HomeTips & GuidesExternally Regulated Alternator: How To Increase Alternator Output Power and Reduce Charging Time

Externally Regulated Alternator: How To Increase Alternator Output Power and Reduce Charging Time

We will look at the functions and benefits of an externally regulated alternator below.

Cars, power boats, and other vehicles that run their engines continuously for long periods recharge their batteries efficiently.

But vehicles like sailboats only run their engines for short periods, then switch to wind power. 

While this propulsion mechanism is eco-friendly, it can damage the battery because the engine won’t run long enough to recharge it.

However, an externally regulated alternator makes the charging process more efficient to hasten power flow into the battery. 

Here’s a close-up look at the functions of this component and why you need it.

Table of Contents

What Is an External Regulator?

Traditional alternators have an internal regulator or one attached to their cases, but these have limited functionality. 

So, they work well in cars, power boats, and other engine-propelled or powered machines.

However, external regulators maximize charging efficiency to ensure the battery bank gets fully recharged even with short engine run times.

Most of these devices utilize digital processing technology to optimize the charging regimes. 

They tailor these regimes to match the power output to the battery type while following this 3-step charging protocol.

  • Bulk phase
  • Absorption phase
  • Float phase

This protocol hastens the process without overcharging the battery bank.

Why You Need an Externally Regulated Alternator

Charging a battery is similar to pumping pressure to a car tire. It takes minimal effort at first because the pressure inside the tire is low, but it becomes more difficult as the pressure builds up inside.

We’ll compare the air you’re pumping to electrons (current output) and the pressure to the voltage. At the start, the pressure difference makes it easy to pump air into the tire.

Similarly, it is easy to charge a battery bank when empty because it has a low voltage. But as the charge increases, the battery voltage level rises, making it more strenuous to pump electrons into the cells.

A car alternator with a drive belt

A car alternator with a drive belt

Therefore, if you increase the charging voltage from the alternator, you can push electrons faster into the battery when empty and even when almost fully charged.

So, if you want to recharge a deeply discharged one in the shortest time possible, you need an externally regulated alternator.

How An Externally Regulated Alternator Works

As stated earlier, this alternator operates in three phases when it has an external regulator.

Bulk/Constant Current Stage

In this first stage, the alternator supplies the maximum current it can generate. It achieves this highest current generation by raising the set bulk charging voltage between 14.2V and 14.8V.

Some regulators keep this phase running for a set time regardless of the voltage achieved in the battery bank. Others monitor the battery to determine when to switch to step two.

It is vital to note one thing. Instead of voltage regulators increasing the charging voltage in the final phase, they raise it during this initial stage.

This operation mode ensures the battery receives as many electrons as possible when the potential difference is high.

A car alternator voltage regulator

A car alternator voltage regulator

Absorption/Constant Voltage Stage

The bulk stage only sets and attains the battery voltage on the battery plate surfaces. So, the absorption phase maintains a constant voltage to drive the electrons deep into the battery’s structure.

The regulator maintains the voltage at the bulk level or slightly below it during absorption.

As the voltage in the battery cells increases, the current flow will decrease due to the reduced potential difference up to a pre-set point.

Regulators can have a minimum or maximum time specified for charging the battery using this second phase.

Float Stage

During this final phase, the external regulators drop the charging voltage between 13V and 13.6V.

They activate this mode after achieving the set absorption time or when the current absorption level drops below the set value.

Most rechargeable batteries operate at 12V, so float state charging occurs slowly because the potential difference between the alternator and battery bank is low.

The regulator maintains the fully-charged battery state by feeding light loads using power directly from the alternator.

External Regulator Properties

Charging Time vs. Overheating

These regulators push alternators hard and can overheat them or the batteries, especially during the initial bulk stage.

They control the current and voltage output from the alternator by varying the input voltage to the alternator rotor’s field coil.

The higher the voltage they apply to this field, the higher the output voltage to drive electric current to the battery. This process can cause overheating and expensive damage.

So, you must install temperature sensors on the battery and alternator to shut off the system or reduce charging if they become too hot.

Without these sensors, the regulator will stick to more conservative charging times to prevent heat damage, and this option will increase the charging duration.

An exploded view of a car alternator with an internal voltage regulator

An exploded view of a car alternator with an internal voltage regulator


Some external regulators come with pre-set battery type selections and require you to program the times to run the three stages.

Although they give you more control over the system, we recommend consulting a professional before programming such units.

Alternator Regulation Compatibility

Most alternators require regulation only in the positive field connection, but some require negative field regulation.

So, the external regulator must match your vehicle’s alternator. Check whether they are P-type or N-type regulators before buying.

An N-type alternator for negative field regulation

An N-type alternator for negative field regulation

And in some cases, you might have to replace the alternator with one built to handle external regulation.

Internal vs. External Alternator Regulator

The most noticeable difference between an internal and external alternator regulator is the former comes as a single package. On the other hand, an external regulator does not fit inside the alternator.

Therefore, alternators with internal regulators are more compact, while the latter takes up more space. You must find space in the engine bay to mount the external regulator.

Also, an internal regulator uses a single wire, but the external type usually has multiple cables.

The former has a rectangular plug with two pins and plugs in from its side to the rear edge of the alternator’s case.

On the other hand, an external regulator comes with a multi-wire plug that features several pins inside.

This plug also connects to the alternator’s case rear edge.

Performance-wise, an internal regulator will make the alternator charge the battery slowly by providing relatively low power.

However, the external type pushes more electrons into the battery pack to hasten and optimize the process.

How To Install an External Regulator to Your Car’s Alternator

Unlike charge controllers for solar systems or wind turbines, external alternator regulators don’t connect to the charging circuit.

They sit outside this circuit because their task is to adjust the voltage input to the alternator’s rotor field coil.

Therefore, the alternator must be compatible with external regulation by having a field connection. You must remove or disconnect the standard regulator before fitting the external unit.

If the alternator is incompatible, you can buy a new one or take it to an electrician for modification.

In some units, you can replace the standard regulator and brush holder assembly by unscrewing it and fitting an off-the-shelf brush holder, making the conversion easier.

Old and new alternator brushes

Old and new alternator brushes

Benefits of an External Regulator

  • Minimizes engine run time, which cuts servicing costs
  • Reduces fuel consumption
  • Maximizes charging efficiency
  • Reduces charging time
  • Extends battery life (fully charged batteries last longer than half or empty-charged ones)

Wrap Up

Although externally regulated alternators are not necessary in vehicles, you might consider installing one to recharge your battery faster, such as for off-grid living.

But remember to fit in temperature sensors to prevent overheating-related damage on the alternator and battery.

You can learn more about alternator terminals in this article for accurate wiring in your vehicle. 

That marks the end of this article. Comment below to share your thoughts and sentiments, and we’ll be in touch.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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