can a coil have a short and still work?

The green wire of your rev limiter should be the pickup wire going to the points, not to +12V. Would leave that unconnected until we know whats wrong with the setup.

Would be great if you can test the optical pickup/XR700 by putting the Dino in the fourth gear and push it a bit forward to move the rotor position in the distributor pickup. If the ammeter stays on about -10 ampere then something with the Crane pickup or input stage is defective.

 

Ignition off & 10.8V, thats a bit low, looks like your alternator is not charging your battery properly. How old is the battery?
Ignition on, would expect 14.0-14.2 Volts battery voltage above 1500-2000 RPM.

 

Jim, you're welcome! I think these are two separate issues, though (alternator not delivering full current, ignition switching on coil even independently of rotor position).

 

Thats exactly how the pickup works. The test with pulling the Molex connector/pushing the car was to make sure that the sensor circuit/pickup is indeed ok. So with a bit of luck your Dinos problem will be fixed with an alternator overhaul already.

 

(On reflection) I believe that there has to be a bunch of other electronics between the detector and what the primary coil current is doing (so it probably shouldn't matter where the optical wheel stops). Although the slot in the trigger wheel initiates the firing (or end of firing) event, it can't be controlling the primary coil current directly. The sizes of the slot and blocked off areas do not correspond to the dwell and open sizes that a coil needs to function -- just a thought...

 

Crane's XR700 looks like a classic two stage transistor circuit with an input transistor for the optical switch, which then controls a larger power transistor for switching ground to the coil. This approach is identical to Lumenitions Optronics ignition made in the UK. Both units have fixed dwell, e.g. the distance between the slots in the trigger wheel define the dwell degrees, which is the same for all engine speeds.

This was the standard with early transistorized ignition in the late seventies, but around the mid eighties features such as dwell control and coil current limitation were quite common. This new generation of ignition controllers did not apply any current to the coil until the first trigger event came in (keeping the coil cool until the starter was turned) and tapered off the current 2-3 seconds after the last ignition trigger to avoid burning out the coil.

Pertronix's Ignitor I has the same restrictions, although it uses a more modern IGBT transistor the dwell angle is still static and depends on the distance between the trigger magnets, also there is no automatic switch off or current control.
The up market versions offered (Crane XR3000, Performance Optronic, Ignitor II/III) do have features such as variable dwell, automatic current switch off and current control, so it seems the manufacturers want us to spend more money for standard features...

 

Got your PM Adrian, and no worries (I had to step out so I deleted that message because it wasn't quite right, and I didn't have time to fix it).

My point is that the ratio between the open and closed areas in the Crane optical wheel does (can) not directly represent the ratio between the dwell (time when current is flowing in the coil primary) and the time when current is not supplied to coil because they are just so different in size. I can certainly agree that the detection of each open slot (I'm not sure whether it's the leading or trailing edge) initiates the process where transistor(s) switch the primary coil current on and off, but I can't yet agree that current flow in the coil primary corresponds directly with what's happening at the optical switch -- do you see it differently (or did I misunderstand your post)?
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Steve,

i believe that the Crane XR700 trigger wheel/transistor switch setup is a simple electronic adoption of the classic points mechanism. Crane mentions in their sales collateral that the XR3000 contains "a computer chip that controls coil current and dwell", but these feature are not listed for the XR700.

The XR700 switches ground to the coils primary winding as long as the rotor blade covers the led in the optical switch (dwell phase). On the leading edge of a slot, ground is removed from the coil (discharge phase).

I fully agree that the trigger wheels covered area looks out of proportion compared to the slots, but please have a look at the drawing i have attached. The black outline is a six cylinder trigger wheel supplied by Crane and the blue outline the cam of a S125C Dino 246GT distributor. The dwell area of the trigger wheel seems to be pretty much in line with the original cam's dwell phase, so i guess there is not much difference between the cam and the trigger wheel regarding dwell.

Regards,
Adrian
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Can't agree with your drawing Adrian. The portion between the two dashed red lines on your drawing does not represent where the points open and close on the dist cam -- they represent where the points are held fully open (constant radius from the dist axis). Additionally, the 246 US OM specifies a point opening angle of 28 deg and a point closing angle (dwell) of 32 deg. The coil doesn't know if a set of points is switching the primary current or if a transistor is switching the primary current, so these values should be about the same for either system. Consequently, I still conclude that the slit on the Crane wheel initiates the firing event, but it's size does not correspond directly to the length of the discharge time.
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Steve,

sorry for the confusion, my drawing was not meant to convey the exact dwell angles but to compare the functional aspects of both approaches. I am not too worried about the different dwell, as the dwell charge time in a fixed dwell setup is defined based on the target coils properties (inductance, primary current handling and saturation time), so depending on the components and application closing angles vary can from 30-38º for 6 cylinder engines.

What i tried to show was that the trigger wheel is not so far off from the original points and cam approach regarding dwell and discharge phase. The XR700 does not seem to be able to correct dwell, it simply supplies ground to the coil based on the trigger wheels design.

regards,
Adrian

 

Leaving your ignition on will heat up the coil/XR700 and drain the battery a bit but as long as you don't leave it on for more than 5-10 minutes there shouldn't be a problem. If you want to play it safe, you could add a 0.9 Ohm Resistor to your 1.7 Ohm coil to keep the current below 5 ampere (the XR-700 datasheet lists 4,5 ampere, you are running it at 7-8 ampere with your current setup).
The XR3000 looks good, you could use the same pickup, have current/dwell control and its quite affordable, but as long as the XR700 is ok and delivers you don't really need to spend money, IMHO.

 

Hmm, thats such a small difference that it could be just the resistance of the wiring leading from the battery plus terminal to your coil. Try this test instead, remove the +12V wire connected to your coil's plus terminal, and measure the resistance between the +12 wire you just removed and the battery's plus terminal. You should see less than one ohm without ballast resistor or >2 ohms if there is a ballast resistor in line

Your measurement of the coils primary resistance with all wires removed resulted in 1.7 ohm, correct?

P.s. if your +12V wire going to the coil's plus terminal is yellow then it is most probably the original wiring coming from the ignition key and has no ballast resistor in line.

 

The 7.58 volts you got in the Crane test indicates a resistance of 0.6-0.7 ohms, this is just the resistance of the wiring coming from the fuse block/ignition key. With a ballast resistor in line you would see a voltage around 4-6 volts in this test, so i am pretty convinced there is no ballast resistor in your setup.

regards,
Adrian