? Volts or Millivolts on Negative/Ground ?

Discussion in 'General Electronics Chat' started by OhmBoy, Jul 16, 2013.

  1. OhmBoy

    Thread Starter New Member

    Jul 16, 2013
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    Hello, I'm new (first post).
    I bought a old motorcycle and the Ignition "Ignitor" was blown. I bought another Ignitor from Ebay but it too was either blown or I blew it. I checked the wiring with my Multimeter and I had 1.5 volts on the Negative/Ground. After unplugging the Turn Signals and everything else on the circuit except the Ignition/Ignitor I still get .5-.7 Millivolts on the ground. If I touch the positive lead with my finger I get a additional .5 millivolts. Therefore, I'm thinking a few millivolts are ok. Am I correct ?
    Also, is it possible to put a Diode or some kind of circuit breaker on the ground to keep power from entering the Ignitor on the negative side ?
    Thanks
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    1,605
    It sounds to me that your ground is not a good ground. The battery terminal is (almost by definition) a perfect ground and I would expect other remote points to be within 50 to 100 millivolts of the battery. 1.5 volts sounds like some corrosion has gotten into your connections.

    (Don't ask for any automotive modifications here, they are not allowed period. However, a straight repair may be acceptable to those with the power to close threads.)
     
  3. OhmBoy

    Thread Starter New Member

    Jul 16, 2013
    8
    0
    Thanks
    So, is there something I can put on the negative wire to prevent a reverse surge ? There is a 10amp fuse on the positive side but since only 1volt (give or take) seems to be on the negative side, what would I put on that wire ?
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    It's hard to say where your spikes are coming from, but if you have a bad ground it is very likely that you are getting currents going places they shouldn't. You need to solve your ground problem. Unplug things one at a time and see which one (or ones) are causing the ground to rise up so much.
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Things that make ground rise up are not the problem: it is the UP itself that's the problem.

    A well connected ground should not rise in any appreciable amount even for the largest devices on the bike. You should rather turn ON the devices that cause ground to rise up and see where the rise occurs.

    A coworked of mine called another when his bike would not start last week, and he fixed the bike by removing a pair of metal body diodes (I know not what they did) and used the curb to rub a clean bright spot, put them back and the bike ran again.

    Corrosion can work its way between metal surfaces and it's the killer of good connections.
     
  6. OhmBoy

    Thread Starter New Member

    Jul 16, 2013
    8
    0
    ErnieM
    If I understand you correct, you said its ok to have around 50-100 Millivolts on the negative side.
    Guys, I've already unplugged everything on the circuit except a relay and the starter. Thats why I'm asking is it normal to have .5 millivolts on the negative wire so I know for certain if they are a issue. I've always been under the impression that negative is supposed to be absolute zero voltage/millivolts. I'm not a expert by any means. The more I play with the multimeter I realize my human body/ skin (me) is putting off about the same voltage (.5millivolts).

    Still, can I get straight answer if I can put a circuit breaker or some type of voltage inhibitor on the negative wire to prevent reverse surge ? A Diode preferably.

    THANKS !
     
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