Electronics > Projects, Designs, and Technical Stuff
Transients in Automotive Inductor Signal
Circlotron:
--- Quote from: floobydust on July 25, 2020, 06:06:16 am ---If you need over 8,000RPM ability then shorten the debounce time a bit but who uses a single ignition coil at that speed.
--- End quote ---
You can get a single coil to go full power past 10,000 if you do it right. I did the electronics box for this one. 8800+ rpm. I've done more than a few.
https://www.whichcar.com.au/tv/video-1100hp-naturally-aspirated-ls-engine-on-the-dyno
floobydust:
I was thinking stock/street use, like OP's HEI. My measurements HEI stock is 2.8mH, 0.35R, around 6A pk.
In the video I see the dual-coil "new 20Amp twin-coil system" and mention of a "10Amp single-coil system".
My math, 8,000RPM on a V8 ignition is 533Hz or 1.88msec period, which isn't alot of time to build primary current, do an arc and then repeat, running a single coil.
A special ignition coil with say one-quarter the inductance and run double peak primary current, you can run short dwell times. But the switching transistor losses go up 4X, more heat. 20A though?
mikerj:
--- Quote from: Circlotron on July 13, 2020, 01:00:13 am ---One approach that worked well for me is have a comparator that triggers at +200V from a resistive voltage divider (no zeners) then feed the comparator output to the micro. Have a micro output trigger a 555 monostable that drives a transistor to clamp the comparator output to ground for 1mS or slightly greater immediately the circuit is triggered. This will make it ignore any noise pulses until the monostable times out. You could increase the monostable time to just a little bit less than the pulse repetition period at max rpm. Ignitions are fun!
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Why wouldn't you just disable the interrupt in the micro for 1ms, or whatever time you need?
Circlotron:
--- Quote from: mikerj link=topic=246930.msg3155840#msg3155840 ---
Why wouldn't you just disable the interrupt in the micro for 1ms, or whatever time you need?
--- End quote ---
That approach would certainly work well. The way I did it was on a design in the late 90's when I didn't know what I know now.
Circlotron:
--- Quote from: floobydust on July 25, 2020, 08:44:30 pm ---I was thinking stock/street use, like OP's HEI. My measurements HEI stock is 2.8mH, 0.35R, around 6A pk.
In the video I see the dual-coil "new 20Amp twin-coil system" and mention of a "10Amp single-coil system".
My math, 8,000RPM on a V8 ignition is 533Hz or 1.88msec period, which isn't alot of time to build primary current, do an arc and then repeat, running a single coil.
A special ignition coil with say one-quarter the inductance and run double peak primary current, you can run short dwell times. But the switching transistor losses go up 4X, more heat. 20A though?
--- End quote ---
The 20 amp system uses two coils in parallel, 150mJ per coil so 300mJ total.
Just now took a scope screenshot for one of those boxes set at 7 amps and running a single coil at 6000rpm. With a 14V supply the current increases by 3.5A in 1.75mS, giving approx 7mH inductance. (resistance may have slowed di/dt a little so inductance is probably not quite as high as that). You are certainly correct in that the coil doesn't have enough time to fully charge up *from zero* at high rpm, but the flip side is it doesn't have enough time to fully discharge down *to zero* either. Identical situation to a flyback SMPS operating in continuous mode. The trick is to find the right ratio of on time to off time. Do that and you have an ignition that will rev to the moon.
Edit - The scope screen shot is now the wrong one! I give up...
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