How do external alternator regulators work?

How do external alternator regulators work?

Are you interested in learning what do alternator regulators measure for alternators and batteries?

Do you own a boat, RV or can and find yourself wondering how external alternator regulators work? Trying to solve some existing issues with your boat or RV alternator regulator? If so, you’re not alone. If so, we hear about these issues all the time at ARCO, and have set out to solve the problem once and for all.


Until very, very recently 99% of alternator regulators only measured voltage. For an automotive alternator this works just fine. However, when you begin using an alternator to charge large house banks of deep cycle lead acid or LiFePO4 batteries it becomes critical the alternator regulator can monitor the following:

  • Alternator temperature
  • Battery temperature
  • Battery voltage (at the battery + & - terminals)
  • Alternator current

Note: Internally regulated alternators measure none of the parameters above.

How Does Alternator Temperature Effect Your Charging?

Measuring the alternator temperature is critical to a reliable alternator charging system.  The reason is simple, a large bank of Lead batteries; Flooded, AGM or Gel can lead an alternator to premature death by working it beyond it’s designed use. LiFePO4 batteries only exacerbates this problem as these batteries continue to remain asking for everything the alternator can deliver and the alternator never catches a break like it eventually does with Lead Acid. The ARCO Zeus can control alternator temperature accurately so you’re not running it in an unsafe manner and keeping it in a safe amperage range output wise.

Lead acid batteries are more forgiving of alternator abuse than LiFePO4 batteries. This is because lead acid batteries have a higher internal resistance, which helps to dissipate heat. LiFePO4 batteries have a lower internal resistance, which means that they generate more alternator heat when they are being charged.

Advanced alternator regulators can help to prevent alternator overheating. It does this by monitoring the alternator temperature and adjusting the output current accordingly. This helps to ensure that the alternator does not overheat and that it does not damage itself.

Advanced alternator regulators are a valuable tool for anyone who owns a vehicle with a LiFePO4 battery bank. It can help to extend the lifespan of the alternator and prevent premature failure.

Here are some additional points to consider:

  • The alternator temperature should be monitored regularly, especially if you have a large bank of lead acid batteries or LiFePO4 batteries.
  • The alternator temperature should not exceed the maximum temperature specified by the manufacturer.
  • If the alternator temperature is too high, you should reduce the load on the alternator or take other steps to cool it down.

It is important to Measure Battery Temperature:

No internally regulated alternator whether in a boat, van, or RV can monitor the physical temp of the batteries and adjust the charging voltage accordingly. Every single manufacturer of deep-cycle lead batteries wants their batteries charged with temp compensation used. Some advanced alternator regulators can do this, and the temp compensation slope can be custom programmed to exactly match your batteries. For LifePO4, these batteries cannot be charged below 32F, and the advanced alternator regulators can be programmed to disable charging when the batteries are below 32F. They also cannot be charged when too hot and the same alternator regulator can be programmed to protect against this too.

This is important because the charging voltage with lead acid batteries needs to be adjusted as the battery temperature changes. A higher charging voltage is required when the battery is cold, and a lower charging voltage is required when the battery is hot. This helps to prevent the battery from being overcharged or undercharged.

Here are some additional points to consider:

  • Temperature compensation is important for all types of lead acid batteries, including flooded, AGM, and gel batteries.
  • Temperature protection is especially important for LifePO4 batteries, which are more sensitive to charging in extreme temperatures than lead acid batteries.

Can an Alternator Regulator Measure Alternator Current?

 Alternator current, also known as alternator output current or simply charging current, refers to the electrical current produced by an alternator within a vehicle's or a marine electrical system. Alternators are key components in these systems, responsible for converting mechanical energy, usually from the engine's rotation, into electrical energy. The alternator current generated is crucial for supplying power to various electrical components, such as lights, sensors, and accessories, while simultaneously recharging the vehicle or equipment's battery. Monitoring alternator current is essential to ensure that the electrical system functions correctly, batteries remain charged, and electrical demands are met, preventing potential issues like undercharging or overcharging.

Before Zeus, there was only one alternator regulator that can monitor alternator current, but it is extremely tedious to program. The entire design philosophy for the ARCO Zeus regulator was “KISS” keep it simple. Zeus is by far the easiest to program, install and set up. The reason measuring alternator current is critical is because some batteries have a max charge current limit. This alternator regulator allows you to set a max current.  Without current sensing you cannot do this.

Why Measuring Battery Voltage is Important:

Most stock alternators only monitor voltage at the alternator itself. This creates issues when you lose voltage between the alt and batteries due to voltage drop. When the regulator is set to charge at say 14.4V but you have a 3% voltage drop (-0.43V) between the alternator and batteries they wind up being chronically undercharged. While a 3% drop sounds like a solid design this is 0.43V in the wire calculation only. This always means you have more than a 3% drop because every fuse, switch busbar, termination etc. adds more drop so the 3% you aimed for could be substantially higher.

To deal with this the advanced alternator regulator uses both positive and negative volt sense wires not just the positive side. Voltage drop occurs in both the pos and negative sides but most stock alts only sense positive side and at the alternator itself. With the alternator regulator programmed for 14.4V this will be the voltage at the physical battery terminals because it uses this non-current carrying sense wires to compensate for any voltage drop between the battery and alternator.

Here are some additional points to consider:

  • The voltage drop between the alternator and batteries can be caused by a number of factors, including the length and thickness of the wires, the number of connections, and the resistance of the connectors.
  • The voltage drop can also be affected by the load on the alternator. The more load on the alternator, the greater the voltage drop.
  • The use of both positive and negative volt sense wires can help to reduce the voltage drop and ensure that the batteries are charged properly.

Measuring heat and current for marine and rv

In conclusion:

Alternator regulators are devices that control the output voltage of an alternator. They measure a variety of parameters, including alternator temperature, battery temperature, battery voltage, and alternator current. This information is used to adjust the output voltage of the alternator to ensure that the batteries are properly charged.

Advanced alternator regulators can measure all of these parameters, while older, less sophisticated regulators may only measure voltage. Advanced alternator regulators are becoming increasingly common, as they offer a number of advantages over older regulators. For example, they can help to prevent alternator overheating, extend the lifespan of the batteries, and ensure that the batteries are always properly charged.

Here is a table that summarizes the key differences between the two alternator regulators:

 Feature Other Alternator Regulators ARCO Zeus
Complexity of programming High Low
Ease of installation Difficult Easy
Ease of setup Difficult Easy
Ability to monitor alternator current No Yes
Ability to set maximum charge current No Yes


If you are considering adding an advanced alternator regulator to your system, it is important to choose one that can measure all of the important parameters. This will help to ensure that your batteries are always properly charged and that your alternator lasts as long as possible.

If you would like to learn more about how alternator regulators are changing RVs and Boating, click here.