52 A coil issue?

The one that was 1.7 volts was, in my opinion, a 6 volt coil ANDDDDD DD it may have been one of those labeled "12 Volts for use with external ballast resistor". If it was used unballasted on a 12 volt tractor it would cause the points to burn up n carbon prematurely. The problem is some people buy n use the coil labeled as above and see the "12 volts" n think its a true 12 volt coil WHICH IT IS NOT and why its labelded "for use with external ballast"

The limiting design factor is the current the points have to interrupt and switch and thats somewhere around 4 amps. Thats why typical 12 volt coils are 3 ohms while 6 volt coils are in the 1.5 range althioug not alllll l are such if more spark energy was needed even if the points wouldnt last quite as long.

Another reason besides excess switching current why points might burn up prematurely is if the condensor is bad or open or weak or simply too low in capacitance or not attached well or not grounded well to the distributor. A simple ohm meter can show if its open or shorted but you need a capacitor tester to really indicate its condition and capacitance.

Hope this helps, let us all know but I can tell ya right now if the new coil you wanna use has around 3 ohms primary resistance the points will sure last longer then one with only 1.7 lol and its okay on a 12 volt system unballasted.

John T

The commonly available (Tractor Supply, TISCO, etc) replacement coil is labeled 12V 504 MADE IN U.S.A. and has a primary resistance of 3.00 +- 0.02 ohms, measure with a bridge unit. So, for a 12.6V(nominal) battery, the current flow with the points closed will be I = V/R or 12.6/3.0 = 4.2 amps maximum, which will produce heat of I*V = 52.9 watts. However, the duty cycle (dwell) is about 90 deg (from a Delco Remy manual for the 1111558 distributor), so 90/360 = 0.250. Thus, unless the key is left on with the points closed (100% duty cycle) the time-averaged power deposited in the coil is 52.9*0.25 = 13.2 watts. Resistance of the other wires in the circuit, and some effects due to an effective AC impedance due to the switching of the coil "on" and "off" by the points, will lower the current and heat values some - detailed measurements would need to be made to get the real numbers.

The other commonly available replacement coil is labeled 6V 505 MADE IN U.S.A. The primary resistance of that coil is 1.08 +- 0.02 ohms, and the primary current would be 6.3/1.08 = 5.83 amps for a nominal 6.3V battery. In this case the power expended would be a maximum of 6.3*5.83 = 36.7 watts, or with the same duty factor 9.2 watts dissipated in the coil.

Both of these replacement coils are oil-filled (you can hear it sloshing around inside).

Deere used two part numbers for the 12V coils, AA4983R, which subbed for AA4879R. These were DR 1115043 and 1115047. I think I figured out which is which, but it doesn't matter because they are listed together in the DR coil test properties, so they must be very similar. I do have a 1115043 which I took apart, and the primary resistance of that coil is 4.22 ohms, quite a bit higher than the 504 replacement. One can only wonder why, but the lower resistances of the replacement coils will allow higher current in the primary, thus a higher secondary voltage. Perhaps modern coil materials and insulating oils allow the higher heat generated to be acceptable, and the higher voltage made available to the (often fouled) plugs won't harm anything. But it is even worse to leave the key on with points closed and current flowing.

I have taken apart several coils, and none of them have a resistor in the can. The different resistance values of the primary winding is due to differences in the wire properties. JohnT is correct in that OLD DR coils used internal resistors, but I expect the localized heat around such a resistor in the coil can caused problems that would be lessened with a more distributed heat source like a winding. Since most of the heat is generated in the primary winding, the secondary winding is on the inside of the "coil", and the primary winding is on the outside, which provides better contact with the insulating/cooling oil.

So, to summarize, a replacement coil labeled 12V, with no note about external resistor required, replaces the AA4983R and the AA4879R. A coil labeled 12V external resistor required (or some such) is really a 6V coil - those were used on numbered series LP ignitions systems, and on the 20 and 30 series, which used the bypass starting system. The latter coil can be replaced by a coil labeled 6V, as that is really what it is.

Sorry for the long message - I'll probably think of more later.

For the most part its 3 ohms primary (i.e. a 12 volt coil) is cuz of it has more wire or the wire has more resistance VERSUS it has any internal discrete separate actual resistor up on top HOWEVER I have seen a few old delco coils that had a ridge/ring portion up top that were perhaps encasing a discrete resistor BUTTTTT TT I sorta doubt that I JUST DONT KNOW DUANE MIGHT

Bottom line if its priamry measures around 2.5 to 3.5 ohms its a 12 volt coil while if its more like 1.25 to under 2 ohms its a 6 volt coil anddddd dd I think its simply just cuz it has either more wire length in its primary or its higher resistance wire VERSUS any built in actual discrete internal resistor,,,,, ,,

Duane or Glen in Tx may have part number specs or data while all I got is theory,,,,, but a simple ohmmeter check of its primary resistance will tell for sure what it is REGARDLESS what its called lol NOTE some 12 votl coils are labeled "12 volts" or "12 volts NOT for use with external ballast resistor" BUTTTTT T BEWARE those labeled 12 votls for use with external ballast resistor are in reality only 6 votl coils i.e. the label needs to be followed.....

Ol John T and all