Help Understanding a CD Ignition

Lostfisher

Petty Officer 2nd Class
Joined
Nov 2, 2009
Messages
147
I am posting this question more for educational so I can understand a little more about the CD ignitions i am use to the older coil ignitions but am confused when it comes to determining what if the problem is in fact the ignition and where in the ignition the problem lays. I would like find out how I can tell if the powerpack, sator, or some other part is defective.
 

Silvertip

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Sep 22, 2003
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28,771
Re: Help Understanding a CD Ignition

You buy the service manual for your specific engine and follow the troubleshooting information (provided you have the tools for the job). In a simplistic way, about the best you can do with a multi-tester (volt-ohmeter) is to Ohm the coils and stator (you will need the manual for specs). Stator output testing generally takes an adapter for the voltmeter that most people do not have. If you don't want to buy the manual (a mistake if you intend to do service work yourself), then the library is the place to go for a manual.
 

Frank Acampora

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Jan 19, 2007
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Re: Help Understanding a CD Ignition

CD ignition means Capacitor Discharge Ignition. It functions by having the stator generate a high voltage to charge a capacitor(s) inside the CD box. It generally has one capacitor for each cylinder and one coil for each cylinder. A low power trigger coil for each cylinder generates a small electrical voltage that signals a transistor to "Dump" the capacitor into the coil. This rapid build up of voltage and the subsequent abrupt drop causes the coil to generate a very high secondary voltage and fire the sparkplug.

The stator generates a very high A/C primary voltage (at least 20 times the 12 volt system) that charges all the capacitors. To do this, it may have multiple separate windings. The ignition A/C is not rectified to D/C. The positive A/C sine wave will charge one capacitor and negative sine wave will charge the other. This happens when the flywheel is turning at or above cranking speed, so if you turn the flywheel by hand with the key on, you will not get spark. On the other hand, the ignition is self energising. Any time the key is on, and the flywheel is turning rapidly, the ignition is energised and you must do something to stop the engine. Thus: Even with a completely dead starting battery, if you are able to pull start (rope) the engine fast enough, it will fire and run. Generally, The CD boxes are shorted to ground through the ignition switch to prevent spark.

Since there are no points and the flywheel magnets and stator are constantly producing power, There is no "dwell" time. The capacitors have MORE time to charge. However, they will discharge much more rapidly (almost instantaneously) than, and build up a greater resultant magnetic field in the coil primary than a points system. The internal capacitors are the same general type but much higher in capacity than the external capacitor in points systems. The capacitor across the points functions only to absorb voltage surges as the points open and close, thereby preventing arcing and extending the points set life.

The advantages of CD ignition are:
1. Less moving parts so timing is more precise. Elimination of the rotor gap inside the distributor so less "noise" interference. Shorter, lower resistance secondary wires (on an outboard).
2. No points to wear or go out of adjustment; primary voltage can be much higher since there are no points to pit or burn.
3. Higher secondary voltage because primary magnetic field build up and collapse is faster and greater. Thus: Plugs get a "hotter" spark and are less prone to misfire
4. Cheaper for the manufacturer to make. (Easier and cheaper to buy the components than to make and machine a precision distributor.)


As said above, without special equipment, you can not troubleshoot the CD boxes. By switching with a known good one, you CAN eliminate it as a cause of no spark. You CAN test the stator for open circuits or shorts, and resistance, and you can test the coils. You can also test the triggers for open, shorts, and resistance.
 

F_R

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Jul 7, 2006
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28,226
Re: Help Understanding a CD Ignition

The preceding is a very comprehensive explaination of a "Mag CD" system. But if the question includes the older, battery CD system, it is a different animal. On those older systems, the 12V boat battery supplied the primary voltage instead of the stator. The 12V input was increased to 300V in the amplifier or pulse pack. The 300V was stored in a capacitor till time to fire. Then, either by points or a magnetic sensor, the amplifier or pulse pack was signalled that it is time to fire and the 300V was discharged through the coil. The coil's output was sent to a distributor, which directed it to the proper spark plug.

"Mag CD" is far better.
 

Frank Acampora

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Re: Help Understanding a CD Ignition

Undoubtably the mag systems are better, but I still prefer my old late 1970s Motorola "Magna-Power" with an electric eye distributor--it has a certain "Je ne sais quoi."

And it is on the engine in the avatar

I Don't suppose many are around anymore so I didn't include them.
 

rodbolt

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Sep 1, 2003
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20,066
Re: Help Understanding a CD Ignition

good old magna power.
kinda like a high tech version of the OMC amplifier system.
mercury used the thunderbolt which did about the same thing.
now we call them TCI ign systems and most yamaha 4 strokes use it as well as the HPDI.
most worked ok when new but just like ponts they required battery power to operate and charging systems of the day were rather small.
no battery power,something about 10V or less and no sparky sparky.
biggest difference between the battery CD set up and the battery TCI is the TCI system uses transistors to switch the 12V ign coil primary circuit on and off.
never a fan of magna-power,magna-power II was decent.
replaced to many years ago under a recall campaign for "erratic operation".
for those of us that have done this 30+ years, the increase in technologly on outboards and sterndrives has been kinda impresive.
glad I ot out of the automotive side years ago.
 

Frank Acampora

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Re: Help Understanding a CD Ignition

Magna-Power II was very much like the later distributorless ignitions except that the capacitor module was located under the flywheel and the trigger ring was different.

It was elegant in design, but unfortunately, poorly executed in manufacture. Yes, it was erratic: Many failed quickly, but some lasted the life of the engine. For a while, it was an orphan system and parts were not available. The only option was to retrofit to a distributor ignition. However, I believe that CDI is now offering repair parts.
 

robert graham

Admiral
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Apr 16, 2009
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6,908
Re: Help Understanding a CD Ignition

You guy's knowledge and understanding of these motors is amazing! The electricals is my weak suit, but I'm still reading and learning. Thanks for sharing your vast experience!
 

rodbolt

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Re: Help Understanding a CD Ignition

I should have a decent understanding of simple electronics.
the US taxpayer spent over 340K on my training.
my first 3 yrs in the USN I never saw even a life raft much less a ship.
all I did was tron schools.
they kept saying do good in this school we will send ya to another, I did and they did.
BE/E, top of my class, FC(A),top of my class,FC(C),top of my class.
not to metion all the general and advanced test equipment schools or the micro-minature repair schools and such.
did not complete the micro-minature school, was sick with the same issue they retired me from on test day.
was at portsmouth navel hospital instead of class.
so any help on altenator ign systems I know I dont mind telling.
yall paid for it anyway, actually,I did to cause even in the USN your pay is taxed.
 

Frank Acampora

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Jan 19, 2007
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12,004
Re: Help Understanding a CD Ignition

OK Rodbolt---then I have one for you: Can the old style, finned aluminum, black Motorola voltage rectifier/regulator used in Chrysler 12 pole alternator battery charging circuit be used with the Prestolite 20 pole alternator or will the different AC frequency mess it up? I would normally experiment, but if you know for sure, that beats experimenting any day.
 

rodbolt

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Sep 1, 2003
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Re: Help Understanding a CD Ignition

the frequency isnt a concern, its system amperage that is a concern.
the more poles the higher the amperage can be.
also there is a concern over is it single,double or three phase?
its been many years since I worked at a chysler dealer.
however the old chysler 75 I owned is still running.
whats the max charging amperage of the battery system vs the CD system?
we converted my old 75 from magna-power to battery distributer when I got it in 84 or so.
 

Frank Acampora

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Re: Help Understanding a CD Ignition

Hmmmm----Well, since both alternator stators are 2 wire to the rectifier and single winding, I suppose that both are single phase. Both are similar voltage output--not enough difference to worry about, close to 16 volts. I would also think that both have similar amp output. If anything, the newer system would probably be slightly lower because it is a dedicated winding to only charge the battery and not meant to power accessories like a an auto alternator. Old Motorola system used the same winding to power the ignition AND charge the battery. To bad it is too cold for me to start the engines and check voltages and amps.

SO: Given that frequency is not a concern, then I just may try the old Motorola rectifier/regulator on the prestolite system next season. Thanks!

BTW: 20 pole is a misnomer; 10 poles are dedicated to battery charging with heavy 12 volt windings. 5 poles with fine windings (to generate 250 volts) are dedicated to each CD box. (not sure about the 5 cylinder stator) Even though the poles to charge the battery are less than 12, the frequency is higher because the continuous magnetic strip inside the flywheel has more + and - poles than the two magnets inside the Motorola flywheel.
 
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