CDI help needed

Discussion in 'General Electronics Chat' started by ukash, Jan 3, 2011.

  1. ukash

    Thread Starter New Member

    Jan 22, 2010
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    Hi every one, I need some help to make a CDI (capacitor discharge ignition) unit for my motorbike, mine has packed up and I cannot afford to replace it
    I have attached a image of which I think is a CDI diagram which takes a AC input? because of the bridge rectifier? My question is that my original CDI was DC powered from the battery, can I just remove the bridge rectifier from the diagram and hook it up straight to my battery?

    Thank you

    [​IMG]
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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    No, you can't, that circuit expected at least a 100V pulse from a magneto, possibly even several hundred volts.

    Please advise exactly which make/model/year bike you have and I can probably suggest something.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Others have posted ignition circuits here, I'm unsure if this falls into the "automotive rules" or not.

    I'll wait for a mod call on it, but at a glance, you should be able to use everything to the right of the bridge rectifier if running from a battery, though it may not work due to inadequate voltage. I'm not sure why they have one of the diodes in the bridge shorted anyway, it could be a ground issue with the alternator, hence the "See NOTA".
     
  4. ukash

    Thread Starter New Member

    Jan 22, 2010
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    hi thanks its a custom build and has a 100cc 2 stroke engine

    3 wires from stator, yellow and white go to the rectifier to power the lights and charge the battery, then a blue/white which is the trigger for the ignition

    old cdi was 4 pin dc, 12v from battery, earth, trigger, and output to ht coil
    old cdi was static ignition had no mapping or advancing on it, it just fires when its triggered

    cheers
     
  5. debe

    Well-Known Member

    Sep 21, 2010
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    184
    This is what i used on a engine that the HV coil & the CDI unit had failed on. The 12V dc inverter replaced the generator coil. The inverter TF is just a very small 12v.o.12v / 250v AC transformer to give 300V(this is no more dangerous than whats already on theengine)
     
  6. debe

    Well-Known Member

    Sep 21, 2010
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    Forgot circt of CDI. If your original CDI ran of 12V DC it would have had a HV inverter built in it.
     
  7. ukash

    Thread Starter New Member

    Jan 22, 2010
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    ok thanks im going to draw these up on a simulator and see if i understand it all cheers

    :D
     
  8. ukash

    Thread Starter New Member

    Jan 22, 2010
    13
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    hi does this look right or did i miss something?
    the inverter

    [​IMG]
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,682
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    Ukash, Where are you? 100cc/2 stroke engines are used in the hobby world. There are lots of commercial CD's and CD designs for them. Do you have a and/or want to keep the magneto? The transformer is the hard part (time consuming) to make. Some even include electronic advance/retard, depending on where you start.

    John
     
  10. debe

    Well-Known Member

    Sep 21, 2010
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    The circuit looks ok to me. Hi John 100cc 2strokes are common small motor bike engines hardly hobby motors. The transformer is a common 240v/24v CT AC. The one i used just happened to be one i salvaged out of some old TVs, they powered the remote reciever part of the TV.
     
  11. ukash

    Thread Starter New Member

    Jan 22, 2010
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  12. ukash

    Thread Starter New Member

    Jan 22, 2010
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    the voltmeter on the simulator goes between 50 and 100v very quickly from what i can see with my eyes maybe its too quick for me to see
     
  13. debe

    Well-Known Member

    Sep 21, 2010
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    The transformer looks fine to me. You need to assemble the circuit & try it in real life, you should get about 300V DC out of it & this is what most CDI ign systems use, it wont have alot of current. The one i built was for a 125cc 2stroke driving a generator that had a faulty CDI & HV winding.
     
  14. ukash

    Thread Starter New Member

    Jan 22, 2010
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    ok ill go down the electrical store and try it out tomorrow, so in real life when i hook up my multmeter to the output it should be around 300v dc? wont shoot up and down and all erratic?
     
  15. debe

    Well-Known Member

    Sep 21, 2010
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    In real life the voltage will be steady.
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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    You're now on the right track provided your magneto didn't step up the voltage &/or advance the timing as the rpm increased. Quite a few people I know swear by these but I've accumulated two good stock CDIs in my parts pile that go to my bike because, in time, 32 years is going to take its toll.

    http://www.ignitech.cz/english/aindex.htm

    Your power supply circuit could be improved on as far as efficiency goes if you're limited as to your supply current.
     
    Last edited: Jan 4, 2011
  17. debe

    Well-Known Member

    Sep 21, 2010
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    Very interesting site marshallf3 taken note of it thanks.
     
  18. marshallf3

    Well-Known Member

    Jul 26, 2010
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    That's a double cross we've got to bear with ours. A bit over 4.5K (they redline at 10K) the ignition voltage increases as does the timing advance which comes from separate pickup coils. That's how they were able to get such good torque on the low end yet still well over 50 HP out of an old pushrod 4 overhead valve per cylinder twin of only 500cc total - of course the engine first made it into public production 33 years ago and was produced in 500cc & later a 650cc variation.

    Everyone that's bought one rave about using the Ignitec unit on ours as not only do we occasionally lose the CDI but we also sometimes lose the HV windings on the stator and their solution takes care of that as well.

    Most say it was a challenge that Mr. Honda (at the time) took on to beat the Harley 750s that were eating up the flat track circuit, (which he won doing) others say it was a challenge between him and Moto Guzzi which produced a similar however air cooled twin.

    Not the best pictures but certainly one of the oddest looking bikes you'll ever see due to the rather unusual and very prevalent engine:
    http://en.wikipedia.org/wiki/Honda_CX500
    300K miles isn't unusual for these with simple maintenance, the hardest being replacing the cam chain but that often lasts for 100K depending on how hard you are on it. You simply keep good oil in them changed on a regular basis of course. Most of us use the Shell Rotellla 15W-40 diesel oil. It still has a high zinc content which is essential since our transmissions share the same oil thus require the shear strength it supplies but it's also an oil that doesn't have those new energy saving additives, most of which will cause our clutches to slip since they also are immersed in the oil. They also produce a 5W-40 synthetic which is more expensive but maintains the same qualities and probably a better choice for our riders in Canada where most of these bikes tend to be seen. Professional semi truck drivers swear by this oil or the Mobil Delvac equivalent who often log 1M miles before they need to overhaul their engines so by reputation they have to keep producing the best oil money can buy but it's only like $12 a gallon. I even use their synthetic in my car since Mobil 1 went to crap not long ago although there are other brands out there that would probably be equally as good for automotive applications.

    I have the 1979 CX500 Custom variant, goes from 0-108 mph in a matter of seconds being the lightest of the variants at 450 lbs. It was all hacked up when I first rode it home and around a bit during 2009 but it spent all of 2010 undergoing restoration to almost showroom condition. All I'm waiting for now is a nice run of spring weather so I can properly shoot paint. 2K Urethane paints are picky but if done right perhaps the best. Duplicolor etch primer on bare metal followed by their primer/sealer then I'm using DuPont's Nason line of base color and clearcoat. 3 coats of base will be easy, putting the clear on will be more difficult since the decals have to go on after the 4th coat followed by two more coats. Proper mixing of the reducer and catalyst is essential as is temperature, humidity and timing but with a good gun and a lot of luck I don't expect to have to do anything more than a light polishing on the last coat.

    Hardest thing to find were exact replica silencers but there's a company over in the UK that has the original patterns and will make them on occasion. Only thing that isn't factory is the radiator fan which I replaced with an electric as many others have but you can't see it. These originally came with a smallish plastic fan driven off the camshaft but over the years the plastic would get brittle and eventually crack, often sending a shattered blade into your radiator. Radiators aren't too hard to find nor are the fans but even the new old stock ones have the years on them so it makes sense not to trust them either, besides that the bike really needs minimal cooling except at an extended stop light in hot weather so a lot of us have been converting to electrics. Most just mount a temp switch on the top of the radiator, I designed and will soon be producing a true PWM controller that utilizes an LM35 epoxied to the bottom of the radiator thus only looking at the return water temperature. In that manner if you're getting plenty of cooling air while cruising the fan will never need to come on. Although not fully documented I've shared that circuit on here before, it's based upon a http://ww1.microchip.com/downloads/en/DeviceDoc/21756b.pdf but I've included a lot of extra stuff into the circuitry to make it universally adjustable to most any bike and added a temp output that's switchable between *C or *F with a simple jumper.
     
    Last edited: Jan 4, 2011
  19. ukash

    Thread Starter New Member

    Jan 22, 2010
    13
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    hi thanks for all the help but ive decided to order the cdi as i have no clue how to put these diagrams into real life
     
  20. marshallf3

    Well-Known Member

    Jul 26, 2010
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    201
    Probably a wise idea despite the cost as designing, building and perfecting your own just takes away riding time. :)
     
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