Typical TRIM MOTOR Circuit

Electrical and electronic topics for small boats
jimh
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Typical TRIM MOTOR Circuit

Postby jimh » Sat Aug 11, 2018 10:04 am

Most outboard engines have a power trim-tilt feature. The electrical circuit shown below is typical:

typicalTrimCircuitDwg685x564.png
Fig. 1. Typical power trim-tilt circuit for outboard engine
typicalTrimCircuitDwg685x564.png (33.38 KiB) Viewed 9914 times


CIRCUIT DESCRIPTION

The TRIM MOTOR M is a reversible DC motor connected by BLUE and GREEN conductors to the common pole of two SPDT relays, K1 and K2. If neither relay is energized, both leads to the trim motor are connected to 0-Volts (or battery negative or chassis ground) via the normally-closed contacts of the relays, and the motor is not energized.

The relay K1 is the UP direction relay; when K1 is energized, the BLUE conductor has 12-Volts via the normally-open contact from the RED conductor, and the trim motor turns in the direction to raise the engine.

The relay K2 is the DOWN direction relay; when K2 is energized, the GREEN conductor has 12-Volts via the normally-open relay contact from the RED conductor, and the trim motor turns in the direction to lower the engine.

The coils of relays K1 and K2 are independently operated by remote control switch S1, located typically on the handle of the remote shift-throttle control lever. Not shown is a second remote control switch, wired in parallel with the first, typically located on the engine cowling. The switches are usually combined into a three-position ON(momentary)-OFF-ON(momentary) arrangement in a single rocker switch. Depressing the UP switch energizes the UP relay and causes the engine to tilt up; depressing the DOWN switch energizes the DOWN relay and causes the engine to tilt down. The circuit for the coil for the UP relay is usually provided on a wire with BLUE with WHITE insulation; the circuit for the coil of the DOWN relay is usually provided on a wire with GREEN with WHITE insulation.

The 12-Volt power to the relay contacts or the high-current circuit generally comes from a heavy-gauge RED conductor that is connected to the battery positive; in some engines there may be a circuit breaker (not shown above) to protect the circuit from excessive current. The 0-Volt power to the relay contacts generally comes from a heavy-gauge BLACK conductor that is connected to the battery negative. It is typical that in most outboards these circuits are made directly to the main battery cable connections to the engine from the starting battery. This conductor is usually bonded to the engine chassis. The relay circuit BLACK conductor is also bonded to the engine chassis.

The 12-Volt power for the relay coils comes from the remote switches; this is the low-current or control circuit. The switches at the remote throttle lever often get their 12-Volts from the ignition key circuit, so the ignition key switch must be in the ON or RUN position for those switches to work. The switches on the cowling often get their 12-Volts directly from the battery connection, so they will work when the engine is not running and the ignition key can be in the OFF position. The UP circuit wiring usually has insulation of BLUE with WHITE; the DOWN circuit usually has insulation of GREEN with WHITE. A simple way to remember the color coding is to associate blue with the sky or up, and green with the grass or down. These circuits are also typically protected by a fuse F1.

TYPICAL PROBLEMS

Although not shown in the simplified circuit diagram above, there are typically several multi-pin connectors for the wiring in the remote control or low-current part of the circuit. Any discontinuity in the electrical connection in those connectors will cause a failure of the control. This is often seen at the remote shift-throttle lever, which is always being manipulated; the wiring to the switches can and does fail due to the flexing.

The circuit to the motor is also often run through a connector; again, any contact problems in this connector will affect the operation.

The process of tilting the engine up to a fully-raised position also causes all the electrical conductors in the engine control cable to be flexed. Abrasion of the conductor's insulation can occur and cause problems.

The remote switches themselves are often exposed to water from spray, splashing, or rain. The switches can fail, particularly ones on the cowling.

The relay contacts are handling high current and an inductive load, conditions which cause arcing of the contacts. Relay contacts can fail due to build up of carbon from arcing or pitting. They can also weld together.

The load of the trim motor when running can cause voltage drops in the battery and associated power distribution wiring; low voltage at the relay coils can cause the relay coil to have insufficient magnetic force to hold the relay contacts closed. When the contacts open the load is removed, the voltage returns to normal, and the contacts close again. This creates a cycle of relay contact chattering open and closed. Such operation is certain to damage the contacts of the relay in a short time.

The relays are sometimes arranged into an assembly, and replacement of the assembly will replace both relays. If the relays are provided separately, they can be replaced individually.

Outside of the relays, the control switches, and the wiring and connectors associated with them, the trim motor itself can also fail.

jimh
Posts: 11677
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

TRIM Motor Circuit

Postby jimh » Sat Feb 26, 2022 10:34 am

Many outboard engines have a power trim feature. The electrical circuity for the power trim may be shown in the factory service manual, but often in pictorial form. Understanding how a circuit works can be made easier in a well designed schematic diagram of the circuitry, rather than in a pictorial of the wiring connections.

Below is a schematic diagram sketch that shows the simplified electrical circuit in a manner to aid understanding of the circuit.

trimMotorCircuit-800.png
Fig. 2. A sketch showing a simplified electrical schematic diagram of a typical outboard engine trim circuit showing the general configuration. For the relay contacts, N/O means normally open; N/C means normally closed.
trimMotorCircuit-800.png (47.08 KiB) Viewed 3108 times


Referring to Figure 1, the TRIM MOTOR is a reversible DC motor that is connected to the common contacts of two relays, referred to as the UP or DOWN relays. With both relays de-energized, both blue and green motor leads are connected to battery negative, and the motor does not operate.

The TRIM SWITCH is a three-position center-off switch with momentary action. In the center-off (normal) position, neither UP or DOWN relay is energized.

When the TRIM SWITCH is moved to the UP position, the UP RELAY is energized, and the blue conductor to the TRIM MOTOR is connected to battery positive (12-Volts DC) in the UP RELAY. The green conductor remains connected to the battery negative through the DOWN RELAY. This energizes the TRIM MOTOR to move in the upward direction.

When the TRIM SWITCH is moved to the DOWN position, the DOWN RELAY is energized, and the green conductor to the TRIM MOTOR is connected to battery positive (12-Volts DC) via the DOWN RELAY. The blue conductor remains connected to the battery negative via the UP RELAY. This energizes the TRIM MOTOR to move in the downward direction.

Not shown in the simplified diagram are other circuit elements such as:
  • a fuse in the battery positive circuit to the TRIM SWITCH
  • a TRIM LIMIT SWITCH in the relay circuit that prevents the UP RELAY from energizing
  • a second TRIM SWITCH wired in parallel with the one shown, and
  • interconnecting wiring that is often part of the engine wiring harness.

COMMON PROBLEM IN TRIM CIRCUIT

A common problem in the TRIM CIRCUIT is a failure of one or both of the relays. Because the motor current always flows through both relays' contacts, an intermittent in either the normally-open or the normally-closed relay circuit can affect operation of the motor. The relay contacts handle a high current flow and must interrupt that high current when opening. Because the DC motor is an inductive load, interruption of the current often produces an electrical arc on the opening of the relay contact. Over time the arcing degrades the contact surfaces, leading to eventual problems or failure of the relay contacts.

In some engines, the two relays are combined into one assembly, so failure of either relay requires replacement of both with a new assembly.

Another common point of failure is the TRIM SWITCH. The circuit may fail inside the switch or in the associated wiring. Often a trim switch is mounted on the handle of a shift-throttle control, so the wiring to the switch is subject to continual motion, leading to failure. Most outboard engines have a second trim switch on the engine cowling, whose wiring is not subject to continual motion, but the switch itself is exposed to water intrusion from the cowling location. Either switch may fail and leave the other switch operational.

Note that if an audible click can be heard from the relay when the TRIM SWITCH is activated, then a relay is being energized. This outcome suggests that if there is a circuit problem, the cause will be in the high-current circuit involving the relay contacts or the connections of the 12-Volt power to the relay contacts.

A failed trim limit switch can cause the TRIM MOTOR to be unable to operate in the upward direction; the downward direction should not be affected.