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Alternator FAQ

Questions about alternator charging? Start with this FAQ and the linked resources to learn more about charging and what we recommend if troubleshooting is needed.

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What is alternator charging?

An alternator is an electromechanical device which uses rotational energy from the engine to generate electrical energy. Your Sprinter comes from Mercedes with an alternator that is dedicated to powering Mercedes systems and charging the Mercedes battery.

Using a DC-DC charger (colloquially known as a “DC to DC charger”, but often written shorthand as DC-DC) allows a limited amount of electrical energy from the Mercedes alternator to be used for charging your camper batteries.

When limited power from a DC-DC charger is not able to charge camper batteries rapidly enough, a second alternator that is dedicated to charging camper batteries at high speed can be added to the Sprinter engine. This alternator is colloquially known as the “auxiliary alternator”.

Revels with RoamRig power systems have two alternators, except for 1st Generation Stage 1 systems, which have only one. You can check your Revel generation here.


How is my alternator connected to my house batteries?

Wires run from the output of the DC-DC charger and auxiliary alternator (if equipped) to the house batteries. 

The DC-DC charger has internal mechanisms and software by which it regulates charging to protect the batteries. In RoamRig systems, the DC-DC charger is from a company called Kisae. This charger also handles solar charging.

The auxiliary alternator uses an external regulator to regulate charging to protect the batteries. In RoamRig systems, the regulator is from a company named Balmar. In RoamRig systems, the alternator may be from Nations or Balmar.


Visit our blog to learn how components in RoamRig power systems fit together.


How do I know if my alternator is working?

Generally, if the house batteries are discharged and there are not any heavy loads on your system (such as using the cooktop or air conditioning), then you should see positive amps on your battery monitor when the alternator is charging the batteries.

There may be a 200 second delay between starting the engine and charging activity occurring, so if you do not see charging shortly after starting the engine, do not worry.

If you have a RoamRig power system, follow this guide and video to check your alternator charging. This guide may also be relevant for non-RoamRig systems, though you’ll need to adjust for any differences.


Alternator charging isn’t working, now what?

If you suspect there may be issues with your alternator charging system, this is a starting point. The best way to debug the system is to take it to a knowledgeable shop that can assess it in person then perform any necessary repairs. Not all shops are knowledgeable about alternators and how they are meant to function in a Revel, so be careful about the shop you select for diagnosis – see Questions to ask your installer below. Many shops will “hot shot” parts in place (i.e. replace an alternator without confirming that an alternator is bad and a charge issue is not caused by something else).

There are MANY variables that can affect alternator charging. If charging is not working, it does NOT mean that the alternator itself is bad. We've seen poorly crimped wires from Winnebago, batteries with intermittent internal issues, faulty regulators/DC-DC converters, incorrect software settings and more that can cause poor alternator performance.

If you have a RoamRig system and suspect that your alternator is not working, RoamRig will only cover warranty claims and professional diagnosis if we’ve already gone through some basic steps with you first to confirm what or where the problem may be. Please do not go to a shop for diagnosis without prior, explicit approval from RoamRig support.

    • RoamRig power systems: begin troubleshooting by following the sections in this guide for checking the DC-DC converter and external regulator. Let us know what you find! We cannot help until you have followed these exact instructions to gather relevant data.

    • Revels with the RoamRig External Regulator upgrade: follow the steps in this video. If the regulator screen doesn’t turn on, you’ll need to use a multimeter and follow the second video on that page.

    • Stock 2nd Generation Revels: follow this video and guide to see what could be wrong. If you can rule out simple causes with this guide, then you will need a multimeter and knowledge of how it works to continue troubleshooting. We cannot offer additional advice for troubleshooting stock systems, but we hope this overview is helpful for giving you a head start!

  • Thor Camper Vans: RoamRig worked with the awesome folks at ABC Upfitters to leverage their Thor/Mastervolt experience to create an alternator update package for your Thor van. The parts/installation are available exclusively from ABC Upfitters. Please keep in mind the products offered by ABC are not related to RoamRig, kitted by RoamRig, sold, or otherwise supported by RoamRig.

  • All other systems: We hope that our alternator resources are a helpful starting point. Given the enormous variety of alternator charging configurations, symptoms and failure modes, we’re not able to offer specific advice for people without RoamRig products.


What does RoamRig recommend?

Revels with RoamRig power systems that are eligible for the Litens Pulley upgrade:

  • If RoamRig support contacted you in late 2023 about the Litens Pulley Upgrade and you have not already requested and installed the pulley, please let us know. 
  • If you have the pulley and still need to install it, here is our guide for the swap. 
  • If you are not sure if your van is eligible for the upgrade, just ask.

We get MANY emails about these problems. While we think a power system upgrade is the best way to upgrade your house electrical system, it might not be right for everyone. Here is some advice that we’ve found is helpful for many people:

  • Stock 2nd Gen Revels: we highly recommend adding an external regulator kit. Read more about why on our blog. Our external regulator kit is available for purchase on our website and can be installed by the upfitter of your choice or as a DIY project for those comfortable with electrical work. When doing this upgrade, it’s a great time to add a 3rd battery for increased capacity.

    Follow our guide for diagnosing alternator issues in Stock 2nd Gen Revels. If you need a new alternator, there are a few options ideas at the end of the guide for what to do next.

  • Stock 3rd Gen Revels: Before any alternator upgrades, make sure Winnebago Recall 178 is completed for your van if it is eligible. Tell Winnebago about any alternator/charging problems when getting this service to see if any related parts are eligible for replacement under warranty.

  • 24V or 48V Alternator systems: we do not have any experience with anything on the market, so unfortunately cannot offer any advice.


Questions to ask your installer

Through extensive work with various shops, we've learned that successful alternator installs require a solid understanding of electrical systems. If a shop can't confidently answer all of the following questions on their own, they shouldn’t be doing the job:

  • Can they determine proper charge current limits (based on batteries, circuit protection, wires, etc)  and configure the regulator accordingly?
  • Do they know how to verify that the temperature sensor is functioning properly?
  • Can they assess whether voltage drop from the alternator to the batteries is within an acceptable range?
  • Do they understand how to confirm the Balmar regulator is reading voltage correctly?

Ignoring these factors can lead to battery damage, alternator failure, and other issues. To prevent customers from being misled by unqualified shops, we’ve had to take a firm stance—installers must take responsibility for failures caused by improper installation. Please make sure any shop that works on your van is qualified and will stand behind their work.


RoamRig alternator products

Visit our Alternator & Belt Part Numbers guide for information about the specific brands and part numbers used in RoamRig alternator-related upgrades, including power systems.

Power Systems


RoamRig power systems include alternator upgrades, along with many other benefits, such as increased battery capacity. Power systems are only available for installation at RoamRig HQ in Connecticut or by one of our power system dealers.

External Regulator Kits


For stock 2nd Generation Revels, we highly recommend adding an external regulator to control charging from the secondary alternator. Here’s why.

External regulator kits are available in our online store and should only be installed by someone who understands alternator charging. The installer must make sure the alternator is functioning correctly BEFORE adding the external regulator kit. These kits are ONLY intended to replace the combiner module in a fully-functioning system to make charge regulation more accurate. They are NOT intended to fix existing “no-charge” issues without careful diagnosis beforehand.

Bare Alternators

Due to the complexity of alternator charging systems, our 12V 250A bare alternators are only available for purchase by RoamRig power system dealers who have the knowledge and experience to properly install them (here’s why). If there are any post-installation issues, support is the installer’s responsibility. RoamRig does not support or warranty the alternator outside of mechanical failures.

Alternator Pulleys

RoamRig has a limited supply of Litens Alternator Pulleys for those with a Balmar XT250 alternator from RoamRig that was installed 02/2022–10/2023. All eligible van owners were contacted in late 2023 about the upgrade. If your alternator pulley is black and says "Litens" on the dust cap (which covers the silver area in the above photo), it is one of the upgraded LItens pulleys.

These pulleys are very robust and can eliminate various noises/problems. They are now standard on all Balmar 250A alternators from RoamRig. RoamRig does NOT offer Litens pulleys a la carte.