HELP! My Vanner Battery Equilizer is not producing 14V on the center tap

[Gary Hatt - Publisher BCM]

In the 1999 H3-45 I recently acquired, I am having a difficult time keeping all batteries charged.  This is a problem because the Series 60 needs 12V to tell the ECM to crank the bus. (According to Clifford, and at 10V, the engine will just shut down.)

I bought a set of four new Group 31 batteries, and when driving the bus, one dash gauge shows an output voltage of 28V, indicating that the big alternator is charging correctly.

However, the 12V dash gauge first indicated 13.5V when starting out, but showed only about 11.5V while driving yesterday, when it started getting dark outside. The other gauges was still showing 28V.

Yesterday when driving, the center tap gage was only showing 10.8V.  It would not even get up to 12V, even though the other gage was still showing 28V.

I did some reading in the Vanner booklet, and apparently, there is no potentiometer on the Vanner to bump up the middle tap voltage.

I hate to take it to the Prevost dealer to fix something that is probably very simple, but I can't figure out what the problem is.

The bus ran fine when it was parked over a year ago (supposedly) but now the alternator will not charge the 12V side enough to keep the batteries up to 12V.   In fact, when I checked the voltage individually, two of the batteries showed about 13V, but the other two showed 11V.

The first time the second battery, wired in series on each side, showed the lower voltage, but the next time I checked it was two of the batteries wired in parallel showed the low voltage.

What could possibly be wrong with the system?

To get from Florida to Dallas, I had to connect a 28V battery charger to keep the batteries charged up some of the way home.

Do any of you have any ideas of what to look for?

[luvrbus]

The center tap is for the 12 v supply like the head lamps and marker lights,your year model of the DDEC can be connected to 12v or 24 v side ,I think it is a ground problem you should not be able to read 12v on the negative post on the batteries, the system gets interesting when they connect a relay to the ground side and it fails .I still cannot believe Prevost Tech told you the constat 12v draw was ok, check all the connections on the back of the alternator if you haven't done that, The Vanner is in place to equalize the charging you can bypass it to check your charging ,the Vanner has a fuse and 2 relays the fuse is outside and the 2 relays inside the Vanner with the circuit boards,? what is the reading on the 3 terminals on the Vanner with the engine running, there maybe a isolator somewhere in the system for charging the house system causing you problems ,when they installed your new house batteries they left off the sensor wire for the isolator       

[Gary Hatt - Publisher BCM]

Cliff, I moved one car full of boxes from my old bus at my sisters house to my new bus in an RV park.  I will work on this soon, but I am only reading about 11.5V on the Vanner now with my 20  charger. I will put my 40A charger on it and also check all the wiring to/from the Vanner after I have lunch and see if I find any problems. I may run a second ground wire just for the heck of it to see if that makes a difference.

[Dave5Cs]

Gary if your 12V tap runs off one 12 V battery then try and move it to another one to see if the same thing happens. You will have to reconfigure two batteries maybe. If same thing happens then you will know it is not a bad battery. I had 4 new batteries and one turned out to go bad but they replaced it and no new problems.

[Gary Hatt - Publisher BCM]

Gary if your 12V tap runs off one 12 V battery then try and move it to another one to see if the same thing happens. You will have to reconfigure two batteries maybe. If same thing happens then you will know it is not a bad battery. I had 4 new batteries and one turned out to go bad but they replaced it and no new problems.

I just replaced all 4 batteries under warranty.  They are all on a 28V 40A charger and they are coming back to life. Tomorrow I will do some testing and maybe run another ground to see if that helps. Everything looks okay, so I am not sure why they are not charging the 12V properly.