Campervan Alternator FAQ

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 suspect there may be issues with your alternator charging system, 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 Finding a qualified repair shop 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).

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.

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 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.

Begin troubleshooting by following the sections in this guide for checking the DC-DC converter and external regulator. Open a ticket to let us know what you find! We cannot help until you have followed these exact instructions to gather relevant data.

Begin debugging the regulator by following 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. Open a ticket to let us know what you find!

• 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.

Your alternator needs 3 things to work:

1. 12V at the large wires going to the alternator
2. 12V on the blue wire going into the alternator body
3. 12V on the yellow wire going into the alternator body

Diagnosis steps - also, see this video

All of these steps assume that the batteries are low (below 13V), the temperature sensor is warm, and the engine is running (unless noted otherwise).

• Download relevant PDF wiring schematics for 2nd Gen Revels

1. Check for 12V at large wires on the alternator. Engine can be OFF.

• If there are 12V, go to step 2
• If you see zero volts, do not proceed further. Replace the alternator fuse above the inverter and diagnose why it blew. It likely blew because the positive alternator cable rubbed the frame near the alternator shorted to the frame. This is VERY common. You can put heat shrink over the portion of the cable that has been compromised and pull some slack forward so it is not tight on the frame. 

2. Check voltage on the blue wire that goes from the positive post of the alternator into the alternator body. Engine can be OFF.

• If you see 12V, go to step 3
• If you do not see voltage, figure out why this is the case. 

3. Check voltage on the yellow wire that goes into the alternator body. 

• If you see 12V and you are still not charging, you have a bad alternator (this is rare). It may be a bad internal part of the alternator or a bad alternator pulley. 
• If you do not see 12V, proceed to step 4

4. In the back of the van, check if you have 12V on wire KE going into the charge combiner with the engine running. Use the battery ground as your reference for the multimeter. 

• If you see 12V, proceed to step 5
• If you do not see 12V, then check the upfitter accessory terminal block EK1 under the driver’s seat to see if you have voltage there (where the other end of EK1 is connected). 

5. Check if you have power and ground at the combiner module. Power is wire LJ – check this vs. battery ground. Ground is wire FM – check this vs. battery positive. 

• If you have both 12V and ground at the combiner module, proceed to step 6
• If you do not have either 12V or ground at the combiner module, diagnose why. Power comes from the 15A breaker on the breaker panel in front of the combiner module.

6. Check wire ALS coming out of the combiner module to see if it is at 12V when the engine is running. Note that if you DISCONNECT the wire from the combiner module to check it, you will see 0V as the power going INTO that wire comes FROM the combiner module. 

• If you see 12V on ALS, proceed to step 7
• If you do not see 12V on ALS, you have an issue with the combiner module. Call Xantrex for further diagnosis

7. Check wire ALT coming out of the temperature sensor to make sure it is 12V when the engine is running. Note that if you DISCONNECT the wire from the sensor to check it, you will see 0V as the power going INTO that wire comes FROM the sensor fed by wire ALS.

• If you see 12V on ALT, proceed to step 8
• If you do not see 12V on ALT, the temperature sensor is either too cold or the temperature sensor is bad. 

8. Check if you have 12V on power (LJ), ground (FM) and 12V on trigger (ALT) at the alternator relay with the engine running. 

• If all of these have 12V, proceed to step 9.
• If you do not have any of these (measured vs. respective posts on the battery), then diagnose why. 

9. Check weather you have 12V on wire LR leaving the relay.

• If you see 12V on LR leaving the relay, proceed to step 10
• If you do not see 12V on LR leaving the relay, then you may have a bad relay, replace the relay. 

10. To diagnose why you have 12V on LR at the relay and do not have 12V on LR (yellow wire) going into the alternator, you will have to dig deep to figure out where the wire broke. We cannot provide detailed guidance for these steps. 

If you need a new alternator:

• Your stock Winnebago alternator is based on a Denso 160A hairpin GM alternator and any decent alternator shop should be able to rebuild and diagnose it. The Denso 160A alternator is a solid platform.
• You MAY be able to get a replacement alternator off the shelf and swap the front drive end housing, which is the portion of the alternator that is specific to Mercedes and custom on this Denso alternator, so that it can fit a Sprinter. 
• You can run almost any alternator that is Sprinter-mount on your van as long as the total output of that alternator is below 200A (so that the fuse doesn’t blow) and stays below the peak total amperage that the batteries are OK being charged at. Some regulators can limit alternator output so a larger than 200A alternator can safely be used on this platform
• We HIGHLY recommend that any replacement alternator is externally-regulated and that the van is modified to have an external regulator, which eliminates the combiner module from the system. 

This van has a RoamRig power system installed. It had some work done on it in South America and the alternator never worked again. See how we diagnosed and repaired it in the video below.

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.

Make sure this is done before doing any upgrades to your van.

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.

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 troubleshooting advice for people without RoamRig products.

If you are interested in a full alternator system replacement that comes with a two year warranty, consider our ARCO Alternator + Regulator kits.