Announcement

Collapse
No announcement yet.

Testing a Model A Coil

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Testing a Model A Coil

    I am looking for some guidance on testing a 6 volt coil with an analog meter. I presume side post to side post will check the primary windings but what should be the setting on the analog meter and what range of numbers constitute an acceptable reading? Almost the same question with regard to checking the secondary windings. I presume side post to center is proper but which side post and what constitutes an acceptable range? Finally, where should my meter be set for each test. Thanks a lot.

  • #2
    Simple, plug it in, see if it fires. If you are taking your VOM to the swap meet and checking as you see them, about the only thing I think you can check is across the poles. That should be 3ohms on the Rx1 scale.
    Last edited by DaWizard; 06-11-2017, 01:31 PM. Reason: spelling
    You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!

    Comment


    • #3
      Bud
      i am sure Tom will chime in with the testing info using a meter. Personally i just drive them to test because when they get hot things change internally with the windings. shorts etc.
      Keep a spare in your back pocket when doing this

      3 ~ Tudor's
      Henry Ford said
      "It's all nuts and bolts"


      Mitch's Auto Service ctr

      Comment


      • #4
        3 ohms would be for a 12 volt coil with internal resistor. The 6 volt Model A coil should be about 1 1/2 ohms, so put the meter on the R x 1 scale, and hope your meter is good enough to read low ohms accurately. I prefer to check them on the battery charger. I use my 6 amp charger set to 6 volts, and look for about a 4 amp draw on the meter.

        As far as the secondary, connect to the center and either side and look for over a thousand ohms. I don't recall the spec, but will see if I can find it again.

        About 3 to 4 thousand ohms should be good for the secondary. I'll measure my original slant pole coil later and post it here.
        Last edited by Tom Wesenberg; 06-11-2017, 04:00 PM.

        Comment


        • #5
          Thanks a lot, everyone.

          Comment


          • #6
            Whew, sorry, my bad. 1.5 ohm.
            You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!

            Comment


            • #7
              This site has info that also includes modern coils.

              Comment


              • #8
                Be SURE to check for cracks/carbon tracking around the tower & terminals!
                Bill Short

                Comment


                • #9
                  I just measured the ohms on the original slant pole coil on my 1928 and it has 3,300 ohms.

                  Comment


                  • BudP
                    BudP commented
                    Editing a comment
                    Thanks, Tom.

                • #10
                  Originally posted by Tom Wesenberg View Post
                  I just measured the ohms on the original slant pole coil on my 1928 and it has 3,300 ohms.
                  Tom,
                  Does that mean the coil's BAD or the meter's BAD???---The reading doesn't sound right???
                  Bill Confused

                  Comment


                  • #11
                    Originally posted by BILL WILLIAMSON View Post

                    Tom,
                    Does that mean the coil's BAD or the meter's BAD???---The reading doesn't sound right???
                    Bill Confused
                    It throws a hot blue spark at least 1/2", so it's good enough for me.
                    3,300 ohms is factory spec.
                    6 volts isn't really what fires the coil. 6 volts only builds the magnetic field.
                    When the magnetic field rapidly collapses, the primary windings get a kick up to 200 to 400 volts, and that's when the secondary fires the plugs.
                    Last edited by Tom Wesenberg; 06-13-2017, 04:42 PM.

                    Comment


                    • #12
                      Tom, earlier, you said a 6 volt Model A coil should be 1 1/2 Ohms, I'm confused by the 3,300 Ohms???
                      Are you measuring from terminal to terminal or terminal to tower?
                      Bill Confused???

                      Comment


                      • #13
                        Originally posted by BILL WILLIAMSON View Post
                        Tom, earlier, you said a 6 volt Model A coil should be 1 1/2 Ohms, I'm confused by the 3,300 Ohms???
                        Are you measuring from terminal to terminal or terminal to tower?
                        Bill Confused???
                        1 1/2 ohms on the primary windings, and 3,300 ohms on the secondary windings.

                        Comment


                        • #14
                          Got it, Tom, I'm SO STUPID!----"Maybe" my too tight skivvies short circuited my "brain"---
                          Bill Embarrased
                          Last edited by BILL WILLIAMSON; 06-13-2017, 10:48 PM.

                          Comment


                          • #15
                            It seems many folks have issues with coils as they get hot from the engine... Anyone test them in the same position and temps of the running engine?

                            Comment


                            • #16
                              I am checking the coils I have in my parts bins. Here are the results:

                              I have a new one marked D-511 D-512 (12V I think) Primary: 1.4 ohm, Secondary 7,610 ohm
                              Old Delco Remy Primary: 1.2 ohm, Secondary 4,660 ohm
                              Repro (?) w/ spot welded bracket: Primary 1.1 ohm, Secondary 2,940 ohm

                              The 6-volt coil offered by Snyders has a note indicating it is marked 12V to be used with external resistor. So assume regardless of 6V or 12V the coil is the same, right?

                              Which one of these will generate a hotter spark?
                              Jon.

                              Comment


                              • #17
                                I'd think the first one mentioned would be the one with the "hottest spark". Any of the 3 should work fine on 6 volts. Yes, many 12 volt coils which use an external resistor are the same as a 6 volt coil. In a pinch, if your coil goes out while away from home, most any coil will get you going again.

                                Comment


                                • #18
                                  Originally posted by mshmodela View Post
                                  It seems many folks have issues with coils as they get hot from the engine... Anyone test them in the same position and temps of the running engine?
                                  I don't trust modern oil filled coils quality as tested and posted in other threads, so I position all the oil filled ones with leads on the top. I now use a paste filled junkyard Bosch 12 volt with good 3 ohm reading even with leads on top (with others as spares). Some like the epoxy filled ones while others say they don't dissipate heat very well........
                                  Last edited by plyfor; 05-10-2019, 10:40 AM.

                                  Comment

                                  Related Topics

                                  Collapse

                                  • WMWS
                                    Coil effecting speedometer
                                    by WMWS
                                    Today I changed out my coil to the flame thrower 40111. My electric tachometer is hooked up to the coil. Now my tac is showing fast for some reason. Any idea why.
                                    09-09-2017, 06:11 PM
                                  • Ray Horton
                                    Slant pole coil question
                                    by Ray Horton
                                    I have what I think is an original slant pole coil in my box-o-stuff. How can I determine if it is a good working one or not?
                                    11-28-2017, 08:09 PM
                                  • canadian
                                    friendly discussion
                                    by canadian
                                    I have read about the big no no about mounting a ignition coil, terminals down on Model A firewall. I have a NAPA 12V internal resistor mounted upside down for 3 years. Brother rumbles by with 72 dodge Demon , nice 340 , while looking around I noticed ignition coil bolted on its side to intake manifold , factory dodge design. the same coil that I am using exactly, He says its been there for 15 plus...
                                    05-12-2018, 05:18 AM
                                  • Chuck Sea/Tac
                                    Question regarding Tom W’s coil tester
                                    by Chuck Sea/Tac
                                    can the 6V tester be used for twelve volt? What changes would be needed to test 12V coils?...
                                    02-16-2018, 09:55 PM
                                  • plyfor
                                    Coil Polarity
                                    by plyfor
                                    Found this little dwg. on the net for checking coils polarity other than the conventional lead pencil test and the vendors' tester. No specificity for 12 volt neg. vs 6 volt pos. systems....
                                    11-24-2017, 12:32 PM
                                  • Chuck Sea/Tac
                                    Coil internal wiring
                                    by Chuck Sea/Tac
                                    some info says the plus is where to check the high voltage, and another says use the minus. I also have seen wiring diagrams showing comman internal connection on both plus and minus. Are different coils wired differently to the + - terminals? Also, I get the same ohm reading from the hi tension tower to either plus or minus. This is on several coils that spark well.
                                    which terminal is the power...
                                    10-15-2018, 08:11 PM
                                  • Cape Codder
                                    Coil Decision
                                    by Cape Codder
                                    I am looking to purchase a coil other than OIL filled. I see that Summit Racing sells Per Tronix Ignition Coils which are EPOXY filled and Primary Resistance is 1.5 ohms with maximum voltage rated at 40,000 volts.

                                    MY QUESTIONS:
                                    How does this coil match up to the original coll in that it is filled with EPOXY and voltage rated at 40,000 volts?
                                    What is the original coils maximum...
                                    10-05-2018, 02:32 PM
                                  • plyfor
                                    12 volt system coil follow up to thread 11-7-17
                                    by plyfor
                                    We have a Standard 12 volt internal resistor UC15T coil for another project. It reads 4.6 ohms across the terminals with 2.6 amps to the points. If an alternator puts out approx. 14 volts , the current to the points is approx 3 amps.
                                    Just want to follow up that this is OK (with stock or modern V8 style points) if we use on a Model A ?
                                    11-16-2017, 04:57 PM
                                  • plyfor
                                    coils (12 volt) primary tests
                                    by plyfor
                                    Updating from another post, used a very accurate volt / ohm meter to compare primary readings on 3 internal resistance coils. The results were that 1 used original German made Bosch solid filled (probably tar substance, not epoxy) measured in at 3.2 ohms ,a new Standard UCT15 (foreign made) measured 4.2, and new old stock Lucas (UK made) measured 4.6 . The Bosch went on our car and could be mounted...
                                    04-09-2018, 12:54 AM
                                  • plyfor
                                    Oil Filled coil orientation
                                    by plyfor
                                    We picked up a (12 volt) Standard -no resistor required- UC15T oil filled coil. The oil does slosh around inside. Research suggests these cylinder types can cool better than epoxy filled when the terminals are facing up. The Model A's have the terminals facing down. Does anyone have concerns about this?
                                    11-06-2017, 11:09 PM
                                  Working...
                                  X