Can the CDI drive two coils simultaneously? I am looking for an ignition system for a inline twin cylinder engine with a single hall sensor pickup and wasted spark. The pistons move in unison, one is on the power stroke while the other is on the exhaust stroke. An ignition system that has a magnet on the crankshaft and a hall sensor that fires a CDI unit once a crankshaft revolution that could drive two coils would produce a spark to the two cylinders simultaneously. One would fire the power stroke and the other would be wasted.
I really like the idea of using the inexpensive 12DV CDI units for skooters and mopeds. But could one fire two coils instead of one? Without knowing the inside circuitry of the CDI unit, the switching transistor driving the coils in parallel would see half the resistance and be required to drive twice the current. Don't know if it could handle that.
there are six cylinder car engines that use this technique, firing two of the six cylinders simultaneously, one with wasted spark. I have not been able to find one of the CDI units as inexpensive as the moped variety.
Any other suggestions? Using a wasted spark ignition would eliminate the distributor.
Thanks
It’s a good solution, All car petrol engines use these now, you can get them for pennies second hand. Also for the signal you can use 12v no issues as it’s just a logic signal, which makes the wiring even easier. I use mine with points on one engine and a magnetic Reed switch on another. Very simple and very cheapA great suggestion, I found this on the web:
Starting in 1997, General Motors used a new (for them) coil-near-plug ignition system for the then new Corvette LS1 engine. The system features eight coils (one per cylinder) mounted on the valve cover, with short spark plug wires to connect the coils to the spark plugs. The General Motors LS1 coils are not just conventional ignition coils. Instead they are complete single-cylinder ignition systems. They contain all the electronics for dwell limiting, current limiting, etc. These coils are controlled directly by a low voltage, low current signal from the sequencer. There is no intervening ignition module (like an EDIS or GM DIS). Because the LS1 coils have the igniters built in, they make for an easy installation and generate less electromagnetic noise in the other wiring under the hood.
The LS1 coil has 4 connections (as well as the high tension terminal for the spark plug wire, of course):
- A = Coil Primary Ground (to engine block)
- B = Signal Ground (to engine block)
- C = +5V Ignition signal
- D = Switched +12V Supply to Coil Primary
Sounds easy, but a bit more expensive.
I am pulling the bits and bobs together for my prototype:
View attachment 133933
You can see in the lower left the DC motor with a magnet mounted on the shaft, with the hall sensor underneath. I have my prototype board ready for the circuit. I'll keep you all posted on my progress.
You might find there is alread a/r built in to the black box if using the originalA little progress:
I am working on my electronic ignition for my twin cylinder 4 stroke. Here I am using a DC motor with a magnet mounted on a collar triggering a hall sensor--this simulates the setup on the engine. I will use a magnet mounted to the crank and fire both spark plugs at the same time, ie wasted spark. I will use a little microcontroller to adjust the timing advance from 5 to 25 degrees before top dead center depending on the RPM. The circuit board has the analog circuitry that converts the hall sensor output to a nice 1 millisecond pulse, and then another transistor stage that will drive the coil over plug (COP)s from a signal generated by the microcontroller. The pulse to the COPs will be 4 millisecond in duration. This will diminish if the RPMs get high enough to not exceed a 50% duty cycle on the COP trigger signal.
Below is a scope trace of a couple of key signals in the analog circuitry. the green is the signal generated by the RC circuit triggered by the hall sensor, and the yellow is the pulse on the output of the NPN transistor, the RC time constant is set for a 1 millisecond pulse.
Below is the DC motor setup to simulate the hall sensor on the engine. I can control the motor speed by adjusting the voltage is sees.
Next up is wiring the COPs and the sparkplugs. We will see what EMI havoc is caused by the high voltage travelling through the sparkplug wires.
The ignitor is built into the COP, that is why they are so nice. All you need to do is provide a simple 5 Volt, low current pulse to trigger it.
@willray
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When the engine is running, the crankshaft rotates and the magnetic sensor produces a reference pulse each revolution. These are fed to the microcontroller, which records the time of each reference to microsecond accuracy on an internal clock. From these times the RPM is calculated and the required timing advance angle is derived. The actual time of the next spark is calculated, and when the clock reaches this value, the pair of plugs fire. For starting, the priority is to prevent kickback and ensure a big spark. To achieve this the spark occurs at 3 degrees AFTER TDC...
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