NEWS AUG. 2019:
This DC-CDI is EOL (end of live)
Consider to build DC-CDI v7 instead
Adaptation done by:
- Same software as AC-CDI v7
- For single cyl.
- 1 advance curve.
- No alternator.
|DC-CDI||Schematic||PCB||Board layout||Partlist||Eagle files|
How does it works?
Software is the same as AC-CDI version 7
Only the Hardware is different: High Voltage is no more coming from a charging coil, but it’s generating from the 12v battery.
A UC3845 is driving a home made transformer that raise the tension from 12Vdc to around 200Vac.
The HV is rectify by D1 and charges C9 capacitor.
A high voltage charging coil is not necessary.
Pulses coming from the 36° pickup are limited to 5 volts by the Zener D7 then trigger the PIC (RB4 – pin 10).
(PIC input detect any tension higher than 1,8 Volts.)
LED D2 turns on at each pulse received from sensor 36°. (You can remove R17 and LED2 if not necessary)
A delayed pulse, according to the programmed advance curve, is available on RA2 (pin 1) and trigger the SCR T3 via LED1,R12-C14.
The polarity of the pickup is very important, don’t hesitate to invert the 2 wires of the pickup.
SCR is BT151-500
FET is IRFZ44
(High power with shottky diodes integrated and very low internal resistance)
Diodes are fast rectifier diodes ( BR307 , UF5408 …3A-1000v)
Same bikes needs to lower R19 resistor value.
Exp: for Suzuki 125cc: R19 must be 560ohm (instead of 330k)
- Bobbin E 19/8/5 + Ferrite core EI19 (width:19mm height:14mm)
Primary : 0.6mm , 15 turns
Secondary : 0.2mm , 350-400 turns (as much as you can because it’s flyback)
- Wind the primary and secondary in the same direction (clockwise or anti-clockwise BOTH)
- Leave a 0.05 to 0.8mm air gap between the 2 legs of the magnetic core.
- Try different air gap walue, it’s critical and can avoid the Transfo to saturate.
- The Transformer behavior depend on many factors: core, ferromagnetic material, shape, size, air gap, tension, frequency, duty cycle, primary coil, efficiency, temperature, etc etc
- It’s normal to face overheating and spikes when dealing with high currents and high voltages…!
- Do not operate without ignition coil (CDI Need a load on output cause it’s a boost converter)
- R4, C7 are used to setup the oscillor frequency.
- Fosc = 1.72 /( R * C ) = 1.72 /( 33k * 1nF ) = 0.50MHz = 50KHz
- Fosc is the input frequency of PWM controller and output frequency provided by PWM controller is Fosc/2 = 25KHz which used as the switching pulse of MOSFET switch.
- The frequency has a lot to do with output voltage. The ON time must be long enough to let current increase to the required level, in order to get the desired output volts.
- You may want to experiment other frequencies.
- The duty cycle of pulse is controlled by the feedback control loop. (pin2 of IC1)
- The greater the duty cycle, the greater the output Voltage. Until some point…
- When FB pin is high it cause the output PWM to switch off and the MOSFET will not get triggered.
- When FB pin is low it generate output pulse of high duty cycle to the MOSFET.
- Use a UC3843 with a Max. Duty Cycle of 100% instead of a UC3845 with max Duty= 50%
- With a UC3845 we get a max voltage of 140Vac at 12000RPM with a transfo wired with primary 12T and secondary 700T
- With a UC3843 we get a max voltage of 280Vac at 12000RPM with a transfo wired with primary 12T and secondary 180T
- If you are facing mosfet overheating, considere switching to UC3845 to lower the duty cycle.
– Thanks to Irfan Galuh Sayoga
- You need to verify if the mosfet goes completely ON and OFF. Measure the voltage across the mosfet both ON and OFF and calculate the internal resistance.
- If the internal resistance in higher than the datasheet value, it mean that it doesn’t totaly turn ON (it needs 10v for a guaranteed Rds)
– Increase Gate voltage by reducing R1 value
– Decrease Drain voltage by lowering the current
(increase R6 or install a low ohm resistor in the current path)
- Use R6 to read volt level across it when the mosfet is ON and when it’s OFF
- Calculate values for current when both ON and OFF.
These are good indicators of what’s going on…
- Mosfet can only dissipate 2watts: Add it a big heatsink with thermal paste.
- When CS pin3 of UC3845 goes beyond 1volt IC1 output is automatically switched off.
If Tx secondary is shorted, Q2 will drive a high current, tension at R6 will increase and pin3 will go high.
- D2, R2, C3 are used as a snubber to protect MOSFET transistor.
- D2 is a fast diode type(BYV26C…)
- R2 goes from 100 to 100k
- C3 goes from 2nF to 10nF
- Use a snubber calculator
- If you MOSFET is getting hot, you probably have to change the snubber value according to your Tx windings…
This ignition fitting a Honda SS50:
Tested with the pickup simulator:
- Version 2.0:
- Initial release with a home made transformer.
- Use AC-CDI v6 software.
- Version 2.1:
- PCB redrawn.
- Use AC-CDI v7 software.
- Version 2.1c1:
- Improve readability of Ref on PCB.