[Archived]

My first reaction is the condenser fan might be the source of the current draw. If you can get a clamp meter that measures amps thaty might help with the diagnosis. My only concern is for a current draw from the fans to be so huge as to draw down the voltage as much as you describe I am wondering why the circuit breakers have not tripped.

[Mike]

Did the tech use a jumper wire to make some part of the A/C system stay on ? Call and ask them

[Hisham]

Your voltages sound like a charging problem to me. I have my voltage regulator turned down to accomodate agm battery protocol and my numbers are 13.5 and at least 27 under light electrical load.

[Karl]

Thanks all. I have found somebody in Denver to take a look at it, and will share your thoughts.. He sounded very familiar with the Prevost electrical systems, and said this was a rather unusual sounding issue.

[Larry & Diane]

Just wanted to give you all a heads up to the solution. After removing the battery cables to check their charge, the problem apparently was a loose battery cable! Once they were all put back on and I was driving the bus, I noticed my voltage was reading properly. Turned on the AC and everything held. But thanks again for your thoughts. I have had coaches on and off for 40 years, but this is my first Prevost.

[Dick]

General Troubleshooting Charging system and Battery Hi/Lo Light, for future reference for anyone:

Check all battery and equalizer connections for tightness first. Look for burnt wiring or cable terminal ends.

The battery HI/LO light is a function of if the Vanner battery equalizer is keeping the battery difference from the “24v” batteries and the “12v” batteries within a half a volt (though diagnostics say 1/10th). There are control loads in the bus air system that, like any load, can cause the batteries to become unbalanced, but the large loads aren’t 12v, they are 24v.

The only diagnostic for the Vanner battery equalizer is whether or not it maintains (as I normally say) within a half a volt between the two banks of batteries in series. Us a DC current transducer type clamp ammeter and see if the current on the 12v cable of the Vanner equalizer is under the rated 100 amps. If it is very low, and the HI LO light is still on, and the batteries are more than 1/2 a volt difference between the 24v terminal and the 12v terminal, and between the 12v terminal and the Ground terminal on the equalizer, then it is bad or failing.

If the current is high, near or greater than 100 amp rating of the equalizer (lets say for sake of arguement 80 amps or greater), then I would investigate further to see where that high 12v amperage is going. One normally doesnt see that high a 12v load on the system. Even with all the exterior lights and headlights on, and the engine running (the transmission and engine comontrols are all 12v) we don’t usually see a draw over 50-60 amps on the 12v side. The wipers, large bus air blowers and dash fans are all 24v loads.

Finally, if the Vanner equalizer IS doing its job, you don’t see 80amps or greater out of the equalizer, and the voltage difference from the terminals I mentioned above ARE withing a 1/2 a volt or less, then check the battery monitor, the Vanner EM70 up on the firewall. Those have a pretty good failure rate and can fail, giving you a false indication of a problem.

Hope this helps someone in the future.

By the way, glad you found a loose battery cable. Keeping them tight and checking them annually should be on everyone’s P.M. list. Yes, the split voltage battery system is unique in motorhomes to Prevost Conversions.