[Vauhtivaunu]

I tried just adding some numbers as a random test but it still wont find a dwell time.

Any pointers??

There is infinite dwell because your coils are for point-type ignition system. They are self adjusted by resistance. That is an issue with ECU driven ignition. You should swap to so called pointless coils ie. coils for igniter you use. 3 ohm is too much primary resistance for system that tries to control dwell in processor level.

[LPG2CV]

To set dwell on my engine (2cv) for my coil.

Warm the engine up and let it idle. reduce the dwell until it starts to miss. Then increase the dwell until it doesn't miss. Your looking for the point where it is just on the cusp. Then add 0.02 ms. This should give you the minimum dwell it needs to idle.

When driving the car, I found I had a miss fire further up the engine rpm. I resolved this by slightly increasing the voltage correction % around 14v ie max voltage from alternator, as it was reducing it by to much.

I believe, there is a new 4 point, dwell correction table due in the next fw release.

[kettlekev]

Thankyou.

The coils I have seem to work OK with the igniter but from what you are saying can never have controlled dwell via the igniter and speeduino.

Can you give me a link to coils that would work with the Bosch igniter so that I can study them. Do they need to be low resistance like CDI coils or are they something different again?

I need small coils like ;
https://www.dynaonline.com/dyna-igntion ... hm-dc12-2/

[LPG2CV]

Coil recommendation is not something I can help with unfortunately

I was using a bosch 211. I guess the method should work with standard coils off of classic engines. mine was wasted spark coil.

Your goal is minimum dwell that gives the necessary spark. over dwell causes overheating of the coil. Generally speaking, if the coil is to hot to hold, then to much dwell. Warm is better.

I'm really not an expert, and just pass on what has worked for me.

Edit
If you have coils, try them with this method. Nothing to lose.

[LAV1000]

Kettlekev,
Looking at the posted settings for the driver, voltagedrop Vce 9 Volts.
So there is only 4 volts left for the coil ?
Are you sure you did get the numbers right ?

[PSIG]

Agreed, your driver V_CE is a weird number. I dug-up a calc I did for EDIS coils with a Bosch 211 driver, and the value I entered was 1.2V. Also, the Current Limit is what you are asking it to dwell the current to. Most "full-size" coils and packs need roughly 4 to 8 amps. I'd start a 3-ohm coil at perhaps 5A. [EDIT - "infinite dwell" often means you are asking the coil to do something it is not capable-of ] Small coils such as COP may need much more, and 10-15A is common in order to create enough energy.

Of-note is that common OEM COP coils generally (not a rule) output 1/3 to 2/3 the energy (in Joules) that typical modern distributor, coil pack and CNP coils do. Hence the need for lower primary resistance and amps for many of those. Also why they may have a trade-off in break-over spark voltage for a reduction in spark burn, or smaller spark gaps for lower voltage and desirable longer burn. That depends on your use and goals.

@JHolland may be correct about the inductance measurements, but whether lucky or random, the $10 ebay LCR meter has put me at-worst less than 0.3ms from published values or final-tuned dwell value. Whatever you buy may not, so IMO good to follow his advice to check for results. While the calculator can provide a reasonable starting point for tuning dwell; the greatest value for me however, is the easy relative curve I can create for % voltage correction.

Note the Spark Plug & Wire Parameters is for both the wire and plug as a unit, so you can include the capacitance for both there. Having said that, also note that if you don't need the output results, then don't worry about those values. Just the coil primary and secondary values, and the important driver values to get the initial dwell value. Then change the voltage and do another one noting the dwell change for entering in your corrections table.

BTW without calc's, I tune dwell using @LPG2CV's basic method, and also verify it at WOT from idle, and through peak torque. I have found many engines see highest cylinder filling (greatest spark resistance up through peak torque or peak VE), showing short dwell as accel hesitation or a 'shuddering' of weak burns, more commonly than outright misfires. This also happens to be the area where many say (and I agree) that acceleration issues are as often ignition-related as they are fuel related.

[kettlekev]

The Vce number came from the bosch data sheet. attached.

igniter 2.PNG (163.78 KiB) Viewed 3871 times

Anyway it looks like the problem with the 3.9 ohms is that the current never gets above 3.333 amps (ohms law: 13 volts/3.9 ohms). It has nothing to do at all with the Bosch driver. It is infinite time to charge because it never gets to the final current, the best I get is 3.33 amps.

So the bottom line, is I cant do programmable dwell with high resistance coils as they were designed for Kettering systems where dwell was a function of points timing and coil design.

If I go to 0.5 ohm coils (like the Dynatek ones I posted ), will there be any issues with Speeduino and the bosch driver? The driver runs at a nominal 8.5 amps. Just using Ohms law I have a lot more than that but I am assuming it doesnt quite work that way?

Thanks guys. great help. Last hurdle on the ignition bit. Gotta love old 2 strokes.

[JHolland]

So the bottom line, is I cant do programmable dwell with high resistance coils as they were designed for Kettering systems where dwell was a function of points timing and coil design.

Dwell is just the time it takes the coil to charge, the higher impedance coils are designed to withstand higher dwell times, they don't necessarily need higher dwell times, points give a dwell based on angle which wastes a lot of power at low RPM. The dwell time doesn't have to be very long, just long enough and electronic ignition can actually give you longer dwell times at higher RPM because you are not limited by having to open and close the points slowly to avoid bounce; back in the late 80s and early 90s we got significant improvements in spark energy at higher RPM compared to points.
I've used lots of different high impedance coils in the past including the 3 Ohm Dyna coils, the other advantage of the electronic ignition was that by controlling the dwell by time you need a lot smaller battery to get through a race, we would often be held for 10 minutes or more in the collecting area.

Edit:
I don't have much info from those days, it was all on floppy discs, I do have a reference to running 5ms dwell on a Lucas Sports coil. I would suggest that you measure the angle that the points are closed for and then calculate the time period at maximum RPM and start there.

[kettlekev]

I will be sticking with the speeduino/igniter combination and the adjustable dwell time option, so just need to know if the 0.5 ohm coils are OK with that setup?

The bosch igniter runs at around 8.5 amps so is that Ok with the 0.5 ohm coils (given Ohms Law is only partially in play)?

Thanks

[PSIG]

I have used coils from 0.23-ohms to over 4-ohms. It's just a matter of finding the combination of settings that enable a good spark at any reasonable voltage, cylinder pressure and rpm, without excessive dwell and overheating of components. JHolland is of-course correct, that the goal is not to see how much power we can pump through the coil, but the best balance for the goals.

Not every coil can be handled by Speeduino, but almost any can. The 0.23-ohm coil was a CDI coil, which worked, but not as well as we would like due to the coil winding turns ratio, designed for a much higher (100V) primary voltage. Low-ohm IDI coils are common, and the old BMW, EDIS and Neon coil packs have versions about 0.4-ohm and controlled well by Speeduino, for example. The 4-ohm coil was an old carburetor & points conversion, and worked very well with the final settings that I don't recall.

Do your thing, but also know ignition has as many factors to consider as any other developed electronic system. Unfortunately, marketing hype and internet corruption has strewn garbage into the topic, making it more difficult to separate good info from bad. An interesting but very limited comparison of a few coil types is here, and probably does more to create new questions as it does to answer some, but that's part of my point.