How to Make a Capacitive Discharge Ignition (CDI) Circuit for Two-Wheelers

The ignition process in any vehicle becomes the heart of the entire system as without this stage the vehicle just won’t start. To initiate the process, earlier we use to have the circuit breaker unit for the required actions.


Nowadays a more efficient and long lasting mechanism has been developed for the ignitions in vehicles, called the capacitor discharge ignition system. It incorporate an electronic circuit precisely functions like the old contact breaker, but in a solid-state electronic manner.

Let’s learn the circuit operations with the following points:

Basically as the name suggest, ignition system in vehicles refers to the process in which the fuel mixture is ignited for initiating the engine and the drive mechanisms.

This ignition is done through an electrical process by generating high voltage electrical arcs.
The above electrical arc is created through extreme high voltage passage across two potentially opposite conductors through the enclosed air gap.

As we all know that for generating high voltages we require some kind of stepping up process, generally done through transformers.

As the source voltage available in two wheeler vehicles is from an alternator, may not be powerful enough for the functions. 

Therefore the voltage needs to be stepped up many thousand folds in order to reach the desired arcing level.

The ignition coil, which is very popular and we all have seen them in our vehicles is especially designed for the above stepping up of the input source voltage

However the voltage from the alternator cannot be directly fed to the ignition coil because the source may be low in current, therefore we employ a CDI unit or a capacitive discharge unit for collecting and releasing the alternator power in succession in order to make the output compact and high with current.

Capacitive Discharge Ignition (CDI) Circuit for Two-Wheelers


Referring to the above capacitor discharge ignition circuit diagram, we see a simple configuration consisting of a few diodes, resistors, a SCR and a single high voltage capacitor.

The input to the CDI unit is derived from two sources of the alternator.

One source is a low voltage around 12 volts while the other input is taken from the relatively high voltage tap of the alternator, generating around a 100 volts.

The 100 volts input is suitably rectified by the diodes and converted to 100 volts DC. This voltage is stored inside the high voltage capacitor instantaneously.

The low 12 voltage signal is applied to the triggering stage and used for triggering the SCR.

The SCR responds to the half wave rectified voltage and switches the capacitors ON and OFF alternately.

Now since the SCR is integrated to the ignition primary coil, the released energy from the capacitor is forcibly dumped in the primary winding of the coil.

The action generates a magnetic induction inside the coil and the input from the CDI which is high in current and voltage is further enhanced to extremely high levels at the secondary winding of the coil.

The generated voltage at the secondary of the coil may rise up to the level of many tens of thousands of volts.

This output is appropriately arranged across two closely held metal conductors inside the spark plug.

 The voltage being very high in potential starts arcing across the points of the spark plug, generating the required ignition sparks for the ignition process.

Parts List for the CIRCUIT DIAGRAM

R4 = 56 Ohms,

R5 = 100 Ohms,

C4 = 1uF/250V

SCR = BT151 recommended.

All Diodes = 1N4007

Coil = Standard two-wheeler ignition Coil 


If you liked the post, Please Share it

Related Posts

Previous
Next Post »

149 comments

comments
October 23, 2012 at 8:06 AM delete

i have a suzuki smash 115cc motorcycle with limited rev cdi, can i use this one instead? thanks

Reply
avatar
October 23, 2012 at 10:46 AM delete

I am not sure how CDI specs are set for different vehicles so cannot give my opinion regarding it...

Reply
avatar
Anonymous
November 6, 2012 at 6:33 PM delete

HI Swagatham Sir,

Recently My 2 wheeler battery was gone and i came to know from my friend he bought one very small capacitor type equipment for substitute of the battery .
But it will work for Horn and indicators very very well if the bike is in acceleration or else it will down.

Do you have any idea what it comprises of .

I have not dared to open the equipment and check what it comprises of.

Thanks in advance
Regards,
Soma.

Reply
avatar
November 6, 2012 at 7:25 PM delete

Hi Soma,

It's probably an ultra capacitor, which is able to charge very quickly and discharge also very quickly with high dump currents.

However these are better researched and designed than ordinary capacitors and therefore are much efficient, but cannot sustain like batteries.... good for horns as these are used only for a few seconds.

These U/capacitors are permanent and will never deplete like batteries and therefore very cost effective in the long run.

Reply
avatar
January 2, 2013 at 9:52 PM delete

HI Swagatham,

Thank you for this.

The Peak Repetitive Reverse Voltage for Nte5461 through Nte5468 SCR's is 50V's through to 800V's.

What would you recommend?

Carl


Reply
avatar
January 3, 2013 at 10:55 AM delete

Hi Carl,

According to me BT151 is better than Nte5461, just compare the datasheets.

Moreover I have tried BT151 practically, and found these to be virtually indestructible.

Regards.

Reply
avatar
January 4, 2013 at 5:02 AM delete

Thanks Swagatham,

Is it typical to dump the charge to the coil core which is ground ?

Carl

PS.....this circuit could save a lot of $$$$$$,s

Reply
avatar
January 4, 2013 at 10:27 AM delete

Hi Carl,

The arcing will generate only when Hi-tension cable is brought close to the ground(-) of the circuit, the ground can be taken from any point, even the vehicle chassis will work.

Regards.

Reply
avatar
Anonymous
January 5, 2013 at 5:16 AM delete

Hitman,

I like this , thanks. One question, is the thick black line shown in the diagram just a ground connection from the coil to the SCR? It appears the coil already has a ground connection as well as the SCR.

Thanks,
Dan

Reply
avatar
January 5, 2013 at 11:31 AM delete

Thanks!

Yes, the grounds must be joined together, the thick line highlights this condition.

Reply
avatar
Anonymous
February 8, 2013 at 10:18 AM delete

thanks for the circuit,one question pls,is this circuit is enable in any type and model of two wheeler.it is also ok in different cc of two wheeler,whether 100,125,155,175?pls reply thanks

Reply
avatar
February 8, 2013 at 12:10 PM delete

this circuit would work for any vehicle that uses a single spark plug for the ignitions....

Reply
avatar
Anonymous
February 19, 2013 at 11:29 PM delete

is it applicable to twostrokes motorcycles? for my yamaha Dt125? i really needs to know if i could use it.here is my EMail:neco_tine@yahoo.com......thanx!

Reply
avatar
February 24, 2013 at 7:24 PM delete

Hello Sir
I have TCI in honda gxh-50cc engine.can i replace it with the circuit you have explained?

regards
prateek

Reply
avatar
Anonymous
February 27, 2013 at 9:07 AM delete

hi swagatam
nice easy desighn. i have a ski-doo 3 cyilinder, but all 3 fire at the same time, im haveing a problem with the original cdi. do you think i might be able to use your desighn as a replacement?

tks rob

Reply
avatar
February 27, 2013 at 1:00 PM delete

Hi Rob,

Thanks!

If your ski-doo uses a single spark plug then definitely the above circuit would be applicable.

Reply
avatar
Anonymous
March 5, 2013 at 9:06 PM delete

Good day Sir,
Thanks for your efforts on this website. I have a 1998 Suzuki DR350SEW (dual sport model), which has two pickup/trigger coils. I'm wondering if this design would work? Is it your understanding that the 2nd trigger is for advancing timing? Would this design limit higher speed performance? Thanks again.

Reply
avatar
March 6, 2013 at 7:19 PM delete

Thanks!

I am sorry I do not have detailed regarding different ignition systems, so cannot suggest my views.

Reply
avatar
March 21, 2013 at 10:42 PM delete

Which BT151 should be used? There are a couple different ones such as, BT151-600R, BT151-800R. Thank you.

Reply
avatar
March 22, 2013 at 9:45 AM delete

600R refers to 600V, and 800R to 800V, both are way ahead of the required specs....so anyone would do.

Reply
avatar
Anonymous
April 29, 2013 at 4:15 AM delete

Is this CDI AC Right?

Reply
avatar
Anonymous
May 13, 2013 at 2:50 PM delete

HI Swagatham Sir,

How can I use Old Nokia BL-5C 3.7v battery to make a LED torch.

How many 5mm LEDS I can connect and Can you provide me the simple circuit to make this.

For charging the battery, I can recharge the battery in my mobile and use that battery for torch.

Can you please provide me the simple circuit Sir.

thanks In Advance

Regards,
Soma.

Reply
avatar
May 13, 2013 at 10:11 PM delete

Hi Soma,

Please refer to the following post:

http://homemadecircuitsandschematics.blogspot.in/2013/05/how-to-connect-5mm-leds-to-37v-li-ion.html

Reply
avatar
August 1, 2013 at 8:03 PM delete

Hey Swagatam Majumdar,

I have a Indian make yamaha Rx 135 (2stroke) and a TVS apache RTR 160.
These bikes have CDi's from the company itself.
Is it possible to enhance the performance of these bikes or a matter of any small cc bikes?
(P.S. I have read a lot about Performance CDi's and want to make one on my own. Please Guide me as this is very interesting topic for me)

Thanks,

Chinmay Bisht
chinmay20002@gmail.com

Reply
avatar
August 2, 2013 at 9:38 AM delete

Hi Chnmay,

I have discussed one such circuit here:

http://homemadecircuitsandschematics.blogspot.in/2013/01/make-this-enhanced-capacitive-discharge.html

Although the circuit is a tested one and it definitely works, I am not sure if it would produce any adverse effect on the bike engine, you can give it a try under the supervision of a qualified auto electrician.

Reply
avatar
Anonymous
August 22, 2013 at 10:44 AM delete

are there RPM limit for this circuit?

Reply
avatar
Anonymous
August 22, 2013 at 10:46 AM delete

is there RPM limit for this circuit?

Reply
avatar
Anonymous
August 29, 2013 at 12:51 PM delete

Hi Swagatam, how do you turn it off? thanks.

Reply
avatar
August 30, 2013 at 10:45 AM delete

when vehicle engine stops, the circuit also stops.

Reply
avatar
September 1, 2013 at 8:24 PM delete

http://www.molla.org/DIY-CDI/SC-DIY-CDI-article-hires.pdf

Reply
avatar
September 1, 2013 at 10:22 PM delete

That's a very interesting and useful link, thanks very much!

Reply
avatar
Anonymous
September 14, 2013 at 9:34 AM delete

I have 2 coils on my bike, can I install 2 CDI units? Also to complicate matters, each coil fires 2 plugs at the same time. Each coil has its own trigger.

Reply
avatar
September 14, 2013 at 2:07 PM delete

yes, if there are two spark plugs, then two CDIs can be used.

Reply
avatar
October 10, 2013 at 6:39 PM delete

Hi sir... I have a honda dio 50cc 2 stroke scooter? Would this work instead of the stock cdi which has 5 pins and limiter?

Reply
avatar
October 11, 2013 at 10:04 AM delete

Hi Ryan,

Yes the above circuit is a standard CDI circuit suitable for all 2 and 3 wheeler, basically it's an Indian, Bajaj 2E Rickshaw CDI circuit.

Reply
avatar
October 16, 2013 at 5:02 AM delete

Hi Swagatam

What is the function of the diode connected across the primary of the ignition coil?
With cathode grounded, won't it obstruct the capacitor's energy from passing on to the primary of the ignition coil ???

Reply
avatar
October 16, 2013 at 11:47 AM delete

Hi I have a honda xr200 1981 the cdi is buggered will I need to get another one or is there a way to bypass this?

Reply
avatar
October 16, 2013 at 12:13 PM delete

Hi Abu-Hafss,

simulating the capacitor discharge pattern could be little difficult, however i am assuming the diode to be reversed biased, because practically the circuit is working perfectly so it means everything is right in the circuit.

Reply
avatar
October 16, 2013 at 12:19 PM delete

It is also working without that diode !

Reply
avatar
October 16, 2013 at 7:34 PM delete

Do you mean damaged? it would be better to replace it then

Reply
avatar
October 17, 2013 at 12:15 AM delete

Yes, the CDI of old model of Yamaha is 95% identical to yours, it does not have that diode.

Reply
avatar
October 17, 2013 at 10:19 AM delete

the above circuit was designed by 'Bajaj" engineers, so the diode does work in someway to protect the longevity of the unit....because conditions in automobile electrical AC are too unpredictable, which show its impact in course of time and not immediately.

Reply
avatar
October 19, 2013 at 3:13 PM delete

Hey just surfing around the net looking at info on CDI design and implementation on the hobbyist level.
I have a 46 cc retrofit kit for a bicycle and it has given me 4 years reliable use even though it is very cheap engine that gets hard used.
I have had an alcohol still for a couple of years and have recently began running it on the head of the still 98% methanol 2% hydro-sol.
It has a magneto coil, I want a little more spark. I understand that i will need to implement a better cdi but also wonder if i can rewind the magneto coil or change the magnet provided there is enough room

Reply
avatar
October 20, 2013 at 12:53 PM delete

yes making the magneto stronger would hep generating stronger sparks, so you can either modify the winding or simply procure a mobike magneto and replace it with the existing one,

Reply
avatar
November 5, 2013 at 2:02 PM delete

Good day Swagatam Majumdar! I have a 2 stroke Yamaha L2GF 110 cc 1970's model that uses points. Can i convert it to cdi and use your circuit? Thanks..

Reply
avatar
November 6, 2013 at 9:25 AM delete

Good day John,

Yes you can use the above circuit for your bike.

Reply
avatar
November 26, 2013 at 12:34 PM delete

I am not clear on the trigger circuit, Can Hall Effect Sensor be added and a Transistor in place of the SCR.

Reply
avatar
November 26, 2013 at 2:05 PM delete

hall effect/ transistor can be used for triggering the SCR, however it's more simply done directly through the AC received from the alternator 12V coil, as depicted across the diagram output terminals.

Reply
avatar
December 3, 2013 at 4:32 AM delete

I have a need for an ignition system for a 6 cyl 2-cycle engine. 2 cylinders fire at a time, two times per revolution. i.e. that's 12 sparks per 360 degrees of crank rotation. I am quite gifted mechanically but alas, electrickery has me by the shorts. Can any reader offer assistance? Thanks, M8 (Mate)

Reply
avatar
December 3, 2013 at 12:13 PM delete

you can try the following circuit,but could be difficult for you considering that you are very new in this field:

http://homemadecircuitsandschematics.blogspot.in/2013/10/universal-multi-spark-enhanced-cdi.html

Reply
avatar
Anonymous
December 13, 2013 at 10:05 PM delete

Hello Sawagatam! I have a 2 stroke engine 29cc ZENOAH, its ignition system has two separate parts, primary coil and the secondary coil. primary coil has power, it seems to have problems with CDI in it, so it does not interrupt power to the secondary coil operation. Thanks for asking me to do. 1 - His strong ignition is used for this machine? 2 - guide me how to connect. thanks in advance and appreciate! Dung Anh

Reply
avatar
December 14, 2013 at 11:16 AM delete

Hello Dung,

It's quite easy, after making the above explained CDI circuit, you will just have to integrate the inputs to the indicated voltage outputs of the alternator.
Next, the C4 bottom link will need to connected with the free end of the primary of your ignition coil.

The other terminal of the primary coil will not require any attention as it would be originally connected to the ground of the vehicle.

That's all, this would conclude the installing of the explained CDI circuit

Reply
avatar
Anonymous
December 19, 2013 at 10:05 PM delete

Sincere thanks to Swagatam Majudar !

Anh Dũng

Reply
avatar
January 27, 2014 at 12:40 PM delete

Hi Swagatam

I am making a CDI tester as per block diagram:

https://dl.dropboxusercontent.com/u/20969135/CDI%20tester.gif

But, I am cautious that the pulse generator circuit might not be isolated from the 220VAC mains.

Your valued suggestions are requested.

Reply
avatar
January 27, 2014 at 9:11 PM delete

Hi Abu-Hafss,

Do not use direct 220V, it can damage the diodes and the scr, you will need to isolate it using two step down trafos connected back to back

Reply
avatar
February 7, 2014 at 6:41 PM delete

Hi Swagatam

Recently I physically made the 555 boost circuit with an output of smooth 600V.
The BJT network was removed. The Coil is super cool but the mosfet gets little warm.

However, when I feed the HV into the CDI....................Nothing Happens.

1) If the triggering circuit is separated, the LED at the output shows perfect triggering. But when the output is connected to the CDI unit, the LED goes off.

2) If manual triggering is done with 9V battery/power supply, a faint single spark could be heard at the spark plug but not visible.

3) One point which might be or not important. The CDI unit is having 400V capacitor whereas, the boost circuit is producing 610V. Could this be the reason?

Reply
avatar
February 8, 2014 at 10:08 AM delete

Hi Abu-Hfs,

What is the gauge of the wire that you have used? It should be selected appropriately for getting the required amount of current.

And the current from the power supply should also be rated high enough for the CDI coil to respond.

even 400V is high enough for acquiring 20000 volts from the CDI coil, so it's fine

Reply
avatar
February 8, 2014 at 12:28 PM delete

I used 50 turns of 21 SWG (0.8mm) on a iron powder toroidal ring.

Reply
avatar
February 8, 2014 at 8:05 PM delete

21 swg looks OK to me.
check the current through the coil and the BJT, this magnitude will actually decide the watts pushed into the ignition coil and will influence the sparks.

what is iron powder, do you mean ferrite?....ferrite core is a must for this application. iron core will only convert current to heat.

Reply
avatar
February 9, 2014 at 2:56 AM delete

Hi Swagatam

I am operating this circuit with 12V-5A supply i.e. 60VA input.
The output is 600V, so the amperes roughly 100mA. This is just for idea. I will check the amperes and will inform you.

Ferrite toroidal rings are the black one whereas the iron powder toroidal rings are made with iron powder......more details could be seen here:

http://www.inductors.ru/pdf/Doc496_Ferrite&Powder_Core_Power_Inductors.pdf

I used Yellow/White ring.

Reply
avatar
February 9, 2014 at 12:08 PM delete

Hi Abu-Hafss,

I think we are forgetting one thing, it's not the current that is important here, rather the voltage.
and it just requires an excess of 100V AC for the circuit to create powerful sparks across the high tension wire of the CDI coil.

Please refer to the first circuit given in this article, please see how it's configured:

http://homemadecircuitsandschematics.blogspot.in/2011/12/homemade-fence-charger-energizer.html

Reply
avatar
February 9, 2014 at 1:13 PM delete

Hi Swagatam


The article you are referring involves 2 transformers whereas, my effort was to use a transformerless design.

I had that point in my mind that current is not an important issue here. For that particular reason, the output is around 600V as long as the input voltage is between 12V-30V !!!

Without the CDI, I have checked the capacitor gets charged within milliseconds. To connect to the CDI unit, I removed the capacitor + diode and connect the mosfet+coil directly to HV input of the CDI unit. (The CDI has its own diode and capacitor).

At the HV input the DVM set at AC is showing 6-7 volts !!! How can that be??? The CDI unit works perfectly in its place.

Reply
avatar
February 10, 2014 at 9:37 AM delete

Hi Abu-Hafss,

I referred you the above circuit to indicate how the low current 220V input from an ordinary trafo works perfectly to produce the required 20kv sparks at the output of the CDI coil

I am afraid removing the diode capacitor network will not help, it's required for the proper functioning of the design, may be because it operates by charging and releasing the capacitor stored energy only when the capacitor charge reaches some optimal point.

The think the CDI coil or any such trafo responds best when bursts of high voltage are dumped in their primary winding instead of a continuous frequency.

Reply
avatar
February 11, 2014 at 12:36 AM delete

Hi Swagatam

It seems to be quite difficult in getting the 555 boost circuit to work as HV supplier to a CDI. I have spent many hours but, not successful.

Presently, since I need the HV supply only for bench test unit for CDIs, I am considering to use a transformer.

I have a 220V-13V 100mA small transformer. Will it be okay, to use it with a 555 astable oscillator at 50-60Hz + TIP31C? Or do I need to have a bigger transformer?

Reply
avatar
February 12, 2014 at 10:57 AM delete

Hi Abu-Hafss,

A high frequency input will not work with a CDI coil, you will have to use the converter in a burst mode or a pulsed mode, and it should match the input winding voltage rating of the CDI.

A 100mA transformer will also work but again it needs to be operated in a pulsed mode that's why the diode/capacitor stage becomes so crucial.

Reply
avatar
February 12, 2014 at 8:49 PM delete

Hi Swagatam

1) If we use the diode+capacitor before the CDI, the HV would turn to 600VDC whereas the CDI needs an AC voltage to operate.

2) As far as the 100mA transformer is concerned, I simply followed your circuit

http://homemadecircuitsandschematics.blogspot.com/2013/01/make-this-enhanced-capacitive-discharge.html

only replaced the darlington with TIP31C. I could get only 130V which, if fed into the CDI results nothing.

3) As per your above statement if diode & capacitor are crucial then how your enhanced CDI worked without them?

4) I also tried this

http://homemadecircuitsandschematics.blogspot.com/2012/02/how-to-make-simplest-inverter-circuit.html

replacing 2N3055 x 2 with TIP31C x 2 and 12-0-12 200mA transformer.

The voltage at primary is 24VAC but the voltage at the secondary is less than a volt!

Reply
avatar
February 13, 2014 at 12:19 PM delete

Hi Abu-Hafss,

All my CDI circuits have a high voltage capacitor stage included, which one exactly are you referring to?

Reply
avatar
February 13, 2014 at 3:55 PM delete

Hi Swagatam

I think you got confused with my long message.

Please see the attached picture:

https://dl.dropboxusercontent.com/u/20969135/CDI%20Bench%20Test.gif

1) With HV Supply 1, I could get 600V. The diode and capacitor has to be removed, only HV AC has to be fed into the CD unit. But the set-up did not worked as I reported on my post of Feb. 7th.

2) I tried HV Supply 2 and 3, got only 130VAC but again the set-up did not worked. This set-up is based on your article of enhanced CDI for 2-wheelers.

3) The HV Supply 4 is based on your article Simplest Inverter with 70% efficiency but this also not worked, I could get less than a volt.

The High Voltage Capacitor you are referring is already included in the CDI unit. I am not talking about the CDI unit (it is untouched). I have been talking about various set-ups for HVAC supply which has to fed into the CDI unit. I hope now everything is clear. Now I await your valued comments.

Reply
avatar
February 14, 2014 at 8:37 AM delete

Hi Abu-Hafss,

The circuit shown in the following link worked very nicely for me:

http://homemadecircuitsandschematics.blogspot.in/2013/01/make-this-enhanced-capacitive-discharge.html

You can make this circuit exactly as it's shown and then compare it with your designs and check why this one works and your designs don't.
I think the gate trigger could be the culprit.

Reply
avatar
February 14, 2014 at 10:56 AM delete

Okay, I'll start all over again.

But what do you say about the HV Supply 1?

Reply
avatar
February 15, 2014 at 1:07 AM delete

Hi Swagatam

Today, I re-started the project from beginning.

Firs,t I checked the HV supply in a bike, I found it to be 125VAC.

Second, I checked the CDI unit. It was working fine.

I rebuilt the circuit same as yours, only changed the RC components to fixed values to get 51.50% duty cycle and 57.75 Hz frequency. The output was 136V.

When I connect these 136V to the CDI unit, they dropped to 40V. But I could not get any sparks at the spark plug :(

Reply
avatar
February 15, 2014 at 10:14 AM delete

Hi Abu-Hafss,

Where did you connect the SCR gate terminal of the CDI (the 470 ohm end with reference to the linked circuit)?

Reply
avatar
February 15, 2014 at 11:07 AM delete

Hi Swagatam

First I connected the triggering input to the output of variable frequency oscillator (max. 5V). When I could not get the sparks, I manually tapped the triggering input with 12V but still no sparks.

Reply
avatar
February 15, 2014 at 8:39 PM delete

Hi Abu-Hafss,

Something is surely wrong somewhere, I think for avoiding doubts you could try following the exact design that's been shown in my circuits, and also use the same ignition coil which has been shown in the drawings.

Reply
avatar
February 18, 2014 at 12:17 AM delete

Hi Swagatam

I checked the coil and found that the secondary has very high resistance in M-Ohms, maybe due to the high tension wire, though it worked perfectly in the bike. Anyway, I bought a new one same the one shown in your drawing. It had perfect reading of about 6k.

However, as reported on Feb. 15th, when I fed 136V thru CDI to the new coil the voltage dropped to 40V and there were no sparks.

Reply
avatar
February 18, 2014 at 7:33 PM delete

Hi Abu-Hafss,
I am not sure what could be the problem, because the circuit is too straightforward and should start working immediately, I have already made this circuit for many different applications and everytime it responded correctly.

You can try the fence charger design and see if it works for you or not.

http://homemadecircuitsandschematics.blogspot.in/2011/12/homemade-fence-charger-energizer.html

Reply
avatar
February 18, 2014 at 9:03 PM delete

One more point.............
When I switch on the circuit the LED connected to the pin#3 of 555 would indicate the oscillation. And sometimes when I connect the transformer, the oscillation would stop.

In other words, sometimes when the transformer is connected to the collector of TIP122 and the +ve rail, the 555 would stop oscillating. And then when I disconnect the transformer, it would resume the oscillation after some time. This does not happens every time.

However, the problem I reported earlier occurred when the 555 was oscillating with the transformer and the output 136V.

Lastly, please remember the transformer I am using is 12V 100mA.

Reply
avatar
February 19, 2014 at 10:39 AM delete

Hi Abu-Hafss,
try the fence charger design without the 555 stage, let's first make the basic design work ad then you can proceed with the other versions.
I think the second trafo should be rated a little higher, may be a 500mA will be more suitable.

Reply
avatar
February 20, 2014 at 3:43 AM delete

Hi Swagatam

Your drawing is bit confusing, I have simplified and reproduced it.

https://dl.dropboxusercontent.com/u/20969135/CDI%20HV%20Supply.gif

Please check and confirm, if I have understood your circuit correctly.

Reply
avatar
February 20, 2014 at 12:01 PM delete

Hi Abu-Hafss,

It's one and the same, to me your diagram looks more confusing:) because in my diagram the bridge is well isolated from the transformers and makes it clearer to understand that it's been installed for powering the 555 circuit.

Reply
avatar
February 21, 2014 at 5:37 PM delete

HI Swagatam

Finally, I have managed to get the tester working with the fence charger configuration without the triac. Actually, I got deceived with the earth sign in your schematic. I separated the negative supply for the CDI + ignition coil and the triggering circuit. However, the sparks are quite weak. I am considering to replace the 2nd transformer with a 6V so that the output is around 400-440V.

Reply
avatar
February 22, 2014 at 10:24 AM delete

Hi Abu-Hafss,

That's great! In DC circuit, the earth symbol generally indicates the common negative rail.
You can also try a 1amp transformer for the one which is connected with the CDI, this could also help to increase the spark strength.

Reply
avatar
February 22, 2014 at 3:03 PM delete

Hi Swagatam

Yes, the earth sign generally indicates the common negative rail, that's why I mistakenly assumed that the 555 is also grounded to that negative rail. Shouldn't I advise you to point out this important note in your article so that people like me may not get deceived.

Right now, I am using 2 x 12V 250mA xformers. I think changing the 2nd xformer to 1A won't strengthen the spark because the sparks are released from the charge dumped in the capacitor. Therefore more higher voltage will result strong spark.

Reply
avatar
February 23, 2014 at 9:52 AM delete

Hi Abu-Hafss,
I'll remove the earth symbol so it doesn't confuse the new hobbyists.

Higher voltage will produce longer sparks but will be weaker in power (not very bright), increasing amps will make the sparks thicker, stronger and brighter.

Reply
avatar
February 24, 2014 at 11:54 AM delete

Hi Swagatam

Ok, but in that case both the xformers should be changed.........because the output from the first would the input for the 2nd. If only the 2nd is changed, the input wattage would remain the same and hence the output would remain the same.

Reply
avatar
February 24, 2014 at 12:38 PM delete

Hi Abu-Hafss,

Yes that's true, you will have to change both the transformers with 1amp

Reply
avatar
March 27, 2014 at 3:16 PM delete

Hi Do you have a CDI circuit that will work for my +ve earth motorcycle which will run from 12 volt battery and points. Thank You Peter pnptrudgeon@gmail.com

Reply
avatar
March 28, 2014 at 9:34 AM delete

Hi, the body polarity is irrelevant here. You can use the above suggested circuit with your vehicle also....just make sure the "earth" lines of the circuit are only connected with the battery negative and not with the body of your vehicle.

Reply
avatar
April 1, 2014 at 2:42 PM delete

Thank you much appreciated. Best Wishes Peter

Reply
avatar
May 2, 2014 at 11:40 AM delete

how to make a adjustable cdi for 180cc 4 stock or can i modify the existing

Reply
avatar
August 18, 2014 at 7:42 AM delete

Dear sir,
what happen if we changing C4 (1uF) to bigger 220uF 250V?

thanks

Reply
avatar
August 19, 2014 at 4:27 PM delete

Dear Nuraniku, it's not recommended, and moreover it would produce the same results as with a 1uF/400V....however, the capacitor will need to be a nonpolar type.

Reply
avatar
October 4, 2014 at 8:02 AM delete

hi sir,
i want to build this circuit,but my question is how can i connect this,,
is it alternator ang magneto are the same?
i found a magneto coil to rectifier on my bike,where i connect this from your circuit?
pls

Reply
avatar
October 4, 2014 at 3:19 PM delete

hi nhark,

yes alternator refers to the magneto in your bike...

locate the 200V and the 5 V to 12 V sync pulse coming out from the magneto and connect them with the relevant terminals of the above circuit, also connect the shown outputs with the ignition coil and the coil output with the spark plug....the circuit will start working immediately.

Reply
avatar
October 6, 2014 at 10:15 AM delete

hi sir,
i built one this day but it can not start the engtine...why?

Reply
avatar
October 6, 2014 at 5:45 PM delete

hi nhark, the problem could be in the circuit assembly or the wiring connections with your bike.

Reply
avatar
November 14, 2014 at 1:24 PM delete

tnx sir...it was my mistake...

hehehe

Reply
avatar
November 15, 2014 at 12:53 AM delete

As Sawagatam said, it is not suitable because a 220µF capacitor would take longer time to charge as compared to a 1µF capacitor which would fully charge within nano seconds!

Reply
avatar
November 29, 2014 at 4:42 PM delete

Hi sir
i want high voltage from this circuit
like 300v to 400v.
Kindly tell me how tjis possible

Reply
avatar
November 30, 2014 at 9:54 AM delete

Hi Mansoor, the CDI coil in the above circuit is capable of producing 20,000 V and is intended to be used in automobiles...

Reply
avatar
December 1, 2014 at 4:32 AM delete

Hi sir thank you for replying.
actuall i mean to say that the above circuit output voltage is 230v to going on ignition coil,
And ignition coil 230v to become 20,000 v.
But it can possible circuit produce 400 V and forward to ignition coil.
And then ignition coil 400 V to become 40,000 Volts?

Reply
avatar
December 1, 2014 at 4:51 AM delete

I wana ask you one question.
And question is
Do you built any plasma ignition circuit?
As you know plasma ignition very much powerful spark.
and its circuit takes dc HV from battery.

Reply
avatar
December 1, 2014 at 7:30 PM delete

Hi Mansoor,, It can be tried but forcing 400V into the coil could make it hot.

making a plasma spark will require a much bigger coil....possibly I'll post the article someday in my blog

Reply
avatar
December 14, 2014 at 8:09 PM delete

Dear sir,
My bike is honda cd 125 and its 10000 rpm
and its ignition build for 10000 rpm.
i am customize engine for 15000 rpm and its require improved ignition.
does above circuite use for this 15000 rpm

Reply
avatar
December 15, 2014 at 2:17 PM delete

Dear Mansoor,

yes according to me 15000 RPM will not be a problem for this circuit since it uses a fast, and advanced SCR for the switching.

Reply
avatar
December 17, 2014 at 11:54 AM delete

Its mean this SCR BT151 competible for 15000 RPM

Reply
avatar
December 20, 2014 at 8:52 AM delete

If we alter some parts change for earn more voltages like 400 V to give ignition coil.
like AC alternator 12v and 1amp change to direct DC 12 V battery input and circuit's change diods 1N007 change to 1N 5408 - 3amp doids.
Does it run and genrate more voltages and more power?

Reply
avatar
December 21, 2014 at 5:09 PM delete

increasing voltage or current won't do any good for enhancing the automobile performance because the spark plug gap is too small and will respond equally to a low voltage or a high voltage.....
The ignition coil and the circuit is already powerful enough, to produce sparks 1/2 inch long....it implies that you could try altering the spark plug gap and make it about 1/2 inch long,,,,this alteration could help the cause.....because longer spark would mean longer area covered by the spark inside the chamber influencing bigger explosions.

Reply
avatar
January 6, 2015 at 4:38 PM delete

you can use a momentary on switch to temporarily ground the signal from the alternator, disabling spark and therefore stopping the motor. kill switch :)

Reply
avatar
January 30, 2015 at 2:19 PM delete

can you tell me what voltage i should expect from the small 2 stroke ignitions used in made pales boat cars etc
usually 23 cc to 35 cc
Zenoah or chung yang
also the zenoah engines use a primary and secondary coil where as the CY uses a single coil
what are the differences between the 2

Reply
avatar
January 30, 2015 at 7:43 PM delete

sorry I have no idea of these bikes...
normally a 2 stroke ignition would be able to produce 10kv

Reply
avatar
February 17, 2015 at 5:57 AM delete

If i want to use this ignition in a 4 stroke 90 degree V twin, can i just use 2 pickup coils 90 degrees apart, hooked to 2 separate ignition boxes? Thanks!

Reply
avatar
February 17, 2015 at 11:25 AM delete

I am not very sure about it, but you can definitely try it out

Reply
avatar
March 8, 2015 at 7:27 PM delete

Not sure if my message went through as my computer is a little crazy at the moment.
CDI unit C4 capacitor, is it polarized or non-polarized?
I plan to try it on a Mercury outboard 402hp (40hp) motor, stator input is 180volt and trigger is 20volt, do you think it will be ok?

Reply
avatar
March 9, 2015 at 9:16 AM delete

C4 is a non-polar capacitor, the circuit is intended for all 2 or 3 wheeler automobile engines, if your system similar to these engines then it'll surely work.

Reply
avatar
March 17, 2015 at 8:40 AM delete

Is there a way to make this adjustable to change the spark timing ?

Reply
avatar
March 17, 2015 at 11:33 AM delete

you can try the modified version of the above for achieving the timing feature

http://homemadecircuitsandschematics.blogspot.in/2013/01/make-this-enhanced-capacitive-discharge.html

Reply
avatar
Anonymous
April 22, 2015 at 6:08 PM delete

Good day Swagatam,
In this circuit, is the trigger a negative or positive signal? Or alternating current?
Also, is the capacitor a AC or non polarised dc capacitor? I used an ac capacitor (1uF, 250v) and the bike would not run properly.

Reply
avatar
April 22, 2015 at 9:04 PM delete

Good day Anonymous,

the trigger is a positive signal from the pick up coil

capacitor is non-polar

1uF/250V should also work, make sure the quality of the cap is good and use only BT151 for the scr

Reply
avatar
May 20, 2015 at 2:45 PM delete

Hi I have a 2005 suzuki gsxr 400 slingshot gk76 and can't find a cdi in south Africa and need to build my own if you can help whit that please

Reply
avatar
May 20, 2015 at 5:24 PM delete

Hi, you can build the one that's shown in the above article, it's a universal type and is suitable for all 2/3 wheeler vehicles.

Reply
avatar
May 22, 2015 at 8:36 PM delete

Hi Pieter

Your GSXR 400 is a heavy bike with high RPM. I am afraid the CDI discussed here is suitable only for smaller bikes 70-125cc. It might work with your bike at low RPM but at high RPM it will fail to synchronize the sparking. The OEM CDI unit for your bike is based on a micro-controller which delay the sparks at high RPM.

If you have no experience of programming/burning micro-controllers and want to get the job done without any hassle/frustration, I would suggest you to buy the original or compatible CDI from eBay or AliExpress. If you still want to DIY, let me know I'll forward you the link.

Reply
avatar
May 22, 2015 at 10:03 PM delete

Hi Pieter, you can try the above circuit by replacing the CDI coil as per the specs, and under the supervision of an expert automobile engineer, the above circuit design is a universal design and can be used fr all conventional motorcycles with some modifications.

here's the image of the CDI coil for your bike

http://i.ebayimg.com/00/s/MzE0WDU0MA==/z/wYYAAOxy0rZRGSaP/$T2eC16R,!zEE9s3!%28Y1TBRGS,PgmwQ~~60_1.JPG?set_id=8800005007

it has a twin coil it means you can try making two of the above circuits and integrate the triggers with the relevant pick up inputs and the outputs with two spark plugs.

Reply
avatar
July 25, 2015 at 5:57 PM delete

Hi,
I'm wondering If u have a printed circuit for this shematic.
(I'm not good at all on that software to make circuit)
If u have please share with us
Regards
Otto V.
Congrats for this page!

Reply
avatar
July 26, 2015 at 9:55 AM delete

thanks otto, I had the PCB design some time ago, but have lost it now, so I am really sorry.... presently it would be difficult to post it back.

Reply
avatar
August 4, 2015 at 10:36 AM delete

hi swagatam, can we replace the bt151 with a 2n3055 instead? also what is your opinion of bedini radiant charging oscillators, have you tried to replicate one yourself with useful success?

Reply
avatar
August 4, 2015 at 8:36 PM delete

Hi Fidel, BT151 is a thyristor, which is completely different from a transistor and therefore the two cannot be replaced with each other....
no, I haven't yet tested the bedini charger, however i feel it could be true since it uses a flywheel concept and we all know how efficient a flywheel can be in terms of output vs input power

Reply
avatar
August 23, 2015 at 9:58 AM delete

thanks for taking time to reply me mr swaga, I hope a man with such great knowledge in modern electronics concepts can build one test for yourself and give us your honest opinion based on the tests, regards!

Reply
avatar
August 23, 2015 at 10:00 AM delete

it is important I also stress that we endeavor to investigate such devices at these times when the whole world is reliant on the $$$ guzzling oil and no one gives much thought about clean energy concepts seriously

Reply
avatar
August 23, 2015 at 8:12 PM delete

I appreciate your thoughts Mr. Fidel, you are right, somebody must take serious initiative and prove the world about the potentials of these efficient machines...in my free time i would certainly want to go ahead and test one of those...

Reply
avatar
August 31, 2015 at 6:33 AM delete

HI Swaga, just wondering the BT151 leg configuration>the BT151 Chip number label facing us: 1st leg-cathode(positive out) , 2nd leg-anode (positive enters), 3rd leg-gate..is this correct?

Reply
avatar
February 6, 2016 at 3:06 AM delete

Hi, i have a kawasaki kdx 220 that does not have a trigger coil! Will this schematic work on it? Thank you.

Reply
avatar
February 6, 2016 at 11:19 AM delete

Hi, without a trigger coil no CDI can work for a motor bike as far as I know...so the above circuit will also not work without a trigger from a pick up coil

Reply
avatar
February 6, 2016 at 2:28 PM delete

3 wires come from magneto, output, ground & lights! You can advance & Retard the stator plate! Could the trigger be in the cdi?

Reply
avatar
February 6, 2016 at 3:33 PM delete

Hi

If your bike does not has the trigger coil then most probably it has the points/condenser based ignition system.

In that case, you can use your points and the capacitor together with a 100Ω/5W resistor, in place of the trigger coil. Please see the link for the diagram:

https://dl.dropboxusercontent.com/u/20969135/Points%20Pulser.png

The resistor is to be connected to 12V from ignition. This resistor provides wetting or whetting current for the points to ensure that there is good contact between the two contact-points when they are closed. This wetting current is sufficient to keep the contacts clean and avoiding and damage to them. The output is to be connected to the Pulse Input of a CDI.

Reply
avatar
February 6, 2016 at 4:44 PM delete

Kevin,

Mr. Abu-Hafss will guide you through the required procedures

Reply
avatar
February 6, 2016 at 6:20 PM delete

Hi Kevin

Kawasaki KDX-220 has trigger coil because this bike has CDI ignition. See the picture in the link below:

https://dl.dropboxusercontent.com/u/20969135/KDX220SRflywheel2.jpg

KDX 220 magneto has 2 coils, 12V for the electrical system and HV-AC for the CDI. Three wires means 12V, 180VAC and common ground.

Reply
avatar
February 27, 2016 at 11:44 PM delete

I have a 1980 4cyl 4 stroke kz 1000 that the ic igniter has become lost due to moving. I was wondering since it is a wasted spark system in which two plugs fire simultaneously can I build my own cdi to use in place of the ic igniter that was used originally? This question is brought about because of the rarity of factory replacements and the high cost of aftermarket replacements. If you have any ideas that will help please blueprint the for mentioned schematics, I will be more than grateful for any help.

Reply
avatar
February 28, 2016 at 1:31 PM delete

There's no harm in trying the above shown design for your bike.

you can try making two such circuits with two separate ignition coils...and connect the relevant connections with the appropriate sources from the bike.

The system will certainly allow you to use your bike normally, if not at extreme high speeds.

Reply
avatar

Readers are requested not to include external links while commenting. For consulting a diagram, upload it on Google Drive and provide the link here.