Capacitor Discharge Ignition Circuit (CDI )

[GQROD]

" Capacitor Discharge Ignition Circuit (CDI)​

The CDI ignition circuit produces a spark from an ignition coil by discharging a capacitor across the primary of the coil. A 2uF capacitor is charged to about 340 volts and the discharge is controlled by an SCR. A Schmitt trigger oscillator (74C14) and MOSFET (IRF510) are used to drive the low voltage side of a small (120/12 volt) power transformer and a voltage doubler arrangement is used on the high voltage side to increase the capacitor voltage to about 340 volts. A similar Schmitt trigger oscillator is used to trigger the SCR about 4 times per second. The power supply is gated off during the discharge time so that the SCR will stop conducting and return to it's blocking state. The diode connected from the 3904 to pin 9 of the 74C14 causes the power supply oscillator to stop during discharge time. The circuit draws only about 200 milliamps from a 12 volt source and delivers almost twice the normal energy of a conventional ignition circuit. High voltage from the coil is about 10KV using a 3/8 inch spark gap at normal air temperature and pressure. Spark rate can be increased to possibly 10 Hertz without losing much spark intensity, but is limited by the low frequency power transformer and duty cycle of the oscillator. For faster spark rates, a higher frequency and lower impedance supply would be required. Note that the ignition coil is not grounded and presents a shock hazard on all of it's terminals. Use CAUTION when operating the circuit. An alternate method of connecting the coil is to ground the (-) terminal and relocate the capacitor between the cathode of the rectifier diode and the positive coil terminal. The SCR is then placed between ground and the +340 volt side of the capacitor. This reduces the shock hazard and is the usual configuration in automotive applications."

The above is an article i came across, it did have a schematic however i cannot post it copy and paste did not work.

Hope at least the explanation can be of some use to those looking for the holy grail on making their own igniters. It may be adaptable to motorcycle ignitions with some tweaking.
I can e-mail the schematic to your personal e-mail from my personal e-mail in word format it comes right up. Just pm me.

 

[focus frenzy]

unfortunatly suzuki GS use a battery powered ignition, not a capacitor Discharge ignition.

many people mistakenly call the ignitor box a CDI.

 

[duaneage]

Used on some bikes, the Hondamatic I owned had it. On the downside, it can fail because it is more complicated. I would not consider it a holy grail of ignition, rather another way to get the job done.

A properly designed "standard" coil system works just fine, the limiting factor is the applied power versus the coil saturation limit. All coils saturate at some point, higher frequency operation causes it.

MSD sold a system that used this design. Very expensive, but overkill. You're not going to get massive power increases from a spark. Displacement, breathing, cam duration, compression increase, etc.

 

[trippivot]

T-transistorized P- pointless I- ignition get it right

TPI is what you should be building (or learn to set points)

cdi is an AC style of ignition that uses a small AC source for power like dirt bikes without a battery. could be called a MAGNETO.. since we carry a 8 pound lump it makes sense to use it to it's potential. hint==( battery)

Honda matic is a tpi too. the trans alp dual sport had a DC-CDI system
if you are bored,why not re invent alcohol... as to not give you a hangover.

saturation is not a limit but a time related to the resistance of the primary side of a step up transformer (coil) Also CDI requires a rising field coil TPI uses a collapsing field coil. different construction inside. try to mix and match you'll never track the mid-hi rev misfire.

by the way stock battery point ignition has over 30,000 volts that work just fine if in tune. dyna is not much higher 40,000 newer stock stick individual sport bike coils go 50,000 from factory.

 

[GQROD]

I know the igniter is not CDI, i had a CDI on my porsche and it was expensive to replace.

This isn't by any means " THE " holy grail, just some help for those still searching for it.

Setting points is far better than having to pay 400.00 to the stealer for a new igniter in my book.

Thought i would post it in case it could be of some help.

I wasn't bored just came across this and thought those that are looking to build their own might be interested in this.

As for re-inventing Alcohol it's already been done.........Star Trek Next Genereation calls it Synthahol. But where's the fun in that?

Live Long And Prosper !