ABS Brake Dash Light

[Jon Wehrenberg]

Bruce..........

"I am being told that because the "House Batteries" are requesting a charge from the Engine alternator to keep the house batteries at a proper level to service the house draw."

Bogus.

"If the Alternator or the regulator is not functioning correctly it appears that one or the other is creating an over voltage (which is tripping off the ABS computer my other problem) ."

That sounds very reasonable, with my money on a bad regulator.

"The final condition is the fact that the generator reduces the voltage dash meter from 29V. to 25V within 1 minute after starting the genset."

Here is where the communications are breaking down. Is the engine running when you start the generator? If so, which voltage are you describing? House or chassis?

Let's do a quick system overview. When your engine is running, with a properly functioning alternator and voltage regulator, both the house and chassis batteries are being charged and because the alternator is so large in terms of output it can handle almost any resaonable load and you will see no difference in the voltage.

With the engine still running, if you start the generator, and the inverters have been left on, the generator power is seen by the inverters, and both the inverters begin to function as battery chargers for you HOUSE batteries.

The alternator voltage regulator should not see that charging voltage because the isolator prevents house voltage from flowing back. Since the voltage regulator battery sense circuit is detecting chassis battery condition the alternator continues to function and should continue to put out 28.4 volts.

So under what specific conditions does the voltage drop to 25, and is this house or chassis voltage?

The dash light fluctuation is an indicator the voltage is varying. As it goes up and down so does the light intensity. The fact that it is dash lighting tells me the variation at that point is with the chassis side of the system. Does the house lighting do the same?

[0533]

Your right, there are 2 equalizers, mine are all on the bulkhead just inside the engine Passenger side door above and behind the chassis battery shut Off switches.

I have the 24V Alt, a regulator inside the main Prevost flip up box above the engine, an Isolator (Big Blue Cylinder) 2 equalizers, and of course 4 chassis batteries and a vanner box that shows Batt Hi, batt Lo, balance etc.

I did some testing today, here is what I found: I ran the engine at 1000 rpm, with load, lights, dash air, blower motor, etc.

1. All batteries read 13.2/.13.7 this was done while the batteries were disconnected.
2. The batteries did need topping off. some low cells, added distilled water.
3. Regulator reads at FLD/Alt between 6 to 7 Volts.
4. Isolator reads 28.2 at both sides, Chassis and House.
5. Both equalizers read 28.2 volts

I then turned on the Genset: Still had load on Chassis batteries, 1000 rpm with lights, air blower motor on.

1. Batteries are all reading fine,
2. Regulator at FLD/Alt reads -.18 V (cannot understand this reading, did it several times
3. Isolator reads between 24.7 and 25V on the Chassis side, 28.4 on the house side,
4. The dash light for battery charging was on.

There was no hunting at all, but I had not run the bus more than 30 minutes.

I really do not know what is wrong, but am wondering about the effects of the Genset on the chassis side.

The dash voltage meter seems to read correctly in all cases, very close.

I also tested the voltage meter by touching each end together, .5 Ohms lose.

[Ray Davis]

When you tested, was the 24V battery charger running via inverter?

Why do I stress this?

The regulator will regulate what is coming out of your alternator, NOT out of your extra charger that is essentially in parallel with the output from the engine charging system.

IF it does not like the modified sine-wave from the inverters, it's possible that the charger could put out a funky 24V, with a large AC ripple. I don't know, but this seems to jive with Tom's experience.

IF you have a large ripple right on the battery posts because of the charger, your dash is going to see this.

28V out of the regulator is fine.

So, without trying muddy the waters, did you turn off the battery charger? IF so, did it behave as expected then? If it's still misbehaving, then you've ruled it out, at least.

Ray

[0533]

When you tested, was the 24V battery charger running via inverter?

Why do I stress this?

The regulator will regulate what is coming out of your alternator, NOT out of your extra charger that is essentially in parallel with the output from the engine charging system.

IF it does not like the modified sine-wave from the inverters, it's possible that the charger could put out a funky 24V, with a large AC ripple. I don't know, but this seems to jive with Tom's experience.

IF you have a large ripple right on the battery posts because of the charger, your dash is going to see this.

28V out of the regulator is fine.

So, without trying muddy the waters, did you turn off the battery charger? IF so, did it behave as expected then? If it's still misbehaving, then you've ruled it out, at least.

Ray

No i took it out of the system for the entire test.

[0533]

Bruce..........

"I am being told that because the "House Batteries" are requesting a charge from the Engine alternator to keep the house batteries at a proper level to service the house draw."

Bogus.

"If the Alternator or the regulator is not functioning correctly it appears that one or the other is creating an over voltage (which is tripping off the ABS computer my other problem) ."

That sounds very reasonable, with my money on a bad regulator.

"The final condition is the fact that the generator reduces the voltage dash meter from 29V. to 25V within 1 minute after starting the genset."

Here is where the communications are breaking down. Is the engine running when you start the generator? If so, which voltage are you describing? House or chassis?

Let's do a quick system overview. When your engine is running, with a properly functioning alternator and voltage regulator, both the house and chassis batteries are being charged and because the alternator is so large in terms of output it can handle almost any resaonable load and you will see no difference in the voltage.

With the engine still running, if you start the generator, and the inverters have been left on, the generator power is seen by the inverters, and both the inverters begin to function as battery chargers for you HOUSE batteries.

The alternator voltage regulator should not see that charging voltage because the isolator prevents house voltage from flowing back. Since the voltage regulator battery sense circuit is detecting chassis battery condition the alternator continues to function and should continue to put out 28.4 volts.

So under what specific conditions does the voltage drop to 25, and is this house or chassis voltage?

The dash light fluctuation is an indicator the voltage is varying. As it goes up and down so does the light intensity. The fact that it is dash lighting tells me the variation at that point is with the chassis side of the system. Does the house lighting do the same?

Hi Jon,

The engine is runnng when i start the genset.

The voltage is the dash meter for the chassis side, 29 dn, to 25.

The chassis batteriesVoltage meter shows 25V when the genset is on, engine running,

The bus lights, dash flucuate not the house side, no effect.

Please see my finding below 3 threads down, it might offer some clues.

[Jon Wehrenberg]

Bruce,

Either the regulator or the alternator is puking. That's my guess.

When the engine is running at high idle, connect the tester to the 24 volt post and a ground on the chassis batteries. If everything is charging you will read about 28 volts.

Then do whatever you do that causes it to drop to 25 volts.

Leave the tester connected and reading your chassis battery voltage. Jumper between the Positive and Field terminals on the regulator. While you are doing this observe the voltage on your tester. If you have a regulator problem you will see the voltage start to climb. Do not leave the jumper in place. All you want to note is if placing the jumper in place causes the voltage to go up. If the voltage rises the regulator is bad. If not suspect the alternator is bad.

You will have unregulated voltage with the jumper in place and after a few seconds that voltage has the potential to climb quite high so don't leave that jumper on if the voltage climbs past 28 volts.

The inverters should have nothing to do with the output of the bus alternator because the isolator should never allow the voltage level of the house batteries to be "seen" by the voltage regulator, HOWEVER>>>MAKE CERTAIN YOUR CONVERTER DID NOT ALLOW YOU TO CONNECT BOTH BATTERY SETS SUCH AS TO ALLOW JUMP STARTING IN THE CASE OF DEAD CHASSIS BATTERIES. IF SO MAKE SURE THAT FEATURE IS NOT ENGAGED. IF THAT FEATURE IS ENGAGED DISENGAGE IT.

[0533]

Hello Jon, I plan on following your directions today and do the test below. Question: The Regulator is labeled FLD. & Alt side by side, are these the 2 you are suggesting I jump???

Regarding your question about the battery Boost dash button on my Marathon. i believe that I do have the ability to connect for short periods of time the house batteries to the chassis to start the bus when the chassis batteries are down??? I am not sure how this accomplished in the system.

Jon Writes: Leave the tester connected and reading your chassis battery voltage. Jumper between the Positive and Field terminals on the regulator. While you are doing this observe the voltage on your tester. If you have a regulator problem you will see the voltage start to climb. Do not leave the jumper in place. All you want to note is if placing the jumper in place causes the voltage to go up. If the voltage rises the regulator is bad. If not suspect the alternator is bad.

[Jon Wehrenberg]

"Regarding your question about the battery Boost dash button on my Marathon. i believe that I do have the ability to connect for short periods of time the house batteries to the chassis to start the bus when the chassis batteries are down??? I am not sure how this accomplished in the system."

I'm not familiar with Marathons, but you do have to make certain you are not connecting the house and chassis batteries. Otherwise the inverter input to the house batteries is seen by the voltage regulator through that jump start circuit, and the two sets of batteries are not isolated.

I don't think you have them connected, but I want to be sure because some of what you are seeing does not make sense to me.

[0533]

Hello Jon,

I jumped the Regulator FLD. and Positive and saw rapid increase in Voltage from 28 to almost 34 in a few seconds, quickly removed the jumper (just touching the 2 connections) and the voltage returned to 28V again. I will order and install a new Regulator in the morning.

[phorner]

Bruce,

I performed the same test and got the identical results.

A replacement voltage regulator solved the issue for me.... just wanted to give you a vote of confidence in your diagnosis....

Good luck!

Paul