Quantcast
Jump to content

  • Do you own an ATV? Join our Forum!

    As a member, you can post in our forums, upload your photos and videos, use and contribute to our downloads, create your own member page, add your ATV events, and even start your own ATV club to host your own club forum and gallery.  Registration is fast and you can even login with social network accounts to sync your profiles and content.

Frank Angerano

What does CDI stand for

Recommended Posts

This is a good question asked by @Johnny Chancellor. I put it in a new topic so it does not get lost.  We all know we need a cdi box but I bet a lot of the members here don’t know how it works. This is a good explanation of a cdi box including what it does, how it works and what “cdi” stands for. 

Ive posted two links here. Feel free to add to the list! 

https://www.elprocus.com/capacitor-discharge-ignition-cdi-system-working/

 

https://en.wikipedia.org/wiki/Capacitor_discharge_ignition

 

 

 

  • Like 1

Share this post


Link to post
Share on other sites


Hey, look, I'm new but a topic I know a lot about!  I'm an ex ignition systems engineer, and I used to work as a test engineer at NGK here in the US. CDI is capacitive discharge ignition. 

This is a VERY complicated topic, but I seem to be pretty good at analogies.  Quick background: an ignition coil is an inductive device, you apply voltage to one side of the coil, and you generate a magnetic field, when that field is collapsed very quickly, the secondary side of the coil will generate voltage that is proportional to the winding ratio on the primary and secondary (12volts in, 40,000volts out).  Capacitance is created whenever you have two metal plates within close proximity of one another.  For example, an ignition coil in the head (like in a coil on plug engine) creates capacitance because of the close proximity between the coil and the head.  Capacitance can be added via special boxes or even some spark plugs (pulstar, if they are still around, but don't use them...)  So, what does that mean for spark?  Well, capacative discharge occurs very quickly over a very small amount of time (think nanoseconds), while inductive discharge occurs over a longer time, think microseconds. 

So, analogy time.  Think of a coil as a gear reduction with a flywheel on it.  The flywheel has a clutch that engages and disengages a water pump.  When you apply a 12 RPM input to the gear reduction, you get 40,000RPM on the output, but it takes a while to spin up.  So, when you start spinning the input and the flywheel is spinning, this is like the dwell time.  Once the flywheel is spun up sufficiently, the clutch engages the water pump, and water starts to flow into a hose.  At the end of the hose is a valve that will open at a certain pressure (this pressure changes, and is analogous to the required voltage to breakdown the spark gap).  "There is some stretch in the hose, so when the valve opens there is a little bit more flow for a short time, once that's done, the pump keeps pumping until the flywheel runs down."  The small stretch in the hose is  like the capacitance of a standard ignition system.  Once the valve is opened, the flywheel energy pumps out what it can, and then it's done.  A CDI system is like adding a big pressure tank to the end of the hose.  Once the pressure starts to build, more and more water is stored in the tank.  Once the valve opens, a HUGE tremendous amount of water comes out, but for a very short time.  Once the tank is done, the flywheel/pump still pumps a little bit out.  So, the pressure tank is like capacitive discharge, and the flywheel pump is inductive discharge. 

So, what's the advantage?  Well, the problem with a spark plug is something called quenching.  When spark occurs, there is a very small flame kernel that is susceptible to quenching via nearby relatively cool metal, like the plug, the head, etc. Increasing ignitability reduces this quenching effect, which is actually the benefit of fine wire spark plugs.  CDI helps this by providing a lot more energy in a very short time.  Some CDI systems help even more by allowing more current on the primary side (hence the need for bigger wires).  

So anyway, that's what I can add, hopefully it helps.  

Edited by Admin
Edited per member request
  • Like 1

Share this post


Link to post
Share on other sites

Need to edit, but I missed my window:

"There is some stretch in the hose, so when the valve opens there is a little bit more flow. 

Should read

"There is some stretch in the hose, so when the valve opens there is a little bit more flow for a short time, once that's done, the pump keeps pumping until the flywheel runs down." 

Share this post


Link to post
Share on other sites


2 minutes ago, Russell Senior said:

Need to edit, but I missed my window:

"There is some stretch in the hose, so when the valve opens there is a little bit more flow. 

Should read

"There is some stretch in the hose, so when the valve opens there is a little bit more flow for a short time, once that's done, the pump keeps pumping until the flywheel runs down." 

Edited 😀

Share this post


Link to post
Share on other sites

Great explanation I would only like to add how that hose valve You talk, is opened  so the spark that ignites the fuel can be generated, Thistask  is performed by the the pickup coil, a  little magnetic sensor  mounted very close to the magneto/rotor .The purpose of this coil/sensor is to send a voltage signal  to the cdi module (also known as ECU) for  spark to ocurr. Everytime the magneto/rotor tab(s) passes by the pickup coil ,there is a variation in  pickup coil magnetic field  producing a voltage change  going  the ECU , this  voltage variation is also known as Hall effect.  usually on the 0 to 5 V range  .The ECU receives this voltage and sends  the ignition coil a signal to generate a spark  at the designated cylinder. But this is  very curious here, because that signal instead of beeing a voltage is just the opposite, It is the suppresion of  voltage sent to the ignition. coil primary winding  that forces the  magnetic field  inside the ignition coil to collapse ,thus producing a high voltage and a spark in the secondary winding which is connected directly to the spark plug. In other words the signal  sent from the pickup coil to  ECU/CDI  grounds  the ignition coil primary circuit , making the  already existing magnetic field inside the ignition coil  to collapse,  creating  a very high voltage inside the secondary winding ,(usually in the 40.000 V range), which jumps to ground via the plug and  so the spark is created.

  Pickup Coils are also known as transducers.These elements convert one type of energy (in this case magnetic) into another (commonly voltage variation).Transducers are  very useful to measure different variables like position, temperature,light,proximity etc.beeing  the more common sensors used in vehicles for their versatility and simplicity.

Share this post


Link to post
Share on other sites


Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Similar Topics

    • By Randel1
      Product warning:  Lighting products manufactured by Larson Electronics LLC  9419 E US HWY 175, Kemp Tx. 75143
      Hi, I’m G. Randel and I have a small business that does boat and motor service and repair and rigging. I also service and repair off road 4 wheelers, lawn equipment and small engines. I have been doing this type of work for over 40 years, so I have accumulated some knowledge about the accessories and products needed to support those things. 
      I recently installed two high intensity LED lights on the T-top of one of my customers boats. He bought the lights after he had done considerable research and consultation with manufacturers. He wanted to make sure he was getting something that would serve his needs which was to see where he was going at night while underway on the water.  He decided on lights manufactured by Larson Electronics out of Kemp, Texas. They were reported to be rugged, weatherproof, waterproof to 3 meters and were warrantied against workmanship or component failure under normal use for 3 years. One light quit working within 10 months, the other is still working after about 16 months.  I removed the defective light and sent it back to Larson Electronics for warranty repair or replacement and they denied the warranty claim. Their reason was “failure was due to environmental damage”.
      At the time of purchase these lights sold for over #365.00 each and the representative that my customer talked to at Larson Electronics assured him that these lights were well suited for the purpose in which they were going to be used. 
      So, if you are looking for electronics, as in lighting, for your ATV, SUV. Boat, or any other outdoor application you might want to keep in mind that Larson Electronics LLC
      9419 E US HWY 175, Kemp, TX 75143 might not fulfill their warranty claims if you have a problem with their products.
       
    • By dook
      I bought a 2018 Rubicon with IRS, DCT, power steering, low range and deluxe package.  I thought I would pass on my observations for others thinking of buying. 
      I could have bought a new one for not much more money, but since they quit putting low range in Rubicons I bought a used one. I wanted a foot shift, but couldn't find one with low range so I bought this one.
      Power steering: This is the first EPS quad I ever rode. I'm an old school keep it simple kind of guy, but I love EPS. When I first rode this thing, I was amazed at the tight turning radius, Then it dawned on me that it only seems tighter because with EPS I make better use of the steering. Yes yes yes.
      DCT automatic shift. I like it, but I would still rather have foot shift. Not only because of simplicity and reliability, but because with foot shift manual transmissions I know the exact moment it will engage, no surprise lunge. If you ask me, DCT is a waste of money. I think they sell 8 times as many DCT as foot shift because they make 8 times as many, not because of demand. I like to ride one handed, I find I don't get tired as fast. Otherwise I would keep it in ES mode. I like to do my own shifting.
      Engine. I love the water cooled engine, so much quieter and I expect it to last much longer than an air cooled one. The fuel injection is wonderful and the gas mileage was a pleasant surprise. I don't buy into the "longitudinally mounted" sales talk. Horsepower is not lost by gears and shafts changing direction, it is lost by friction and slippage. This engine is mounted way too high, forcing them to make the seat much higher than it should be.  I don't like the resulting high center of gravity. A cylinder at a 45 degree angle under the gas tank instead of the seat is a better design. Power and smoothness is more than adequate.
      Suspension. I have the shocks all adjusted to the softest setting and wish the springs were a little weaker. Otherwise I like the IRS.
      Ride quality/rider fatigue:  This is the main reason I bought a Rubicon. I'm old. I love my Kingquad 300's but I hurt all over after 50 miles. I had High expectations of the Rubicon. The foam in the seat seems to be of very high quality and absorbs bumps well. There is one major flaw in the design of the Rubicon that impacts the ride quality....they mounted the handlebars much too far away from the seat.  About 5 inches too far. I find myself riding with my bottom on the front third of the seat and even then wishing I didn't have to reach so far for the grips.  Now I'm 5'11" so about average size rider. A short guy would be riding this thing all hunkered over like a kid on a crotch rocket bike with his neck kinked and peeking thru his eyebrows to see where he's going. That kind of riding has it's place, but not on a utility quad designed and marketed for ride quality. Vertical spine is comfort.
      I thought about finding different handlebars, but the cables might not fit, or bind when I turn.  If I was about 6',6", I probably wouldn't notice.
      If I find a small frame Rancher with EPS and IRS, I will buy it. If it is as  good a ride quality as the Rubicon, I'll sell the Rubicon, otherwise I will keep both.
       
    • By gareth leifheit
      Ive got a Big Bear 350 4x4 that has been sitting for a couple years. It was put away running but now the pull start wont move and the starter wont turn it either. Any ideas what I can lube up or bang around to loosen it up? Thanks
    • By jay rear
      Hi im new to the site. I have a 99 sportsman 500. I has been sitting for about a year now. I bought a new battery for it the other day and now i dont have any power to anything but the winch. Any help would be great. I already cut the pouch and checked voltage on both sides of the circuit breaker. 
    • By Beretta7
      Need help trying to figure out how to find the open wire for turning off my Big Bear.  Will srat with no issues and both the kill switch and main switch fail to kill the motor.  Any ideas where the open is
  • Recently Browsing   0 members

    No registered users viewing this page.


×
×
  • Create New...