I doubt you have a 200-300 VAC alternator on your jetski.
This is probably true, but it is not uncommon for the voltage across, for example, the primary of a regular car ignition coil, to spike at 100-200 volts. When 12 volts is applied, and then quickly removed, the voltage in the primary often spikes to a couple hundred volts. This may be what the OP was talking about.
The storage capacitor is charged to 200-300Vdc. The SCR then fires and applies the cap voltage across the coil primary. The 100:1 or so coil turns-ratio generates the 20kV-30kV at the secondary that fires the plug(s).Hi Der Storm8, I was referring to the site that was linked that shows 200-300 volts are required for CDI ignition. Do you know why such high voltage is required ( I ask because of your high-voltage experiments )
I have worked extensively with 2 stoke engines.
all 2 stoke twins fire at the same time , when one piston is on the compression and the other on the exhaust. they have 2 pickups 180 degrees opposed on the stator housing. 1 coil splits into 2 leads , each going to a cylinder. The reason they program cdi's is to get better low and top end power by varying the timing. effectively if your 2 stoke revs to say 8000 rpm its going to be sparking at 8000 x 2 = 16000 rpm.
a small car coil WILL work , its one of the tricks to get a higher voltage spark at the pliugs or if the original coil burns out.
btw - I have a 1982 yamaha RD 350 LC with 45k km's on the clock and the coil is still working , coils seldom burn out.
Hi again, it occured to me that just because your module burned out, that doesn't mean your coil is bad. Chances are it's still good and can be re-used. I should stand corrected in my comment that you probably don't have CDI. Guess all my 2strokes are too old, and I'm not up on the newer technology. I'm glad to hear these old PWC's are still running, because I'm looking for a good deal on one myself
Hi Der Storm8, I was refering to the site that was linked that shows 200-300 volts are required for CDI ignition. Do you know why such high voltage is requried ( I ask because of your high-voltage experiments ) But on further refilection, I take back what I said ( see my post just above ) There are more small engins that are using CDI than I realized. This is an interesting subject for me, as I own and operate a number of small marine motors.
PS: Thanks buju357, you validated what I thought was right,but wasn't quite sure.
The storage capacitor is charged to 200-300Vdc. The SCR then fires and applies the cap voltage across the coil primary. The 100:1 or so coil turns-ratio generates the 20kV-30kV at the secondary that fires the plug(s).
This is unlike a Kettering type ignition which uses the coil inductance in a flyback type circuit. With the points closed the current builds up in the coil primary. When the points open the inductive energy from this current generates the couple hundred volt spike on the primary which is then stepped up by the coil secondary turns ratio. The CDI uses the coil only as a transformer, the coil inductance is not used for energy storage.
This is probably true, but it is not uncommon for the voltage across, for example, the primary of a regular car ignition coil, to spike at 100-200 volts. When 12 volts is applied, and then quickly removed, the voltage in the primary often spikes to a couple hundred volts. This may be what the OP was talking about.
The storage capacitor is charged to 200-300Vdc. The SCR then fires and applies the cap voltage across the coil primary. The 100:1 or so coil turns-ratio generates the 20kV-30kV at the secondary that fires the plug(s).
This is unlike a Kettering type ignition which uses the coil inductance in a flyback type circuit. With the points closed the current builds up in the coil primary. When the points open the inductive energy from this current generates the couple hundred volt spike on the primary which is then stepped up by the coil secondary turns ratio. The CDI uses the coil only as a transformer, the coil inductance is not used for energy storage.
I cannot tell myself right now, but how else should it work?
I am still not sure how it works with these coils. I have a constant current running through my primary, with what voltage? And then when I discharge the capacitor, it wil create a spark?
The storage capacitor is charged to 200-300Vdc. The SCR then fires and applies the cap voltage across the coil primary. The 100:1 or so coil turns-ratio generates the 20kV-30kV at the secondary that fires the plug(s).
This is unlike a Kettering type ignition which uses the coil inductance in a flyback type circuit. With the points closed the current builds up in the coil primary. When the points open the inductive energy from this current generates the couple hundred volt spike on the primary which is then stepped up by the coil secondary turns ratio. The CDI uses the coil only as a transformer, the coil inductance is not used for energy storage.
Thanks crutschow for answering this. To be honest, I don't know much about ignition, and I guess I misunderstood what you were saying, BrownOut. All I know is what I have read, and I have not had much experience with CDI. I guess I should have stayed out of this one
How can it give more top end power by decreasing the times it spark?
Here, read this post from crutschow. It seems to explain it fairly well
That's not quite right. When you apply a sudden high voltage to the primary from the capacitor, the high primary inductance prevents the inductive current IP, from significantly increasing in the short time the voltage is applied (a few microseconds). The majority of the primary current that flows is simply due to the transformer action between the primary and the secondary spark current.Another way to get a rapidly changing magnetic field is to apply a high voltage to the primary. Thus, the equation IP=LP∫VP*dt, where IP is the primary current, LP is the primary inductance, and VP is the voltate applied to the primary, this current rises quickly, due to the high voltage being applied. This created a rapidly expanding magnetic field that induces the high voltage in the secondary given by the equation above. So, the high voltage is created upon the application of the primary voltage, rather than on the interruption of the primary current.
You are still somewhat confusing the small magnetizing current of a normal operating transformer with the large inductive current of a flyback transformer.Magnetic flux is always proportional to current, per Ampere's law, and not voltage. The only way to get a rapid change is magnetic flux is to rapidly change the primary current. In the low voltage case, that can only be accomplished by suddenly interrupting the current flow in the primary, becuase the primary inductance prevents the current from rising quickly. But in the high voltage case, the primary current rises proportionally higher, to the higher voltage. The governing equation is: IP=∫VP*dt. If the applied voltage is say 300/12=25 times higher, then the result of the equation will be 25 times higher, thus the primary current rises that much higher.
crutschow said:You are still somewhat confusing the small magnetizing current of a normal operating transformer with the large inductive current of a flyback transformer.
In a flyback transformer, the primary inductance stores energy when the primary is conducting for transfer to the secondary when the primary current is interrupted. The stored primary energy is transferred to the secondary at that time. It is a two-step process -- Storage of energy in the primary in the first step. Transfer of this energy to the secondary in the second step.
Even though the primary voltage is much higher with a CD ignition, the generated primary inductive (magnetizing) current is much smaller due to the short duration (high frequency) of the applied voltage.
The energy transfer is through the flux connecting the primary and secondary, not by the energy stored in any inductive current
The rate of voltage rise has nothing to do with whether it is operating as a "normal" transformer. For the CD ignition the transformer is indeed operating in a normal transformer mode. By normal I mean it is simply converting the voltage on the primary to a voltage on the secondary, and the primary and secondary voltages and currents are proportional to the turns ratio.Primay current in the CDI system can be very high, and have a short diration. The voltage in the primary has to rise >10KV/uS. I don't see this operation as being comparable to a 'normally' operating transformer.
I described two different and seperate cases. I think you've somehow combined the two cases into one.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?