losing 1 volt on gauge with E waterpump andfans on

General Mopar Tech Discussions

  1. Bluefish

    Bluefish Well-Known Member

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    Would it be normal to lose .5v when you turn on your electric water pump and another .5v when the dual spal fans come on? fans are 20a units and the w pump is 5.5a. Using a one wire denso alt from a Toyota 4runner. I think the alt could be a 100a unit, but may be as little as an 80amp unit. Brand new optima blue top with 1gauge wire to starter. Idling with all accessorys off gauge reads 14.2v. Electric fuel pump makes no difference to volts when turned on. Gauge reads 13.1 with lights and all acc on.
     
  2. toolmanmike

    toolmanmike Moderator Staff Member FBBO Gold Member

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    Normal .Pretty good at idle.
     
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    • Bluefish

      Bluefish Well-Known Member

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      Good to hear that. No worrys here.
       
    • 67Charger

      67Charger FBBO Gold Member FBBO Gold Member

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      One-wires will do that. They can only regulatre to the voltage they see, which is at the output terminal. Something with a sense circuit will read the voltage remotely, like at the fuse panel, and adjust to that. I run a GM CS130 alt with the sense tied to a fuse off the main fuse panel. It keeps the voltage very steady at 14.2 - 14.5 unless the circuit draws more amps that it can output.
       
    • toolmanmike

      toolmanmike Moderator Staff Member FBBO Gold Member

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      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

      This.
       
    • Bluefish

      Bluefish Well-Known Member

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      I played with this again yesterday using a voltmeter and meturing battery voltage to compare with my autometer volt gauge. I found I had 14.2 volts with all acc off. Turn on the water pump and voltage dropped to 14.0 on my VM and 13.8 on my autometer gauge. Turn on dual electric fans and voltage dropped to 13.2 on VM and 13.0 on autometer gauge. I'm trusting my volt meter. Either way, looks like my battery should stay charged just fine.
       
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      • 67Charger

        67Charger FBBO Gold Member FBBO Gold Member

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        What is the voltage at the alt output stud with all of that on?
         
      • toolmanmike

        toolmanmike Moderator Staff Member FBBO Gold Member

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        Yes your battery will stay charged. A little over idle and the voltage will come up. I had the same thing with my tool truck especially with the engine driven a/c on. A/c compressor running, 2 a/c units running on high blower speed and all the interior lights on. It was pulling more current than the alternator could produce at an idle. I wired in a A/C solenoid to kick the idle speed up and it made quite a difference. You will find even a few hundred rpm will make a difference. Both of my cars do the same thing, idling with the lights, blower, and say wipers too. The alternator just can't produce that much current at idle.
         
        Last edited: Mar 25, 2020 at 9:32 AM
      • Bluefish

        Bluefish Well-Known Member

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        I believe it was 14.2 last time I checked. I will check again to be sure.
         
      • Bluefish

        Bluefish Well-Known Member

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        I use small pulleys on everything, so everything spins pretty quickly.
         
      • 67Charger

        67Charger FBBO Gold Member FBBO Gold Member

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        If that's the case, it looks like you have sufficient amps available, since the alt output isn't dropping voltage. Just volt loss from load downstream. That's where the sense circuit alts shine. Either way, you're still fine. One wires tend to have good idle output once you get them to kick on.

        Sorry if this is too elementary, but it is actually an easy to understand analog.

        Think of it like fuel and a pressure regulator. One-wires are like regulating fuel pressure at the pump, but the actual pressure at the carb is whatever is left after all the drains on the system (small hose, filter, hose length, nitrous fuel solenoid, etc). A sense-circuit alt is like regulating after the carb with a return system. Everything before the regulator is at the same pressure and the excess is bled off as return fuel to the tank. as long as the pump puts out enough volume to maintain pressure, the pressure remains constant. If the demand is higher than the pump's ability to maintain that volume at that pressure, there will be no excess and the pressure will drop to a point it can maintain volume at the new pressure. Now substitute Volume with Amps, and Pressure with Volts.

        Technically, it's more like a PWM fuel pressure controller with a sensor on the fuel rail, but we'll leave that alone.
         
      • Bluefish

        Bluefish Well-Known Member

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        Yep, I understand. I'll know more once I get driving it. Thanks guys.
         
      • Bluefish

        Bluefish Well-Known Member

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        I measured 14.0 at the alt output with all acc on.
         
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