What Does a Regulator Rectifier Do On an Outboard?

Your outboard motor contains a lot of parts on it, some you probably understand and many you might not. Have you ever stopped and wondered what the regulator rectifier is in charge of?

The regulator rectifier is in charge of not only regulating the voltage produced by the alternator or stator, but it also rectifies the voltage by converting the AC power to the appropriate amount of DC power.

In this post, we will look closer at what the outboard rectifier does, what happens when this part goes bad and how to troubleshoot issues that may arise with it!

What is a Rectifier on Outboard?

An outboard motor’s voltage regulator takes the voltage supplied from either the flywheel and the stator or the alternator. And then it regulates it to the appropriate amount. That is unless there is an issue with the stator or alternator.

Where it is not producing voltage, but we cover that material more in our article about whether the engine will run with a bad stator or not here.

Typically, the output should measure about 13.6-14.3 volts. On newer voltage regulators, there is also a rectifier, which can convert the AC current from the power generated to DC output. Since boats use DC power opposed to AC power that you will find in your home.

Rectifiers also convert tachometer output from the stator, allowing the tachometer to receive the appropriate pulse type and display the motor RPM.

What Does a Voltage Regulator Do on an Outboard?

The voltage regulator is strictly used to regulate the voltage of the outboard. In comparison, the rectifier is responsible to convert AC power to DC.

Because of where the voltage regulator is located on the outboard ignition system, it endures a lot of abuse. If you are using a 40-amp output stator, there will be a large load put on the regulator.

Over time, the regulator can suffer from a lot of heat. Air-cooled regulators are common, but there are also some that are water-cooled. This water cooling can take it’s own toll on the component, if you are running in harsh warm saltwater opposed to cold clean freshwater.

The regulator keeps the voltage coming out of it to a specific amount, which will protect the boats batteries from that damage that overcharging can cause.

Seeing that the alternator or stator will produce up to 26 VDC or even more sometimes! If left unchecked by the regulator.

What Happens When the Regulator Rectifier Goes Bad?

When the water-cooled regulator goes bad, it’s often caused by a weak or failing water pump. This malfunction causes the regulator to burn out because of intense heat buildup.

In some cases, the regulator can become so hot that it causes a fire, which no boater wants to deal with.

Additionally, having an excessively low or bad battery can also lead to an overheated or burnt-out regulator.

The stator can also become damaged, as the regulator is in direct connection with this vital component. And a blockage at the regulator can mess up the stator because it is producing voltage but the voltage has no where to go! Creating more heat and more issues!

If the air-cooled regulator goes bad, it might be due to a lack of air flow. As with the water-cooled option, it’s essential that everything works smoothly to keep the regulator as cool as possible.

How Do I Know if My Regulator Rectifier is Bad?

To determine if you have a bad rectifier, you will need to test it.

Disconnect the Battery

Turn your multi-meter onto the diode function.

Connect the Multi-meter

Now, you want to take various readings with the multi-meter.

  1. Connect the positive lead to the positive diode.
  2. Connect the negative lead to the stator input. There shouldn’t be a reading on your meter.
  3. If everything looks good, connect the negative lead to the positive diode before you connect the positive lead to the stator input.
  4. This time the meter should have a reading, although the number itself is not important.
  5. Repeat the same process with your negative diode. First, connect the positive lead to the negative diode, with the negative lead to the stator input.
  6. Just like before, there should be no reading on your meter.

It’s important to remember that this is a general test. And depending on what brand and model of engine you are working with. Will determine how the regulator rectifier is tested using the diode feature on your meter.

You will want to double check the service manual for your engine to ensure the test procedures and wire colors for your engine.

Check Battery Readings

Next, you want to connect the leads to the battery, while it’s running. You shouldn’t see a reading of more than 14.3 volts or below 13.5 volts. If it is higher, it could mean that the battery is overcharging, requiring you to replace the regulator rectifier.

Replace the Rectifier

Thankfully, it doesn’t cost much to replace the regulator rectifier on your outboard, especially if you do the work yourself. Most manufacturers will include a wiring diagram to make the process smoother for you as well!

Symptoms of Bad Rectifier on Outboard Motor

So, how can you tell if the regulator rectifier is bad before testing it? Most of the time, there are two scenarios that indicate the regulator has failed.

First, if a diode burns out, it will cause the battery to drain. If the battery leads to a faulty regulator rectifier, this is easy to determine.

When the battery causes the problem, you will struggle with poor starting, accessories malfunctioning and fluctuating meter readings.

While these symptoms are generally clear-cut, we still recommend using our testing method above to ensure your problem is the regulator.

The regulator rectifier could also fail if the system overheats, as discussed earlier.

When the regulator rectifier can no longer moderate voltage levels, your boat battery will begin to overcharge.

To confirm this, you simply need to use the voltmeter to diagnose that the battery has too high of a charge while the engine is running and producing voltage. Back to those 13.5-14.3 VDC readings. This indicates that the rectifier has failed to convert excess power appropriately.

You might also notice the accessories running sporadically as the additional voltage is causing trouble.

Whenever the regulator rectifier goes bad, you always want to check other components of the system. Sometimes, there is a defect that leads to the failure of multiple parts.

Will Outboard Run Without Rectifier?

It really depends on your boat’s setup.

Usually, the outboard will start and run without the rectifier. However, it might be running down the battery, allowing it to quit once the battery runs out of a charge.

However, this is not the case if you are using a two-stage stator.

Either way, running your outboard without the voltage regulator at high RPMs can cause the stator to fry, leading you to more trouble down the road.

For the low cost of a new rectifier, it doesn’t make sense to operate the outboard without it.

Installing a New Outboard Regulator Rectifier

So what do you do when the time comes to install a new regulator rectifier?

The best place to start is to look at the diagram that comes with your new parts or look at the existing setup to replicate it.

In many cases, these are the basic steps you will need to replace the regulator.

  1. Remove the old rectifier and examine how it is connected.
  2. Be careful not to cut any wires that can be re-used with the new setup. Otherwise, you won’t be able to install a direct replacement.
  3. If you get a direct replacement, you should simply be able to connect the wires to one another.
  4. If you need to make modifications, connect the appropriate wires together and solder them to prevent corrosion.
  5. You can also use adhesive-lined shrink wrap connectors and seal them with a heat gun.
  6. Start the engine to test the regulator.

Again, you’ll want to check with your service manual for your specific engine and model to make sure you get all the torque specs correctly.

But the replacement of this part is relatively easy and usually doesn’t require any special tools at all!

Check Us Out!

We hope this article has helped you out in figuring out if your regulator rectifier is operating correctly and what it does! Now that you know all about them! We encourage you to stop by our YouTube channel for more guidance and practical tips!

Plus, browse our helpful blog articles for additional information about your boat and the engine.

Brian Jones

Brian Jones has spent most of his career as an ASE Certified Master Tech. Today, he spends his time freelance writing and consulting. He lives outside of Dallas, TX with his family and loves anything mechanical.

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