When is a Ballast NOT a Ballast ?

The Standard OEM Ballast for a 6 volt Front Mount Coil has a starting resistance of .55 ohms @ 1 amp and resistance increases to 1.5 ohms @ 3 Amps. I have several 1970’s Ballasts that have similar response curves.

When is a Ballast not a Ballast? Its when you use today’s automotive Ballasts. They are a “FIXED” resistance that can be measured and are marked (stamped) on the Spade lug connector. The ICR23 is 1.2 ohms period. The ICR 11 or RU4 is 1.3 ohms period. The ICR13 is 1.8 Ohms Period. Sometime since the 1970’s the parts suppliers have switched material such that no Ballast (change in resistance) occurs.

How does this affect an N user? The Standard OEM Ballast is still a Ballast and good for 6 Volt operations but the 12-volt conversions need to recalculate the amount of resistance
in the circuit if adding a fixed (automotive) resistance.

Example: 6 volt coil operating on 12V: OEM Ballast + ICR23 + ICR23 = ~3.8 ohms, plus the coil resistance of 1.0 = 4.8 ohms total. This will result in ~2.8 amps @ 12.5V and 3.0 amps @ 14.5V. (The OEM Ballast will look after the starting Voltage Drop)

I hope this helps someone, and may explain why PPL are Smoking Coils. I know it did surprise
me.

They show a certain ballast resistor, which is PTC, for "systems WITHOUT A STARTING BYPASS".

The other option is a "Non-PTC" ballast resistor, for systems WITH A STARTING BYPASS.

(I don't have the catalog at hand, I can post the part #'s later, if anyone is interested, and I HAVE explained this, and posted the part #'s before.)

So, that is the key to the mystery.

Engines, such as our "N's", which have no "starting bypass" tend to use PTC ballast resistors, for a HOT spark during initial cranking.

Engines WITH a starting bypass (which bypasses the ballast resistor during cranking) use a NON-PTC ballast resistor.

Phil, you are DEFINITELY on to something.

In the past, the coils sold as "12-Volt" apparently had a primary resistance up in the 4-Ohm range, and, with these coils, "Dell's Secret Current Limiting Resistor" of 1/2 Ohm added just enough resistance to the circuit to make it easier on the coil.

Now, it seems front-mount "12-Volt" coils" commonly are made with primary resistance closer to 3 Ohms, and need the added resistance of the tractors "OEM" ballast resistor to keep primary current to a safe level.

Apparently, ALL requests for "what resistor to use" should include more than "it's a aftermarket 12-Volt coil", and will need to include the coil's actual primary resistance.

That DOES seem to be the right "recipe" for setting up today's "12-Volt" coils, as opposed to those produced in the past, that had a higher primary resistance.

Notes:
The Ballast also has a Temp (thermal) limit that needs to be considered (I X I) X R (3X3) X 2=18W @ 14.5 volts. That is why I try to only rate 1.5 ohms @ 14.5V (3 amps) for the OEM.

The 12 volt conversions would benefit from a PTC Ballast that is 1.0 ohms @ 1.0 Amp (the OEM is .55 ohms @ 1 amp) and 2.0-2.2 ohms @ 3 Amps. The ceramic case should be potted such that the element is held in place and rated @ >20 watts. This Resistor (X) could be used with both 12-volt conversions. The 12 volt (2.5 ohm) coil would only use the X Ballast and the OEM 6 volt coil would use the OEM ballast + X Ballast.

The use of fixed resistors has some luggage that needs to be considered. The Electrical dwell is determined by the formula TC= L/R. This means that increasing circuit resistance will increase Electrical dwell (a faster rise time to Max Current). It would be interesting to measure dwell on a 6 Volt OEM coil on 6.5 volts System and then the same coil with the added resistance (fixed VS. Ballast) @ 12 volts system. BTW: I suspect that the 12 volt 2.5 Ohm coil would have good dwell if used on a 6 volt system (3amps @ 7.5 volts) without any ballast.

Measuring Coil Resistance: The Manufacture, most likely, rates the coil by the wire and its length but I like to have the coil under 2 amps of load. I use my Lab Power supply and a 1.0 ohm test resistor in series with the coil. I measure volts (fluke) across the 1.0 test resistor and set the PS voltage for exactly 2 volts (this = 2 amps). The voltage Drop across the coil can then be divided by 2 to give an accurate Ohms rating of its in "circuit" impedance.

JMHO,

The Standard Ignition numbers are RU-10 and RU-11, but I can't recall which is which, and won't have access to the catalog 'til I stop by the shop this evening.