E-TEC Trim Sender Circuit Details
Posted: Sat Apr 28, 2018 11:34 am
Below is a sketch that shows the E-TEC legacy engine TRIM SENDER circuit with some detail.
Circuit Description
Current from outside the EMM, typically from the boat cranking battery is switched on at the ignition key switch at the helm. The current is limited by a series resistor in the wiring harness or if an actual TRIM gauge is installed by the circuitry of the gauge, not shown in the sketch.
The current is carried back to the engine on the remote control wiring harness (MWS Harness) and loops through the EMM. In the EMM a current measuring device measures the current. The current will be proportional to engine trim (explained below). Also in the EMM a resettable thermal fuse or circuit breaker protects the EMM circuity from excess current flow.
Current leaves the EMM and is carried on the engine wiring harness to the trim sender. In the trim sender a rheostat with resistance range 10 to 88-Ohms is linked mechnically to the engine mount so that the engine position actuates a lever that moves the rheostat wiper connection. This changes the total resistance in the circuit and alters the current flow to be proportional to engine position.
The trim sender resistance will be near 10-Ohms when the engine is fully up and near 88-Ohms when the engine is fully down. We can estimate the current flow in the circuit as follows:
AT FULL DOWN
The total resistance will be 47 + 88 = 135-Ohms. With 12-Volts applied the current will be 0.088-Amperes
AT FULL UP
The total resistance will be 47 + 10 = 57-Ohms. With 12-Volts applied the current will be 0.21-Amperes
This change in current is measured in the EMM by some method, and from the measured current the EMM develops a digital signal of 0 to 100 representing engine trim position. The EMM can also be adjusted (using the EV-Diagnostics software) to calibrate the conversion of current to the digital signal representation so that only a portion of the total range of resistance is used, as will occur when there are mechanical and electro-mechanical limits that constrain the engine movement to a smaller range.
Circuit Description
Current from outside the EMM, typically from the boat cranking battery is switched on at the ignition key switch at the helm. The current is limited by a series resistor in the wiring harness or if an actual TRIM gauge is installed by the circuitry of the gauge, not shown in the sketch.
The current is carried back to the engine on the remote control wiring harness (MWS Harness) and loops through the EMM. In the EMM a current measuring device measures the current. The current will be proportional to engine trim (explained below). Also in the EMM a resettable thermal fuse or circuit breaker protects the EMM circuity from excess current flow.
Current leaves the EMM and is carried on the engine wiring harness to the trim sender. In the trim sender a rheostat with resistance range 10 to 88-Ohms is linked mechnically to the engine mount so that the engine position actuates a lever that moves the rheostat wiper connection. This changes the total resistance in the circuit and alters the current flow to be proportional to engine position.
The trim sender resistance will be near 10-Ohms when the engine is fully up and near 88-Ohms when the engine is fully down. We can estimate the current flow in the circuit as follows:
AT FULL DOWN
The total resistance will be 47 + 88 = 135-Ohms. With 12-Volts applied the current will be 0.088-Amperes
AT FULL UP
The total resistance will be 47 + 10 = 57-Ohms. With 12-Volts applied the current will be 0.21-Amperes
This change in current is measured in the EMM by some method, and from the measured current the EMM develops a digital signal of 0 to 100 representing engine trim position. The EMM can also be adjusted (using the EV-Diagnostics software) to calibrate the conversion of current to the digital signal representation so that only a portion of the total range of resistance is used, as will occur when there are mechanical and electro-mechanical limits that constrain the engine movement to a smaller range.