DIY: How to make your own Electronic Ignition for contact point engines

[Chef Noob]

*Meledson - Try building one for it na!...Its not as hard as it looks.

*Kinyo - Where did you get the CDI layout sir? Does it have the multi-spark feature?

*Sirkosero - Thanks for the heads-up sir. Actually, I did notice the coil heating up more than usual.
Also, I do see a slight flaw in the design layout. It indicated there to bypass the ballast resistor(rated at 1.5ohms) found on the positive side of the coil. Although they added a resistor in the circuit, it only had 0.5ohms resistance & 5 watts output. This in effect, increases the current & voltage passing through the coil - giving you a bad ass spark, but pushes your coil to its limits.

The thing about ignition coils; even though it is installed in a 12volt system...it is meant to run on only 6 volts of power.(If it was made to run at 12 volts, then you wont be able to start your car since the starter eats up half of the current)...

Based on my observations, there are three ways to remedy this.
1. change the resistor in the module with one that has 1.5ohms rating.
2. Replace it with a heavy duty ignition coil.(the red Bosch coil will work just fine)
3. DO NOT bypass the ballast resistor.

For me, after noticing the heat being produced by my stock coil, I did the 3rd option. It did decrease the power output of my engine just a little bit, but made my coil cooler. I do plan to install a Bosch unit though, so I can take advantage of the added power given by the module.

How to tell if your coil is running more current than it should?
Step 1. Get a multitester or Volt meter and set it to DC. If using digital, set the max voltage to 20V.
Step 2. Hook up the positive needle to the + of the coil. Hook up the neg needle to the (-) of the coil.
Step 3. Turn ignition to ON position. It SHOULD read more or less 6V.
Step 4. Start the engine. Slowly rev the engine and watch the meter. It should rise up to 9V while your revving up the engine. If it reads more than that, your coil is biting off more than it could chew.
Do keep in mind, ignition coils are able to withstand harsh currents. They are made that way. However, it still comes down to how well each coil is made. Meaning, quality coils will be more durable while cheap ones will burn easily.

NOTE:
When acquiring Bosch coils, try to get the red one since the blue one has a resistor already built in the unit.

[kinyo]

*Kinyo - Where did you get the CDI layout sir? Does it have the multi-spark feature?

the CDI i built did not have multi-spark feature ... it was a very simple circuit consisting of a bjt (2 x 2N3055 plus transformer) multivibrator circuit to charge the capacitor to almost 400 volts and an scr to discharge onto the primary of ignition coil.

[Chef Noob]

the CDI i built did not have multi-spark feature ... it was a very simple circuit consisting of a bjt (2 x 2N3055 plus transformer) multivibrator circuit to charge the capacitor to almost 400 volts and an scr to discharge onto the primary of ignition coil.

Nice design! How were you able to overcome the hard starting symptom of the CDI?

I always wanted to build one myself. Unfortunately, I'm still looking into the "safety" factor - for myself & the car's sake. Getting an electric shock from a 400v CDI module just doesn't sound that appealing to me.

[Ginnova]

hope you can post where to have the pcb's fabricated.

[kinyo]

Nice design! How were you able to overcome the hard starting symptom of the CDI?

I always wanted to build one myself. Unfortunately, I'm still looking into the "safety" factor - for myself & the car's sake. Getting an electric shock from a 400v CDI module just doesn't sound that appealing to me.

Not sure if i understand the question, because i did not experience "hard starting" with the CDI. It consistently starts the car quickly even on cold starts.

Yes 400V could be a bit shocking, but it is still considered low voltage by electrical standards.

[Chef Noob]

Not sure if i understand the question, because i did not experience "hard starting" with the CDI. It consistently starts the car quickly even on cold starts.

Based on the research I done regarding CDI, it increases the voltage produced by the spark plug but shortens the spark duration considerably. This in some way, creates situation for certain engines to have a hard time starting...

Although I havent witnessed it personally.

[duskylim]

Hello Chef Noob:

Your work reminded me of when I opened up and copied a Nippondenso igniter (the electronic ignition of Japanese cars in the 80's) using locally sourced components from Raon.

I too had my share of problems with it, a straight copy of the design was less than satisfactory because at first I didn't insulate it well enough.

The igniter design uses a PNP to NPN overdriven switch triggered by the original contact points where the turn on current (base-to-collector) is multiple of the hfe gain.

Basically you looked up the transistor's specs - particularly the hfe and rated current it could switch, and multiplied the hfe by a factor of 5 or so.

When you do this, the transistor ceases to behave as a linear amplifier and at that point and simply becomes a high-speed switch - like the contact points themselves.

Although the design gives up a lot of gain (amplification) the excess turn-on current makes a bipolar junction transistor's internal resistance drop dramatically - typically to 0.5 to 0.1 ohm - which is the key benefit of providing excess turn-on current (aka overdrive)!

This means that when switched on and carrying the full load of the coil primary - the transistor itself has the least resistance of all the ignition circuit's components.

In this design the stock contact points only had to switch 1/150th of the original current (from carrying 10 amps to just 0.067 amps) so that they no longer pitted, only very slowly (over a year or more!) got light grey oxidation.

A smaller PNP transistor was switched by the coil and it's output drove the larger, main NPN transistor.

The 1st problem was that if you didn't insulate the main NPN power transistor (2SD458) well enough, during the switching, the coil's primary winding voltage would temporarily go to 400-600 volts at the NPN transistor's collector and this would produce shorts into the aluminum heat sink frame.

You had to use mica insulation, nylon bushings an lots of silicone grease to insulate it properly.

Still even after all that there were still problems.

Basically the main failure was due to punch-through - the transistor would break down from the extremely high collector-to-emitter voltage.

The original Nippondenso design addressed this via a voltage divider (resistors) parallel the collector-to-base-to-emitter circuit, limiting the speed at which the transistor turned on and thus reducing the induced voltage at the coil primary - reducing the tendency of the voltage to punch through.

This also reduced both the voltage and power output to the spark - the slower switching rise meant lower induced primary voltage - hence lower induced secondary voltage - and lower energy transfer from coil primary to coil secondary to boot!

After loosing several igniters to this punch-through problem, rather than copy the original Nippondenso solution (i.e. - surrender), I decided to mimic the solution of the original ignition circuit.

Here's what I did:

In the original contact point circuit the points themselves to switch the coil primary.

However the points are not the only component in that circuit there is one more thing there that if you remove will prevent the ignition circuit from working correctly.

That's the capacitor which is wired in parallel to the points.

When the points close, current flows across the coil primary, and builds up a magnetic field, storing energy that becomes the spark in the coil secondary.

When the points open, the coil produces an induced current that tries to keep flowing - the faster the points open the higher the voltage of the induced current.

If there were only the points in the coil primary circuit - the induced voltage would jump the gap and spark and burn the points.

The capacitor is there to stop that from happening.

In fact, the 1st ignition circuits (before 1920s?) put the contact points INSIDE the combustion chamber - using that induced spark to create ignition, the ignition coils of that era had no secondaries only primaries!

When the points open the capacitor stores the coil's induced voltage spike instead of allowing it to be borne completely by contact points.

This allows them to separate without too much sparking and allow the transfer of energy from coil primary to secondary.

Using this as my model I computed (very roughly) the energy stored in the coil primary and added a capacitor in parallel to the NPN circuit - effectively storing the energy and preventing punch-through.

Its been a long time since I did that.... thanks for the memories.

Best Regards,

Dusky Lim

[Chef Noob]

Thank you for the very well explained theories. I can tell by your post that you also enjoyed the time you spent doing this.

I was amazed that you were able to create primary voltage up to 600v using only transistors. Even up to now, only CDI modules are able to produce those levels of voltage. Though it may prove very beneficial for the power gains in the engine, considering the cost & wear on your parts(coil, plugs, etc.) wont be cost efficient. Even if you were able to extend the life of your power transistor, I think the plugs were not meant to handle those voltage & currents. I myself also seen a few designs where they attached the capacitor in parallel to the transistor.


Honestly, the main reason we are discussing here right now is because of this capacitor aka "condensor".
In a perfect world, if it were able to work perfectly...I think most production cars right now will still be using the points system.
Theoretically, the capacitors are able to absorb the "back EMF" created by the induced current.
In the standard points system, when the points open, the capacitor absorbs the extra spike of current thus eliminating the dreaded "gap spark". However, that power is still stored within the capacitor. The problem lies from the closing of the points. Since the charge from the capacitor have no where to go, it "grounds" itself as the points closes, creating a "mini" spark as this happens. This spark may not be that much but after doing this for atleast 1000 times a minute, that tiny spark will do damage to the point surface. (based on the laws of electrolysis)
That is why in the real world, you can still see burnt points even though the capacitor still works perfectly.

The option I'm dwelling on right now is to induce a stronger spark...not by reducing the resistance of the transistor to induce more current...but to increase the output on the coil - at the same time prevent it from over heating.

As you stated in your post above, transistors are more fragile than we think. It can easily fry when subjected to extreme currents.
However, if you increase the current on the ignition coil, you can still attain good spark from it. One problem is: What if the coil overheats? What I'm thinking of is putting a cooling system to reduce the temp of the coil. A finned heatsink perhaps? Or even water-cooled? :-)

[Chef Noob]

*Ginnova I was trying to PM you sir but it says that your Inbox is full.

[bongski214]

Sir Chef Noob, where did you buy your mj10012 power transistor? I was able to source out the other parts at electronics stores near my place but its one part thats really hard to get. Thanks.

[Chef Noob]

At Alexan... They don't have the original Motorolla but they have the generic type...

News has it that Motorolla stop producing them already...but you could always use other brands with the same or higher specs. Try looking for MJ10015...I hear it is still in production.

[mr,niceguyy]

*Meledson - Try building one for it na!...Its not as hard as it looks.

*Kinyo - Where did you get the CDI layout sir? Does it have the multi-spark feature?

*Sirkosero - Thanks for the heads-up sir. Actually, I did notice the coil heating up more than usual.
Also, I do see a slight flaw in the design layout. It indicated there to bypass the ballast resistor(rated at 1.5ohms) found on the positive side of the coil. Although they added a resistor in the circuit, it only had 0.5ohms resistance & 5 watts output. This in effect, increases the current & voltage passing through the coil - giving you a bad ass spark, but pushes your coil to its limits.

The thing about ignition coils; even though it is installed in a 12volt system...it is meant to run on only 6 volts of power.(If it was made to run at 12 volts, then you wont be able to start your car since the starter eats up half of the current)...

Based on my observations, there are three ways to remedy this.
1. change the resistor in the module with one that has 1.5ohms rating.
2. Replace it with a heavy duty ignition coil.(the red Bosch coil will work just fine)
3. DO NOT bypass the ballast resistor.

For me, after noticing the heat being produced by my stock coil, I did the 3rd option. It did decrease the power output of my engine just a little bit, but made my coil cooler. I do plan to install a Bosch unit though, so I can take advantage of the added power given by the module.

How to tell if your coil is running more current than it should?
Step 1. Get a multitester or Volt meter and set it to DC. If using digital, set the max voltage to 20V.
Step 2. Hook up the positive needle to the + of the coil. Hook up the neg needle to the (-) of the coil.
Step 3. Turn ignition to ON position. It SHOULD read more or less 6V.
Step 4. Start the engine. Slowly rev the engine and watch the meter. It should rise up to 9V while your revving up the engine. If it reads more than that, your coil is biting off more than it could chew.
Do keep in mind, ignition coils are able to withstand harsh currents. They are made that way. However, it still comes down to how well each coil is made. Meaning, quality coils will be more durable while cheap ones will burn easily.

NOTE:
When acquiring Bosch coils, try to get the red one since the blue one has a resistor already built in the unit.

sir chef noob tumawag ako sa warren automative nag tanong alp tungkol sa coil e ang sabi nila un red na bosch e un ang may resistor at ung blue ang wala.. gusto ko din kasi mag palit ng coil ng fx ko kasi naka electronic ignition din po ako at ung nga nagiinit ung coil ko kaya balak ko magpalit nag coil ano po ba dapat ipalit ung red o blue na bosch?

[Chef Noob]

I'd go with the RED...the Blue bosch coils does NOT have an external resistor packaged with it since it ALREADY has one built in...
Yung RED, it is sold together with an external resistor to give the user the option whether to use it with the Ballast resistor or not.

Actually sir, gagana yan kahit alin dun sa blue or red...yun nga lang, you will get full performance when using the red without the resistor...pero mas iiksi buhay ng coil mo...Yan ang Pro's & cons dito.

[mr,niceguyy]

I'd go with the RED...the Blue bosch coils does NOT have an external resistor packaged with it since it ALREADY has one built in...
Yung RED, it is sold together with an external resistor to give the user the option whether to use it with the Ballast resistor or not.

Actually sir, gagana yan kahit alin dun sa blue or red...yun nga lang, you will get full performance when using the red without the resistor...pero mas iiksi buhay ng coil mo...Yan ang Pro's & cons dito.

sir hindi ko po magets tong linyang eto?ang ibig nyo po ba sabihin dyan eh iiksi talga buhay ng coil ko dahil sa E.I. kit?o mas maiksi ang buhay ng blue coil kesa sa red coil?pasensya na na po kung slow?hhehe

[Chef Noob]

Okay lang sir, no problem...
Try ko po sagutin.

Pag bumili po kayo ng Bosch RED coil, may kasama na yan na ballast resistor (yung white na ceramic).
Pag iinstall niyo po sa ordinary CONTACT POINTS IGNITION without the resistor, siguradong sunog yang RED coil at contact points niyo. Kaya nila sinama yan para dun sa mga naka contact points pa...Yung problem netong resistor, pinapahaba niya nga ang buhay, pinapa hina niya naman ang OUTPUT...so pag ang OUTPUT ng coil niyo eh 50,000 volts, magiging 38,000 volts nalang.

Now sa E.I. niyo, pwede ninyo huwag na gamitin ang resistor since wala nang points na masusunog. So THEORETICALLY, dapat lahat ng 50,000v derecho na sa spark plug...making your coil perform at 100% ALL THE TIME. Now alam naman natin na lahat ng bagay pag piniga mo sa maximum, mabilis ma sira diba.


Pero yung sa akin, hindi ko tinanggal ang ballast resistor...so ang output ng coil ko is only 38,000v(example figure lang to)...roughly 75% of the coil OUTPUT. Making my coil last longer (possible 10 years or more) and not prone to overheating.
Since hindi naman ako nagkakarera at parati malayo biyahe ko, masaya nako sa setup ko na to. Yun nga lang, paglagpas ng 3000 RPM, medyo makupad na siya. Okay lang sakin, since the main reason na kinabit ko to is sobrang sawa nako magpalit ng points.
Kung gusto mo pang racing setup, huwag mo na gamitin ang ballast resistor...yun ngalang, asahan mo hindi aabot ng 3 taon ang coil mo...not to mention prone kapa sa tirik pag malayu-an ang biyahe.

Regarding the RED & BLUE bosch coil...
The reason I suggested the RED, since ang BLUE nila is the low-end model. Hindi ganun ka matibay ang ginamit na materials...kaya siya may built-in na resistor sa loob...para limited ang output. If Im not mistaken, max output niya ata is only 25,000v.
Uubra na to, yun ngalang...huwag ka na umasa sa magandang performance & lifespan.\

Ang RED naman, max rating niya is 50,000v(or is it 75,000v? please correct me on this)...so it means na kahit ang output ng coil mo is 45,000v...kayang kaya niya parin. Only downside is, MAS MAHAL... Also, I read a few feedbacks na mataas daw ang tolerance neto sa PRIMARY voltage. Ibig sabihin, kaya niya ang EI mo at max output(without the ballast resistor).

My advice, if your car is for keeps, then get a RED...