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    Diesel Engine RPM Readings via Alternator-gctid358624

    I have run into another situation with various options available and I'd like to get feedback. The build on the Perkins 4.108 I'm using for my repower is not fitted with a mechanical tachometer port near the flywheel. I'm left with the option of either taking RPM readings from the alternator or installing a magneto sensor on one of the pulleys. I'd rather avoid the magneto sensor option all together.

    I did come across this primer on taking RPM readings from an alternator but there are some noted disadvantages.

    As far as the easiest way to do this, I found this unit from Autometer, which has a sender that attaches to the alternator via a hose clamp. There is also another unit available from Teleflex that takes readings from the wire, as opposed to attaching a sender to the alternator.

    What are your thoughts on taking RPM readings from an alternator? Are there better options for Diesel engines? If anyone has experience with this, I'd be interested in receiving some feedback.

    Thanks in advance.

    #2
    Ed, I spent a few years as a heavy equipment manufacturing mechanic. There were occasions and installations were we used the alternator to pulse the tachometer.

    Both the Alternator and the Tachometer must be correct for this type of usage.



    If you want more accuracy, I'd use the Hall Effect flywheel triggering system.

    There may even be a photoeye sensing system available today!
    Rick E. Gresham, Oregon
    2850 Bounty Sedan Flybridge model
    Twin 280 HP 5.7's w/ Closed Cooling
    Volvo Penta DuoProp Drives
    Kohler 4 CZ Gen Set

    Comment


      #3
      there are also pulse pickups that clamp onto one injector pipe. The sensor feels the pulses in the line.



      http://www.tinytach.com/tinytach/diesel.php

      Comment


        #4
        auto meter via alternator on my cummins deadly accurate...:rif-

        Comment


          #5
          Does your engine have a threaded hole for a magnetic pickup on the bellhousing?

          KEVIN SANDERS
          4788 LISAS WAY - SEWARD ALASKA
          www.transferswitch4less.com

          where are we right now?

          https://maps.findmespot.com/s/36S4

          Comment


            #6
            Kevin, I was wondering that myself.

            Do you know if a photo eye sensor/tachometer of some sort is available for this application?
            Rick E. Gresham, Oregon
            2850 Bounty Sedan Flybridge model
            Twin 280 HP 5.7's w/ Closed Cooling
            Volvo Penta DuoProp Drives
            Kohler 4 CZ Gen Set

            Comment


              #7
              2850Bounty wrote:
              Kevin, I was wondering that myself.

              Do you know if a photo eye sensor/tachometer of some sort is available for this application?
              Exactly

              A magnetic pickup will put out a 2 volt pulse for every flywheel tooth. This will work with the tach.

              I'm being very careful here. Remember the fuel shutoff thread? I tried to apply industry standards to the problem and this particular engine did not meet those standards. I don't want to give out advice only to find it inaccurate on this application. :arr

              KEVIN SANDERS
              4788 LISAS WAY - SEWARD ALASKA
              www.transferswitch4less.com

              where are we right now?

              https://maps.findmespot.com/s/36S4

              Comment


                #8
                Kevin, I was thinking more along the lines of a single hall effect sensor that would require one magnet placed in the flywheel....... or I suppose it could be several magnet units.

                Or... in the event of Photo Eye.... one single window that would disrupt the light beam.... or I suppose it could be several windows.

                You'd certainly know more about this than I would.

                I'm thinking that the alternator may be the simplest means. Yes/No???

                .
                Rick E. Gresham, Oregon
                2850 Bounty Sedan Flybridge model
                Twin 280 HP 5.7's w/ Closed Cooling
                Volvo Penta DuoProp Drives
                Kohler 4 CZ Gen Set

                Comment


                  #9
                  Thanks everyone for chiming in. Here is a video describing the alternator pick-up and its installation:



                  ksanders wrote:
                  Does your engine have a threaded hole for a magnetic pickup on the bellhousing?
                  Unfortunately, the build on my engine never included it. I looked all over the vicinity of the flywheel and couldn't find anything resembling a tachometer connection. After contacting Perkins, I was told many of the earlier builds did not include it.

                  2850Bounty wrote:
                  Kevin, I was wondering that myself.

                  Do you know if a photo eye sensor/tachometer of some sort is available for this application?
                  A photo eye sensor is going to be far more accurate than taking RPM's from the alternator. I looked carefully but could not find a permanent photo eye tachometer for this application. The only photo eye units I found were handheld test units. In fact, I bought one for calibrating whatever tach option I end up with.

                  ksanders wrote:
                  Exactly

                  A magnetic pickup will put out a 2 volt pulse for every flywheel tooth. This will work with the tach.

                  I'm being very careful here. Remember the fuel shutoff thread? I tried to apply industry standards to the problem and this particular engine did not meet those standards. I don't want to give out advice only to find it inaccurate on this application. :arr
                  Kevin, I find your advice very useful and appreciate it. The advice you gave me about the engine shut off prompted me to explore it further and learn something new about my engine. If there is an industry standard that is not consistent with my engine's design, that knowledge is extremely valuable.

                  Comment


                    #10
                    Astral Blue wrote:
                    Thanks everyone for chiming in. Here is a video describing the alternator pick-up and its installation:



                    Unfortunately, the build on my engine never included it. I looked all over the vicinity of the flywheel and couldn't find anything resembling a tachometer connection. After contacting Perkins, I was told many of the earlier builds did not include it.

                    A photo eye sensor is going to be far more accurate than taking RPM's from the alternator. I looked carefully but could not find a permanent photo eye tachometer for this application. The only photo eye units I found were handheld test units. In fact, I bought one for calibrating whatever tach option I end up with.

                    Kevin, I find your advice very useful and appreciate it. The advice you gave me about the engine shut off prompted me to explore it further and learn something new about my engine. If there is an industry standard that is not consistent with my engine's design, that knowledge is extremely valuable.
                    Thanks Ed...

                    Your new engine just threw me for a loop. It appears to be a old engine that was marinized specifically for the sailboat industry. Its just a bit challenging because we tend to throw out suggestions based on what we work on, and much of my experience is with generator sets. The magnetic pickup feeding a tachometer is another example. On a generator set I would use a engine controller that uses the AC from the generator end, if a magnetic pickup port was not available.

                    Here's a thought. You might give the nice folks at Aetna engineering a call. They make one of the best, most reliable tachometers on the market, its really all they do. They could probably help.

                    Here's a link to their web site

                    http://www.aetnaengineering.com/default.asp

                    KEVIN SANDERS
                    4788 LISAS WAY - SEWARD ALASKA
                    www.transferswitch4less.com

                    where are we right now?

                    https://maps.findmespot.com/s/36S4

                    Comment


                      #11
                      Ed, you're no doubt wanting a 3" diameter tachometers in order to fit your instrument panel... yes/no?

                      If you can pulse these tachometers (Kevin????), I have two nearly new, matching Datcon p/n 100245, SS besel, 3" round, adjustable for A, B, 4, 6 and 8 cylinder, 0-4k tachs with hour meters in them.

                      One is @ 70 hrs, the other @ 78 hrs.

                      They look similar to this, but w/ SS besels, 0-4K, and with hour meters.



                      Can you use these?

                      BTW, since you are now diesel, I have an older Chrysler 100 amp automotive alternator that is in excellent working condition. I'd be glad to donate to the cause.

                      With diesel, I believe that it meets requirements.

                      Edit:

                      Looks more like this one, but ranges from 0 to 4k.


                      Rick E. Gresham, Oregon
                      2850 Bounty Sedan Flybridge model
                      Twin 280 HP 5.7's w/ Closed Cooling
                      Volvo Penta DuoProp Drives
                      Kohler 4 CZ Gen Set

                      Comment


                        #12
                        I built a tachometer/run time meter (microprocessor based) with an output from the altenator. I broke into the altenator, and picked up the waveform pre-diode. This yeilded a 15v square wave which worked very well as a rpm base.

                        I wouldn't really suggest this route though. It should be easier to pick the AC waveform off the DC via a capacitive coupler (Or high frequency transformer using the output lead as the primary), then amplify it, send it to a switch and you have your tach waveform. This is probably how the clamp on style ones work.

                        Either way, the altenator will have to be 'online' to get the signal. If you have one of those altenators which are self priming, it may take a quick rev up to get your altenator, and thus tach, working.

                        As previously said, the tach has to be compatible with the input signal. For example, some old tachs require 30+ volts to trigger (typical primary inductive kickback from a inductive coil style ignition). The newer ones can use a far greater range of voltage.

                        Chay

                        Comment


                          #13
                          cfoss wrote:
                          I built a tachometer/run time meter (microprocessor based) with an output from the altenator. I broke into the altenator, and picked up the waveform pre-diode. This yeilded a 15v square wave which worked very well as a rpm base.

                          I wouldn't really suggest this route though. It should be easier to pick the AC waveform off the DC via a capacitive coupler (Or high frequency transformer using the output lead as the primary), then amplify it, send it to a switch and you have your tach waveform. This is probably how the clamp on style ones work.

                          Either way, the altenator will have to be 'online' to get the signal. If you have one of those altenators which are self priming, it may take a quick rev up to get your altenator, and thus tach, working.

                          As previously said, the tach has to be compatible with the input signal. For example, some old tachs require 30+ volts to trigger (typical primary inductive kickback from a inductive coil style ignition). The newer ones can use a far greater range of voltage.

                          Chay
                          This makes sense. I had a chance to read people's accounts of taking RPM's off the alternator and on more than one occasion heard a mention of receiving no readings until the alternator becomes live. This can pose a problem in a number of areas -- as I will likely not receive a RPM reading until it is excited. It's not a big deal, but something I'd rather avoid all together if possible. If I can get an optical sensor and take the reading off a pulley, it would be ideal. Also, using an optical sensor to convert the signal into an analog one to allow it to be used with my existing analog tachometer would be great too, lol. But I think I'm wishing for too much here.

                          Comment


                            #14
                            This subject isn't exactly my cup of tea, but a quick search came up with these tidbits....

                            http://www.4crawler.com/Diesel/Cheap...er/index.shtml

                            http://www.tinytach.com/tinytach/diesel.php

                            This one may be just the ticket, Ed:

                            http://www.dieseltruckresource.com/d...l-t236340.html

                            http://www.dakotadigital.com/index.c...rod/prd129.htm

                            Hope these help!

                            Comment


                              #15
                              Pau Hana wrote:
                              This subject isn't exactly my cup of tea, but a quick search came up with these tidbits....

                              http://www.4crawler.com/Diesel/Cheap...er/index.shtml

                              http://www.tinytach.com/tinytach/diesel.php

                              This one may be just the ticket, Ed:

                              http://www.dieseltruckresource.com/d...l-t236340.html

                              http://www.dakotadigital.com/index.c...rod/prd129.htm

                              Hope these help!
                              Thanks, Pete! I really appreciate the effort you put into this. I'm going to call the guys at Dakota Digital tomorrow. This seems to have pretty good potential and is worth looking into. The price is very reasonable as well!

                              Comment

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