Diminishing output from CDI - 30 Volts to 2 Volts By FlyingBlindOnARocketCycle (Read 15,981 times)

[FlyingBlindOnARocketCycle]

 I've gotten my bike to the point where there seems to be only a single problem remaining. There's a thread on that here somewhere, or was. But anyway, at this point everything is working nicely with the exception of the output from the CDI. When attempting to start, the stator will put out around 80 volts steadily. The output from the CDI however will start around 30 V and drop over the course of a few seconds until it's down to 1 or 2 V.
 Results are identical using 2 different brand new CDIs. 
 It's a typical GY6 50cc.

[Bashan]

Your thread is around here somewhere, I'll find it. Listen, we bumped heads a little. I apologize, I was a jerk. Maybe we can start fresh and we can get you fixed up.

Is the bike starting or just cranking? The 80 volts you're referring to, that's the red/black wire?

Now the output from the CDI, what exactly are you referring to? Voltage to the coil on the yellow/black wire? One last question, are you getting any spark?

[JR]

Mar 6, 2014 14:25:04 GMT -6 FlyingBlindOnARocketCycle said:

 I've gotten my bike to the point where there seems to be only a single problem remaining. There's a thread on that here somewhere, or was. But anyway, at this point everything is working nicely with the exception of the output from the CDI. When attempting to start, the stator will put out around 80 volts steadily. The output from the CDI however will start around 30 V and drop over the course of a few seconds until it's down to 1 or 2 V.
 Results are identical using 2 different brand new CDIs. 
 It's a typical GY6 50cc.

First of all measuring voltage output for the CDI is not practical with a volt meter, it takes a special instrument to measure output on a CDI.

I'll echo Rich, is the 80 volts on the red/black and is this AC voltage. If the results are the same with two CDI's then it's time to see if the voltage on the red/black wire from the stator to the CDI is fluctuating. Also ground wires play a big role with a non-sparking engine.

JR

[Bashan]

You can access the thread you were referring to right here. I tried to edit it for brevity but it is still a bit of a tome. Again, I apologize for rudeness on my part. I agree the CDI to coil voltage is difficult to test. Sometimes just getting anything can tell you a little bit. Usually if the CDI isn't dead in the water you'll get something. I've had good results by putting my tongue between the Y/B and coil....KIDDING...KIDDING! Don't do that! Sorry Flash, I'm a boob. If you shorten your handle I won't call you Flash. I promise.

[DrRocco]

Hey JR, I don't know much about exactly what the CDI does, but I am curious why it takes a special instrument to check it out. What instrument is required? I'm not having any problems. I'm just curious, that's all.

[DrRocco]

I like "Flash" better too. Flash! Waa-Ah! Savior of the Universe.

[Bashan]

Hi, this is Jack Ryan aka JR here..... . The stator sends a constantly changing frequency of AC voltage to the CDI where it is processed by capacitors and released to the coil in bursts determined by the trigger coil. The frequency of the voltage is constantly changing dependent on the speed of the spinning stators magnets passing by the coils. The frequency is not important, it is the aggregate amount of current delivered by the capacitors delivered to the coil. The secondary winding of the coil is energized by the primary without regard for frequency. The highly variable nature of the current frequency makes measuring with a multimeter inaccurate. Timmah! Sorry Jack....just goofing. Correct me if I'm wrong.

[JR]

Nope and I'll add the speed at what the CDI charges and releases it's voltage is so fast that the ordinary multimeter is not capable of reading it.

Old Oscilloscopes and Fluke makes a meter that is basically called a speed pickup meter that can do the trick but you'll need to dig deep into your pocketbook to buy one.

www.scooter-assassins.com/files/D50_17_Ignition_System.pdf

[DrRocco]

I might be more confused than ever. Just to make sure I understand, the stator frequency is all over the place but is stored in a couple capacitors of opposite polarity. Then, when the trigger coil "triggers", they both release a burst of DC of opposite polarities. This DC then hits the rectifier, where it is smoothed into a somewhat steady DC voltage?

[DrRocco]

And, JR, by "old" o-scopes, do you mean analog ones?

A analog o-scope will work.

[JR]

You are confusing the R/R with the CDI. The stator puts out AC period, no DC involved. A typical 8-coil stator has 7 coils dedicated to one thing, the charging and lighting system. It is converted to Dc and regulated through the R/R (rectifier/regulator)

The 8th coil is a AC output that has only one function to supply Ac voltage to the CDI. Once the CDI gets voltage it stores it up to a certain amount then it's discharged to the coil which amps it up to as much as 20k in voltage to the sparkplug.

It discharges when it receives a message from the pulse coil (trigger coil) which is located on the outside of the flywheel and sends a weak voltage signal telling the CDI to fire at a time when the piston is at TDC on the intake and exhaust stroke which is timed by the location of the magnets on the flywheel.

The pulse coil and AC coil that feeds the CDI can be good and the charging coils be bad and the scooter will still run even with a totally dead battery.

JR

[DrRocco]

I see. Makes perfect sense. Thanks!

[tvnacman]

To get a reading from the cdi's output voltage to the coils primary winding , is reding a capactors discharge voltage .

Did you burp or fart this out , Hi, this is Jack Ryan aka JR here..... . The stator sends a constantly changing frequency of AC voltage to the CDI where it is processed by capacitors and released to the coil in bursts determined by the trigger coil. The frequency of the voltage is constantly changing dependent on the speed of the spinning stators magnets passing by the coils. The frequency is not important, it is the aggregate amount of current delivered by the capacitors delivered to the coil. The secondary winding of the coil is energized by the primary without regard for frequency. The highly variable nature of the current frequency makes measuring with a multimeter inaccurate. Timmah! Sorry Jack....just goofing. Correct me if I'm wrong.

This was very well said and reads easy . Commit it to the tech section !!!

John

[FlyingBlindOnARocketCycle]

A voltmeter might not be the ideal tool, but it's what I have. I do plan on getting an iscillocope at some point, but today I can only use what I have today.
The stator output to the CDI is measured from the Red/Black wire where it attaches to the CDI.
The CDI output to ignition coil is measured from the Green/Yellow wire where it attaches to the ignition coil.

The readings are consistent and predictable. The stator is generating 80+/- Vsc, the CDI receieves this voltage and sends 30Vac to the ignition coil at first, then it's output drops steadily until it reaches about 2Vac.
Additional attempts at starting show the voltage from the CDI starting not at 30, but closer to 2Vac.
I spliced an additional wire into the CDI ground wire and mounted that to the frame. The wires were cleaned, tinned, soldered, tested and covered with heat shrink tubing.

[FlyingBlindOnARocketCycle]

I spent some time searching around to see if there was anything online regarding this particular problem, but this was all I was able to find -
forums.atvrideronline.com/70/7757269/atv-repair-maintenance/my-atv-chinese-made-4-wheeler-will-not-start/page3.html
Look for a post from Kayh about 2/3 of the way down, posted 10/18/09 at 6:13PM
His solution was this "Well guess what....it didnt work. There was only 2 VAC going to the coil. I unhooked the green wire coming from the CDI and into the black wire (grounds). Guess what.....50VAC to the coil and a spark at the plug. "
I'm not sure what it is he was trying to say...