So here's my project
I have a 1949 Ford 8n tractor, 4 cylinder side valve with 6volt electrics, which the previous owner converted to 12volts and used a regular GM alternator instead of the generator. This is a common conversion but leads to problems with the ignition.
The distributor is on the front of the engine and has the 6volt coil integrated, like this:
That's the coil balanced on top.
When it's converted to 12 volt a different ballast resistor is put in the circuit to keep the current down to
about 6 amps through the coil. As it wasn't the most reliable system to begin with I have decided to bring the
ignition system into the 21st century.
Simple enough idea, replace the points with 2 digital hall sensors placed 90 degrees apart and activate them
with 2 magnets on the old points cam placed 180 degrees apart. This means hall sensor 1 will switch at 0 and
180 crank degrees and hall sensor 2 at 90 and 270 crank degrees.
These signals will be used to activate 2, N channel IGBT's, such as the Fairchild ISL9V3040D3S which is
purpose built as an ignition coil driver and needs no external components. From there to either a Ford Ranger
or Dodge Neon coil pack which both use the wasted spark principal.
My problem is, what if the magnet stops opposite one of the hall sensors and keeps the IGBT 'open' sinking a
high amperage and cooking the coil until the engine is cranked?
Can anyone suggest a circuit that would turn off the IGBT after say, 20 milliseconds of inactivity (maximum
dwell will be around 5 milliseconds) but re-active it when it received a new pulse from the hall sensor?
Sorry, still working on posting circuit diagrams.
I have a 1949 Ford 8n tractor, 4 cylinder side valve with 6volt electrics, which the previous owner converted to 12volts and used a regular GM alternator instead of the generator. This is a common conversion but leads to problems with the ignition.
The distributor is on the front of the engine and has the 6volt coil integrated, like this:
That's the coil balanced on top.
When it's converted to 12 volt a different ballast resistor is put in the circuit to keep the current down to
about 6 amps through the coil. As it wasn't the most reliable system to begin with I have decided to bring the
ignition system into the 21st century.
Simple enough idea, replace the points with 2 digital hall sensors placed 90 degrees apart and activate them
with 2 magnets on the old points cam placed 180 degrees apart. This means hall sensor 1 will switch at 0 and
180 crank degrees and hall sensor 2 at 90 and 270 crank degrees.
These signals will be used to activate 2, N channel IGBT's, such as the Fairchild ISL9V3040D3S which is
purpose built as an ignition coil driver and needs no external components. From there to either a Ford Ranger
or Dodge Neon coil pack which both use the wasted spark principal.
My problem is, what if the magnet stops opposite one of the hall sensors and keeps the IGBT 'open' sinking a
high amperage and cooking the coil until the engine is cranked?
Can anyone suggest a circuit that would turn off the IGBT after say, 20 milliseconds of inactivity (maximum
dwell will be around 5 milliseconds) but re-active it when it received a new pulse from the hall sensor?
Sorry, still working on posting circuit diagrams.
