Fenced operation boat-engine It requires all systems to work in a stable way, and the electrical part plays a key role here. Tohatsu M18 There are often questions about battery charging and sparking, which are responsible for the rectifier assembly. If your boat has started to stall at high speeds or the battery has stopped charging, the first thing to do is check this component, since it is the link between the generator and the energy consumers.
The owners of two-stroke engines of Japanese production are well aware that Tohatsu 18bhp It is a reliable workhorse, but even it has electronic failures due to vibrations or moisture. Voltage regulator When assembled with a rectifier, it takes on the task of converting the AC to the constant current needed to operate the onboard network. Ignoring the symptoms of a malfunction can lead to a complete discharge of the battery directly on the water, which will turn a pleasant walk into a complex tow process.
Next, we will discuss in detail the design of the unit, methods of its diagnosis with the help of a multimeter and the features of replacement. diode bridge This will allow you to resolve the problem without contacting the service center, saving time and money.
Design and principle of operation of the rectifier node
Electrical circuitry Tohatsu 18 It is built according to the classical low-capacity scheme with an external rotor. Generator It generates alternating current that flows to the rectifier unit, and inside that unit are semiconductor diodes that only transmit current in one direction, converting the sine wave into direct current. The voltage at the output without a load can reach high values, so it's often built into the circuit. stabilizer or a regulator limiting battery charging to a safe 13.5-14.5 volts.
Structurally, the rectifier on this model is an aluminum plate with radiator ribs, to which diodes and capacitors are attached. Heat vent It's critical because the diodes get hot when the current passes, and the housing is usually sealed with a compound or a plastic casing, but over time, moisture can get in through the omentums or damaged seals, and it's the oxidation of the contacts and the breakdown of the diodes by moisture that are the main enemies of the system.
⚠️ Warning: Before starting any work with the electricians, be sure to disconnect the "mass" wire from the battery. A short circuit in the generator circuit with the engine running can instantly disable not only the rectifier, but also the ignition coil.
On the engines. Tohatsu It's a common combination unit where the rectifier is combined with a ignition coil or a thyristor switch, which makes the assembly compact, but makes it difficult to diagnose, and when one unit fails, you often have to change the entire unit assembly. WiringThe rod running from the stator to the rectifier usually has yellow or white wires, and the output to the battery is marked in red.
Symptoms of malfunction and primary diagnosis
Determine that straightener yours Tohatsu 18 The most obvious symptom is that the battery is not charged, which is easily checked with a voltmeter at the battery terminals when the engine is running, and if the voltage does not rise above 12 volts when the gas is added, then the current from the generator does not enter the battery.
Another common sign is the unstable operation of the engine at high speeds. diode If you go through a bridge or it goes into a cliff, the shape of the signal is distorted, which can cause sparks to pass, the motor can confidently start and run on idles, but when you try to go into plane, you start to see dips or a full stop.
Also worth paying attention to the state of the battery itself. If the liquid in the banks is constantly boiling out, and there is a plentiful white plaque on the terminals, this may indicate a malfunction. voltage regulatorOverheating of the rectifier unit itself (if it can be touched by hand while working) is also an alarming signal.
Necessary tools for verification
For qualitative diagnostics of the electrical part Tohatsu 18bhp You're going to need the minimum set of tools that every hydraulic motor should have. multimeterIt's a machine that can measure resistance, constant and variable voltage, and without it, checking the rectifier becomes a fortune-telling on the coffee grounds.
In addition to the measuring device, prepare a set of screwdrivers and keys to remove the flywheel protective casings. Often access to the rectifier is difficult, and a partial disassembly of the device is required. contact spray for cleaning the connectors and tape or thermal shrinkage to restore the insulation after inspection.
- 🔧 Digital multimeter with diode vertebrae function
- 🔋 Charged battery or load simulator
- 🧼 Contact Cleaner (Contact Cleaner)
- 📏 A set of crocodile probes and clamps
It is important that the multimeter probes are in good working order and the battery in the device is not discharged, otherwise the resistance readings may be incorrect. circuitry Always keep on hand the circuit of the electrical equipment for your modification. TohatsuAs the colors of the wires may vary depending on the year of issue.
Step-by-step instructions for checking multimeter
The diagnostic process begins with visual inspection and removal of the protective casings. Find the connector going from the stator to the rectifier. Usually it's two or three wires (yellow or white), disconnect the connector to exclude the influence of the rest of the circuit on the measurements, set the multimeter in the mode of measuring resistance (Ohm) or checking diodes.
First, check the stator windings for a break or a mass circuit. Put one probe on the metal part of the engine (mass), and then touch each contact in the stator connector. The device should show infinity (or one on the screen). If you see any resistance values, then you can see the infinity. isolation The winding is broken and the stator needs to be replaced.
☑️ Stator and rectifier check
Then we go to the rectifier itself, and you switch the multimeter to diode testing, and you connect the probes to the diode bridge contacts, and in one direction, the device should show a voltage drop (usually 0.4 to 0.7 V), and in the other direction, infinity. If it shows zero or infinity in both directions, then you can see the difference between the two. diode bridge It's defective.
⚠️ Warning: Never check the resistance or circuit integrity when the engine or battery is on, and this is guaranteed to cause the fuse of the multimeter or the device itself to burn.
If the rectifier is combined with the regulator, also check the output voltage. Connect the battery, start the engine and carefully (observing safety precautions) measure the voltage at the terminals of the battery. It should grow with revs, but not exceeding 14.5-15 volts. Exceeding this value indicates a breakdown. regulator.
Table of normal indications and malfunctions
For ease of diagnosis, below is a table with typical values that should be observed with a serviceable ignition and charging system. Tohatsu 18Deviations from these values in a greater or lesser direction require more in-depth analysis.
| Parameter of measurement | Normal value. | Possible malfunction |
|---|---|---|
| Stator winding resistance | 0.5 - 2.0 Ohms (between contacts) | Break or interturn |
| Resistance to mass | Infinity (∞) | Breakdown of stator insulation |
| Voltage drop on the diode | 0.4. - 0.7 B | Diode failure or break |
| Charging voltage (on revs) | 13.5 - 14.5 B | Failure of the regulator or rectifier |
| Candle tension when scrolling | A bright spark | Coil or switch failure |
It is worth noting that the values of the resistance of the windings can vary slightly depending on the temperature of the engine. engine It's going to show less resistance than the heated one, and the key is that the values on all the coils are symmetrical.
Effects of contact oxidation
Oxidation of connectors often creates additional resistance, which the multimeter may not detect in vertebrae mode, but which, under load, leads to a voltage drop. Always clear the contacts before the final assembly.
Replacement and features of installation of a new rectifier
If the diagnosis confirms a malfunction, straightener We need to replace it. Tohatsu This unit is often sold assembled with a bracket or part of the wiring. When installing a new part, make sure that the contact surface with the engine body is clean and fat-free. To improve heat removal, it is recommended to apply a thin layer of thermal paste to the back of the aluminum rectifier plate.
When you build, you should carefully monitor the routing of the wires. They should not touch the hot parts of the engine or have tension. Use regular clamps and locks. Isolation. The wires should be whole, any damage must be eliminated by thermal shrinkage, since vibration on the water quickly destroys the usual isolating tape.
Use a spray preservative for electrical contacts after assembly, which will create a protective film that prevents the contacts from oxidizing from salt water and moisture throughout the season.
Once all the connectors are installed and connected, do a visual recheck, make sure the flywheel is not touching the wires and that all the mount bolts are tightened with the right force, and then you can plug the battery in and test the start.
Prevention and care of motor electrics
And straightener and all the electrics Tohatsu 18 It's important to keep the daylights on the ground, and after each salt water trip, it's recommended to wash the dayweight with fresh water, avoiding direct jets to the electrical connectors, and pressure water can push the seals and cause corrosion inside the blocks.
Once a season, when you conserve or re-conserve, check the tightening of the battery terminals and the condition of the wires going to the motor. Oxidized contact at the battery terminal can give the false impression of a rectifier malfunction, since the current simply will not pass through the circuit. Grounding The engine should also be perfect.
- 🛥️ Keep the boat in a dry room or cover the engine with a cover
- 🔌 Periodically lubricate the electrical connectors with a special lubricant
- 👀 Visually inspect the wires for cracks and scuffs
- 🧼 Remove oxides from the battery terminals in a timely manner
⚠️ Warning: Do not use aggressive solvents or gasoline to clean the electrician. These can melt the plastic straightener case and damage the insulation of the wires, which will lead to short circuit.
And if you follow these simple rules, you can avoid sudden failures. The main reason for the failure of rectifiers on outboard motors is not a production defect, but moisture and corrosion of contacts..
Timely diagnosis and protection from moisture is the key to the long service of the electrician Tohatsu 18.
Frequently Asked Questions (FAQ)
Can I install a rectifier from another motor, such as a Yamaha or Mercury?
Theoretically, it's possible if the electrical parameters (current, voltage) and the circuitry of the connection match. connector And the mounts are almost always different. Tohatsu or proven analogs specifically designed for this model to avoid installation and operation problems.
Why does the scalper warm up while working?
A little heat, because the current is straightened out, but if the block is hot so that it can't be touched, it indicates overload, short circuit or failure of the diode bridge itself. heat sink).
How often should I change the straightener to Tohatsu 18?
With proper operation and the absence of extreme conditions (constant driving on full gas, storage in the sun), the rectifier serves the entire life of the engine. Replacement is required only when malfunctions occur. Preventive replacement is not required.
Can I drive without a battery if the rectifier is working?
On many two-stroke Tohatsu The ignition system is autonomous (magdino) and the motor will run without a battery, but the battery is necessary to run the starter (if any) and stabilize the voltage in the mains. Driving without the battery can lead to power surges and other electrical equipment failures.