gemellocattivo.com

I think the front caliper brackets are done. I still need to make the sensor bracket but that will be a simple bolt-on...maybe 1-2 hours and I can move on to the rear.

coils will draw the most wherever the dwell time is longest, either bench testing or the data points provided by the mfg can give you the relevant amp draw to dwell time. From what I've seen on the vids from the bench testing the D585 a 4~5millisecond dwell ranges from 10~12amps, So if it idle your running 4~5ms then the amp draw on the system will be 120~144 amps. That honestly seems like too much dwell but it really comes down the pressures and spark energy needed to run the engine best. You'll probably be in the 6.5~7.5 Amp spot so that's only 78~90Amps at idle dropping from there.

Went back thru some notes, twin post waste spark coils are actually two 6V coils in series. Also make sure that your B+ wiring loom to the coil is less resistance then the primary coil.

Now the fun starts with all the EE work right...

For those reading at this point and may not know...
The lower the primary coil resistance the faster the B field can build and the less dwell needed, however that lower resistance means higher current draw. Dwell is the period of time the circuit is closed and the electric charge is moving into the coil. Once open the field collapses and that back EMF induces an electric charge in the secondary coil. Ignition coils with high primary resistance will draw less current when charging and take longer to do so, that limits the amount of secondary energy made. Some coils utilize an internal resistance on the primary side as means of current limiting, some do not. The coils that do not have a primary internal resistance need to be matched with a high resistance wires and plugs. Ignition systems require being impedance matched, otherwise things 'fry' or short. External resistance is nice when fine tuning and designing the system for maximum efficiency in a custom setup, but requires a fair amount of more math and worksheeting to figure out. Internal resistive coils take out all that but also cut a compromise.

Damn it you made me do math this morning!

dwell is a constant 4ms if voltage is constant so current goes UP with rpm

for a V12
1000rpm = 100 cycles/sec x .004sec Dwell x 6A = 2.4 Amps total
10000rpm - 1000 cycles/sec x .004sec Dwell x 6A = 24 Amps total


so a 30 Amps circuit with 6g wire or 2 15A circuits with 10g

Below is what I found for the coil charging. These coils fire when the current gets to 8-8.5A according to this test and that is about 5.5ms dwell so looking at the shape in integrating in my head.....6A is probably too high, 5 maybe for a total draw for 20A at redline might be a closer guess.

http://rennlist.com/forums/944-turbo-an ... tem-9.html

The dwell table is trying to maintain a fixed energy flux field in the primary coil. As voltage fluctuates the time it takes to get to 100% field saturation will vary, hence the table. When the voltage drops it takes longer to get to 100% so the dwell increases and when voltage goes up the dwell goes down. In all cases that means a target of a fixed current draw. Some coils have a current limiter as noted in the link that cause the coil to discharge so as to avoid internal damage from over saturation. The energy of the spark needed for a specific application will dictate how the coil is designed. Akin to octane in fuel, you don't always need high octane. In many cases you don't need massive amounts of spark energy to start the kernal flame front. Taking a page from astrophysics, the goldilocks principle.

In anycase the primary current is going to be based on the dwell time one chooses or the design of the coil and the resistance of the primary RC and RCL circuit. So if for example it's 4ms and for that dwell at 14V it draws 7amps then that coil will draw 7amps for every event.

Rpm only factors in when needing to calculate the time available for each event, esp for waste spark as it is firing for each rev vs sequential on each otto cycle. I.e. at 9k rpm there is only 6.6ms per revolution. That may seem like enough but you have to account for advance. So lets say total of 42* advance that gives 5.8ms between each trigger in waste spark mode. We can see why COP and sequential is preferred, you couldn't run a single coil for a V8 with enough advance at high rpm, hence multiples.

Here's a good lab sheet on the physics of an ignition system:
http://www.fas.harvard.edu/~scphys/cour ... E1b_3b.pdf

I know more homework..

And a another good page without having to do the lab work...
http://www.dtec.net.au/Ignition%20Coil% ... ration.htm

With 12 coils it's not waste spark, that's why I just switched to 12 coils



The coils are well...coils, so they resist voltage changes and don't draw 7A for the 4ms, they draw about 0 to about a 7A at the 4ms point with what looks like an average over the 4ms of about 4A or maybe 5A.

Rpm matters becasue the charge time for the coil is 4ms PER CYCLE, so more rpm is more cycles/sec which is more average power draw proportional to the rpm.

I just need to hook them up...now quit trying to make this too hard!

wait a sec... are you quibbling over the integration of current draw for 4ms ??

Just bustin yer chops...

Doing some mental math... V12 @ 1k rpm is a firing event every 5ms or 200 per sec. 200Hz 0-7amp hysteresis. Let's see for 8k rpm that's 1600Hz or an event every 625us. Why does this matter? I'm bored... and it's a distraction from other pressing heavy calcs... The alternator has a ripple current based on it's pole count and rotational speed.
Alternator ripple:
N= (120*F)/P
N= RPM
F = Hz
P = Number of poles

It'd be interesting to calc the frequency of the inductive load to the alternators synchronous impedance regulation and see if it points to needing an alternator with pole count higher then 12.

Why should it ever be easy?

If only there were some kind of big damping device of some kind in the system.....like a big battery maybe. I'm not falling for that and doing math twice in 1 day

but I think I am going to put the same connectors on the innovative WB controller as come on the GM bosch NB sensor so I can move a WB any place I want easily. There, accomplished something today!

Part of me is intrigued enough to run some calcs and see what the per phase output is on a 12 pole alternator is and cross check that to the Hz of the inductive load from the ignition to see if at any rpm point the ignition draws more then the alternator can support. Obviously the battery acts as the buffer but if the draw at any point is more then the alt it will drain down the battery.

I think "well I wrote a quick program that calculates the frequency and plasma rate of a high voltage xenon tube based on trigger and extinguish voltage. This can't be that hard"... heck it even outputs a wave form!

I need to get my work done and stop throwing extra credit work at you

This is what I hear!

http://youtu.be/sZwn6vn6hHY

My eyeballs are bleeding, dang you engineer guys are bada@@.
I just make stuff out of metal.

_________________
Wade Williams
Master Ferrari Tech
Restoration Tech
Engine Machinist
Fabricator
Racecar Driver

I was thinking of posting that video. Scott left engineering and went into physics a few years back so sometimes he needs to be pulled back into the real world