E-TEC Trim Sender Circuit Details

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jimh
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E-TEC Trim Sender Circuit Details

Below is a sketch that shows the E-TEC legacy engine TRIM SENDER circuit with some detail.

Legacy E-TEC engine trim sender circuit.
etecTrimSenderCircuit.png (33.23 KiB) Viewed 1143 times

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.

jimh
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Re: E-TEC Trim Sender Circuit Details

A problem reported by several E-TEC engine owners is intermittent loss of the digital engine trim signal, usually correlated with the engine temperature rising to normal operating temperature range. The cause is assumed to be the trim circuit current is being interrupted in the EMM by the action of the resettable thermal fuse.

The opening of the resettable thermal fuse is related to two conditions: current flow in the circuit being protected and ambient temperature. A further assumption is that the current threshold for the resettable fuse to open must be higher than the normal current in the circuit. If stray currents flow in the circuit, the fuse should open due to excessive current. A thermal fuse operates on temperature rise. It is assumed that rise in local ambient temperature for the fuse device will make the fuse more sensitive to opening when current passes through the fuse and causes additional heating. The behavior reported by users who experience the problem of the fuse opening matches these assumptions: the fuse tends to open only when the engine temperature has risen to the normal operating range, which can be as high as 190-degrees-F.

The EMM housing is cooled by water flowing through a central passage where heat is being generated by devices in the EMM handling high currents. The devices are bonded thermally to the heat sink, and a water passage through the heat sink carries heat away from the heat sink to the engine cooling water system and then overboard.

The rate of cooling water flow through the EMM is assumed to affect EMM temperature. Insufficient cooling will result in higher EMM temperatures. Higher EMM temperatures may be causing the trim circuit resettable thermal fuse to become more sensitive than originally intended to current flow in the trim circuit, causing the fuse to open the circuit even though the current flow is in a normal range.

jimh
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Re: E-TEC Trim Sender Circuit Details

There are three remedies suggested to eliminate the problem of loss of trim signal:

1. Eliminate all current flow through the EMM by installing a conventional trim gauge and rewiring the trim sender to connect to the gauge without passing through the EMM. This is reported to cure the problem but it does so by eliminating the digital trim signal entirely.
2. Add a higher value series resistance. Increasing the series resistance to be greater than 47-Ohms will reduce the current flow in the circuit. This has been tried by at least one person. They report that the time for the EMM fuse to open increases, but eventually the EMM fuse does open. Increase in resistance appears to be only a temporary remedy to the problem.
3. Replace the EMM. This is a very expensive and drastic remedy. I do not recall anyone trying this approach.

jimh
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Re: E-TEC Trim Sender Circuit Details

A fourth remedy has also been reported: replace the trim sender with an improved version, used in E-TEC engine production beginning in 2012 models.

The 2012 trim sender appears to have been designed to remedy a related problem: excessive current flowing on the ground circuit of the trim sender wiring harness. In the original trim sender, the ground conductor is bonded to the engine mount at the trim sender, and the circuit is then carried to the engine where it is bonded to the main engine chassis ground connection. If a poor connection develops between the battery negative and the engine chassis in the primary connection using large-gauge battery cables, apparently a sneak circuit exists where battery negative to engine chassis current could flow on this very small gauge sender ground conductor, including engine cranking motor currents. Large currents flowing on the small ground conductor would burn off the conductor. These problems are usually associated with battery connections with loose fasteners (such as wing nuts).

There does not appear to be any change in the internal resistance range of the 2012 trim sender, so it is not known how it could reduce current flow in the trim circuit. However, at least one user has reported that installation of the 2012 trim sender solved a problem with intermittent trim signal.

For more about the improved E-TEC trim sender assembly, see
http://continuouswave.com/forum/viewtopic.php?f=10&t=3361&p=19072#p19072

jimh
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Re: E-TEC Trim Sender Circuit Details

A fifth remedy may be: increase cooling water flow in general so the EMM temperature remains lower. Increased cooling water flow can be obtained by installation of the water pump impeller with the recommended method explained in the installation literature. The impeller is locked onto the drive shaft in a slightly different manner that results in better pump pressure output and increased water flow.

Increased water flow for the EMM cooling may also be obtained if there are any obstructions in the hoses to the EMM or in the passage through the EMM. These parts of the cooling water system on the engine should be checked to see if there are any obstructions. Also, any downstream obstructions could reduce flow. Cooling water from the EMM flows downstream to the fuel vapor separator tank (VST) and then out to the overboard indicator nozzle. Obstructions in those areas of the path could also reduce cooling for the EMM.

jimh
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Corollary: Power Dissipation in Trim Sender

We consider the power dissipation in the circuit, particularly in the trim sender resistor. The solution is simpler if we consider a general case.

Assume we have a supply voltage of 1.00-Volts and connect two resistors across this voltage. One resistor is 1-Ohm and the other resistor is R. The resistance of R can vary over a range from 0.1 Ohms to 2-Ohms.

Because the current is the same in both resistors, we call the current i. Because we know the voltage (1) and the other resistor (1), we can write a definition for i as

i = E/R where E=1 and the total resistance is 1-Ohm plus the value of R, thus
i = 1/(R+1)

According to Ohm's law, the power associated with a load resistor is equal to the resistance time the square of the current. The power dissipated in R will then be

P = i2R

Substituting for i we get

P = [1/(R+1)]2R

This simplifies to

P = 1 / [R + 2 + (1/R)]

The power will be maximum in R when the denominator [R + 2 + (1/R)] is the smallest.

Now we can plot this relationship to see where the maximum occurs:
Power dissipated in second resistor in series circuit; peak power occurs at 1-Ohm.
graphPowerInResistor.png (27.5 KiB) Viewed 1091 times

It easier to see if we just plot the denominator and look for a minimum:

Denominator of power equation; power is maximum when this value is minimum. Again, minimum is at x=1, i.e., when the resistors are equal in value.
graphPowerInResistorDenominator.png (27.43 KiB) Viewed 1087 times

The outcome is a bit unanticipated: the most power is dissipated in the second resistor when its value is the same as first. At any other value, the other resistor (1-Ohm) dissipates more power. This result is obtained no matter what the resistance of the other resistor is assumed to be.

To evaluate at the conditions for the actual circuit, we use E = 12 and the other resistor = 47-Ohm. This results in the trim sender dissipating a maximum of 0.77-Watts when its value is also 47-Ohms.

Proof: we find i from 12/(47+47) = 0.128
i2 = 0.016
P = i2R
P= 0.016 × 47
P = 0.77-Watt

jimh
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Corollary: Maximum current in trim sender circuit

Because one of the notions of a possible cause of intermittent operation of the trim circuit is from an over-current condition causing the EMM to open the circuit with its resettable thermal fuse, we can investigate the circuit to see when maximum current flows. This analysis is easy. Again, we look at the relationship for current in the circuit:

i = E/R

Current will be maximum when R is minimum. Since R is formed from the combination of the fixed 47-Ohm resistor and the variable trim sender resistance, current maximum occurs when the trim sender resistance is the lowest.

The trim sender is at lowest resistance when the engine is in the maximum tilt-up position. This is actually an interesting design detail. Most of the time the trim circuit will have current flow at all will be when the engine is NOT trimmed up to full up position, but is much closer to fully-down trim or maximum resistance, thus minimum current flow. Designing the circuit this way means the current flow in the trim sender is kept to a minimum for most operating conditions of engine trim.

What will be the maximum current flow?

i = E/R
i = 12/(47+10)
i = 12/57
i = 0.21-Amperes

jimh
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Re: Fault Current

If we assume a fault occurs somewhere in the trim sender circuit in which some current leaks to ground, the location of the fault affects whether the fault current is passing through the EMM, where it could cause the resettable fuse to open. If the fault occurs upstream of the EMM, the fault current does not pass through the EMM current measurement device. This is illustrated below.

R1 = current limiting resistor, nominally 47-Ohms
R2 = trim sender resistor, nominally 10 to 88-Ohms
R1 = abnormal fault resistance to ground; possibly very low resistance

Current flow in trim sender circuit. In this instance, fault current does not pass through the EMM current measurement sensor.
faultCurrent.jpg (10.33 KiB) Viewed 1056 times

Current i1 = total current
Current i2 = the normal current passing through the EMM and the trim sender
Current i3 = current flowing in a fault to ground. The EMM only measures current i2

If the fault is downstream from the EMM, then the fault current passes through the EMM and is measured there, affecting the resettable fuse protection. This is illustrated below:

Current flow in trim sender circuit. In this instance, fault current does pass through the EMM current measurement sensor.
faultCurrent2.jpg (10.18 KiB) Viewed 1055 times

Current i1 = total current, in this case passing through the EMM and being measured
Current i2 = the current in the trim sender
Current i3 = fault current flowing in a fault to ground.