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Old 10-14-2021, 04:20 PM   #1
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Diagnosing potential alternator issue

So the last time out I noticed that the voltage gauges were reading a little low at the dash. By gauges I mean the dash gauge, the ScanGauge D, and two others at the dash.

The readings started around 12.4 and then dropped during the drive to around 11.5. However, the next morning the reading at the rear compartment read 12.4. The posts under the windshield read 12.2.

Running the Cummins did not changes those readings. The coach drove fine and behaved as it should.

So what should be my plan to diagnose the issue? Does the alternator have a direct path to the battery bank? I know it doesn’t to the dash. So what/where should I be checking?

Oh the batteries are Interstate AGM’s. I do not know the age of them. Oddly enough it was not marked on the top of the batteries.

I plan on looking into this, this weekend. Thanks

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Old 10-14-2021, 06:18 PM   #2
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to find the date on your batteries: https://itstillruns.com/manufacture-...s-8192048.html
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Old 10-14-2021, 06:47 PM   #3
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If you have a diode type battery isolator, the alternator output goes to that. It then splits to both battery banks.

If you have an isolation solenoid, the alternator output goes directly to the chassis battery bank, often times to the battery cable on the starter.

Check belt tension, the wire connection on the back of the alternator and on the isolator, if equipped.

Measure for battery voltage on the large terminal of the alternator, if isolation solenoid equipped. If not there, it needs to be.
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Old 10-14-2021, 07:43 PM   #4
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Ok here the easy way.
I assume you have a volt meter. If not, get one, because it’s like living without a thermometer in your house lol.
Now set it to DC Voltage and place the probes on the positive and the negative of the battery.
Let’s say your chassis battery reading is 12.8V … ok great just take note of whatever it reads.
Now without removing anything have someone start your engine.
Within one minute the reading of 12.8V (our example) needs to go up. It will probably not go right away to 14V but eventually will make it there as the state of charge of your chassis battery comes up to the supplied alternator voltage (usually a tad above 14V).
So … if the voltage fluctuates a bit up and down in the beginning that is normal as some high amp consumers of the engine are supplied I.e. grit heater.
If the Voltage does not increase but will be down from your initial reading after about 2 min your alternator is not charging.
Hope this helps.
Jörg.
PS: yes it does make a difference if you have a diode controlled battery isolator but my example will still apply.
And if the voltage fails to increase report back and we can go the next step.
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Old 10-14-2021, 08:06 PM   #5
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Quote:
Originally Posted by twinboat View Post
If you have a diode type battery isolator, the alternator output goes to that. It then splits to both battery banks.

If you have an isolation solenoid, the alternator output goes directly to the chassis battery bank, often times to the battery cable on the starter.

Check belt tension, the wire connection on the back of the alternator and on the isolator, if equipped.

Measure for battery voltage on the large terminal of the alternator, if isolation solenoid equipped. If not there, it needs to be.
This^^^^
Sounds like no alternator output to the batteries. Normal alternator charge output voltage should be around 13.8vdc with no load and reasonably charged good batteries.
I believe your 03 still uses a diode style battery isolator. The center cable should be alternator output. Ours went kaput once. A temporary fix was to move the chassis battery cable over and pair it together with the alternator cable at the isolator until we found one in Missoula. Fluke meter, don't leave home without it!
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Old 10-15-2021, 05:20 AM   #6
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Diode style battery isolater. The 2 small wires are from the echo charger.



This is how my coach was wired in the battery compartment. Note that I added buss blocks - Western RV puts all the cables on the battery posts. Your coach should charge from the alternator when the engine is running. The batteries charge from the inverter/charger when on shore power or generator. The echo charger/isolater allows both the coach and the house batteries to be charged in each power source.


The illustration below shows how the power works in my 2001. Your coach may be different. Your issue might be caused by any one of several components. I agree that the alternator is the most likely culprit. The cables or cable connections are another. The diode battery isolater as mentioned in a post above. The batteries could be bad. There may be other pieces and parts too, but I would clear the big ones first. A multimeter/voltmeter helps. The meters work best if you know what you should see when you read voltage. Some basic electricity knowledge is necessary. Electricity can hurt you, even low voltage DC. Doing the wrong while working thing can damage components and multiply your problems. A mobile RV tech is a good solution to electrical problems if you are new to working on these kind of issues.



The first thing I would do is verify that my alternator is putting out charging voltage (13-16.0 volts - 13.6-14.0 is normal). Then I would verify that the charging voltage is reaching the batteries. Then I would verify that the batteries are good.
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Old 10-15-2021, 07:02 AM   #7
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If you have the diode-based isolator as in the post immediately above, diagnosing the issue is very simple.


With engine off, the two outer lugs should read battery voltage-- one to chassis, one to house. The negative voltmeter probe to any clean metal= chassis ground.



With generator off, shore power disconnected, start engine and raise engine RPM to around 1,100.


Now, check voltage again at the isolator.


Center lug is from alternator and should read about .7 VDC HIGHER than either outer lug.



Please post what readings are for center and two outer lugs.
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Old 10-15-2021, 07:43 AM   #8
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Thanks All

I will be working on this issue this weekend. I do have a digital multimeter.

With the information that all of you provided, I will post up better testing results over the weekend.

I am pretty sure I did see the diode style isolator that was pictured above. I also know I have an Echo Charge system installed.

Mike.
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Old 10-15-2021, 07:51 AM   #9
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Mike,


With the diode-based isolator, you will have a DUVAC alternator. There will be a small wire to the SENSE terminal of the alternator. The purpose of the sense wire/terminal is to tell the alternator exactly what the voltage is on the chassis battery side of the isolator. That automatically raises alternator output voltage to compensate for the loss across the diodes in the isolator.



It goes to the chassis battery side of the isolator-- can connect to any place that reads chassis battery voltage.



It is a small gauge wire and as suggested, is there to sense voltage, not convey charge. Just a good idea while you are in there to make sure that wire is not broken, poorly connected, etc. Any problem with it and the alternator is "stupid".
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Old 10-16-2021, 03:50 PM   #10
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Alright here are the voltage readings. Klein multimeter

All of these were taken on the chassis batteries

Batteries nothing running 12.7
Batteries main engine running 12.5 - this is after a couple of minutes
Batteries with generator running 12.9

House batteries generator running 13.4

Pictures. The last picture is of the rear of the alternator. Discoloration of the left connection
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Old 10-16-2021, 04:04 PM   #11
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Quote:
Originally Posted by wolfe10 View Post
If you have the diode-based isolator as in the post immediately above, diagnosing the issue is very simple.


With engine off, the two outer lugs should read battery voltage-- one to chassis, one to house. The negative voltmeter probe to any clean metal= chassis ground.



With generator off, shore power disconnected, start engine and raise engine RPM to around 1,100.


Now, check voltage again at the isolator.


Center lug is from alternator and should read about .7 VDC HIGHER than either outer lug.



Please post what readings are for center and two outer lugs.
I did not get a voltage reading on the center lug. (Negative probe on chassis battery negative post)
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Old 10-16-2021, 04:22 PM   #12
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Quote:
Originally Posted by Astasoftride View Post
I did not get a voltage reading on the center lug. (Negative probe on chassis battery negative post)

You should be able to physically trace that large gauge wire from the alternator B+ terminal to the center lug of the diode-based battery isolator.


Clearly, alternator charge is not reaching the batteries. And, its "first stop" is the center lug of the isolator.
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Old 10-16-2021, 04:32 PM   #13
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Quote:
Originally Posted by andy29847 View Post
Diode style battery isolater. The 2 small wires are from the echo charger.
This is how my coach was wired in the battery compartment. Note that I added buss blocks - Western RV puts all the cables on the battery posts. Your coach should charge from the alternator when the engine is running. The batteries charge from the inverter/charger when on shore power or generator. The echo charger/isolater allows both the coach and the house batteries to be charged in each power source.


The illustration below shows how the power works in my 2001. Your coach may be different. Your issue might be caused by any one of several components. I agree that the alternator is the most likely culprit. The cables or cable connections are another. The diode battery isolater as mentioned in a post above. The batteries could be bad. There may be other pieces and parts too, but I would clear the big ones first. A multimeter/voltmeter helps. The meters work best if you know what you should see when you read voltage. Some basic electricity knowledge is necessary. Electricity can hurt you, even low voltage DC. Doing the wrong while working thing can damage components and multiply your problems. A mobile RV tech is a good solution to electrical problems if you are new to working on these kind of issues.



The first thing I would do is verify that my alternator is putting out charging voltage (13-16.0 volts - 13.6-14.0 is normal). Then I would verify that the charging voltage is reaching the batteries. Then I would verify that the batteries are good.
I love wiring diagrams and illustrations, they help with problem solving.

But I noticed a few errors when comparing yours, namely:
- your 'buss blocks' should be shown in the diagrams.
- your chassis disconnect is identified in different locations
- yer HWH and solar are not shown in the 2nd illustration,
- chassis batt disc not shown but house batt disc is.
Need I list more? I do have to ask why the chassis battery disc is where it is... it only disconnects the alternator charging?
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Old 10-16-2021, 05:35 PM   #14
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Originally Posted by OldWEB View Post
I love wiring diagrams and illustrations, they help with problem solving.

But I noticed a few errors when comparing yours, namely:
- your 'buss blocks' should be shown in the diagrams.
- your chassis disconnect is identified in different locations
- yer HWH and solar are not shown in the 2nd illustration,
- chassis batt disc not shown but house batt disc is.
Need I list more? I do have to ask why the chassis battery disc is where it is... it only disconnects the alternator charging?
Thanks for the feedback. I can't see, type, or proof read, so I oftem make embarassing mistakes. In this case, the mistake is I posted an early version of my drawing, not the finished version (I think). I made this early drawing when I was planning to add the buss bars. Here is the drawing I should have posted:



About the chassis battery disconnect - the drawing is intened to be a representation of the battery compartment. Wire(s?) to the field side of the disconnect are not shown. I htink there is one wire that goes through a fuse and then to the cab positive post. About the solar - I have removed that from my coach, so I didn't show it on my drawing.

I felt like I needed a drawing for my project because the factory drawing seemed to have many errors. Since you love this kind of stuff, here is the factory drawing where I tried to correct some of the errors. It is damn hard to read.



The HWH system is not shown on the illustration because I didn't see it as part of the power system.
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