-
Alternator question
We are having an alternator issue. Picking up the coach after oil change service, upon starting the engine, the dash Battery symbol was on and an unlabeled red light directly above it was on. Battery voltage on the dash gauge was low. Bus started ok.
I had to drive about 4 hours. Battery light went out as did the unlabeled red light above it. Battery voltage returned to normal. This happened pretty quick.
For sometime, previously, when the generator was running, and the engine was at idle (600 RPM), the unlabeled red light (directly above the battery symbol light) would be on until I added throttle. There would be a buzzing warning sound, not very loud, that would increase in pitch as I increased throttle and the RPM increased. The buzzing sound would cease and the unlabeled red light (directly above the battery symbol light) would extinguish at about 1000 RPM. This is happening now with the generator off.
We installed new chassis (start) batteries last year at Marathon. We installed a rebuilt alternator (50 DN, the oil cooled one) about 3 years ago. Alternator belt looks ok. Airbag belt tensioner looks ok.
Does anyone know what the unlabeled red light (directly above the battery symbol light) monitors? Our coach documents are kind of a mixed bag and don’t represent our coach exactly.
How do you know when the Bosch alternator (air cooled) goes bad – could that be the problem?
Thank you for your thoughts!
-
7 Replies
-
I see 3 “battery” lights in the Prevost owners manual for your coach. Rather than ask which one was lighted, below is a link to the manual. Go there and then go to page 3-11. I believe what you are looking for is there.
-
Thanks Tim,
The manual doesn’t really explain but it looks like the blank could be Battery2. So does this monitor your House alternator (the Bosch)?
The light we have on(below 1000RPM) is a red blank directly above the Battery Symbol – it is not the BAL or Hi/Low nor is it the Battery Symbol
-
The Bosch would be chassis not house, assuming you don’t have Prevost OTR.
-
Thank you for the post. I Understand the unlabeled red light monitors the 50 DN 24v 270 amp oil cooled alternator which charges the house batteries.
So what would cause the light to illuminate at low RPM? And what is the sound that increases in pitch and ceases when the light goes out?
I assume it is not normal for the red light to be on when the engine is running at low RPM. Red Light goes out above 1200-1300 RPM. I’m just wondering if it is a voltage regulator, relay, alternator, slipping belt or are my 5 year old house batteries causing it? How can I tell?
I do not have OTR air. This is a 2000 Marathon, Detroit Series 60. Two belt driven alternators, Delco 50 DN oil cooled for the house, and a Bosch air cooled for chassis batteries.
-
The easiest way to determine what is going on is to start by using a multi-tester and measure voltage at the chassis and house batteries with the engine off, engine at low idle and at high idle.
I think warning lights on your vintage coach are controlled by the Vanner monitor. If your voltages are OK then the monitor is suspect. The only way to know for sure is to know the voltages.
Alternators do not put out a lot of current at low idle, but if they are working all warning lights should be extinguished.
-
The battery light was coming on due to a short. TEC in Coburg found chafing wires that were grounding. All repaired, no warning lights! Alternators are both good. The grounding wires provided the ‘excitation’ power for the alternators.
-
That is good news! Always great to hear a good outcome!
Log in to reply.