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Technical Where is my voltage going?

Discussion in 'The Hokey Ass Message Board' started by 41 C28, Apr 12, 2015.

  1. 41 C28
    Joined: Dec 17, 2005
    Posts: 1,772

    41 C28
    Member

    I'm only reading a little over 10 volts on my dash volt meter, car running at idle. I even hooked up another volt meter to a different hot source to check the first vm. Same thing and yes I made sure I had a proper ground.
    BUT, when reading voltage at the battery terminal with my old Triplett Meter I get a little over 12 volts. Engine running at idle.
    I disconnected the wire from the "B" terminal on the alternator. Then I could read 14 volts from the "B" terminal on the alternator to ground, engine running at idle.
    I'm running a 318 with the MoPar voltage regulator, the one with the two wire triangle plug.
    So, where is my voltage going ? Do I have a bad regulator ? Will the alternator put out more with no load? Why won't my dash gauge read correctly??????
    The car runs and starts good and I've been driving it like this for a long time but I bugs me to look at that low voltage reading and wonder if my battery will die at a bad time.
    Thanks
     
  2. Hnstray
    Joined: Aug 23, 2009
    Posts: 12,355

    Hnstray
    ALLIANCE MEMBER
    from Quincy, IL

    You could have one or more of several problems. A defective battery or poor connections in any number of places, are the most likely causes, in my opinion. Possibly a regulator problem, but then how does the Alternator 'know' to produce 14 volts? Bottom line, if you have 14+ at the Alt, the problem lies elsewhere and will take a search with voltmeter or ohm meter to track down the connections.

    As I recall, from searching for voltage drop on old VW's, you connect the ground terminal of the voltmeter to battery ground terminal and use the plus lead to check either side of 'hot' connections, starting closest to the battery, and compare voltage readings. That should show a drop within the connection if that connection is poor for any reason. You do essentially the same thing with an ohmmeter using the ohm meter probes across the connection checking for excess resistance within the connection.

    Ray
     
    Last edited: Apr 12, 2015
  3. You probably have excessive voltage drop to the dash gauge. Start by measuring voltage from the positive terminal on the gauge to the positive battery terminal. Any voltage you measure is 'lost' voltage, either through too-small wiring or a poor connection. To pin down just where you're losing it, measure between each point (splice, terminal, switch) starting at the gauge or the switch, checking to the other end. If you see roughly the same drop between each point, all the wire is small. If you see a big drop in one place, then either the wire is small or you have a bad connection. The voltage readings should be small, less than a few hundredths if everything is good. You're losing more, you just need to pinpoint where. Note that the car needs to be running to accurately check this.

    One other thing to try; the wire from the alternator/regulator that connects to the ignition switch, make sure that runs uninterrupted all the way to the switch. This is probably a 'sense' wire, if it's connected too close to the battery, it won't take into account voltage drop upstream from the connection.
     
  4. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,285

    d2_willys
    Member
    from Kansas

    Sense wire is suppose to go to the battery. That way it takes into consideration the drop from alternator to battery. Dash gauge voltmeters should draw very little current. 18 ga wire should be fine for a voltmeter, both hot and ground. Just find a good ground (- of battery is best), then go down the line till you find where the voltage is too low.
     

  5. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    I would start by holding a wire from battery ground cable to the instrument case with car running...I bet you'll see the voltage pop up to 13.
     
  6. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    You may have a regulator that is set low and while it keeps the battery charged it doesn't kick the voltage output of the alternator up like you see on a lot of rigs.
    The alternator Is going to put out what voltage and amps the system demands from it. If you don't have things in the car that draw a lot of amps the battery most likely gets recharged quickly after you start the car and run a few minutes and the alternator loafs along supplying enough power to keep things going but doesn't have to kick out a full 14.2 volts all the time. We are used to seeing the gauge in our late model daily go to work car kick over to 14V because the car/truck has ac, 200Watt sounds system and power everything plus a pair of headlights that draw a bunch of power to turn the road into daylight at midnight and forget that the rod only has headlights and maybe and electric wiper motor drawing power.
    One thing I have found is that not all alternators kick out full voltage at an idle and many need some rpm to be able to kick out full voltage. Even then if there isn't a demand for power in the system the regulator may not call for it to charge more than needed to keep the battery charged and keep the ignition supplied with power to run.

    I'd still go though the system and check for spots that may cause a resistance though. any place where wires connect or the plug at the firewall or grounds for the gauges. If you have full battery voltage here <> and only have 11 volts here() then there has to be a resistance between those points causing the drop.
     
  7. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,285

    d2_willys
    Member
    from Kansas

    Funny, the GM manuals all say to bring sense wire to the battery. Let's say the big wire from the alternator to the battery has a so-so connection on it. The battery charging voltage would then be raised since the sense wire senses a lower voltage at the battery. Sense wires always go from the regulation device to the load destination, in this case, the battery. Madelectrical might want to clarify what they are actually telling us.
     
    Hnstray likes this.
  8. It depends on where the 'main' power junction is, if the wire feeding it is big enough, and what is an 'acceptable' voltage drop beyond that point. And remember, the OEM manufacturers rarely use anything bigger/longer than what's absolutely necessary. Get into an altered or aftermarket harness and the 'OEM' configuration may or may not work. What MAD is advocating will compensate for that...
     
  9. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,285

    d2_willys
    Member
    from Kansas

    Agreed. Fords use the starter relay terminal from the battery. GM used the battery stud at the solenoid, older Chryslers used the starter relay too.
    Aftermarket harness is an unknown as you put it. You still would have to worry about the actual wire coming from the battery to the junction point.

    Here is a scenario that really puts a wrench in the works. Say the main alternator lead goes directly to the battery. But the sense wire goes to a junction point. Now the wire from the battery to the junction point is corroded and has resistance in it. In this case the sense wire would show the drop in voltage and compensate by upping the alternator output. The battery then gets overcharged!

    Next, if the main alternator lead gets connected to the junction point, along with the sense, then that point is voltage regulated. However if the battery to junction lead has resistance, then two things happen: 1) the battery will be undercharged if it is extremely discharged. 2) The vehicle, in all likely hood will have trouble starting. This will throw the mechanic off as it could be a bad battery to him or a bad battery lead.

    This all leads up to confusion for most people that do not understand electricity.
     
    Last edited: Apr 15, 2015
    Hnstray likes this.
  10. 41 C28
    Joined: Dec 17, 2005
    Posts: 1,772

    41 C28
    Member

    Thanks for all the suggestions, I guess I'll start reading out wires and looking for bad connections.
     
  11. Brand Apart
    Joined: Jan 22, 2011
    Posts: 808

    Brand Apart
    Member
    from Roswell GA

    I am 100% certain your battery will not die at a good time. so you are right in original post.
     
  12. garyf
    Joined: Aug 11, 2006
    Posts: 283

    garyf
    Member

    Chrysler charge system sense wire is the ignition switch which is also hooked to the + battery. (1)Be sure your voltage regulator case is well grounded.(2) If you full field your wires at the regulator you should read around 13.9 at the battery. If your readings are 13.9 suspect a bad regulator (3)See if your charge output readings are the same across the battery and at your dash guage, This will tell you if there is a problem between alt. and guage. .(4 ) Also, if you have a 45 amp alternator it may be putting out only 25 amps, due to one of its 3 diodes burnt out. It will keep your battery alive when few acc. are on but when several are needed,a no start. If you can not test for alt. out put. If you remove the alt some parts store may be able to test its output to its rating.
     
  13. 41 C28
    Joined: Dec 17, 2005
    Posts: 1,772

    41 C28
    Member

    Installed a one wire alternator and all is good.
     
  14. n847
    Joined: Apr 22, 2010
    Posts: 2,724

    n847
    Member

    You going to be at the Franklin cruise in a few weeks? My uncle wants us to come down again this year.
     

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