Chassis Voltage/ Over & Under Voltage Issues

[0533]

Jon I am now getting ready to head over to the bus and do these test,

I believe that on the isolator there are 3 connections, one is "Main" One is "Alt". and one is "Aux" I get the lower reading off the "Main" which I believe to be the Chassis Battery. It is my plan to disconnect the "Alt" cable and the "main" cable and connect the 2 together. then go through the process of testing and running the Genset or even the shore power I guess. I also plan on turning off the shore, the 12/24 the house and the inverter power before disconnect and connections are made. i will also test the lines before turning any wrenches

[Jon Wehrenberg]

I don't think you need to do any disconnects when you detach the two cables from the isolator if the engine is not running.

The alternator cable should be easily traced to confirm it comes from the alternator and I agree the main sounds like the chassis.

Just as information, as long as none of these contacts a ground there is no hazard associated with what you are doing. Even if you connect the wrong ones together there will be no problem. You may not get the answers you seek but there will be no damage to anything because when the bus engine is running and the inverters are not powered you already know the alternator power on the bus powers both other cables through the isolator, effectively tying all three together.

By connecting the alternator and chassis together, and running the generator or connecting to shore power you have separated the chassis from the house unless the jump start relay is closed. By separating the two systems you should see the chassis charged via the alternator, something apparently not happening now when the house inverters are chargers. If the jump start relay was closed it is my opinion the chassis batteries would be charged via the inverters and would not drop down in voltage.

[gmcbuffalo]

Bruce
Any news on your latest troubleshooting?
GregM

[0533]

I have been traveling on business, as this is my busy season and I have been putting the bus off I am afraid. Had hoped that when I returned the bus would be healed on its own, buses have a way of doing that you know.

Before leaving I went through several tests, changed out a few parts and pieces, but am still planning on heading back to Jax. for a Prevost look see, can't seem to spend enough at Prevost.

I was actually considering bringing in an electrician to take a look around, but canceled the idea as I was not sure what to tell them.

I will be heading down to Fiesta Key on the 23rd., a few POGGERS will be there, if I am still having problems by then maybe one or two will give me some clues, steer me in the right direction.

It does not take much to elude me when dealing with mechanical stuff.

PS> I replaced the Valve in the Steer Bay that controls the Step, it was leaking air fast, it went well, no leaks all went together just fine, but there was a little resistor ??? that ran between the two leads, I was able to move it over to the new connection without too much trouble, except one small problem the step will not slideout, no power, need a new dohicky I guess as the connection worked out fine, "NO LEAKS" half way there, says aired up.

[Jon Wehrenberg]

Prevost will happily keep changing parts as long as you have a line of credit or money in your wallet. (Next time maybe you should ask them if they will take back the parts and credit you for the cost of labor if their parts replacement does not work.)

The key to all this Bruce is diagnosis, and Prevost apparently isn't doing that and you are aiding and abetting them.

[0533]

Actually Prevost is not at fault here, I am. The only thing they did last visit in this regard was to reset my ABS light, nothing else in the electrical troubleshooting process as there was not a big problem.

It has however become more of an issue since I was at Prevost, they did connect a new ground strap on the Alt. a few odds and ends house keeping stuff on the engine, a few upgrades etc, but nothing other than the ground strap and the resetting of the ABS light.

I however changed out the Regulator as I was convinced it was bad, as it was showing high voltage on the chassis batteries when I conducted the test by placing a jumper wire on the Fld and Alt for a few seconds, the Chassis voltage ran up quickly to 32volts output, so I replaced it. I also replaced the EM70A Vanner monitor (crossed my fingers on this one) it sure looks pretty.

I inspected all wires, batteries, leads, you name it, tightened, cleaned, painted (corrosion stuff) everything. It was almost 6pm dark and I did not want to bother my neighbors with the noise of running the bus, went home and flew out of town, am now back plan on checking out my handy work. Do not expect much as I was doing three things at once, voltage, step and Auto Fill, think my solenoid is bad, on the water fill everything else is fine.

It is funny though, that it is either nothing wrong with the bus or there are a few issues, I prefer nothing.

[0533]

I am just finishing up a few details here at Jax Prevost, am up in the air inside Bay #2, the one where you have to leave your wallet at the front desk before entering.

Here is what we found and what was done to address the problem. Let me first say that Wally and Cliff here at Prevost Car really spent the time to actually sort out all aspects of the problem and truly resolve the issues.

Anyway: 0533 is a XL45 1998 shell converted by Marathon, this will create the baseline for discussions moving forward.

Marathon equipped this coaches electrical system as follows: There is 1 270 Amp alternator that goes to a series of Vanner equalizers and on to an Isolator, big blue finned cylinder that separates the alternator from the the house battery bank. Housed inside the Isolator is a solenoid that has 2 leads attached that can be used to jump start the chassis batteries in the event of a chassis battery drain, switch is on the dash. The isolators solenoid is housed inside the sealed housing, bad idea. Costly one as well.

Testing process: If we placed a voltage meter on the Chassis side of the isolator (chassis leads removed) we saw 24.87 volts which was the same as the House battery bank. If we removed the house battery leads from the isolator there was no current passing across to the battery side.

Conclusion was that the isolator had failed, and the internal solenoid was allowing current to pass current across the isolator from the house to the chassis side, not the other direction, we replaced the isolator. No current issues after this was done.

We also disconnected all batteries both house and chassis, tested each with a meter (Snapon meter clip leads and three readouts) that could check the values of the battery beyond its current voltage, discharge and had a meter that once pressed would create a colored scale to check the condition of the lead acid plates etc, not exactly sure here but the results were interesting, had 3 bad chassis batteries and 2 bad house batteries, all of the rest were reading good or very good.

Operation: Replaced all chassis batteries and 2 Lifeline house.

Next we took a look at the regulator to check output as the values were still higher than they should be, 29.2 range.

this where things got a little strange. Wally wanted to see where the battery wires (Prevost) from the Regulator inside the Prevost control box above the engine terminated, as he thought they would end up at the switch for the chassis battery shutoff, they did not, the Prevost wire ended up terminating into a Marathon wire that connected to the 24 volt emergency shut off switch above the door at the curbside engine compartment. In other words the regulator was regulating the house battery bank not the chassis battery bank.

Here is why: It appears that Marathon has designed the so called single alternator setup to supply charge first to the house batteries so that when the house shows a need for a charge the alternator will charge the house bank so that the house batteries can be fully charged while the bus is running down the road without the need for the generator running. In fact if you do run the generator the alternator stops charging completely, in fact the chassis batteries are getting no charge at all to my knowledge (maybe they would as a result of the Vanner equalizer sensing an unbalanced condition, not sure here), anyway it is completely the opposite of how Prevost ties the regulator battery wire to the chassis batteries.

Here is what we think was happening to cause the problems overall: First the regulator output was too high and needed to be cut back, it is now set at 27.9 volts. 2. When the house battery bank was calling for power (2 bad house batteries one really dead) the alternator (which works just fine) starting sending power to the house and at the same time was overcharging the chassis batteries (isolator was not isolating) frying them not a pretty site.

With 3 out of 4 chassis batteries failing or near death I was getting all kinds of strange events going on in the coach, not now, all is fine, no surges, no over voltages, nice solid clean 27.9 volts readings under all loads, no spikes.

I had a chance to change the way the regulator is connected to the house side, could have moved the wire over to the chassis side but did not, will monitor all from now on with a better understanding of how the system works and why.

That is all for now, hope I have been able to explain this so that Marathon owners will be able to use the info.

[Kenneth Brewer]

Thanks for taking the time to explain the problem(s). what was done to solve the problem(s), and the converter based wiring system/philosophy impact. While our coach is by a different converter, it is still instructive to have this info.

Good luck and thanks.

[JIM CHALOUPKA]

Thanks for the update Bruce, I am sorry you had to go through the ordeal of figuring out how your system worked, and in such a troublesome and expensive way.
It would have been nice to have had printed information in your manual as to the principles of your systems method of operation.
It has been said here many times that one only learns by their mistakes. Now I hope we can learn from our experiences, or in this case yours.
Even though our systems may be different, your experience shows that some operations are concealed inside devices and that nothing should be assumed when diagnosing a problem.

JIM

[Ray Davis]

So Bruce,

Is it a fair summary that the issue was that (1) the isolator had failed and (2) the regulator was putting out too high a voltage? That caused the fried batteries, which ultimately displayed the issues you saw?

Ray