Red battery light on

[nrhareiner]

Good afternoon,

Driving today when we were 10 miles from destination. We were running the OTR air. Suddenly the red battery light came on, and the OTR air stopped (no rear fan, and no compressor). I pulled over to the side, and checked the following; alternator putting out correct voltage, chassis batteries fine, house batteries fine getting charged from the alternator. I have read the threads on the vanner monitor, but that sounds like resulting in yellow balance light. Any help appreciated.

[garyde]

Hi Kim. Did you measure the voltage at the Regulator?

[nrhareiner]

Yes I did, and it was fine. The regulator was one of the first places I looked since just replaced it 1 month ago.

[Jon Wehrenberg]

Kim, I'm shooting from the lip here so take this with a grain of salt. The light is driven by the monitor. If I was looking the first thing I would do is check the voltages there.

I believe the OTR AC needs good voltage or it will cease operating. I just do not know if the monitor plays a role in that. If the voltage to the monitor is OK perhaps disconnecting the overvoltage lead (to extinguish the light) might isolate the problem to the monitor.

This was just a brain fart, unaffected by actual facts.

[nrhareiner]

Jon,

Makes sense to me because all of the voltages everywhere measures correctly. I am going to do that now and see if it works. If things okay then I will order a new monitor.

[Jon Wehrenberg]

Kim let us know if that works. If so I suspect there is a relay on that circuit that disables OTR because that is a large battery draw and for safety I presume Prevost biases the system to power lights instead of the AC.

[nrhareiner]

I removed the high voltage wire to the monitor, nothing changed. I wonder about the low voltage wire since when looking in prevost owners manual it talks about that light coming on when engine batteries not being charged. Let me know what you think

[Jon Wehrenberg]

Kim,

I haven't looked at the wiring diagram (no sense actually being informed I always say) the light is a hi/lo indicator if I remember. I would have to go look at the bus to be sure. If the monitor thinks it is reading low voltage that might be the issue. Isn't there a low voltage output on the monitor?

[nrhareiner]

Jon, yes there is a low voltage line. I will pull that one and let you know

[nrhareiner]

Tried the low voltage light, and the dash warning light still on and no OTR AC. I have checked all of the cb for the OTR air, and all normal. I have some fuses in line with the 12 and 24 volt lines to the monitor. All look ok, but I will check every one.

[Jon Wehrenberg]

I won't have a chance in the next few days to get into it because we have visitors, but as soon as I have a chance I will try to find out how the two are related. I was always of the opinion that disconnecting the lo/hi battery or balance wires from the monitor would extinguish the light.

I have no clue why the AC quit when the light came on.

I will be at Prevost in Nashville on Monday. If we haven't figured it out by then I will try to learn what's happening.

[Mark3101]

Jon: Are you going to be at Prevost on the 11th? If so, I will see you there as I have an appointment then for several things.

[Jon Wehrenberg]

I'm going to be there thru the 14th.

I am taking Prevost training on AC systems and electrical systems. Just hope I can get shore power, otherwise I am going to find a campground. I want to come back to a cool coach at the end of the day.

[Mark3101]

I'm going to be there thru the 14th.

I am taking Prevost training on AC systems and electrical systems. Just hope I can get shore power, otherwise I am going to find a campground. I want to come back to a cool coach at the end of the day.

I plan on getting there on Sunday afternoon and hope to get a spot. If I get there first, I will try to save one for you. I will likely be there for three to four days.

[Jon Wehrenberg]

Sounds good. I think I will get there Sunday afternoon also.

[nrhareiner]

Thanks everyone. I will continue to try and trace this problem. Jon thanks for asking when at Prevost. More later if any positive results.

[BenC]

The red light that JUST has a picture of a battery is the "Alternator Failure" Tell-tail light. It is intended to let the driver know when the alternator is not charging for whatever reason. At the same time you see this light, a relay disables the OTR a/c and the hot water booster pump on dash a/c only coaches. The OTR a/c is disabled to prevent the chassis batteries from being discharged and quickly disabling the bus in the event of a loss of alternator output.

There are various reasons for the alternator to stop producing, or if is still is, a bad relay or wiring could be the issue. If the dash voltmeter for the chassis still indicates 26-28vdc, then you have an indication that the alternator is outputting dc current. If it reads lower than that, and gets lower over time, that is a good indication that the warning light is doing it's job and that there is no alternator output. Hope that helps.

[nrhareiner]

Thanks Ben. The alternator is functioning fine with good output. The equalizer is also functioning fine. According to Prevost, I need to see if the monitor is putting any voltage down any of the monitor lines. If it is then the problem is the monitor. If not, and there is any current on any of the lines, then the problem is a probable rub through one of the lines (hope it is the Vanner monitor since that is an easy fix). By any chance do you know what relay could be bad?

Thanks in advance

[Jon Wehrenberg]

Kim,

I couldn't tell the Prevost techs your exact model year but they shared some information regarding your problem. The Vanner monitor does not drive the relay to take the AC out of service. What will is the 12 volt wire coming off your 50DN alternator. I think it is wire #25. They said they have problems with that wire. Voltage will check good at the post (should be 12 volts AC not DC) and the wire has broken at or just beyond the terminal. It may look good but is broken inside.

If that is not the case check further starting with looking for power at the relay. On some models they stated there is a small black box with LEDs which indicate the presence of power. I think that is in the front electric compartment but I am not sure. If that is not lit properly it indicates there is a problem with the circuit. The electrical diagrams which you can access on the Prevost site specific to your model year and serial number will help you trace the wiring. The starting point however is going to be the #25 wire at the alternator 12 volt post.

[jack14r]

Jon,I had that exact wire break just past the terminal crimp,IMHO I think that the crimp was done with too much force and not in the exact correct location and it basically cut the wire.

[Jon Wehrenberg]

That's what the Prevost techs said happened. They had a number of problems of that nature and it was frustrating to them because the break in some cases was not evident. The wire looked good but was not and the post checked good for power.

[jack14r]

Mine looked perfect as you stated,just by luck the technician touched it and it fell apart.

[nrhareiner]

Jon and Jack,

I think you are correct that is where the problem is in the coach (by the way it is a 2000 shell).

Quick question, with that wire in trouble what other symptoms besides the red tell tale battery light on the dash (and not being able to use OTR air) should I see? All of the measurements stay fine at battery, alternator etc.

Thanks

[Jon Wehrenberg]

Kim,

I did not get into it with Prevost, but I did learn they use that signal from the alternator to tell the coach if the alternator has output. When the wire breaks as they described it affects the tell tale light and the AC but they did not mention anything else. I am sure I heard right about that being 12 volts AC as in alternating current so it is a unique power so its use may be limited. On my 1987 coach it was used to power the relay that closed without the power to light the low voltage tell tale light. It sounds as if the function has not changed. The default is to take away AC when the batteries are not being charged so perhaps the bus can limp home with lights. The bias is for seated coaches.

I hope that is the problem because that is an easy fix. If not you likely need to find the relay, verify power to it and then check its operation. I find the wiring diagrams on the Prevost site very good to use for trouble shooting although it takes a while to learn them and they are much easier to see them if you can print them larger.

[nrhareiner]

Jon, I have checked, and everything working fine (except the light and OTR a/c) reference batteries, and charging system. If necessary can the coach be driven?

[jack14r]

If the DC voltage is in the correct range 26-28 volts and not dropping I would think that you could drive it.I have a guest charger and I just cranked the generator which activated the charger and continued on. Just keep tabs on the DC voltage and do not let it go below 24 volts,bring a battery charger with you.

[Jon Wehrenberg]

What Jack said. On our previous coach which had the 8V92 a field wire broke at the alternator and I lost the 50DN but we cranked up the generator and were able to keep the chassis and house batteries charged. Since you won't have OTR you will need the generator anyway to run the AC.

[nrhareiner]

Thanks everyone. I am going to take the bus to Prevost in Nashville since I also have some other work that needs to be done. I have run the bus, and the voltage always stays good. I will need to run the gen set for the AC. I can run two off the inverters, but not going to do that with the present situation.