What Does a Rectifier Do on a Motorcycle? (Explained!)

Rectifier with text - rectifier on a motorcycle

Rectifier. Regulator. Alternator. These can be confusing components on a motorcycle. Especially the rectifier. For a long time, I had no idea what they do.

So, what does a rectifier do on a motorcycle? The rectifier converts the alternating current (AC) from the alternator to the direct current (DC). This converted direct current (DC) is then fed to the battery to charge up.

Along with the rectifier, a regulator also exists in the motorcycle to help the battery charging. The regulator moderates the voltage coming from the alternator. This helps in battery voltage regulation.

This is the basics. Let’s dive into more details.

What is a rectifier?

Five Diodes

A rectifier is a device that converts an alternating current (AC) into a direct current (DC).

A rectifier comes in various different forms. In motorcycles, they are diodes. To be precise, a combination of p-n junction diodes.

Rectification, the process, refers to the straightening of alternating current into unidirectional direct current.

Purely rectifier as a component comes in various shapes, sizes, and forms.

There are half-wave rectifiers and there are full-wave rectifiers. There are single-phase rectifiers and there are three-phase rectifiers. There are three-phase bridge uncontrolled rectifiers and there are three-phase bridge controlled rectifiers.

You got the idea. There are far too many and this post does not dive into these details. If you are interested in these rectifier types, here is the Wikipedia link on rectifier types you can check out for a start.

What does a rectifier do on a motorcycle?

In a motorcycle, the alternator generates electric current but in the form of AC (alternating current).

The battery which stores the electric charge and powers the electronic accessories can only receive DC (direct current).

Since the alternator generates AC and the battery can only receive DC, you need a device to address this problem.

And that’s where a rectifier fits in.

The rectifier converts the AC coming from the alternator in the motorcycle to DC and feeds it to the battery.

In motorcycles, the rectifier is accompanied by a regulator.

These two components have a defined role to play in the motorcycle charging system.

  1. The rectifier converts the alternating current (AC) from the alternator to the direct current (DC).
  2. The regulator moderates the voltage coming from the alternator.

Both are of equal importance. Even if one of the components- either the regulator or the rectifier is not working, there will be problems in battery charging.

Since both these components and circuits are clubbed together, they are often referred to in a singular fashion as – regulator-rectifier.

Without a rectifier, the battery won’t charge

Motorcycle battery with multimeter

Now, we know that a rectifier converts AC from the alternator to DC. And the regulator regulates the current voltage.

Once the current is converted to DC with the voltage moderated, it flows to the battery and is stored there.

If the alternator is not working, there will no power generation at all. As a result, the battery won’t be charged up.

If the rectifier is not working, the generated alternating current (AC) from the alternator is not converted into direct current (DC). This, again, leads to the battery not storing the charge since the battery requires direct current (DC).

In both these cases, where either of the two, the alternator or rectifier, is not working, then the battery won’t be charged.

And when the battery is not charging up, the remaining charge in the battery will soon be used up by the different electronic accessories including the starter motor, and eventually, the battery will die out.

Once the battery dies out, the motorcycle which requires the battery charge to start up, will not be able to start.

Will a motorcycle run without a rectifier?

Motorcycle battery testing with a multi-meter

A motorcycle will not run without a rectifier.

No rectifier means no battery charging. And no battery charging means no motorcycle running.

This is because – first, modern motorcycles are completely reliant on their batteries to power them up including ignition. No battery power, the motorcycle will not even start.

Second, the motorcycle battery is charged by the combination of the alternator and the rectifier regulator. We have discussed this in the previous section.

If any one component of the alternator and rectifier regulator combo is not working, the battery won’t charge.

Bottomline. With no rectifier, the motorcycle battery won’t charge. And with no battery to power up the ignition as well as other electronic units, the motorcycle won’t start and won’t run.

That’s why it is essential to ensure the rectifier as well as the regulator is working fine on your motorcycle.

Without them working, the battery will be drained and can even go dead.

How do I know if my motorcycle rectifier is bad?

Bad motorcycle rectifiers are a tough nut to pinpoint (crack ;)). But there are a few symptoms that you can use to zero in on the rectifier problem.

So, here are the symptoms you can use to identify a bad regulator rectifier in your motorcycle.

  • Dimmed or flickering headlights:
  • Problems in starting the motorcycle
  • Dead or drained battery
  • Malfunctioning electronic accessories
  • Overvoltage

For a more in-depth view, you can check out our post on bad rectifier symptoms in a motorcycle.