I looked quickly at what happens when you drive Denso stick coils with a Bosch igniter. In this case they are Denso 129700-5150 coils as used in some Honda bikes. The igniter is a Bosch 0 227 100 211 that happened to be pulled from an Audi.



When driving a single coil in the most obvious way possible we get the results shown below. "Battery" voltage is 13.3V and the logic input to the igniter is 5V. Note that 2 ms dwell is plenty.



I read on the Interwebz that some people are driving two of these coils in series. That's easy enough to wire up. Note that when running this setup from a factory ECU with 7ms dwell the series setup might be a better. Maybe someone with more experience can comment. You need to run wasted spark anyway.



Thanks to The Scary One for loaning me the parts to measure. In fact he sent me an Hitachi igniter, but my dog ate it. He's been very patient with me so far. Send him gifts.

 

Wait, what?

What is the scale for Coil Current (A)? Is there a multiplier?

 

That's what I measured in amps. It's not what you expect?

 

Way too low. Were you using an attenuator? I'd expect to see values at least 10x what you're showing. For reference, stock coils probably draw 6 or 7 amps. Honestly it's been a long time since I've scoped stock Miata coils, but a half amp is way off the mark.

 

I think you're right. Based on the total resistance of two coils in series plus the sense resistor I expect the coil current to approach 3.5A not 0.35. I did check the attenuation settings on probes and scope. Everything is right... I'll try a different probe.

In the end, I don't think it matters as we can see appropriate dwell times even with no scale at all on that axis, but I would like to get to the bottom of it.

 

Yes it did generate some dwell information, but current information sheds light on how strong the coils are. It's been my position based on the data available so far that these coils are not a good choice for inductive ignition.

 

I'm not even going to lie about this. It was just pure operator error. The scale was off by exactly 10x. Fixed the plots in the opening post.

Ben, what are your thoughts about running coils in series? It would seem to me that in theory it should work, but the higher DC resistance means the "charging" current never gets as high.

 

10x original scale (so 5 amps at saturation) makes sense, but helps to confirm what I've been saying about the CBR coils: They're not worthwhile as an upgrade.

My thoughts on running a pair in series are that it would be a downgrade from a stock ignition system.

 

For those of us playing along at home, can you explain why they are not a worthwhile upgrade? What would one want to see in these plots to show that they are "better" than the OEM setup?

Not arguing... just trying to learn a bit about ignition coils.

Thank you

 

The stock coils draw 6 or 7 amps as Ben mentioned. Therefore they are producing a much hotter/stronger spark than these guys at 5 amps (ohm's law, at the same voltage, higher amp means more energy).

 

Well, at least I know these won't work.

 

Humm... what about with the fancy MSD or AEM CDI box rather than the Bosch 211?

 

I would prefer a healthy inductive ignition, but if you must go CDI, M&W has a 4-channel box. However you're looking at an extra $800.

What's the fascination with these coils? There are so many better options.