I have been getting ready for a trip today so I have had the generator running all day. I started engine to bring coach back home from the ranch and everything was ok. On the way, the check engine light and beeper came on. Looked at the VMSair and it said alternator potential. Looked down and the voltmeter read a little less than 12v. I assumed I had lost the alternator so I turned on the boost switch. Driving down the highway, I turned of boost to see if alternator would reset. Nothing happened, but I noticed the voltage on the monitor went to 17.2V. I was thinking the generator was now overvolting, so I turned it off. The voltage on the coach batteries stayed at 17.2V. I pulled up off the tollway and as I slowed down the voltage dropped to 16.6. I finally realized the alternator was overvolting, so I stopped and switched the battery disconnect.
Besides the alternator, what else should I check. Doesn't the isolator work as an over voltage protection or is it fried now since I only get battery voltage on the voltmeter? Has anyone put in overvoltage/overcurrent protection on their coach?
You should be able to Remove the belt for the alternator. It will cook you batteries.
Steve
Before suspecting the alternator or isolator I would suggest checking/cleaning/tightening all your battery post, isolator and alternator connections. The alternator might be trying to compensate for increased resistance by raising the voltage.
Also, how old are the batteries and have you tested them recently...an open or partially shorted cell can cause unexpected voltage readings.
Keep us posted.
Steve,
The answer is that you have lost the voltage sensing input to the alternator. I would not suspect alternator, isolator or batteries until AFTER you have established that the voltage sensing input to the alternator is intact and is showing engine start battery positive terminal voltage.
Here's the logic:
Without the sensing voltage input to the alternator, the alternator thinks the voltage is low on your engine start batteries, and it keeps increasing it's output until the alternator output reaches its maximum possible voltage (17.2 Vdc in your case).
Because the dash voltmeter reads low, I would suspect that alternator charging current flow through your engine start batteries has ceased as well, although it may still have a current flow path to service peripherals based on your driving/engine running for a while before your got an alarm. The VMSpc and monitor voltage is high because you have current flow to your house batteries and they ARE being overcharged.
To troubleshoot, I would check the voltage sense terminal (engine off) to verify that it is 0.0 Vdc (should be B+ but you have lost the connection somewhere). If it is 0.0 Vdc, then I am correct and you need to take every terminal off of your engine start batteries including the ground path cable to frame, clean and dielectric grease all of the connections, then reland the terminals. Check the voltage sense post at the alternator again (engine still off) and if it is back at start battery positive terminal voltage (B+), you have likely solved your problem. If not at B+, then either run a new alternator remote sense wire or check every connection until you find where B+ is lost.
The isolator, batteries, alternator and wiring can withstand short term insults like this without permanent damage. But more than short term (more than an hour or two) and damage will start to occur.
An easier way to protect from Alternator over voltage is to remove and insulate the center terminal on the isolator (the feed from the alternator to the isolator, then through the diodes to the batteries). Then with the boost switch closed, you can drive forever with the generator running/invertor-charger woking/associated wiring without running down either battery bank.
The isolator has no over-voltage protection function. An isolator contains only diodes (and heat sink fins) that prevent one battery bank from feeding current to the other battery bank(s).
The voltage dropped from 17.2 Vdc to 16.6 Vdc when you slowed down because the alternator was not spinning as fast and the maximum voltage possible just naturally drops off.
Call me if you need more explanation/help.
Neal
603 seven seven zero 7459
Don't need to drive it without alternator, because I am at home. I was suspecting connections, but I am waiting for the engine bay to cool down. My batteries are relatively new, but after treating them to 17 volts I likely will replace them. I wish I had current sensors like aircraft so I could really monitor what each of the busses were doing. I intend to take alternator to shop tomorrow to have it tested/repaired. I will forward whatever I find
Where is the isolator located on a 2005 U320T? Batteries are on the left side forward of the engine, but I don't see isolator. Engine is still to hot to mess around too much.
As long as the sealed batteries were not overcharged to the point of overheating and "off-gassing", the 17Vdc has done no harm. Military and power plant applications "equalize" charge both wet cell and sealed cell batteries periodically (and routinely) to drive contaminants off of the battery plates. Of course, equalizing charges are closely instrumented and monitored, but a short application of 17 Vdc might have even be beneficial.
I doubt that the alternator needs repair. If you are doing it simply to "refresh" the alternator, then more power to you but make sure your rebuild shop understands "RV remote sense technology", with a battery isolator involved. As noted in other threads, many (most?) shops do not and they often do more damage than good.
Neal
Steve,
I'm not able to help with that if the isolator is not on the forward engine compartment bulkhead. I also don't know if FT had gone to a voltage sensitive relay, to replace the isolator, by 2005.
I have worked on many coaches with voltage sensitive relays and I have never seen one that I like. Unlike isolators that are easy to understand and troubleshoot, VSR's (being solid state devices with many functions) have confusing failure modes and throw wild indications. Most factory consults result in black-box, "easter-egging" it (dispose of it and plug in a new one), because even the engineers can't figure out the symptoms, so the answer is always just replace it.
Neal
Steve,
FOT Spec sheet says that all three models have a 200 amp Isolator in 2005.
So I'd look for it on the forward engine compartment bulkhead. That was fairly standard after 1999 or so.
1998 and older were out in the weather, aft of the duals.
Neal
I figured out my defect is the isolator. The half that powers the engine batteries is blown. That is why with boost ON, the alternator is sensing voltage, but with it OFF, the alternator senses the battery voltage and not the alternator output. I will pull interior engine cover and see if I can find it. Very limited access to front of engine with a tag axle.
Steve,
Your isolator should look something like this (the blue finned component):
Neal
Found the isolator and it is bad. It is under the engine hump in bedroom
Steve,
Engine Start Battery side Melted? Diode open (high resistance in both directions)?
Be aware, just replacing your isolator may not be the final answer because some other Root Cause, may have caused the isolator to fail. It may have been isolator age but it may also have been because the alternator voltage failed high due to a loss of it's sensing voltage. So, make sure everything is operating normally after you replace the isolator.
Good find!
Good learning!
Neal
Diode shows open. To confirm I am going to switch the alternator sense wire to the coach battery side. Since it regulates with the boost switch closed I am relatively certain alternator is okay.
Neal,
I think Steve saw a fault warning that the alternator potential was out of range. VMSpc does not measure or display house battery voltage only the voltage supplied to the ECM voltage sensor (start batteries).
Make sure the sense wire shows start battery voltage at the sense terminal on the alternator. As I understand externally sensed LN alternators, if the sense fails the voltage regulator will go back to a base level rather than increase to a maximum. High voltage maybe a bad voltage regulator or failed diodes. There are trouble shooting flow charts on the internet.
Roger, this is also the way the Delco 40SI works - for members that are using this alternator. See red circled information on the second page of the 40SI brochure. Loss of "Sense" will just result in a 1 volt or so lower than normal voltage at the batteries due to isolator losses - if everything else is working correctly. I have verified this by disconnecting my sense wire.
Delco 40SI brochure (http://www.foreforums.com/MGalleryItem.php?id=3056)
Isolator definitely bad now. The center stud spins. Prestolite service bulletin indicates you will get a high voltage with loss of sense.
Hmmm, that is strange as when my sense wire broke on last trip my voltmeter in Dash showed almost zero volts. That made me think it was alternator till I found the sense wire broken at soleniod on starter.
JohnH
Roger,
FT replaced my 1998 U270 Leece Neville alternator several times until I finally figured out my remote sense problem and corrected it myself. Each of those various alternators failed at 17 or more Vdc when the sense voltage was lost. And yes, isolators and batteries suffered the consequences.
Because I paid those dues on the first coach, I have also experimented with my 2002 U320 Leece Neville remote sense (just to know for sure how it works) and when the sense voltage is removed (goes to 0 Vdc), the alternator output in the 2002 also fails at 17.2 Vdc output.
Steve's 2005 is doing the same thing (Engine Start Battery Voltage low = output fails to max).
I wonder why other FT Leece Nevilles would be different, unless new technology, post 2005, has evolved to a different standard.
I have no experience with the Delco 40SI but it would be good to have an alternator fail near nominal voltage output. I would make sure, though, that Delco doesn't mean that the 40SI will fail at a nominal voltage
when the remote sense is not connected AND the output sense is wired in the conventional manner (i.e. - installed such that alternator sense is wired to B+ output). Using a solid state device, it would be easy for Delco to design the alternator voltage regulator such that if remote sense = 0.0Vdc, then internally the voltage regulator would shift to a nominal reference voltage and adjust output voltage/current accordingly. But that's a design feature that would be somewhat confusing to the average owner and any repair facility, because isolator diodes seldom fail at 0.0 Vdc. Often when a diode fails, there is still a leakage path and some voltage is present, rather than a completely opened circuit. Many repair facilities can't handle the thought of an isolator's diode voltage drop, much less an automatically "toggled" voltage regulator, based upon a 0.0 Vdc remote sense input.
Curious,
Neal
If the engine is C-8.3 or ISC, the alternator belt probably has to be left in place to keep the engine water pump turning. Removing the center cable from the isolator or alternator end would accomplish the same as removing belt. But the problem is more likely a bad connection from alternator to start battery bank. Consider running a fused wire directly to battery.
My sense signal is not lost, it is only showing battery voltage because the diode is blown in the isolator. The regulator sees 12v so output increases. Since the sense stays the same, voltage goes to maximum. When I closed the boost switch, the voltage sense was then connected to the alternator output through the boost switch and voltage dropped to normal.
Would a 30 amp fused 10 gauge wire be too large? I can replace the 30 amp fuse with 10 amps or whatever would be more apropos.
Thanks,
Trent
It would be OK to use heavy wire, but not necessary, the sense wire carries very little current. For mine I used 14 gauge red wire with a 5 amp fuse.
The existing wires are 12 or 14 ga. My FT has 15 amp fuse on E59, the Battery Voltage to Alternator Sense wire. The Excite wire, E6, has a circuit breaker in the front dash panel, #33, 6 amps.
From drawings B-2179 and B-2126, 2001 U320.
It looks like the Delco 40si goes back to normal voltage if the sense wire fails or is not installed.
Steve
How soon can you get a new isolator? Looking forward to the results.
Isolator arrive in morning. James called this morning responding to my call late yesterday and confirmed what would happen with a bad isolator.
Installed new isolator and alternator system works.
Now I get a fault code SPN 412 (4) that means I am getting an EGR temperature sensor low voltage. No idea how I ended up with that, but it will have to wait till I get back to town.