Chassis Voltage/ Over & Under Voltage Issues

[0533]

All was great when I went to TGO on Thursday. But when I returned I started to get an over and under voltage problem again.

I am still having problems with my Chassis voltage output.

Here is what I am experiencing:

When I start the bus the voltage meter reads out at around 28.2 volts.

Once I warm up the bus for a few minutes it is still ok.

The second I hit the Air Parking Brake the voltage runs up to about 30.5 and I get an over voltage. It also happens when I use the Jake Brake, but not when I turn on lights, or dash air conditioner. It appears to be isolated to the brakes. (My last visit to Prevost Car Dec. 4, 2008 they reset my ABS system which showed an over voltage)

Here is where it gets tricky: If I turn on the genset the voltage drops from 28.2 to 25.5 and stays there unless I use the Jake Brake in which case the voltage will swing up to around 30.5 wildly and then back down.,

1. Question: How is it possible to have the genset that is providing energy to the house side effect the chassis side:

Here is what the Service manager at Marathon Florida told me to do, which I did: John is a great guy and really helpful.

John (Marathon) Said to Do: The generator powers the inverters in charging the "house batteries" not
the engine batteries, the only thing in common would be the "jump start"
relay stuck on. This would allow the engine alternator to stop charging
causing the light to come on at the dash.
To test this turn off shore and generator power.
Check voltage at the chassis batteries.
Turn on house or generator power.
Check voltage at the chassis batteries and see if it increased.
Jump start solenoid is usually mounted above the engine batteries, check
both sides for voltage should be different. If the same solenoid stuck,
turn off house 12 and 24 volt house disconnect switches for 20 seconds
then turn them back on and recheck voltage.

2. Question: What possible relationship is there between the Jake Brake, Parking brake, and the ABS system, could there be a short to ground somewhere, maybe in the ABS system??? Have no clue but need to sort this out as the voltage swing is not good for the equipment.

PS> I have replaced the Voltage regulator, it is new. I am also replacing tomorrow the Vanner Monitor EM70A the little one that monitors input, balance etc, as I am also experiencing a balance issue as well, but only from time to time.

Love some ideas on this one.

Thanks,

Bruce

[Jon Wehrenberg]

Bruce, As I read the process the Marathon service manager recommends I have to concur. When you first posed this question if you will recall the jump start relay was a consideration.

However, what is puzzling is the voltage going up with the Jake or parking brake release, and with it going down with generator start.

I am not familiar with the Marathon system design so anything I say is speculation and should be treated as a guess. I am going to start thinking about this to see if I can conjure up any events that would cause what you describe. This is a serious issue, but I do not think it is impossible to solve.

[0533]

Good morning Jon.

It is certainly an odd one without a doubt and seems to be getting worse than better with the various attempts that I have made.

My system consists of a 270 Amp alternator, an Isolator, a regulator (new) 3 Vanner systems, one for each Chassis and House side and one that is a monitor that monitors the 12V, 24V, balance, etc. And of course the Jump Start Relay.

What does the Jump start solenoid that is usually mounted above the engine batteries look like??

Important maybe: While at TGO I did take off each lead to the Vanner EM70A (the little one) and clean all leads and place them back on. This wild swing of voltage really ramped up after this. maybe nothing. I will be replacing the Vanner EM70A monitor tomorrow morning, as I was told they can start to go, but have no clue what affect they could have on the system.

It is really odd that when I start the genset it will lower the voltage on the chassis side down to 25.5 It makes no sense at all to me. It stays at 25.5 as long as I do not use the jake Brake. in which case the power will swing up for a moment to 30.5 V and back down.

PS> I have the battery charger off, no charging power to the chassis batteries.

I wish I new more about what was happening. I will test anything and replace whatever to get this figured out.

It does sound a little like there might be some type of short to ground issue with the ABS or the braking system ???This of course does not answer the Gen question though.

[Jon Wehrenberg]

Still thinking here, but I have questions.

When you turn on the genset, is the engine running?

What happens when you connect to shore power under the conditions I question above, but with the genset off?

Are you reading these voltages at a display in the bus or are you taking them with a meter at the chassis batteries?

Do you have a chassis battery charger and is it turned on?

Here is what I think I know. With the bus engine running, both sets of batteries should be charging and the 28.2 volts is a good number.

If the engine continues to run, and the generator is started, that should provide 120V AC to the inverters and now they are functioning as battery chargers for the house batteries only and that charging current should not reach the chassis batteries because the two sets are isolated. However the alternator should continue to charge chassis batteries at 28.2 volts.

The inverters will charge the house batteries at the output voltage they are set up to provide based on their charging protocol.

Since the bus alternator voltage is regulated via the regulator if the engine continues to run, but the chassis battery voltage drops to 25.5 with the engine running, that tells me that the voltage regulator is sensing excess battery voltage on the circuit which is connected to batteries (or the sense circuit) and it is not providing power to the field wire to make the alternator function.

I'll wait for you response to the questions, because they are important. I wish the bus was in my garage so I could play with wires and jumpers to trace why the voltage regulator is getting mis-information in the form of high voltage on the sense circuit. (High voltage in regard to its set output, not necessarily excess voltage)

[0533]

Let me answer each question below:

Still thinking here, but I have questions.

When you turn on the genset, is the engine running?

Yes: This is all happening while I am running the engine.

What happens when you connect to shore power under the conditions I question above, but with the genset off?

Nothing, no issues at all

Are you reading these voltages at a display in the bus or are you taking them with a meter at the chassis batteries?

Yesterday while in the bus looking at the Voltage dash Chassis meter.

Do you have a chassis battery charger and is it turned on?

I do, it was turned off

Here is what I think I know. With the bus engine running, both sets of batteries should be charging and the 28.2 volts is a good number.

If the engine continues to run, and the generator is started, that should provide 120V AC to the inverters and now they are functioning as battery chargers for the house batteries only

When the gen is running this is what is happening, at least in part.


and that charging current should not reach the chassis batteries because the two sets are isolated. However the alternator should continue to charge chassis batteries at 28.2 volts.

Is it current that is getting to the chassis?? or is the genset causing some type of current drop, as the voltage actually goes down when the gen comes on 25.5V from 28.2

The inverters will charge the house batteries at the output voltage they are set up to provide based on their charging protocol.

House seems fine and charges up nicely.

Since the bus alternator voltage is regulated via the regulator if the engine continues to run, but the chassis battery voltage drops to 25.5 with the engine running, that tells me that the voltage regulator is sensing excess battery voltage on the circuit which is connected to batteries (or the sense circuit) and it is not providing power to the field wire to make the alternator function.

Jon, what is the "Sense Circuit" is this the vanner EM70A small system monitor??? Black box about 4" x 8" maybe 1" deep??

I'll wait for you response to the questions, because they are important. I wish the bus was in my garage so I could play with wires and jumpers to trace why the voltage regulator is getting mis-information in the form of high voltage on the sense circuit. (High voltage in regard to its set output, not necessarily excess voltage)

I wish it was in your garage as well.

When the over voltage occurred yesterday (when applying the Jake Brake driving along at highway speeds) the voltage would swing up to 30.5 just for a moment the blower would increase speed as well. This is with the Genset running.

When I got into the park where I leave the bus and while at idle my battery light comes on, the voltage output was 25.5V on the dash chassis meter.

I also turned off the bus to unhook the toad, and when I restarted the bus an Battery imblance light came on.

I wonder if the vanner systems monitor is acting up here or who knows. There is for sure a real voltage surge and not a false reading by the meter, this I am sure of as there is real evidence of a surge in power.

When

[Jon Wehrenberg]

Bruce,

Ignore the Vanner monitor. It does not do anything to regulate or control voltages, so for the moment take that out of the picture with respect to it being part of the voltage variations. As to the battery low voltage light and the imbalance I would say it is working because it is lighting warning lights when this goofy stuff is happening.

Let me see if I can make an off the wall statement that might resolve this. I have some concerns which I will express, but let's start here if you are willing. I assume you have a big voltage regulator that has a positive or 24V terminal, a ground terminal and a field wire terminal.

When you have the condition that drops the chassis battery voltage to 25.5, can you put a meter on the 24Volt terminal and tell me what it reads? Once I have that it may not give me an answer or maybe it will. I do want you to set up the bus so the chassis voltage is down when you get that reading.

I hope it reads some higher voltage like 30 volts. If it does I have more questions. If not it is back to the drawing board.

[0533]

Jon,

John Kincaid at Prevost Car jax just wrote asking questions regarding this issue.

Take a look at at his questions:

John K wrote:


Good morning,
Question 1 does the coach have an isolator the splits the voltage to
house and coach that would be the tie

Yes

#2 has there been any bulbs changed on the brake lights or wires rubbed
on tow connectors in rear of coach

I do have one light out

or does it have aftermarket towing
light converter for two bulb tow vehicle

Yes I do

John Kincaid
Prevost Jacksonville
Service Manager
800-874-7740 phone
904-886-0092 fax

[0533]

I will do this today and report back.

My plan now will be to run the bus, run the genset and check the 24 volt output of the alternator.

[Petervs]

Since you mention effects of the Jake Brake, air brake, and connecting/disconnecting the toad , I thing there might be something amiss in the brake light circuit.

The Jake brake activates the brake lights, as do the air brakes.

Maybe the toad wiring is sending power somewhere it is not supposed to go?

At least these things should be eliminated as causes, if nothing else.

[jelmore]

I also had wild voltage swings on the chassis side and tried (lamely) to pin it on some repeatable sequence. It would be fine for a while and then start acting up. After much diagnosis and many phone calls, it was a loose battery cable.