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01-28-2025, 11:37 PM
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#1
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Senior Member
Join Date: Mar 2020
Location: Las Vegas, NV
Posts: 168
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Chassis 12V Question
Driving to an indie RV shop, I got my 1st ever "Check Engine" light on the 2005 D.S. No symptoms of trouble; pulled over, shut down and restarted .... light extinguished. Came back on a couple of miles down the road. Repeated this process 2 more times, hoping it would just go away. But it came back fairly swiftly and I drove the remaining 20 miles with a Check Engine light on. I had already checked fluid levels, and all dash panel gauge values were normal. This anomaly was added to the work list for the shop. A Cummins Insite scan revealed a charge error that the tech said could be an alternator fault or a battery issue. Some diagnostics revealed the alternator as not charging at all. The shop owner told me any recent history of no charging would have been masked by the chassis batteries drawing a charge from the house batteries, which have been continuously fed by my charger/inverter while plugged in at the home. He said that if not for the dash indication, I might have never recognized the zero alternator output until I took a long drive. Is his assessment valid? Aside from sharing a charge from the alternator, I didn't realize there could be any cross-flow from house to chassis. I'm pretty sure vice versa does not occur, because we have run the house to zero when the coach was new to us and the batteries were beyond aged-out of service. Zero energy on the house, but the mighty ISL cranked right up, indicating to me the 12V chassis batts were as separate as can be.
If chassis batteries can indeed draw from the house, I have to rethink my rationale for milking life from old batteries. I have refreshed my 4 battery 6V bank at the first sign of weakness, but I've been letting the 2 Group 31 chassis batts "ride" until they hiccup. I think now is that time, in order to play nice with a brand new alternator and simply based on age.
Just curious about how these seemingly separate purpose banks might share power. The shop owner sounds confident, but they started as a mobile truck/tractor trailer service and then branched into RVs, so I'm not totally sure about the depth of their house knowledge. Judging by the solar systems they build and a structural repair they are doing on a Northern Lite camper (total tear down with some aluminum fabrication and welding involved), there seems to be little question about their abilities.
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01-29-2025, 08:36 AM
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#2
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Senior Member
Newmar Owners Club Freightliner Owners Club
Join Date: Aug 2023
Posts: 306
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The shop is probably correct because most coaches do, but not all. You'll have to check your owner's manual to be certain or call Newmar to find out, but I would guess, yes, when hooked up to shore power, your chassis batteries are getting charged.
BTW, your alternator should be putting out about 14-volts, if it was less than that (the shop should have told you its voltage output), whether or not your inverter is charging your chassis batteries, you need a new alternator.
Good luck
__________________
'22 Newmar Dutch Star (Freightliner)
'20 Jeep Wrangler JL
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01-30-2025, 12:57 PM
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#3
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Senior Member
Spartan Chassis
Join Date: Mar 2017
Posts: 1,746
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How old are the batteries?
You didn't say how old the batteries are but, I more than a couple years old, you likely should replace them as well. When the alternator dies it will kill most likely kill older batteries. I will concur with the shop's diagnosis. Either way, the alternator needs replaced.
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01-30-2025, 06:24 PM
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#4
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"Formerly Diplomat Don"
Newmar Owners Club
Join Date: Apr 2005
Location: Moorpark, Ca.
Posts: 25,296
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Around 2005, they were just starting to install systems that charged the chassis batteries when the coach was parked and on shore power. As an example, my 2005 Diplomat did not charge both, so I added a simple system. These systems were often called B.I.R.D.s (Bi-Directional charging systems).
With that said, you need to not guess at what occurred, but simply test the alternator output, check the chassis batteries with a load tester and then determine if your coach charges both banks after the first two items are determined. Three separate things.
__________________
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2024 GMC Sierra 1500 Denali 4x4 6.2L
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01-30-2025, 06:55 PM
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#5
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Senior Member
Join Date: Mar 2020
Location: Las Vegas, NV
Posts: 168
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Quote:
Originally Posted by Rev. Roy
You didn't say how old the batteries are but, I more than a couple years old, you likely should replace them as well. When the alternator dies it will kill most likely kill older batteries. I will concur with the shop's diagnosis. Either way, the alternator needs replaced.
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Shamefully > 5 years in my estimation. Coach purchased 4 years + ago with no claim of freshness for any of the batteries. I glanced at all six and saw no telltale signs of trouble, and then relied on my PPI. Although thorough in some ways, the inspector’s clean bill of health was aided by a generally well maintained rig. But obviously he missed pulling out the battery rack. The house side was a corrosive mess! Bulging caps on two of the 6V batts and lots of white powder (not baking soda leftover from maintenance, sadly). The tray and side rails were terrible and the bearings were useless. Disassembled the whole thing, stripped and repainted everything I could. Difficult to source outside of Newmar, but I found new bearings at a specialty shop for 25% of Newmar. Four new golf cart batteries and a clean and good test of the chassis batteries. I knew their days were numbered and put replacement off too long. Never saw a slow engine turnover nor indication of poor charging, even on long drives.
New alternator installed and producing 14.4 to 14.6 volts. 12V batteries next.
Every time there’s an issue, I learn something.
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01-30-2025, 07:17 PM
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#6
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Senior Member
Join Date: Apr 2024
Location: WI Driftlesser
Posts: 2,518
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Failing batteries killing an alternator is massively overblown, and vice versa. I've never seen an alternator fail slowly, it's always been charging fine, then not. As long as you charge the battery back up reasonably soon, it should be fine. What WILL put more load on an alternator is a GOOD battery that is not charged when starting, then takes a huge amp draw. An old or failing battery will usually take MUCH LESS charge current than a new one.
I also disagree with the tech that the shore charging will mask a failing alternator. The warning lights that I've seen come on immediately when the alternator stops charging. The fully charged chassis battery would maintain 12.7v max, while it should be close to 14V with the engine running. That's assuming you have a working "battery" light with the ignition on, engine off. I don't know what voltage the ECU throws a check engine light code at.
__________________
"Bringing third world electrical work to first world luxury." RV makers of Murica!
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01-30-2025, 07:24 PM
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#7
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Senior Member
Newmar Owners Club Freightliner Owners Club
Join Date: Aug 2015
Posts: 3,316
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I believe your year may have had the Diesel2 bidirectional relay controller. It monitors the coach and activated the solenoid that joins the two banks.
https://intellitec.com/wp-content/up...ICE-MANUAL.pdf
You can take a peek in your storage bays to identify the hardware components.
I have had great success capturing the charging cycles on my coach for the house to chassis charging. My coach stays plugged in at home…but also has solar so it is charging the house even when unplugged if there is sunlight. With the motor OFF…generally, about every four hours my two banks connect…bring the chassis batteries up to the same voltage as the house whilst it is in float or higher voltage. Then the two revert to being separated. This stays that way until the chassis battery voltage slowly dissipates the surface charge…and reaches something close to 12.7 v. This varies with temperature. Then the process repeats. I haven’t really spent much time looking at the reverse..purely because I mainly drive during daylight hours…meaning my solar is charging the house even though I’m not plugged in or running the generator. We occasionally do get the two tied together while driving. Going under a bridge in a cloudy day…or my wife placing a big load in the inverter to make microwave popcorn. That usually gets the alternator tied to the house batteries.
The difficult part of these devices is catching them in operation. My solar installation included shunt based battery monitors..and I have a device with gathers data (Victron Venus GX) that hooks up to everything a records packets for later viewing. Without it…you are forced to have someone look at voltage readings…like the House and Chassis reading on our DigiLevel display. If both are reading the same voltage within a tenth of a volt..they are probably joined. If there is a split in voltage they are disconnected from one another. And if yours cycles every four hrs…you can see it can take a while to catch it in action. There are techniques to speed the connection by added loads. Turning in headlights with the engine off while the coach is plugged in… or making if popcorn in the microwave while driving down the road. These loads my sped up the frequency of the charge sharing…and make it easier to witness.
__________________
Charlie & Ronni
2016 Ventana 4037
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01-30-2025, 07:35 PM
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#8
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Senior Member
Newmar Owners Club Freightliner Owners Club
Join Date: Aug 2015
Posts: 3,316
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Here is an example of what my chassis battery voltage does during the day. This was captured while the coach is on shore power…no engine/alternator. All of the peaks are evidence the bi-directional relay has closed and is sharing the Inverter’s built-in battery charger that charges the house bank…with the chassis bank.
__________________
Charlie & Ronni
2016 Ventana 4037
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02-01-2025, 12:27 PM
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#9
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Senior Member
Join Date: Mar 2020
Location: Las Vegas, NV
Posts: 168
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Quote:
Originally Posted by C.Martin
Here is an example of what my chassis battery voltage does during the day. This was captured while the coach is on shore power…no engine/alternator. All of the peaks are evidence the bi-directional relay has closed and is sharing the Inverter’s built-in battery charger that charges the house bank…with the chassis bank.
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Nice explanation! Looking back on the scenario, as I got ready to "roll" I disconnected the 6V batteries from the house, using the factory disconnect switch, a rarely used function. In this case, I knew the coach would be void of shore power for days, if not weeks at the shop. So as I embarked on my 45 minute drive, it would have been the first time in ages the house was entirely de-powered, thus supporting the idea that house to chassis power sharing is a "thing." Never got a battery light, but the ECU picked up on something amiss. Since the engine cranked well even at the destination, I believe the 12V batteries remained healthy enough due to relatively low demands.
I concur with the assertion that the alternator failure was likely sudden, and insidious due to sharing across the banks. I will have a closer look at how the system works going forward. New alternator installed and soon, chassis batteries. Thanks again!
If you don't mind C. Martin, I'd like to PM you regarding your solar system. Going solar is on my mind, as we enjoy boondocking sometimes. Love our Onan QuietDiesel and really don't care about 2 qts. per hour of diesel, but sometimes we are proximate to other folks who probably don't appreciate our "gentle rumble." Although I'm happy with our home solar, it's not stand-alone (grid dependent), so I have a lot of learning to accomplish regarding systems with storage.
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02-01-2025, 12:36 PM
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#10
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Senior Member
Join Date: Mar 2024
Location: Bohemia NY
Posts: 1,908
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Quote:
Originally Posted by zippinbye
Driving to an indie RV shop, I got my 1st ever "Check Engine" light on the 2005 D.S. No symptoms of trouble; pulled over, shut down and restarted .... light extinguished. Came back on a couple of miles down the road. Repeated this process 2 more times, hoping it would just go away. But it came back fairly swiftly and I drove the remaining 20 miles with a Check Engine light on. I had already checked fluid levels, and all dash panel gauge values were normal. This anomaly was added to the work list for the shop. A Cummins Insite scan revealed a charge error that the tech said could be an alternator fault or a battery issue. Some diagnostics revealed the alternator as not charging at all. The shop owner told me any recent history of no charging would have been masked by the chassis batteries drawing a charge from the house batteries, which have been continuously fed by my charger/inverter while plugged in at the home. He said that if not for the dash indication, I might have never recognized the zero alternator output until I took a long drive. Is his assessment valid? Aside from sharing a charge from the alternator, I didn't realize there could be any cross-flow from house to chassis. I'm pretty sure vice versa does not occur, because we have run the house to zero when the coach was new to us and the batteries were beyond aged-out of service. Zero energy on the house, but the mighty ISL cranked right up, indicating to me the 12V chassis batts were as separate as can be.
If chassis batteries can indeed draw from the house, I have to rethink my rationale for milking life from old batteries. I have refreshed my 4 battery 6V bank at the first sign of weakness, but I've been letting the 2 Group 31 chassis batts "ride" until they hiccup. I think now is that time, in order to play nice with a brand new alternator and simply based on age.
Just curious about how these seemingly separate purpose banks might share power. The shop owner sounds confident, but they started as a mobile truck/tractor trailer service and then branched into RVs, so I'm not totally sure about the depth of their house knowledge. Judging by the solar systems they build and a structural repair they are doing on a Northern Lite camper (total tear down with some aluminum fabrication and welding involved), there seems to be little question about their abilities.
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You don't have a voltmeter on the instrument panel? That will tell you if the alternator is working or not.
__________________
Dennis
Bohemia NY
2008 Nimbus 342 SE Carlyle
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02-02-2025, 12:23 PM
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#11
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Senior Member
Join Date: Mar 2020
Location: Las Vegas, NV
Posts: 168
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Quote:
Originally Posted by d23haynes57
You don't have a voltmeter on the instrument panel? That will tell you if the alternator is working or not.
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I appreciate what you're saying, but here's my thoughts about the voltmeter; it's in a general "big picture" scan of the panel, but it does not have the same priority as more crucial items like air pressure, oil pressure and coolant temperature. I never noticed an irregularity on the volt meter, nor did I have reason to pay particular attention to it. On the day that my Check Engine light illuminated, I did not have the presence of mind to look at the gauge, although I did go straight to oil pressure and temperature. I'm guessing I might have noticed if the needle were pegged left. Remember, there were no symptoms whatsoever - just a Check Engine light.
When I shut down and restarted at the shop that was my destination, neither the tech nor myself thought to look directly at the volt meter. I'm probably predisposed to assuming an ECU does not monitor charging, but evidently it does on this ISL. I have owned or operated something like three dozen OBDII equipped cars and trucks since the system came out after 1996, and I have never seen a charge or battery-related DTC, including through multiple alternator failures and even a battery explosion. Google says OBDII can monitor such things, but I don't think it's encoded on many vehicles.
Had I looked at the voltmeter, perhaps I would have saved an Insite connection fee - we would have started with a multimeter at the source. I don't feel too bad, since even the mobile Cummins tech didn't think to consider a charging issue up front. It's all "water under the bridge" now.
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02-02-2025, 01:05 PM
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#12
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Senior Member
Join Date: Mar 2024
Location: Bohemia NY
Posts: 1,908
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If my response came across as insulting, I apologize. Now to try to be more educational.
Due to the complexity of RV or truck charging systems as simple alternator failure light is not going to be reliable. System voltage while usually not immediately detrimental is one of many conditions that should be monitored. From the condition point of view, it indicates not only that the system is functioning, but also at what level. Is the charging system keeping up will all the varying loads including house battery charging and anything connected there also. This can be very important low speeds or idling. Alternator voltage can also indicate a mechanical failure. Alternator belt failure may disable water pump and/or fan drive. Your ECU set the fault code as at some point it will not be able to reliably function with the voltage out of range. The code can also be set if the voltage goes too high. Yes that can also happen.
Some vehicles do have the ECU monitor battery voltage and current and control alternator output. Very common on vehicles with AGM batteries. Unnerving when the alternator gets turned off during long trips.
So yes, the electrical system is something that needs some level of management. Develop a good understanding of how everything interacts especially with the house battery system and related loads. Get a good multimeter, preferable with a clamp on DC ammeter. Learn Ohm's and Kirchoff's laws and how to use the meter and there won't be a DC problem you can't lick.
Dennis
__________________
Dennis
Bohemia NY
2008 Nimbus 342 SE Carlyle
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02-03-2025, 01:04 PM
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#13
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Senior Member
Join Date: Mar 2020
Location: Las Vegas, NV
Posts: 168
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Quote:
Originally Posted by d23haynes57
If my response came across as insulting, I apologize. Now to try to be more educational.
Due to the complexity of RV or truck charging systems as simple alternator failure light is not going to be reliable. System voltage while usually not immediately detrimental is one of many conditions that should be monitored. From the condition point of view, it indicates not only that the system is functioning, but also at what level. Is the charging system keeping up will all the varying loads including house battery charging and anything connected there also. This can be very important low speeds or idling. Alternator voltage can also indicate a mechanical failure. Alternator belt failure may disable water pump and/or fan drive. Your ECU set the fault code as at some point it will not be able to reliably function with the voltage out of range. The code can also be set if the voltage goes too high. Yes that can also happen.
Some vehicles do have the ECU monitor battery voltage and current and control alternator output. Very common on vehicles with AGM batteries. Unnerving when the alternator gets turned off during long trips.
So yes, the electrical system is something that needs some level of management. Develop a good understanding of how everything interacts especially with the house battery system and related loads. Get a good multimeter, preferable with a clamp on DC ammeter. Learn Ohm's and Kirchoff's laws and how to use the meter and there won't be a DC problem you can't lick.
Dennis
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No offense taken! This is a good lesson overall. Surprisingly, my very old chassis batteries are testing rather well (but they are being replaced nonetheless). They have no business being healthy! When I got home yesterday, all six batteries, house and chassis combined, had not seen a charge in about three weeks. The chassis actually had 45 min of drive time home, but the house was isolated. When activated before connecting to shore power, the house came online at 92% capacity and 13.8v and the chassis were clocking 14.5v.
As you say, more understanding and attention to all things electrical will serve me well. I acknowledge that I am a victim of fortune at this juncture. I have never lost an alternator powering anything that rolls, flies or floats without an associated battery problem (resultant or otherwise), but these aging flooded lead acid batteries react as if they have been impeccably maintained. The chassis batts predate my ownership and the house have not had electrolyte service as often as they should, and they have been run down to dead more than once. However, I would strike out on a long weekend camping trip as-is, even though new batteries are coming as soon as I have the time to take care of the installation.
The chassis are going, period. I will load test each house battery individually and make a decision based on the results. Ideally, they will have enough service left to allow me time to research and plan a solar-ready L-ion bank. Otherwise, it's time for more inexpensive Sam's Club golf cart batteries, because I cannot complain about their value-to-service ratio.
Thanks.
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02-03-2025, 03:53 PM
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#14
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Senior Member
Join Date: Apr 2024
Location: WI Driftlesser
Posts: 2,518
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You do know a capacity test for deep cycle batteries is different from a load test for starting batteries, right?
__________________
"Bringing third world electrical work to first world luxury." RV makers of Murica!
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