New owners to a '07 Nimbus with Cummins ISM 500. I have this intermittent issue with low voltage which trips the Check Engine Light.
We saw this first a couple weeks ago. We drove from Houston to Waco for the weekend w/o issue, but about 10 min into our 3.5 hr drive home, the check engine light began to alarm. I scanned the gauges and noticed that the voltage was a little below 12 V (about 11.9). I remembered that we still had the roof ACs on and the generator was off. As we continued down the road, I had DW shut off the ACs, and I started the generator. After about 5 min, the voltage increased and the alarm stopped when it to about 13 V.
I assumed I had found the problem and we could put it behind us, but this happened 2 more times. Each time, the voltage was about 11.9, and the alarm would activate for 5-10 min, and it would clear when it got to 13V.
Roads were wet first thing that morning, and we didn't see the problem again once they dried up. Probably not related, but I'm including it here for completeness.
Today, I took another trip and saw the low voltage with CEL issue again - about 20 min into the trip. It alarmed for 5 min or so, voltage never dropped below about 11.9, and it cleared once the voltage climbed up to 13V. I engaged the boost button and turned on the generator hoping to clear it faster, but didn't see a difference.
One thing I noticed is that the dash volt gauge is often sitting right at 12 or 12.1V while driving - I'd expect 13+. Other times it will climb to 13V and stay there.
I haven't had the alternator or chassis batteries checked, maybe that's the first thing to do. It just seems like they're capable of the load, but maybe there's a relay or something that isn't allowing the alternator to charge?
Yes, first thing you need to do is troubleshoot the alternator, battery isolator and wiring to chassis battery. Could be nothing more than a loose connection, but you need to pull out your voltmeter and confirm.
1. Congrats on your new-to-you 2007 model Nimbus. I'm sure it is a beautiful coach.
2. If you can run
two roof air conditioners while driving,
with the generator off, your coach must have a
substantial battery bank and one (or two?) powerful inverters! You may even have dual alternators? I suspect your electrical system is a bit more complicated than the ones we normally encounter on our older model coaches. Do you have solar panels on the roof?
3. Regardless of the sophistication of your electrical system, you are correct that seeing 12 or 12.1 volts on the dash gauge is troubling. Even 13 volts is rather low. I think I am safe in saying that most Forum owners, under normal conditions, will see 14+ volts on the dash voltmeter whilst cruising down the road. This is the level of voltage required to properly charge a "12 volt" battery. If you have lithium batteries in your coach, they may have slightly different charging voltage requirements, but it will still be in the 14+ volt range.
4. So, as Brett stated, start with basic troubleshooting.
A. Is alternator (or alternators) producing voltage? What is the voltage reading at alternator B+ output post (with engine running)?
B. Where does the alternator send the voltage? Do you have a battery isolator, or some sort of VSR (voltage sensitive relay) that directs charging voltage to the two battery banks?
5. Let us know the answer to question 4.A. and 4.B. (above) and we can go from there.
6. Do you have a schematic of the 12 volt system on your coach? Hopefully you do, as it is a great troubleshooting aid.
Do you have anything that can read the engine codes? That could help too.
Thanks for the info!
1. Yes, I do think she's beautiful.
2. One solar panel, not sure that it does much.
4A. I started the engine and it showed 13V at the dash. I went back to the engine compartment and pulled voltage from the alternator: 14.2V. I went back to the dash and it was about 12.6/12.7V. You mentioned the B+ post - I'm not completely sure which that is, but I pulled voltage from the post with the biggest wire and grounded to the alternator housing. In the pic, I pulled voltage from the post the arrow points to
4B. I have a battery isolator in the engine compartment.
6. Yes, I have schematics, I'll see if I can make sense of it. Still trying to take it all in, ya know?
@kgrover - I don't have anything to pull codes, but I'd be willing to get a scanner.
Go to the battery isolator.
Center lug is from Alternator B+ terminal.
The outer lugs go to the respective battery banks-- house and chassis.
Voltage at the chassis battery lug with engine running and around 1,100 RPM should be in the 13.2-13.5 range.
Center lug should read about .7 VDC more than that.
Let us know what you find.
Please provide a better (sharper) photo of the alternator back side (wiring terminals) and alternator top side (data plate).
It helps if we know exactly what model alternator you are working with.
I am having a similar issue, although it appears to be intermittent. Had the coach out for a short trip and the check engine light came on. The Silver Leaf reported a code of 167 Alternator Volt/Low.
I headed back to storage with the generator on and part way back the check engine light went out as the dash voltage gauge showed higher voltage.
Got home and checked my go to source for information.....this forum!
Went back to storage a few days later, fired up the coach and no check engine light. When I checked the voltages I got what I expect were normal readings:
Alternator: 12.41
House Battery Post at the Isolator: 13.11
Coach Battery Post at the Isolator: 13.13
Alternator Post at the Isolator: 12.69 (this was checked a few minutes before the voltage at the alternator was checked)
With no check engine light or error codes on the Silver Leaf the readings were about what I expected.
All connections appeared to be sold, clean and rust free. I didn't check the battery post connections.
Any additional thoughts on diagnosing an intermittent low voltage issue?
NOPE, not good.
With engine running as at least 1,100 RPM, the center post of the battery isolator (same for alternator B+ lug) should be a full volt higher than your reading (about .7 VDC higher than the batteries read).
Brett,
Thanks for straightening me out. Does that point toward an alternator issue?
Tom and Lisa,
Your alternator B+ output (big red) cable connects to the INPUT post on the battery isolator. The isolator sends charging voltage to the ENGINE and COACH battery banks. Since the alternator is not connected directly to either battery bank, it cannot "see" the voltage on the batteries. With no reference voltage available, the alternator cannot self-regulate its output. Foretravel solves this problem by fitting its coaches with a DUVAC modified alternator. A DUVAC alternator
in most cases has two "extra" connection terminals on the back. One is called EXCITE and the other is called SENSE. The EXCITE terminal is wired to a source that is
only hot with ignition key ON. The SENSE terminal is wired to a source that is
always hot with ENGINE (start) battery voltage. Using the SENSE wire connection the alternator can "see" the voltage on the ENGINE battery bank, and will automatically adjust its output to properly charge the ENGINE battery bank. This same charging voltage is also sent through the isolator to the COACH batteries.
Your alternator is turning on, so the EXCITE wire is working. Your alternator is
not putting out correct charging voltage. One possible reason would be a disconnected or broken SENSE wire. You will need to locate the SENSE wire on the back of the alternator and make sure it is properly connected to a ENGINE battery voltage source. Search the topic DUVAC on the Forum for many detailed posts on this subject.
...hours pass, food consumed...
When the dash reads 13.0V with engine running at idle, the left post (house?) reads 13.5V, middle (alt) 14.1, and right (chassis) 13.2V.
Brought RPM up to 1100, chassis still at about 13.0V
Here's a better image of the alternator, looks like model number is 102200.
102200 is the voltage regulator model number. It says "replaces" on the tag which indicates a generic clone. Should be another tag somewhere on the alternator body showing the alternator model.
See my post above (Reply #10) about DUVAC alternators. Check the two small wires on the back of your alternator. One should be hot only with ignition switch ON. The other should be always hot and read the same voltage as you get at the ENGINE start battery positive post.
I keep looking at the photo of your alternator and thinking it doesn't look "right". Even if it is a clone of a real Leece Neville model, it should have the same cable connections. All the photos I have seen of Leece Neville DUVAC alternators connect the positive B+ output cable to the big post on the right side of the case. The big post on the left is for the negative ground cable. In your photo the red output cable is on the
left post and there's no ground cable. See photos in link below (Reply #17):
Alternator, Isolator or both? (https://www.foreforums.com/index.php?topic=43830.msg442251#msg442251)
Looking at those isolator voltage readings...is the generator on or are you plugged into shore power? Boost switch on?
Ah - I was on shore power (boost not on). ::)
I disconnected from shore power, started the engine, ran up to 1100 RPM and the right post (chassis) was 12.7 while the center was 13.5. Dash gauge was high 12s.
Of the small posts, the left is always-on hot at 12.4V (same as positive terminal on jump post). With the ignition set to ON, the right post gets 11.0V.
I tested continuity across the large right post (that has no wire) and it measure 35 ohms to ground, so maybe the main posts are backwards compared to the Leece-Neville??
Alternator is aftermarket, Wilson model 90-04-7059 12V 3421.
I know nothing about Wilson alternators, so I can't advise you in this case. The voltage reading would seem to indicate that the alternator is not seeing a SENSE signal, because the output voltage is too low. It is possible that the two small wires are reversed, but I wouldn't try swapping them because you might blow the regulator. You really need to find a wiring diagram for the Wilson alternator, but I'm not having any luck with that.
Here is a simple experiment you could try without danger of smoking anything. Move the cable that runs from the alternator to the center post on isolator over to the ENGINE battery post on the isolator. This bypasses the isolator internal diodes and connects the alternator directly to the ENGINE battery bank. Start the engine and take a reading at the alternator B+ outpost post. See if the voltage goes higher than the 13.5V you have been getting so far.
I found two online listings for the same model Wilson alternator. They have good photos of the wiring connection labels. According to the photos, the LEFT small post should be the ignition EXCITE connection, and the RIGHT small post should be the DUVAC SENSE connection. This is exactly the
opposite as the way your alternator is wired. Up to you if you want to try swapping the wires.
Also, looks like either the left OR the right large posts can be used for alternator output. Strange setup...
90-04-7059 (https://www.bbb-cv.com/wilson/90-04-7059/product/90-04-7059)
WILSON 90-04-7059 ALTERNATOR (https://www.filterspro.com/WILSON-90-04-7059_p_1906671.html)
Try Chuck's experiment in reply #15. That would be a good time to also clean up the connections on the isolater.
I'm not sure I'd trust the accuracy of the dash voltmeter. I'd only consider it "in the ballpark".
I don't have enough slack to move the center post to the chassis side. Electrically, it would be the same to move the chassis to the center?
I'll check out the links on the Wilson, maybe wait to see if anyone else chimes in.
@Dave - I don't want to put all my faith in the dash gauge either, but I don't want to listen to it alarm or unplug it either.
As soon as I touch the chassis wire to the center post, I get sparking, a fan kicks on in the engine compartment, and my low air alarm activates - like it's going through the ignition on sequence.... keep going?
No, stop and let's figure out what's happening.
Is there anything else, besides the alternator cable, connected to the isolator center post?
No, just one thick wire on the spade/post connector.
The chassis post has a couple wires on it - one similar in size to the alternator cable, then one a bit smaller.
Here is my armchair remote diagnosis guess:
IF the two small wires on the alternator are reversed, then you have the ignition EXCITE wire connected to the DUVAC terminal. The DUVAC terminal is electrically connected (inside the regulator) to the big output post on the alternator. When you connected the chassis battery cable to the center isolator post, that sent full chassis battery bank voltage back through the alternator cable to the alternator output post, and from there it went through the small EXCITE wire all the way back to the IGNITION solenoid. This would have the same effect as turning the ignition key to ON, and would most likely quickly melt a wire somewhere in the circuit.
Which further supports that the small post wires are reversed, no?
My schematic shows that the small wire on the chassis post goes to a 15A rectifier (?) which then goes to the DUVAC post. Give me a couple minutes and I'll mark up the schematic.
The 15A device in your diagram is probably a auto resetting circuit breaker.
DUVAC trace (1 is the isolator, 2 is the circuit breaker)& Wilson pic showing IGN and DUVAC
If my theory is correct, yes, having the small wires reversed on the alternator could cause what you observed.
Do you think there's a less risky way to switch them (ie, only connect one)?
I can't think of any other way to test. Both EXCITE and SENSE wires are required in order for the alternator to function properly.
The ignition wire is only hot with the key on and the sense wire is hot all the time.
Your diagram shows two alternators. Does your Nimbus have dual alternators?
Just one alt - the diagram shows options (dotted lines) for different models: 160A for Nimbus, 200A/270A for Phenix
Switched the wires and started it up, dash shows 13V, 13.4 at the chassis on isolator, 14.2 on alternator post. Didn't see any magic smoke escape. I think it might be good...
Better - I believe the wiring is now correct. Go have a cold one! :thumbsup:
PS: When your batteries are pulled down a bit (discharged) you could see a lot higher voltage on the isolator center post. You might see over 15 volts at times - this is fine. It can take well over 14 volts (at the battery post) to recharge a depleted 12 volt battery bank, and the center post (on a diode isolator) always runs about 0.7 volts higher than the battery posts.
Holy cow - such a small detail - I would never have been able to troubleshoot that on my own. Thanks for your help, hopefully I can pay it forward soon! Beers on me at the next campground! 8) 8) 8)
The Winter 2024 issue of MotorCader included an article in the Service News discussing the issue of intermittent low voltage. The author, Mark Crick, stated that the isolator may be the issue and to test by checking for voltage between the "center post" (alternator post based on my coaches wiring diagram and the markings on the Cole Hersee Co. No.48160 Battery Isolator) of the isolator to a ground. If there is voltage, that points to an issue with the isolator, probably a diode failure.
Sure enough there was ~13 volts.
In anticipation of this I purchased a Victron Argofet 200-2 battery isolator.
The wiring diagram for my coach shows an an Ignition Exciter wire going from the alternator to wiring that is energized when the ignition switch is on.
My question is the Victron unit has an "optional energize input" can that be ignored and use the input, output 1, output 2 and ground consistent with the existing wiring?
IF your alternator is working correctly with the old isolator, then you can ignore the "optional energize input" on the ArgoFET. Hook the new isolator up just like the old one. Leave the alternator wiring alone - do not change anything. The "energize input" on the ArgoFET is only required if you convert to a Delco alternator. See the post by prfleming (linked below) if you want more info:
DelcoRemy 28SI alternator (https://www.foreforums.com/index.php?topic=30873.msg269451#msg269451)
Some progress. When I got to the coach today, set high idle and checked voltage at the alternator and the alternator post on the isolator both readings were approximately 12.5 volts. At that point I started investigating the sense wire. On a wild guess I checked continuity across, what I believe is a fuse or auto reset circuit breaker. Circled in blue in the attached picture:
No continuity....when measuring ohms with my Fluke 117 it should OL. I started to take it out and naturally it fell apart....one post came out.
I do not know how to determine the size of the circuit breaker. I had a 15 amp, so I installed that. Set fast idle and bam 14.2 volts at the alternator and center post of the isolator.
I shut everything down, buttoned it up, put all the tools away and fired it up. I backed it out and suddenly got the check engine light and the Silverleaf gave me the same low alternator voltage.
Unfortunately I was too tired to tear it all apart again. I will leave that until tomorrow.
Any suggestions as to how to figure out the appropriate size of the auto reset circuit breaker, if that should have gone south again?
If it didn't go south any thoughts about how to continue troubleshooting?
I did not install the argofet isolator because I thought I had figured out the problem.
The sense wire normally does
not carry any significant amperage. A 15A circuit breaker should be fine. In many cases, there isn't
any type of circuit protection provided on the sense wire.
If you continue to see that breaker opening, that would tell me that something is wrong inside the alternator voltage regulator, which is causing an abnormal current draw from the isolator battery post back to the alternator.
Something like perhaps a intermittent dead short.
Reference your questionable circuit breaker - there are three possible types. See link below:
Bussman Automotive Circuit Breakers - Wiring Products (https://wiringproducts.com/collections/bussmann-short-stop-circuit-breakers)
This is an old thread but I wanted to bring it to a true close. To save you from reading everything that transpired above - I had an issue with low voltage from my alternator that would intermittently cause a check engine light until the voltage rose again.
My alternator was an aftermarket Wilson DUVAC 200A and we found that the sense and ignition wires were switched. That helped the situation, but I would occasionally see CEL and my voltage never was very high per my dash voltmeter. I'd see 13.8V at my center lug on the isolator and 13.1 at the battery lugs. I had O'Reilly test the alternator and it showed a bad voltage regulator.
I didn't think it was truly bad - it was charging, just not charging at a high enough voltage. So, I bit the bullet and bought a Leece Neville since that's what came with the coach. I found a brochure in my paperwork and determined I should get the 4884JB. The thing I found interesting is that brochure listed the value for Voltage Adjustment as +1.0V.
That's when it clicked - these DUVAC alternators need a voltage offset to account for the drop across the battery isolator. I swear I came across a way to change the offset voltage on the regulator - but that would make sense to be the culprit to my charging woes.
Tonight I swapped out my alternator with the new one. Dash voltage is now excellent! Over 14V - I've never seen a value that high.
I'll hold onto the Wilson, maybe consider seeing if I can adjust the regulator get it replaced. I'll keep in tucked away in a compartment with my 41188 hydraulic pump, extra belts, fuel filter, and whatever else I add to The Kit.
The purpose of the "sense" connection on a DUVAC alternator is to ensure that the alternator output voltage is high enough to correctly charge the start battery bank. If the sense wire is connected to the start battery bank (or another spot that reads start battery voltage) then the alternator
should automatically output whatever voltage is required to properly charge the start battery bank. The fact that there is a voltage drop across the isolator diodes then becomes irrelevant.
Interesting - so maybe my old regulator was bad afterall.
What is function of the regulator set point voltage and voltage adjustment specified here?
Seems (to me) self explanatory.
1. The standard 4884JB regulator set point is 14 volts.
2. If, for some reason, 14 volts is insufficient then the set point may be increased by (up to) 1.0 volt.
Voltage Set Points | Smith Co Electric (https://smithcoelectric.com/blogs/tech/voltage-set-points)
And, that is perfect, as long as the SENSE WIRE goes to the chassis battery side of the diode-based battery isolator. That has alternator output around 14.6 (and should measure that at the center lug of the isolator which comes from the alternator B+).