Bosch Red Ignition Coil for '85 QV?

With the Bosch red coils is no danger of burning them up *if* you use them with a ballast resistor. Without using a ballast resistor the Bosch red coils will saturate (e.g. the magnetic field cannot store any additional energy) so the additional current is just converted into heath, damaging the coil in the mid to long run.

Rule of thumb, a correctly set up inductive ignition coil will get warm, but never so hot that you can't touch it (which is a bit hard to verify if it's installed in the engine compartment).

The BAE504 coils are at 0.3-0.6Ω primary resistance, which is a good match for the setup with the Digiplex.

Secondary resistance is a result of the amount of secondary windings and the wire material. The more important factory is the winding relationship between the primary to secondary winding relationship (the BAE504 will have around 80:1, e.g. 80 secondary windings per primary winding), which influences the secondary output voltage.

Classic inductive coils usually have a 30-60% higher secondary resistance than modern coils due to the (less advanced) wire materials available at the time.

 

P.s. this is how a current limitation by an electronic ignition looks like. If ~6A are reached then the electronic ignition keeps the current at that level (for around 3 ms) to preserve the magnetic field until the ignition takes place (shown as negative spike in the scope shot).

Modern ignitions shift the charge cycle forward to keep the time as short as possible where the field is sustained to save energy/create less heath.
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BAE504.

I hope I have the correct ones

 

BAE504F is the correct replacement for a BAE209B.

 

I was told yesterday that I do not need an external ballast resistor on my red coils because I have electronic ignition.

Just to be clear; that is true - but due to the nature of the coils, they will simply fail sooner without it.

Am I correct ?

 

This is only true for a transistor ignition coil, which usually has a 0.5 Ohm resistance and can handle 6-8 Ampere. A

The Bosch red coil is a points ignition coil, which only handles 3-4 Ampere, so it must be used with a ballast resistor. With the Bosch ballast resistor the current is 3-4A, without the ballast resistor the current would be 6-8 Ampere which is much too high for the Bosch red coil. All the excess current is directly turned into heath as the field cannot store any more energy.

 

I don't have a ballast resistor. It's been 10 years this year.

Can you believe that? I hope I haven't screwed anything up. Right now, it seems to be running just fine.

 

The Bosch coils are quite robust but the winding might have taken some damage in the meantime. I don't think that anyhting else would get damaged by overloading the coils.

 

Sorry for posting in a very old thread -- but I have a question directly related to this discussion. Which terminals do you measure across with a multimeter to determine primary and secondary resistance on the BAE504F? I have a coil I bought new from a Ferrari supplier many years ago, but never used. As I measure it across the 2 closest terminals, I see around .3 ohms on both sides -- so it seems like either I am measuring it wrong or the coil is bad.

 

The two male spades that are very close to each other (on each side) are connected to the same place. Measure between the two groups of male spades (either spade in either group) = primary coil resistance. Measure from the coil wire terminal to the metal frame = secondary coil resistance.

 

Thanks for the guidance Steve. When I measure across the two groups of terminals, it reads 0.4-0.5 ohms. When I measure from the coil wire terminal to the metal frame, it is an open circuit (no connection). However, when I measure from the coil wire terminal to any of the 4 terminals, it measures a steady 4.88 k-Ohms to all 4 terminals.

 

You're right, I got that wrong. I believe your measurements are correct; however, if you could detect this (but you probably can't), I believe the measurement from the coil wire terminal to one of the pairs of the male spades would be 4,880 Ohms (only the secondary coil resistance) and the measurement from the other pair of male spades to the coil terminal would be 4,880.5 Ohms (the resistance of the primary coil and secondary coil connected together).

 

Awesome, sounds like the coil checks out. I just tried measuring again for each spade pair, but my multimeter only reads to 2 decimal places on kohms, so it doesn't register the difference. This time it reads 4.87 kohms instead of 4.88, but it's the same on all 4 because of the low resolution of the meter. Thanks very much for your help!