Mosfet ignition system  - Page 1
Forum section: electronics / projects

author: tomcer34
author_rank: Contributor
timestamp: July 11, 2023, 04:00:33 pm
content: Hi, i want to make mosfet ignition, but a little differently than usual, because my induction coil is wired weird, via photo. I did bootstrap, but spark produced is way to weak. But if I wire other way around, spark is huge and strong (spark gap 3.4cm). What did I do wrong. In pictures there will be another schematic of my previous ignition that works great, but has huge power consumption and EMF field.

author: langwadt
author_rank: Super Contributor
timestamp: July 11, 2023, 06:28:07 pm
content: Quote from: tomcer34 on July 11, 2023, 04:00:33 pmlooks pretty normal. End of primary to battery, center tap to ground via a mosfet (or IGBT)keep in mind transistor needs to be good for 350-400V

author: Miyuki
author_rank: Frequent Contributor
timestamp: July 11, 2023, 06:53:34 pm
content: Any expected benefits from using the MOSFET instead of ignition-rated IGBTs?What is your dwell time?It is a common ignition coil design, just use the transistor against the ground

author: tomcer34
author_rank: Contributor
timestamp: July 11, 2023, 09:17:32 pm
content: Sorry, what is a dwell time? Couldn't find any good explanation on the internet(English is not my native language). I'm not using conventional schematic, because this ignition is for my "race" bike. Just old soviet moped, but planty of races still going. I need ignition coil tied to the ground, because other wise,those pesky high voltages leak to my "alternator" (just 3 coils and in the middle are 8 magnets). I tried that but it keeps messing up my voltage regulation.For those IGBT's, I didn't consider it, thanks for suggestion, I will look in to that

author: tomcer34
author_rank: Contributor
timestamp: July 11, 2023, 09:22:57 pm
content: Quote from: langwadt on July 11, 2023, 06:28:07 pmWhy? Because of the massive induction present in the circuit? Measured it with oscilloscope, peak on the coil is only 40V, but that seems low, maybe there is a problem? Frequency that I'm feeding is 500Hz, so that spark will be fired twice. It helps with the limited power of the moped

author: gjvdheiden
author_rank: Contributor
timestamp: July 11, 2023, 09:27:48 pm
content: Quote from: tomcer34 on July 11, 2023, 09:17:32 pmHow long your "contact points" are closed. Also dwell angle. Sort of duty cycle of a PWM.

author: langwadt
author_rank: Super Contributor
timestamp: July 11, 2023, 09:52:30 pm
content: Quote from: tomcer34 on July 11, 2023, 09:22:57 pmwhen the transistor turns off the primary voltage rises until the spark strikes, the turn ratio of most ignition coils are only ~1:100 if you ahve misfire or a loose ignition wire the primary voltage can get quite highcoil needs time to charger and a the spark needs to be exactly at the right time, what's the point of firing twice??

author: langwadt
author_rank: Super Contributor
timestamp: July 11, 2023, 09:54:50 pm
content: Quote from: tomcer34 on July 11, 2023, 09:17:32 pmthe time the transistor is on charging the coil before the spark

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 11, 2023, 10:00:40 pm
content: I've made a mosfet-"assisted" ignition circuit for an old car in the past. It was merely "assisting" the ignition following the dwell time with only a few µs of error. I didn't try to get clever and adjust the timings or trigger multiple sparks. It worked fine for several years before I sold the car.If you mess with the timings you may create misfirings, the engine will not like that very much.

author: Benta
author_rank: Super Contributor
timestamp: July 11, 2023, 10:05:01 pm
content: Quote from: tomcer34 on July 11, 2023, 09:22:57 pmYou're aware that 500 Hz equals a single-cylinder 4-stroke at 15000 RPM? And a 2-stroke at 30000 RPM?Most ignition coils will be at or over their limit there.

author: tomcer34
author_rank: Contributor
timestamp: July 12, 2023, 09:44:18 am
content: Quote from: Benta on July 11, 2023, 10:05:01 pmIt two speed, 50cc tunned moped(pipe, carb, exhaust flange, transfers, timing of canal...) max RPM ever recorded was 14600rpm while going 96km/h. Double spark is because, yes, ignition coil is at its limit. Double spark solved that, also in low rpm it added some torque. Did dyno session once. Original ingintion caped at 12800rpm and 7.2 HP(due to pipe hitting and back pressure, spark did not fire and limited rpm) . My last design, seen at the top, was able to push rpm to 14600 rpm and 8.3hp. Ignition timing was controlled by ESP where I made timing map.

author: tomcer34
author_rank: Contributor
timestamp: July 12, 2023, 10:13:45 am
content: Quote from: SiliconWizard on July 11, 2023, 10:00:40 pmDo you still have schematics for it? I'm not using conventional method of mosfet ignition, because spark is introducing extreme noise to my ground and it's messing with my logic, ESP and hall sensor. I found out the method that I'm using is mutch better for my electronic and any noise left could be filtered out. Sorry if I'm using wrong terminology and being dumb, I only studiedVocational high School of Electrical Engineering

author: darkspr1te
author_rank: Frequent Contributor
timestamp: July 12, 2023, 10:44:03 am
content: I think you should check this out, it will help spark a great deal, very simpla , few components ,https://www.homemade-circuits.com/how-to-make-capacitive-discharge/darkspr1te

author: coromonadalix
author_rank: Super Contributor
timestamp: July 12, 2023, 10:55:10 am
content: i think you have open ecu projects, you could get some ideas ..