outboard motor Tohatsu 18 It is a popular choice among fishermen and small boat owners due to its reliability and economy, but even such time-tested units require high-quality electrical equipment, especially when it comes to battery charging systems. Tohatsu 18 It's responsible for converting the alternator current to the constant current needed to charge the onboard battery, and without a serviceable rectifier, you risk being left without power to the sonar, the navigator, or even the starter at the most inopportune moment.

In this article, we will discuss all the nuances of choosing, installing and maintaining rectifiers for Tohatsu 18 From factory solutions to generics, you'll learn how to diagnose malfunctions, which rectifiers are suitable for different years of engine production, and why cheap Chinese counterparts can turn out to be expensive repairs, and you'll focus on the connectivity circuits and the typical errors that even experienced water turbines make when replacing this unit.

Why do you need a voltage rectifier in Tohatsu 18?

outboard motor generator Tohatsu 18 produce alternating-currentWhile the boat's onboard network and battery are running on permanentThe rectifier (diode bridge) has three key functions:

  • 🔄 Current conversion: converts the alternating voltage of the generator (usually 12-14V) to a constant, suitable for charging batteries.
  • 🛡️ Battery protection: prevents the battery discharge back to the generator when the motor stops.
  • ⚡ Stress stabilization: smoothes out voltage peaks that can damage electronics (echo sounder, radio, lighting).

On the engines. Tohatsu 18 (depending on the year of release) two types of rectifiers are used:

  1. Built-in Integrated into the generator (typical for models up to 2015).
  2. Removable - a separate unit installed on the motor bracket (after 2016).

The absence or failure of the rectifier leads to:

  • 🔋 Quick discharge of the battery even with the engine running.
  • 💥 Overheating of the generator due to reverse currents.
  • 📵 Electronics malfunctions (e.g., sonar) Garmin It may show incorrect data).
📊 What type of rectifier is installed on your Tohatsu 18?
Built-in (until 2015)
Removable (after 2016)
I know.
I have a different engine.

Signs of rectifier failure

Diagnose problems with the rectifier on Tohatsu 18 You can have a few symptoms, and if you notice at least two of them, it's time to check the diode bridge.

A symptom. Probable cause Action.
The battery is not charged when the motor is running Diode failure, chain break Call the rectifier with a multimeter
The voltage on the battery exceeds 15V Failure of the regulator or diode bridge Replace the rectifier + check the regulator
The generator is warmer than usual Back current due to broken diodes Urgent replacement of rectifier
Electronics work unstable (lights flicker, sonar settings are reset) Stress pulsations due to diode wear Checking with an oscilloscope or replacement with a known serviceable

The easiest way to check is to measure the voltage at the battery terminals when the engine is running (revs above 1500 rpm):

  • ✅ Norma.13.8–14.4V (depending on the temperature and condition of the battery).
  • ❌ Problem.: less than 13B or more than 15B.
⚠️ Attention.: If the battery voltage is running at the engine exceeds 16BTurn off the engine immediately! This could cause the battery to explode due to overheating of the electrolyte.

To accurately diagnose the rectifier, you have to dismantle it and ring each diode with a multimeter in diode check mode. The correct diode only lets current in one direction. If the device shows conductivity in both directions, the diode is pierced.

How to call a straightener without dismantling?

If it is not possible to remove the rectifier, you can check it "on the spot":

1. Disconnect all wires from the rectifier.

2. Transfer the multimeter to diode check mode (or 2000 ohms).

3. Connect the probes to the conclusions "+" and "~" (generator): should show 400-800 Ohms in one direction and "OL" (cliff) in the other.

4. Repeat for conclusions "-" and "~".

If in any case the resistance is zero or the same in both directions, the rectifier is defective.

Top 5 straighteners for Tohatsu 18: a review of models

They are presented on the market as original rectifiers. TohatsuWe analyzed the feedback from owners and specifications to rank the best options for engines. Tohatsu 18bhp:

  1. Original Tohatsu 186A0-87600-0 rectifier (for 2016–2026 models)

    ✅ Pluses: perfect compatibility, long service life (50 000+ motor hours), fasteners and thermal paste are included.

    ❌ ConsHigh price (from 4500 rubles), counterfeits on the market.

  2. Sierra 18-6405 (universal)

    ✅ Pluses: suitable for most two-stroke engines 15-20 hp, inexpensive (about 2200 rubles), easy to install.

    ❌ Cons: requires further development of the mounting for Tohatsu (hole drilling)

  3. Mallory Marine 9-32501

    ✅ Pluses: Enhanced protection against moisture (IP67), built-in fuse, compatible with motors up to 25 hp

    ❌ Cons: dimensions are larger than the original, the price is ~ 3,800 rubles.

  4. Moeller Marine 030501

    ✅ Pluses: compact, lightweight (only 120 g), suitable for Tohatsu 9.8/15/18.

    ❌ Cons: weak heat resistance (can overheat during prolonged operation at high speeds).

  5. Chinese analogues (for example, For Tohatsu 18HP)

    ✅ Pluses: price from 800 rubles, quickly delivered.

    ❌ Cons30% of defect, low quality diodes (season 1-2 service life), no warranty.

For engines. Tohatsu 18 until 2015 The stains will be marked with markings. 186A0-8760E-0 (built-in type) For models post-2016 need a takeaway block 186A0-87600-0 Or its analogues.

⚠️ Attention.: When buying a universal rectifier, check it out maximum current - Tohatsu 18 It should be at least 12A.Models with 8-10A will burn out quickly!

Compatible with the year of your engine

Maximum current (minimum 12A for Tohatsu 18)

The presence of fastening holes under your model

Components (wires, thermal paste, instructions)

Manufacturer's Guarantee (minimum 1 year)

Connection scheme of the rectifier to Tohatsu 18

Incorrect connection of the rectifier can lead to short-circuitThe following is the standard motor circuit. Tohatsu 18 with a retractable rectifier (after 2016):

1. From the generator. go jock-wire (alternating current) - connected to the terminals of the rectifier, marked as AC or ~.

2. Red wire. ("+") goes to battery through the safety lock (10-15A).

3. Black wire. ("-") is connected to mass motor (can be used to the negative terminal of the battery).

4. White/green wire (if any) is a signal cable for a tachometer (not required for the work of the rectifier).

For clarity:



GENERATOR


│


├───► Yellow (AC) [SPRING]


├───► Yellow (AC)


│


ACCUMULATOR


├───► Red (+) [SPRING]


└───► Black (-) Motor weight

For engines. until 2015 With a built-in rectifier, the scheme is different - there the diode bridge is located inside the generator, and it can only be replaced in the assembly with the rotor.

⚠️ Attention.: Never connect the rectifier safety-free It can cause a fire if you short-circuit it. 10A. for battery capacity up to 60Ah and 15A. 70Ah and up.
💡

Before connecting a new rectifier, clean the generator and battery contacts with sandpaper (grindness 600-800). Oxidized connections can cause a voltage drop of up to 1-2V, which is critical for charging!

Step-by-step instructions for replacing the rectifier

Replacement of rectifier with Tohatsu 18 does not require special skills, but will require accuracy and tools: a cross screwdriver, a key for 10 mm, a multimeter and a thermal paste (for example, a sleeve of the sleeve). KPT-8Follow the algorithm:

  1. Preparation

    Turn it off. minus-plate Remove the plastic engine casing (unscrew 4 screws around the perimeter).

  2. Dismantling the old rectifier

    Unplug all the wires (better take a picture of the connection circuit!) Unscrew two bolts of the rectifier mount to the bracket.

  3. Installation of a new unit

    Apply a thin layer of thermopaste to the back wall of the rectifier (for better heat sink).

  4. Connecting wires

    Follow the diagram from the previous section. Check the reliability of the contacts - weak connections lead to sparkling and overheating.

  5. Testing

    Connect the battery, start the motor and measure the voltage on the battery. 13.8–14.4B at 2,000 rpm.

If after the voltage is replaced by AKB below 13BCheck it out.

  • 🔌 Quality of contacts on the generator (oxidation or break).
  • 🔄 Polarity of connection (the confused "+" and "-" will bring the rectifier out of action!).
  • 🔋 Battery state (plate sulfation may block charge).
💡

After replacing the rectifier, be sure to check the engine at idle speeds for 5-10 minutes. If the rectifier starts to warm up (body temperature above 60 ° C), immediately turn off the engine and check the connection!

Tuning and modernization of the charging system

Standard rectifier Tohatsu 18 It does not always cope with increased loads, especially if additional equipment is installed on the boat (inverter, powerful sonar, LED spotlights).

1. Installation of a rectifier with increased current

For boats with energy-intensive equipment (for example, an electric winch), a standard rectifier for 12A may not be enough. 20-25A (for example, Sierra 18-6425Important:

  • 🔧 Replacement of generator windings with more powerful ones (or installation of an additional generator) will be required.
  • 📉 Increased load on the engine (power drop by 1-2 hp).

Two-stage charging system

Two rectifiers shall be used:

  • 🔋 Basic (12A) - for charging the starter battery.
  • 🔋 Additional (10A) - for powering the onboard network (echo sounder, lighting).

Pros: unloading the main battery, the ability to use batteries of different capacities. Cons: complexity of the scheme, the risk of confusion when connecting.

3. Replacement with modern adjustable rectifier

Models with plug-in (for example, Bass Pro boats 12V 20A) automatically maintain the optimal charging voltage (14.2–14.6V) regardless of engine speed, extending battery life by 20–30%.

⚠️ Attention.: When upgrading the charging system Make sure to install a separate safety unit. This will protect the equipment from the surges of voltage that are common with the use of non-standard rectifiers.
How to connect two batteries to Tohatsu 18?

This will require:

1. Two rectifiers (or one dual channel, for example, Guest 2630A).

2. Diode insulator (e.g., Blue Sea SI-ACR) for chain separation.

Safety locks for each line (10A for starter, 15A for onboard network).

Connection diagram:

- Rectifier 1 → Starter battery (through the insulator).

- Straightener 2 - Onboard battery.

The insulator connects the + of both batteries, but blocks the back current.

This will allow both batteries to be charged at the same time, but to be used independently.

Common Mistakes When Working with Recreators

Even experienced owners Tohatsu 18 Sometimes they make mistakes that cause the rectifier or the electrical equipment to break down, and here are the most common ones:

  1. Ignoring polarity

    The entangled + and - will knock the rectifier out of action in a split second. Always check the terminal markings!

  2. Lack of safety lock

    Without the protection of the plus line, a short circuit can burn not only the rectifier, but also the generator.

  3. Using a cheap thermal paste

    The low-quality paste dries out over the season, causing the straightener to overheat. Use Arctic MX-4 or KPT-8.

  4. Spark-spark-spark-straightener check

    Some "masters" check the performance, briefly touching the contacts with wires from the battery. This leads to a breakdown of the diodes!

  5. Savings on wires

    Thin or oxidized wires create resistance, which is why the battery can come only 12-13V instead of the necessary 14V.

Another common problem. incompatibility of the rectifier with the voltage regulatorFor example, if you install a rectifier from Yamaha 20 on Tohatsu 18Due to the different specifications of the regulator, the voltage on the battery can jump from 12 to 16V, which is detrimental to the battery.

To avoid mistakes, always check with circuitry of your model (It can be found in the manual or on the website) Tohatsu - by the engine's lead code.

FAQ: Frequent questions about rectifiers for Tohatsu 18

Can I drive without a battery if the battery is new?

No. Without the rectifier, the generator will produce alternating currents that not only won't charge the battery, but can damage it due to reverse currents, and the electronics on board (echo sounder, radio) are designed for direct current and can fail.

Which rectifier is suitable for Tohatsu 18 2010 release?

Motors are required by 2015. rectifier narcissistic 186A0-8760E-0It can only be replaced with a generator, and universal remote models will not work without a redesign.

Why does the battery not charge after replacing the rectifier?

There may be several reasons:

  • Faulty. generator (Check the resistance of the windings: it should be 0.2-0.5 ohms).
  • Oxidized. contact It's a generator or battery.
  • He's out of action. voltage-regulator (under the flywheel)
  • Battery sulfated (not taking charge)

Check the voltage on the generator terminals (it should be 18-20V AC), if it is not, the problem is the generator.

Can I use a rectifier from another motor (for example, Mercury 20)?

Theoretically, it is possible, but only if the following are the same:

  • Maximum current (at least 12A).
  • The type of attachment (the size of the holes, the distance between them).
  • Connection scheme (number of contacts and their purpose).

However, we do not recommend such experiments – different motors have different specifications of generators, and an incompatible rectifier can fail or damage electronics.

How often should I change the rectifier to Tohatsu 18?

The service life of the original rectifier - 5-7 years (or 30,000-50,000 hours of motorized driving) But it can fail sooner because of:

  • Moisture intake (if the compounds are not sealed).
  • Overheating (due to lack of thermal paste or poor cooling).
  • Short circuit in the onboard network.

Check the straightener. seasonly multimeter, even if there are no obvious signs of malfunction.