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Big Boy or Alternator?


rpasetto
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I've been noticing that the voltage, as displayed on the dash gauge, the Alladin, and my VMSpc, seems to be getting lower.  A few months back it was in the 13.6 to 13.8 range, but in my last trip it seems to be showing lower, down in the low 13's.  As I was driving I noticed once in a while down at 13.0 to 13.2.

Does this indicate problems with the BigBoy? ... or Alternator? ... or something else?  Where do I start diagnosing?  

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The voltage will be lower if there are devices that are consuming battery power.

Or if the batteries aren't fully charged (they are then the ones consuming the charge voltage).

Diagnoses starts by ensuring no devices are On

Then check the battery water level (if serviceable).

Check the voltage at each battery when they are disconnected from the system to see if one coach battery is getting weak compared to the others.

Check the voltage output from the charging circuit.  Sorry, I don't know what a "BigBoy" is.  Is that a nickname for the charger/ invertor?

You might find that there is nothing wrong.

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I'm assuming you are talking about chassis battery voltage since you mention dash & VMSpc.  Aladdin shows both chassis & house.  It is doubtful that it is the Big Boy, as it only fictions to connect the two battery sets together.  Since you are driving, and looking at chassis voltage, the Big Boy is unlikely the problem.  That leaves the alternator or the chassis batteries. This also assumes you don't have some unusual load on the system that want there when comparing readings before.  First, turn off all accessories, blowers, lights, etc., then with the engine running, measure the voltage as close to the alternator output as possible.  This may be the chassis battery itself.  This should be above 14.0 (typically 14.2 - 14.4) VDC.  Measure to a good ground and also across the battery itself.  The readings should be the same. If you get over 14.0 VDC, then the alternator is likely good.  You can confirm by adding a load, headlights as example, and the voltage, at the battery, should remain fairly constant.  If you don't have 14.0 VDC at the chassis battery, I'd do a load test on the batteries first (usually the easiest) to ensure the batteries are good.  If they are good, next I'd test the alternator. There is a procedure to test on the vehicle, if you have good access to the alternator (no rear radiator).  Some find it easier to remove the alternator and take it in for testing.  

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Thanks for the advice.  After pouring thru wiring diagrams I learned that the alternator directly connects to the chassis batteries; the Big Boy doesn't get in the way.  (This was unlike my previous 03 Dynasty which had a diode-type isolator between alternator and battery banks.)  My 05 Sig Wiring book shows only two connections, one direct to chassis batteries and the other ground.

image.png.1c5be4a0951e0f964c0124c0703c5a13.png

 

Looks like my next step is some testing voltages, although I am becoming increasingly suspicious of the alternator.  Toughest thing in removing that will be to move the belt tensioner which looks like it's made to be moved using a 3/4" drive breaker bar which I don't have.

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I think my old Cummins used a 1/2" breaker bar - I say that because I don't have a 3/4" breaker bar.  I may have found another way around it, but don't recall it being a show stopper.  That was a 325 in my old Dynasty.  Please take pictures and mark the wires.  I can't tell you how many mechanics have reconnected them wrong. 

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7 hours ago, DavidL said:

The voltage will be lower if there are devices that are consuming battery power.

Or if the batteries aren't fully charged (they are then the ones consuming the charge voltage).

Diagnoses starts by ensuring no devices are On

Then check the battery water level (if serviceable).

Check the voltage at each battery when they are disconnected from the system to see if one coach battery is getting weak compared to the others.

Check the voltage output from the charging circuit.  Sorry, I don't know what a "BigBoy" is.  Is that a nickname for the charger/ invertor?

You might find that there is nothing wrong.

 

5 hours ago, waterskier_1 said:

I'm assuming you are talking about chassis battery voltage since you mention dash & VMSpc.  Aladdin shows both chassis & house.  It is doubtful that it is the Big Boy, as it only fictions to connect the two battery sets together.  Since you are driving, and looking at chassis voltage, the Big Boy is unlikely the problem.  That leaves the alternator or the chassis batteries. This also assumes you don't have some unusual load on the system that want there when comparing readings before.  First, turn off all accessories, blowers, lights, etc., then with the engine running, measure the voltage as close to the alternator output as possible.  This may be the chassis battery itself.  This should be above 14.0 (typically 14.2 - 14.4) VDC.  Measure to a good ground and also across the battery itself.  The readings should be the same. If you get over 14.0 VDC, then the alternator is likely good.  You can confirm by adding a load, headlights as example, and the voltage, at the battery, should remain fairly constant.  If you don't have 14.0 VDC at the chassis battery, I'd do a load test on the batteries first (usually the easiest) to ensure the batteries are good.  If they are good, next I'd test the alternator. There is a procedure to test on the vehicle, if you have good access to the alternator (no rear radiator).  Some find it easier to remove the alternator and take it in for testing.  

I made multiple tests today. 

  • First with the chassis batteries only and House battery bank disconnected, at fast idle 1200RPM; let it idle for a few minutes.  I get 14.1v at the chassis battery terminals but 13.8v readings at VMSpc and Alladin.
  • Next I connected the house battery bank, fast idle at 1200RPM waiting a few minutes.  Turned on headlights and the inverter with refrigerator on.  Engine battery voltage readings 14.0 - 14.1v  House batts: 13.7-13.8.  VMSpc and Alladin readings: 13.4 to 13.6
  • Next Headlights off, dropped idle to 1000RPM.  Engine Batts:  14.0 - 14.05, House Batts: 13.80 to 13.84.  VMSpc and Alladin reading 13.5 to 13.6.

Seems that the alternator and battery readings are marginal and are affected by RPM and load but not much.  The coach is new to us and I do not have records of the last time batteries were purchased.  Engine batteries are X2-Power SLI31AGMDPM, Group 31M, rated  1150 CCA.  The eight House batteries are Duracell Ultra SLI GC 115's.  Both appear to be lines sold by Batteries plus.  The old invoice which I did find in the coach records is from 2011 for Interstate batteries, so if those were kept around 5 years this set would be 4 years old.  About three months ago, I removed all cables from batteries, cleaned and reconnected; also cleaned ground and starter connection.

Maybe I missed something.  I am guessing that the easiest thing to do is to take out the two chassis batteries and have them tested... Next easiest is probably is to take the alternator to be tested... Checked the belt tensioner; it will need a 3/4" breaker bar.

 

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17 minutes ago, DavidL said:

What's wrong with those numbers?

It is puzzling, because on my last trip these were not the numbers I was getting on VMSpc and Alladin.  Voltage showing ranged in the low 13's, sometimes down at 13.0 to 13.2.  It has occurred to me that I use a charge line connected to my Jeep when I'm towing, but I've always had that.   A short run without toad in the next week or so is in the plan.

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Those numbers are what one should expect.  Yes, they do vary by RPM by design of the alternator.  I didn't want to confuse the issue by changing the RPM until I got the results.  I feel very safe saying there is nothing wrong with the alternator.  I don't see a problem with the batteries.  I'm guessing you thought there was a problem because of the remote readings.  That's why I had you check right at the batteries. I thing you have a poor connection somewhere between the batteries and where ever those devices are reading voltage.  I think it is likely a ground based on all the bad grounds reported on Monacos. Remember that tree current that makes its way via wires to the load, has to make it back to the negative terminal of the battery.  That's accomplished via a wire from the load to (usually) a point on the metal chassis.  

As far as the lowers readings you experienced, it is poisonous tag the house batteries were needing sufficient charging, but normally the Big Boy would drop them off the alternator when the voltage got that low. 

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9 hours ago, waterskier_1 said:

Those numbers are what one should expect.  Yes, they do vary by RPM by design of the alternator.  I didn't want to confuse the issue by changing the RPM until I got the results.  I feel very safe saying there is nothing wrong with the alternator.  I don't see a problem with the batteries.  I'm guessing you thought there was a problem because of the remote readings.  That's why I had you check right at the batteries. I thing you have a poor connection somewhere between the batteries and where ever those devices are reading voltage.  I think it is likely a ground based on all the bad grounds reported on Monacos. Remember that tree current that makes its way via wires to the load, has to make it back to the negative terminal of the battery.  That's accomplished via a wire from the load to (usually) a point on the metal chassis.  

As far as the lowers readings you experienced, it is poisonous tag the house batteries were needing sufficient charging, but normally the Big Boy would drop them off the alternator when the voltage got that low. 

First concern is the significant voltage differences between idle and driving down the road.  Based on the VMSpc/Aladdin values, the difference is as much as 13.8v to 13.0v.  Second concern is the ~0.4v difference between voltage readings at the engine battery and what the Aladdin & VMSpc show; both get their data from the ECM.  The latter is probably a ground issue; the former appears to be the difference between idle and Engine running under load.

Your 05 Exec probably has the same Leece Neville 270amp alternator as mine.   Do you get such a difference between engine idle and engine load? 

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51 minutes ago, rpasetto said:

First concern is the significant voltage differences between idle and driving down the road.  Based on the VMSpc/Aladdin values, the difference is as much as 13.8v to 13.0v.  Second concern is the ~0.4v difference between voltage readings at the engine battery and what the Aladdin & VMSpc show; both get their data from the ECM.  The latter is probably a ground issue; the former appears to be the difference between idle and Engine running under load.

Your 05 Exec probably has the same Leece Neville 270amp alternator as mine.   Do you get such a difference between engine idle and engine load? 

Coming in late. Here is one simple (at least to me) test(s) that you can make

Pull the leads, one will do, from the Big Boy. That takes out the entire circuit. 

Get a 50 ft spool of #18 Line Cord (extension cord wire). Use alligator clips or put ring terminals on one end. Put that across the Positive and Negative of the Chassis Battery. Run those lead out of the battery box up to the closest window and into the motor home and pull them up front. Use painter's tape to hold the wires to the side of the MH. NOTE WHICH LEAD IS NEGATIVE (or test it).

Hook up (alligator clips) a VOM to the leads. Now DRIVE it and test it and note the voltages as you drive compared to the dash and the VMSpc. I THINK that you will see a difference of about 0.2 VDC (Lower) on the dash. That is the case with my Magnum remote. The remote always reads 0.1 - 0.2 less than the actual battery voltage.

OK...make all your readings at idle and on the highway and such.

NOW...remove the alligator clip from the line cord NEGATIVE.  Find the GROUND wire (incoming) to the MVSpc. Use a pin or tap into it. REPEAT THE READINGS. If you have a BAD ground, then that should show there. 

A lot of folks have run a new or supplemental ground from the DASH Ground (you can see it, usually, if you pull the dash top panel) INSIDE to the Chassis Stud outside. Typically, Monaco had a Ground Stud on the Firewall on the ROAD side. If you open the Genny and peer in from the Road Side, look directly UP from the side (road) of the Genny Cabinet.  There is a cross bar or the frame about 2 feet up. If you look on that frame member, maybe a little to the right...say a foot, you will find a Chassis Stud there. Mine has TWO Green (#8?) leads which are the Dash Grounds. 

NOW, if you want to test, then reconnect the Big Boy. MEMORY says that when the House Batteries are down and the Magnum is pumping 95 Amps and in Bulk Charge, then the dash will read north of 14 VDC...maybe 14.2 or so. It helps to have someone read the Magnum. Whatever the voltage is on the Magnum Remote, I THINK that the Dash will read about 0.1 - 0.2 higher. I KNOW that when I turn on the Genny for AC in the summer, that the Dash voltage goes HIGHER as the Genny is charging the House and the Big Boy locks them in place.

You can also test the Big Boy by having LOW house batteries and having the Genny running.  Push the Battery Boost. If the Dash Voltage changes, then BINGO, the Big Boy is NOT engaged.

Hope this helps...

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@Tom Cherry:  Thanks for the testing suggestions.  I found  "spare cable" in my WD book which I need to check out.  The diagram shows a few wires already going from under dash to the rear of the coach ao I need to find two that are working to hook up a VOM to watch while I drive.

@ Rick N:  Thanks for your reminder about Monaco bad grounds and suggestion about taking pictures of the generator.

image.png.33aa4c5efc3cdf44438dbf3fc0e492a0.png    image.png.16496e68108ab8b1c7340cb97b5fd50e.png  

I think the next step will be to unbolt the two big cables, + and -,  and clean them.  But there are 2 small wires also which I am not clear about.  Could it be one is an "excite wire? Just a guess;  the other for voltage output to the ECM?  I have no clue here and the Monaco WD book didn't help in this case since the print from the WD book (below) shows only the + and - connections. I'll appreciate it if anyone has a more detailed diagram for this.  Based on the other diagrams in the WD book I think I need to disconnect batteries, not just flip the switches.

image.png.a5493676e656318c402b95d5276c1116.png

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5 hours ago, rpasetto said:

First concern is the significant voltage differences between idle and driving down the road.  Based on the VMSpc/Aladdin values, the difference is as much as 13.8v to 13.0v.  Second concern is the ~0.4v difference between voltage readings at the engine battery and what the Aladdin & VMSpc show; both get their data from the ECM.  The latter is probably a ground issue; the former appears to be the difference between idle and Engine running under load.

Your 05 Exec probably has the same Leece Neville 270amp alternator as mine.   Do you get such a difference between engine idle and engine load? 

I don't know where the Aladdin gets its voltage sample from.  I've gone through all my wiring diagrams, and can't find anything, but I don't have a diagram for the ECM.  The wiring diagram shows the dash voltmeter does not get its sample from the ECM.  

If you monitor the difference, you might find it easier to just add 0.5 Volts to the dash and Aladdin mentally, assuming all else is working. 

5 hours ago, rpasetto said:

First concern is the significant voltage differences between idle and driving down the road.  Based on the VMSpc/Aladdin values, the difference is as much as 13.8v to 13.0v.  Second concern is the ~0.4v difference between voltage readings at the engine battery and what the Aladdin & VMSpc show; both get their data from the ECM.  The latter is probably a ground issue; the former appears to be the difference between idle and Engine running under load.

Your 05 Exec probably has the same Leece Neville 270amp alternator as mine.   Do you get such a difference between engine idle and engine load? 

Forgot to answer about voltage vs engine RPM.  Yes, the voltage will increase up to about 1400 RPMs.  All alternators work this way and that does not indicate a problem.  I think your real problem has to do with the intermittent voltage drop with will be hard to find since it will have to be acting up to troubleshoot.  That is not a common failure mode of alternators. 

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5 hours ago, waterskier_1 said:

I don't know where the Aladdin gets its voltage sample from.  I've gone through all my wiring diagrams, and can't find anything, but I don't have a diagram for the ECM.  The wiring diagram shows the dash voltmeter does not get its sample from the ECM.  

If you monitor the difference, you might find it easier to just add 0.5 Volts to the dash and Aladdin mentally, assuming all else is working. 

Forgot to answer about voltage vs engine RPM.  Yes, the voltage will increase up to about 1400 RPMs.  All alternators work this way and that does not indicate a problem.  I think your real problem has to do with the intermittent voltage drop with will be hard to find since it will have to be acting up to troubleshoot.  That is not a common failure mode of alternators. 

I was wrong about the Aladdin.  I couldn't find it in my Wiring Diagram book either, probably the same diagrams as yours for the most part.  I made a bad assumption that Aladdin gets voltages from the ECM, like VMSpc which plugs directly into the diagnostic connector to get ECM data.  I did find a passage in the Aladdin Troubleshooting book which says: "DCI (DC Interface) - Module measures voltage and current of the house batteries and solar panels. Location: On the module board in the cargo bay area."  So it seems the Aladdin DC interface is picking up voltage readings from wiring somewhere.  but I made enough bad guesses.  (By the way If you don't have that Aladdin Diag book I'll email it to you).

So if I understand correctly, at road speed, the alternator should be producing its max voltage output, internally regulated, I think, to around 14.0 to 14.2v.  I am think that the voltage drop which occurs going down the road may be related to load on the alternator so my next step is to clean those terminals pictured in the earlier post.  

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