flybridge and inside only show 12v/ not charging. Where to start looking? Thanks.

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                    #11
                    Anything else kicking on on your DC circuit that draws a load will show the lower voltage readings.... Your DC powered fridge has been known to cause voltage flux.. etc etc..

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