Rotax Ducati Dual Circuit (DCDI)
Ignition Testing

Contents ...

System Overview ...

Circuit Diagram ...

Component Tests and Expected Results ...

Tests in more detail ...

What next? ...

System Overview ...

The Ducati DCDI (Dual Capacitor Discharge Ignition) as it's name sugguests is a dual ciruit ignition system so there is built in redundancy. This means that if one circuit fails the engine can continue to run on the other circuit. The basic principle at work in a CDI system is that a charging circuit charges a high voltage capacitor. At 18° BTDC the system stops charging the capacitor, the capacitor discharges it's output to the ignition coil which in turn sends it's HT (High Tension) output via the spark plug cable to the spark plug. The trigger to discharge the capacitor comes from two independeant trigger sensors mounted close to the flywheel e.g. one trigger coil per circuit.


There are a total of 12 magneto poles with windings mounted on the stator plate assembly in the magneto of a Ducati DCDI system. Four of these poles go to power the ignition system. The four ignition system poles make up two independant ignition Charging coils e.g. there are two stator poles worth of windings, wired in series, to make up each individual ignition circuit Charging Coil. There is one independant Charging coil assigned to each ignition circuit. The other 8 poles worth of windings, all wired in series, make up the one complete Lighting Coil. The Lighting Coils are rated at 170 Watt max power output but it is important to remember that this is a MAXIMUM output figure. At 3,000 RPM the output is only 140 Watts and at 6,000 RPM the output is only 160 Watts.


The Charging Coils

These coils are connected to the SOLID GREEN wire and SOLID WHITE wire. This is the coil that is solely used to power the ignition system described above.


The 170 Watt Lighting Coil

This is the main coil that is connected to the SOLID YELLOW wire and YELLOW WITH BLACK STRIPES wire. The output of the Lighting Coil varies between 18 volts - 50 volts depending on engine RPM. The output of this coil can be used in it's raw AC form or be connected to a rectifier / regulator to convert it to DC.


The Igntion "Kill" Wires.

Coming out of each of the E-box's (amoungst others) is a YELLOW AND BLACK striped wire. These are shorted to earth via your aircraft's "Mag" or "Kill" switches to prevent the ignition system from firing and thus stop the engine.


Circuit Diagram ...

Please see below image for a typical Ducati DCDI System circuit diagram.



Component Tests and Expected Results ...

Please see the table below for a list of the components to be tested and acceptable test result ranges ...


Component  Test Type   Expected Value 
Charging Coil  Resistance   230 - 280 Ω 
Lighting Coil 170W  Resistance   0.3 - 0.35 Ω 
E-box Primary Winding  Resistance   Not measurable 
E-box Secondary Wind'g  Resistance   5.1 - 6.3 kΩ 
Trigger / Pick-UP - Older   Resistance   50 - 70 Ω 
Trigger / Pick-UP - Newer   Resistance   140 - 180 Ω 
Rev Counter Pick-Up  Resistance   30 - 35 Ω 

Tests in more detail ...

See below for some images of what you're testing, component by component, how to test it, and an interpretation of the possible test result ...


Rotax Ducati Ignition Charging Coils

Charging Coil Test

There are two Charging Coils. They are the two coils (mounted on the stator plate behind the flywheel) that power the ignition system. Here is a photo of the DCDI stator plate asssembly fitted to a Rotax 582 mod90 with flywheel removed. There are two stator pole windings wired in series to each Charging Coil. Note two pairs of green and white wires. One pair of wires feeds each E-box.

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Rotax Ducati DCDI Charging Coil wires coming out of crankcase

This is where the green and white wires emerge from the crankcase / magneto housing. One pair of green and white wires feeds the right-hand E-box. The other pair has a protective black plastic sheath around it and routes over to the left-hand E-box

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Rotax Ducati E-box charging coil connectors

They are connected to their respective E-box's via a plastic connector.

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Rotax Ducati DCDI E-box connector plug disconnected

This is a close up of the left hand E-box connector disconnected. To test the Charging coils disconnect this connection. Set your test meter to the ohms scale and connect your probes across the connections on the connector that go back to the stator NOT the connections that go to the E-box. Referring to the table above we can see that the resultant measurement should be in the range of 230 to 280Ω. If the result is lower than 230Ω it may be that the lacquer insulation that insulates the copper windings has broken down. This will mean that your charging coil's output may be lower than is necessary to produce a reliable spark. Your options are to remove the coil and get it re-wound although there aren't so many places that offer this service anymore. Or replace the faulty coil assembly - Rotax supply a replacement "coil kit". If the result is more than 280Ω the connection to the coil may be suspect / unreliable or the windings themselves damaged in some way. Examine the green and white cables going back to the stator to see if the cable is damaged. Be aware that the outer insulation may appear OK whilst the inner copper cable is severed. Trace the cables all the way back to where they connect to the stator coils if necessary. Test BOTH Charging coils and repair / replace as necessary.

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Rotax Ducati Lighting Coil Test

Lighting Coil Test

The Lighting Coil is not a part of the ignition system. Strictly speaking it is a part of the power circuit. If you wish to test the Lighting Coil it is the YELLOW wire and the YELLOW WITH BLACK STRIPE wire that connect to the lighting coil. There is only one lighting coil in the Ducati DCDI system. There are a total of eight stator pole windings (going from point A to point B in this image) wired in series to make the one Lighting Coil. Referring to the table above we can see that the resultant measurement should be in the range of 0.3 to 0.35Ω. If the result is lower than 0.3Ω it may be that the lacquer insulation that insulates the copper windings has broken down. This will mean that your Lighting coil's output may be lower than the Rotax quoted figure. Your options are to remove the coil and get it re-wound although there aren't so many places that offer this service anymore. Or replace the faulty coil assembly - Rotax supply a replacement "coil kit". If the result is more than 0.35Ω the connection to the coil may be suspect / unreliable or the windings themselves damaged in some way. Examine the YELLOW wire and the YELLOW WITH BLACK STRIPE wire along their route back to the stator to see if either cable is damaged. Be aware that the outer insulation may appear OK whilst the inner copper cable is severed. Trace the cables all the way back to where they connect to the stator coils if necessary. Repair / replace as necessary.

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Rotax Ducati E-box Primary Winding Test

E-box Primary Winding Test

The Primary winding of the ignition coil is an internal part of the E-box. The E-box is an unserviceable sealed unit. There is no way of testing the Primary winding in isolation as there are other electronic components effectively in the way thus preventing you from being able to connect your test meter directly to the primary winding. Do not connect any kind of testing meter across the GREEN and WHITE wires that go INTO the E-box in case the CDI circuit is inadvertantly damaged by doing so. You can however test the resistance of the E-box's Secondary Coil (see below). If the E-box's Secondary winding's test result is as expected then the only way to test the rest of the E-Box's funtionality is by swapping a suspected faulty one out by a known good one. If the fault dissapears then it is a fair assumption that the E-box is faulty. Not terribly scientific but reasonably conclusive all the same!

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Rotax Ducati E-box Secondary Winding Test

E-box Secondary Winding Test

The Secondary winding of the E-box ignition coil is an internal part of the E-box. One end of the Secondary winding of each E-box goes via the spark plug cable to the PTO cylinder and the other goes via the spark plug cable to the MAG cylinder. To get a reliable test result you will need to remove the plug caps (and thus spark plugs with them) by unscrewing the spark plug caps. This eliminates both the resistance of both the plug caps and spark plugs from the test result. Set your test meter to the kΩ's scale and connect one probe to the end of the spark plug cable of PTO cylinder and the other probe to the end of the spark plug cable of MAG cylinder. The reading should be between 5.1 - 6.3 kΩ's. If the result is lower than 5.1 kΩ's it may be that the insulation around the internal windings has broken down and the E-box therefore rendered unserviceable. If the test result is infinite resistance e.g. open circuit then the E-box is faulty or you have a damaged spark plug cable. If the test result indicate zero Ω's then you have an internal short and the E-box is faulty. If the result is marginally more than 6.3 kΩ's the connection to the coil may be suspect / unreliable. Either way if the results are out of the permitted range then this item will need to be replaced as it is non repairable. Test both E-box's.

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Rotax Ducati E-Box trigger wires coming out of crankcase

Trigger / Pick-UP - Old "Hole Only" Type Test

This picture shows the pick-up / ignition trigger wires emerging from the crankcase / magneto housing - see labelling to identify them. For testing purposes you will need to isolate them from the E-box's. This may entail disconnecting them (there is normally a bullet type connector) OR cutting them and re-joining them depending upon the installation. Set your test meter to the Ohms and connect one probe to the trigger wire and one to earth / the crankcase. The result should be between 50 - 70 Ω's. If not the pick-up is faulty and requires replacing.

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Rotax Ducati E-Box ignition triggers old type

This picture shows the actual pick-up (old "hole only" type) mounted in place. Note that it is only designed for minor adjustment in the direction of the arrows.

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Rotax Ducati E-Box ignition triggers new type diagram

Trigger / Pick-UP - Newer "Slotted" Type Test

This drawing (in the absense of a photo) shows the newer Slotted" type of ignition pick-up with open ended mounting lugs that allow for adjustment in the both directions as indicated by the red arrows. These newer type of pick-ups can be tested in the same way as the older type of pick-up (see above) except that the result should be between 140 - 180 Ω's. If not the pick-up is faulty and requires replacing.

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Rotax Ducati Rev Counter Pick-up wires

Rev Counter Pick-UP Test

What is normally reffered to as the Rev Counter "pick-up" is not a pickup in the sense that the ignition trigger are. It is a tap off an ignition Charging Coil. The grey wire emerging from the crankcase housing is the rev counter connection. Set your test meter to the Ohms and connect one probe to the grey rev counter wire and one to earth / the crankcase. The result should be between 30 - 35 Ω's. If not the connection is faulty and either the connection to the stator plate is unreliable or the stator plate coils require replacing - Rotax supply a replacement "coil kit".

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What next ...

Hopefully by now you will have indentified any faulty components and replaced them or repaired them if this is possible. You may be able to observe a spark at the spark plugs even if it may not be timed correctly. Next you need to set / verify your ingition timing. Do not run your engine without having the timing set correctly as you risk seriously damaging it!

Ducati DCDI Ignition System - Setting / Verifying Ignition Timing

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