’93 15hp electric start issue

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  • June 29, 2016 at 1:23 pm #39228
    johnyrude200
    Participant

      Are there any methods/tools to carry this out beyond a simple multimeter and logical process of elimination?

      June 29, 2016 at 2:20 pm #39230
      fleetwin
      Participant

        US Member

        I remember learning about the voltage drop test in OMC training, but being completely stumped as to how/why it worked. Years later, I think it makes sense to me. It is important to perform these drop tests just as outlined in the manual to avoid false conclusions and replacing expensive parts needlessly. In this case, my money would have been on that "CPS" switch, but the problem could have been something as simple as a corroded cable or lousy connection somewhere. The voltage drop tests, when performed properly, can isolate each cable and connection….
        Before doing the voltage drop tests, it is very important to verify battery condition (load tests), and starter condition. In this case, Joel verified that the starter was OK by hardwiring it to the battery and it worked OK.

        June 29, 2016 at 3:06 pm #39235
        johnyrude200
        Participant

          I followed the test procedures as outlined in the service manual (ran through the same sequence withoit the manual and ran into the issue, then used the service manual progression…somewhat common sense approach IMHO).

          I admit I usually only fall back to the service manual when running into either a new situation or an oddball one, and have not read the thing(s) cover to cover.

          Have I overlooked any section explaining this voltage drop test or was this something taught at the OMC schools? Id love to have gone to one of these schools.

          Ive considered going to the new BRP ones and paying my own way (used to do this in my prior career teaching physiology/biomechanics), but dont think there would be a huge amount of utility in todays schools of computerized EMM training compared to old carbureted motors.

          Principles Im sure are the same, but application totally different. The reality is that Ill end up having to learn the new stuff to stay relevant because in 20 years selling these older motors is going to get difficult, and todays technology will be yesterdays news and be sold used much like what I deal with everyday now.

          June 29, 2016 at 4:34 pm #39238
          fleetwin
          Participant

            US Member

            Yeah, attending current BRP training would not help with the engines you/we are working on. Needless to say, BRP has little/no interest in carbureted engine produced by OMC years ago. I’m pretty sure the voltage drop test is outlined in most of the OMC manuals of the late 80s/90s era for engines that had electric start.
            Go to the electrical section of the manual, and look for the voltage drop test in the chapter outline/table of contents. Like I say, the tests will seem very strange, and the methodology will make no sense (at least didn’t to me), but it works and all but eliminates the usual guess work when troubleshooting 12 volt cranking problems. The key to understanding how the tests work is in the terminology itself: "voltage drop test". You are simply measuring the difference in voltage potential between the two ends of a cable/wire, or the two sides of a connection.
            Again, it is very important that the tests be performed exactly as they are written to avoid false conclusions or a damaged volt meter!

            June 29, 2016 at 7:41 pm #39246
            frankr
            Participant

              US MEMBER PAY BY CHECK

              Don’t let the term scare you. The biggest challenge is knowing what is "normal" so you recognize a defect when you see it. Voltage drop may be thought of as a reduction of voltage because of resistance in the circuit. I’ll try to give a quikie lesson here.

              Refer to the hasty diagram. Notice we have the battery, two cables, a push button start switch and the starter, all in a string (in series). As far as this example goes, the resistance between the battery and starter is the sum TOTAL of all the individual resistances in the string. Everything has some resistance, but in this case the resistance of all the parts would be so low we can assume it to be zero. If it is zero total, we can expect the voltage coming out to be the same as voltage going in.

              So, what do we know here? We know the starter is good because it works with a jumper cable. For the same reason we know the ground circuit is reasonably good. So, let’s check the supply circuit.

              With a voltmeter connected between test points 1 and 8, and the start button pushed, we expect to see 12V at the starter. But the test showed little or no voltage at the starter. That means there is a high resistance in the string. We can test the voltage drop across any two test points, as convenience allows. Let’s put the voltmeter leads between test points 4 and 5 (the switch). We expect no voltage drop (0 Volts) when the switch is closed because we expect no resistance through the switch. But Aha! We get 12 Volts drop because there is a very high resistance through the switch. That means either the switch is not closed, or it is burned up. In this case, it was burned up.

              You can do the same thing anywhere along the line. For instance you can check the drop on everything between test point 1 and 7 by connecting the voltmeter between those two points. As before,we expect 0 Volts because we expect zero resistance. A real handy test would be between test points 1 and 2 (the cable connection to the battery post). We expect 0 Volts drop because we expect zero resistance. What if we get 8 Volts drop?? Dirty, corroded, or loose cable connecton causing high resistance. That’s 8 Volts wasted through the resistance and only 4 left to run the starter (12 – 8 = 4)

              Clear as mud???

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