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Author Topic:   Power Generation and Distribution in E-TEC Engines
jimh posted 05-23-2015 12:34 AM ET (US)   Profile for jimh   Send Email to jimh  
The following review of the electrical power generation and distribution in an E-TEC may be helpful to understand the unusual electrical power generation and distribution system of the Evinrude E-TEC.

Power Generation and Distribution in E-TEC Engines

The E-TEC engine is somewhat unusual among outboard engines in its power generation and power distribution. The primary power generation is provided by a permanent magnet alternator (PMA). The permanent magnet alternator has coils arranged in two or three sets, depending on the engine horsepower. The wiring of the coil sets can be made to be either series or parallel, depending on the engine speed range. The switching between series and parallel wiring in the PMA is done with solid-state devices. Typically the coils are wired in series at low engines speeds to get the desired voltage output. As engine speed increases and coil voltage output increases, there is sufficient voltage in each coil set, and the coil sets are switched to be in parallel to deliver more current.

The 55-Volt Circuit

The PMA output is designed to provide 55-Volts. In the E-TEC engine wiring harness, the 55-Volt circuit is generally wired with conductors having insulation of WHITE with RED Stripe. The 55-Volt bus has a large electrolytic filter capacitor connected across it. The capacitor helps to stabilize the voltage and to absorb any voltage transients.

The 55-Volt circuit powers the following devices in the E-TEC engine:

--E-TEC voice-coil fuel injectors

--oil injector pump

--ignition coil primary winding

--the EMM itself (but likely with voltage regulation to a much lower level, like 5-Volts)

--the high pressure fuel pump; because the fuel pump is a 12-Volt device, the circuit that operates it--wired with a RED with WHITE Stripe conductor coming from the EMM--may be a 12-Volt circuit, but that circuit appears to not be the same circuit as the 12-Volt bus that is carried on conductors with RED insulation.

55-Volt to 12-Volt Convertor

The 55-Volt circuit also powers a 55-Volt to 12-Volt convertor circuit. The 55-Volt to 12-Volt conversion takes place in the EMM itself on the larger engines, and in an external module on the small two-cylinder engines. The 12-Volt output from the 55-Volt to 12-Volt convertor circuit is connected to the 12-Volt bus.

On the larger E-TEC engines, from 115-HP and up, the 55-Volt to 12-Volt convertor is contained in the EMM and had two parallel output circuits. (It is not clear if there are actually two completely isolated 55-Volt to 12-Volt convertors, or if there is just one convertor and its output is divided into two branches.) Each output circuit has four conductors carrying output from the EMM. (I suspect the use of four conductors is a result of the size of the electrical contacts in the multi-pin connector of the EMM. The individual contacts are too small to carry the total current output of the convertor through the connector, so the current is spread among four pins. It could also be that there is only one circuit and it is divided among eight contacts on the connector.) One set of four conductors has RED insulation. The second set has RED with BLACK Stripe insulation.

The second output from the 55-Volt to 12-Volt convertor with the RED with BLACK Stripe insulation is routed through an additional connector, and then joins the 12-Volt bus. If an Auxiliary Battery Charging Kit is added, this second output is disconnected from the 12-Volt bus and routed out to a external 12-Volt storage battery.

12-Volt Bus

Typically an external 12-Volt storage battery is connected to the 12-Volt bus. When a 12-Volt storage battery is connected to the 12-Volt bus, electrical power from the E-TEC can flow into the battery, charging the battery, or electrical power can flow from the battery into the E-TEC, discharging the battery. The interconnection of the battery and the E-TEC 12-Volt bus does not have any sort of isolation or one-way flow of electrical energy. It is a common circuit, and current can flow in either direction--to the battery from the E-TEC (for battery charging) or to the E-TEC from the battery (as happens during engine cranking or anytime the E-TEC is not creating enough electrical power to carry the loads on the circuit). Conductor on the 12-Volt bus usually have insulation with RED insulation

The 12-Volt bus powers the following devices in the E-TEC engine:

--the cranking motor solenoid coil circuit

--the cranking motor (of course, this is not powered by the engine because the engine is not running yet when the starter motor is needed)

--the trim and tilt relay circuit

--the trim and tilt electric pump circuit

--the ignition key panel and any accessories connected to the ignition key accessory circuit

Starting Assist Circuit

When a 12-Volt storage battery is connected to an E-TEC, the engine can be started by the electric cranking motor. Current to run the cranking motor comes from the battery, and also powers the 12-Volt bus of the E-TEC. There is no 55-Volt power until the engine begins to spin and the permanent magnet alternator (PMA) begins to generate its 55-Volt output. To help produce electrical power on the 55-Volt bus when the engine is first beginning to rotate during cranking, an electrical circuit tries to use current from the 12-Volt bus (being supplied by the attached battery) to boost the voltage on the 55-Volt bus. This is called the Starting Assist Circuit. Voltage from the PMA is a function of the speed of rotation of the engine, so in the initial seconds of rotating the engine at cranking speed, which may be as slow as 300-RPM, the Starting Assist Circuit helps the 55-Volt bus produce electrical current for its loads.

Loads on the 55-Volt Bus

We see that all of the electrical devices on the E-TEC that are part of its engine operation are actually run from the 55-Volt bus. These devices will also operate at some reduced capacity if the bus voltage is lower than 55-Volts, as occurs during starting. Using a higher voltage for operation reduces the size of the conductors needed, as the current flow will be less with 55-Volts than it would need to be with 12-Volts. In essence the 55-Volt bus runs all of the electrical systems needed to run the engine.

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