Plug the BNC molded plug of the low-amp current clamp in to Channel A of the scope. If the motorbike has a single fuse for the cooling fan, it may be possible to remove the fuse and use an extension fuse test lead to connect the current clamp as shown in Figure 1. Alternatively, the wiring for the fan will need to be exposed, which on some machines may require the removal of a side fairing. Extreme care should be taken if fairings are to be removed.
With the example waveform displayed on the screen you can now hit the space bar to start looking at live readings.
The current waveform seen above shows a typical current draw from the motorcycle's cooling fan. The average current in this particular instance is about 7 amps. The small ripple that is seen oscillating between 6 and 8 amps is as a result of the cooling fan's individual motor windings.
The cooling fan invariably has an ignition-fed voltage, while the earth path is through either the motorcycle's ECM (Electronic Control Module) or a thermo switch situated in the radiator. If the system operates via the motorcycle's ECM, the information about when to activate the fan comes from the engines coolant temperature sensor. It is imperative that the cooling fan operates at the correct temperature to avoid the engine overheating while the motorcycle is stationary in traffic. The temperature at which the fan cuts in is usually around 100 to 105 °C.
Too high a current can be the result of a seizing cooling fan. As the fan is set in a position where it is subjected to water spray and road salt, it can be susceptible to seizure. A lower-than-anticipated current reading is not considered to be a problem provided the fan is running at the correct speed and provides adequate cooling. A consistent blip in the waveform on every 6th or 8th oscillation shows a fault in one of the individual motor windings.
We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.