Roadmaster RR8R Alternator Charge Warning

[fry5family]

We are full-time RVers. During the last 20 miles to our boondocking spot yesterday, the Alt Chg indicator light and warning would cycle on for a while then off.

The meter on the dash normally shows 13.5v, but it would slowly increase to about 13.75v and the warning would start. The meter would gradually drop to 13.5v and the warning would stop.

The 2 NAPA commercial AGM 12v batteries (2 years old) are sitting at 12.86v.

What would make the alternator charging go up?

Cummins 330ISC. Daytime running, just the blower fan, Garmin, and radio. Cycled again after turning those items off.

Mike Fry
2005 Monaco Knight

[twinboat]

You have solar or generator running ?

If the isolation solenoid is closed, the higher charging house battery voltage gets to the chassis batteries, fooling the alternator into thinking its not .

[fry5family]

I have a Victron MultiPlus II inverter/charger that automatically inverts when shore power is disconnected. I had about 500w solar going into the house batteries while the inverter was working during the drive. But, as far as I can tell, the house batteries are isolated from the chassis batteries. For example I do an hour generator run in the morning when boondocking. I was feeding 800w from generator and 200w solar this morning to the house batteries and the chassis batteries are still sitting at 12.81 (isolated?).

[wolfe10]

IF (repeat IF) you have a DUVAC alternator, check that the wire to SENSE terminal is clean and connections tight at both ends. A little resistance in this circuit can falsely cause the alternator to output higher voltage, as the sense terminal is seeing lower voltage.

[153stars]

Isolator also means combiner , I usually include both with a with a slash between. Isolates when no extra charging available or need, combines when there is. The combining of batteries is most likely cycling.
The lamp is from low output relay and what you see is known idiosyncrasy with Monacos when charging from another source like solar or genny going down the road or on shore power with engine running also .

[nehog]

Odd, this light should only come on when the alternator is not charging! It is tapped off of one of the three phases of the alternator and powers a six volt relay that is in the electrical bay under the driver's feet. In my HR the relay is on the rearmost wall of that bay. There is also a fuse in that circuit at the alternator (near it, actually) that you can find by tracing a small wire away from the alternator. There should be several wires, and several fuses, check 'em all. All the fuses are 5A as I recall. If the fuse is bad, making a bad connection, etc., that will light the bulb!

[twinboat]

Originally Posted by nehog

Odd, this light should only come on when the alternator is not charging! It is tapped off of one of the three phases of the alternator and powers a six volt relay that is in the electrical bay under the driver's feet. In my HR the relay is on the rearmost wall of that bay. There is also a fuse in that circuit at the alternator (near it, actually) that you can find by tracing a small wire away from the alternator. There should be several wires, and several fuses, check 'em all. All the fuses are 5A as I recall. If the fuse is bad, making a bad connection, etc., that will light the bulb!

The light comes on when the battery voltage exceeds the output voltage of the alternator.

It's technically not charging because the other charging system is out performing it.

[YC1]

Originally Posted by twinboat

The light comes on when the battery voltage exceeds the output voltage of the alternator.

It's technically not charging because the other charging system is out performing it.

_____________________________________

Spot on and not a problem. If you did some research on BIRD devices you would find they have a generator input line so the device will not combine battery banks/charging systems if there are two competing charging systems.

Solar can cause the competing issue as well.

Turn on your lights and even the Dash Air conditioner to put a load on your engine batteries and the light may go off.

If it really bugs you, stop and put a voltmeter directly across each bank of batteries. If they are in the range of 13.5 -14 ish then things are ok.

The symptoms can often be duplicated while running the engine and being connected to shoreline, The battery combining systems are NOT disabled during this type of setup normally so you can get an Alt alarm while airing up and connected to shoreline..

[JellyBean]

Originally Posted by wolfe10

IF (repeat IF) you have a DUVAC alternator, check that the wire to SENSE terminal is clean and connections tight at both ends. A little resistance in this circuit can falsely cause the alternator to output higher voltage, as the sense terminal is seeing lower voltage.

2X

When I lost my Alt I purchased a new one. Everything look fine "at a glance". However on the day I went to remove the old unit, with better light, THIS is what I found. It must have happened before because that blue connector isn't factory.

New 10 cent connector and everything works fine. I also have a $350.00 spare gathering dust. (well the box is....)

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[jacwjames]

Originally Posted by JellyBean

2X

New 10 cent connector and everything works fine. I also have a $350.00 spare gathering dust. (well the box is....)

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I'd like to say you'll never need the new alternator but chances are sooner or later you old one will crap out.
I had to have mine rebuild back ~9 years ago, luckily I was at home when the Alt Fail light came on and I confirmed no voltage. Pulled it and had it replaced for ~$185.

[JellyBean]

Originally Posted by jacwjames

I'd like to say you'll never need the new alternator but chances are sooner or later you old one will crap out.
I had to have mine rebuild back ~9 years ago, luckily I was at home when the Alt Fail light came on and I confirmed no voltage. Pulled it and had it replaced for ~$185.

If I do need it at least it will be an upgrade. A0014874JB 270Amp

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