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TR4/4A Ballast or Non...

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Marla

Marla

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Did the 1964 Tr4 have a ballast or non ballast ignition coil?...ordering a flame thrower coil and have to know...Thanks...Marla
 
Okay - I am confused by the terms 'ballast or non ballast ignition coil'. The TR4 ignition system has no ballast resistor.

It has the coil (like TR3s and many earlier vehicles) that does not use a ballast resistor or ballast resistor wire.

Some make the assumption that there is a ballast resistor inside the coil but I don't think that is quite accurate.

Some refer to the 2 styles as 6V and 12V coils which is accurate but possibly confusing. In that parlance the TR4 uses a 12V coil.

Edit - I see that the Moss site specifies 'Ballasted Systems' and 'Non-ballasted systems' in which case 'Non-ballasted' would refer to the TR4 ignition system.
 
Geo Hahn said:
Some make the assumption that there is a ballast resistor inside the coil but I don't think that is quite accurate.
Click to expand...
Well, there has to be extra resistance somewhere, to limit the DC current through the coil once the magnetic field is saturated. Normally, the length of wire used for the primary isn't long enough to do that; so either there is a discrete resistor inside, or the wire is a special alloy with higher resistance than copper.
Some refer to the 2 styles as 6V and 12V coils which is accurate but possibly confusing. In that parlance the TR4 uses a 12V coil.
Click to expand...
But I have coils that are marked "For 12v use. Requires external ballast".

To add to the confusion, there are various coils designed to be used with various electronic ignitions, that have even lower primary resistances. Those ignitions have their own means of limiting saturation current (eg adaptive dwell or capacitive discharge). So, for example, Pertronix offers canister type coils with primary resistances as low as 0.32 ohms!

Likewise, different electronic ignitions have different requirements. So for example, a Crane XR700 needs a 3 ohm coil (or a 1.5 ohm coil plus a 1.5 ohm ballast), but a Crane XR3000 takes a 1.5 ohm coil. And Pertronix actually specifies lower resistance coils for V8 applications, for example when using an Ignitor ignition on a 12 volt V8, they say to use a 1.5 ohm coil instead of the 3.0 ohm used on 4 & 6 cylinder. (6 volt V8 applications use the 0.6 ohm coil.)

So IMO, the safe way is to talk about primary resistance. Stock TR4 coil is a 3 ohm coil.
 
I believe Moss had a fairly simple test to determine whether you have a ballast or non ballast coil. They had a video on their website I believe. Some simple tests with a multimeter. It took me about 5 minutes. That was I was SURE I was ordering the right components.
 
The test for the coil is simple; just pull off one of the low tension wires then use an ohmmeter or DMM to check the resistance across the two low tension posts. If it's around 3 to 4 ohms, you've got a 3 ohm coil that doesn't require an external ballast. Around 1.5 to 2 ohms (many DMMs will read a bit high for such low resistances) indicates a 1.5 ohm coil that does require an external ballast when used with points. Whether it still needs a ballast when used with an electronic ignition depends on the ignition.
 
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