Community Forums

map747 · 08-14-2020, 03:22 PM

Just got this rig and the voltage gauge read 12v on my way home. Previous owner only purchased to use on a trip, he ran the generator all the time, so that would probably keep the battery's charged. Is there a quick test I can do to check the alternator and if it is bad, is it a difficult job and where can I get the correct alternator? The window sticker says 5.9 Cummins 275hp, but it also says it has a Roadmaster 315hp upgrade. It also was running close to 220 degrees as it was 100 outside. I guess I should clean the radiator to start. All the fluids/filters were recently changed.

jacwjames · 08-14-2020, 03:30 PM

Check the voltage at the chassis battery with the engine running, should see ~14 volt if the alternator is putting out.
Not sure how hard a job would be on your rig since I believe you have a rear radiator. Pull the engine hatch cover in the rear closet and see if you can reach from there. If not it will have to be from underneath.
My alternator failed ~6 years ago. No voltage so I just pulled it, took it to a rebuild shop and had it rebuilt for ~$185 (6 years ago).

CountryB · 08-14-2020, 03:32 PM

Just put a voltmeter on the batt terminal at the back of alternator. You would see around 13.5 to 14 volts if it is charging. If you have that voltage at the alternator then check next at the batteries. You could have a working alternator but a bad "battery isolator" so the voltage is not getting to the batteries.

Based on the year of Coach, I assume you have a DUVAC charging system. Can you confirm? Do you have something that looks like this?

Outbound · 08-14-2020, 03:42 PM

Your gauge could also be off, I have a approx. one volt drop between battery's and gauge.

map747 · 08-14-2020, 08:46 PM

I will take pictures tomorrow, but it does not look like yours CountryB. I have the 12v batteries on charge now and the needle went straight up to 6amps, which is max charge for my unit. I need to understand how the charging system works. You are right, it doesn't necessarily have to be the alternator.

jacwjames · 08-15-2020, 07:50 AM

Not sure if it's possible but if you don't have copies of the electrical schematics you might try to give Monaco tech support a try. In most cases they won't help but if you talk nice and maybe cry a little they'll supply.

Take a picture of your rear run electrical bay so we might be able to figure out what you have. I know some coaches do not charge house batteries when plugged in, not sure if yours fall into that group.

map747 · 08-16-2020, 10:06 AM

I completely charged the 12v batteries and then started the engine and I got 14v. So, I believe they were in need of a good recharge. I also added water to the 6v batteries as some were low. The 12v are sealed. Is there a thread that anyone knows of that walks through how the batteries are charged?