Main Motorcycle: Bonneville T100 Black2012
Join Date: May 2012
Location: South Australia
Other Motorcycle: prev: BSA,Suzuki,Yamaha
Problem: motor fails to start - pressing starter PB causes partial cranking then stops even with start
button still fully depressed.
Action: to monitor and carry out Cranking Volts Survey.
Test equipment: Fluke 89 IV multimeter with Australian NATA test certification (readings are within specifications) using Auto DC volt scale, meter set to Fast min/max recording
Test Study : Bonneville T100 2012 1042km, Battery condition - as new Battery voltage no load - 12.595v
Battery voltage: Ignition ON - 12.163v
Motor start min Volt recorded Motor start status
Crank test 1 - 7.14v FAILED to start
Crank test 2 - 7.10v STARTED
Crank test 3 - 7.17v STARTED
Crank test 4 - 7.24v FAILED to start
Crank test 5 - 7.14v STARTED
Battery Volts after 5 crank starts - 12.43v
Results: somewhat surprised the battery volts fall so low at initial cranking start. As a Electrical Technician I do understand the principal of what is happening here. The starter motor at point of start is in a stalled position, meaning there is no magnetic field
built up in the armature, therefore the battery sees the motor as a purely resistive load until the armature magnetic field reaches saturation point and impedance of the circuit restricts current. so not having measured the motor resistance assume a resistance of say
0.05 ohms the maths tell me Volts divide by Ohms = 240amps. Since the power source is a small battery of limited cranking current and a british motor (very close motor tolerances) at a cold start the motor
would be somewhat tight to turn over initially. Long stroke and at different points of the stroke cycle at start would vary initial cranking torque required.
The results are inconclusive, but satisfy me in my mind that the bike still starts, the load on the
battery is enormous to pull it down to 7v(this occurs for a very brief time eg.milliseconds) as the motor starts the current falls and the voltage will rise (voltage is inversely proportional to amps when the circuit resistance/impedance is constant)
LIMITATIONS OF TEST: short but tells me a story of what the battery is doing, it would be nice to log the DC amps and have a digital trace oscilloscope with memory to trace the voltage, but this was just a quick look. Also to log the voltage after each interlock and ECU output to see who stops the start.
Conclusion: the testing proves my battery is ok, the cause of the problem is unresolved. The probability of it being the choke is false as it only affects motor idle rpm and A/F ratio.
The clutch/neutral/stand switches are only start interlocks.(new bike their fine). The ECU being microprocessor based would have a 3 or 5v supply rail from a DC to DC convertor with filtering, as the min volts stayed above 7v a 3 or 5v rail would not be compromised. As no one but TRIUMPH has the source code to the ECU we have no way to decifer the program logic behind the controls.
The only conclusion may be is that the duration of sustained low voltage below a preset voltage will trigger a ECU start abort. As pre-empted by others on this forum.
HOW DO I FIX THIS: Triumph wont, but in the back ground may change this threshold on future models.
A bigger battery will uphold the voltage better with high cranking current.
Fit a kick starter? but they put a electric starter on it because 865cc is just hard work to kick over
- could be why a small starter motor with a small limited battery sometimes just struggles to do its job.
Me, I think I'll put up with it for now until it becomes a real bitch!
it ain't over till the fat lady sings, but sometimes she just wont sing!