Charging issue with Alternator on 2001 Signature

[Mike Wahl]

Last evening we were head for our weekend destination and ran into an issue with the alternator/charging system.  I noticed we were slowly losing volts on the chassis battery's.  I found a spot were we could safety stop and check the problem out before we ran the chassis battery to low.  When I stopped, I checked the voltage at the battery's and I was getting 11.9 volts on the chassis battery's and 15.8 volts on the house battery's.   For some reason the system is overcharging the house battery's and not charging the chassis battery's when running off the alternator. 

When I would press the battery boost switch, I could watch the volts increase on the chassis battery's.

To get to a place we could overnight, I took a pair of heavy jumper cables and connected them from my house battery's to my chassis battery's.  This worked fine and both sets of battery's then charged.    When I run the generator both battery banks look to be charging properly.  My understanding of the system is that when supplying 110 volts the battery's charge off of the invertor. 

My question is what can be causing the charging problem?  I haven't researched or worked on this part of the electrical system so I don't know it that well.  From my initial investigation it looks like the alternator is working, however I'm not sure what is not functioning properly to cause this.

On a side note:  When we purchased the coach 3 years ago, one of the recommends from this group was to get a engine monitoring system.   We purchased a Bluefire and I have been working on updates to the custom dash.  I quickly saw that we had an issue with the voltage on the Bluefire dash.  I would have not noticed this issue nearly as quickly with the dash gauges.

[Ivan K]

I have a 2000 Sig with the large diode isolator in passenger side engine room RRB and a Duvac 200A alternator. Do you have the same setup? If so, I could imagine that a failed chassis side isolator diode could cause the alternator to pump out all it can as the chassis voltage is dropping.

[Tom Cherry]

39 minutes ago, Mike Wahl said:

Last evening we were head for our weekend destination and ran into an issue with the alternator/charging system.  I noticed we were slowly losing volts on the chassis battery's.  I found a spot were we could safety stop and check the problem out before we ran the chassis battery to low.  When I stopped, I checked the voltage at the battery's and I was getting 11.9 volts on the chassis battery's and 15.8 volts on the house battery's.   For some reason the system is overcharging the house battery's and not charging the chassis battery's when running off the alternator. 

When I would press the battery boost switch, I could watch the volts increase on the chassis battery's.

To get to a place we could overnight, I took a pair of heavy jumper cables and connected them from my house battery's to my chassis battery's.  This worked fine and both sets of battery's then charged.    When I run the generator both battery banks look to be charging properly.  My understanding of the system is that when supplying 110 volts the battery's charge off of the invertor. 

My question is what can be causing the charging problem?  I haven't researched or worked on this part of the electrical system so I don't know it that well.  From my initial investigation it looks like the alternator is working, however I'm not sure what is not functioning properly to cause this.

On a side note:  When we purchased the coach 3 years ago, one of the recommends from this group was to get a engine monitoring system.   We purchased a Bluefire and I have been working on updates to the custom dash.  I quickly saw that we had an issue with the voltage on the Bluefire dash.  I would have not noticed this issue nearly as quickly with the dash gauges.

Comments & questions.  I assume from your description that you do not have a BIRD system.  That was not something that since we talk in acronyms, that is a Bidirectional Battery Isolator Device …how they got BIRD???  Any way, that is a device or system where on shore/genny, your chassis bank is charged. Conversely driving, your house is charged.  Monaco was experimenting with different BIRD systems so I don’t know what may have been OEM, as the Sig’s had more top drawer systems and always got new hardware or technology first.

Read your owners manual on chassis electronics (chpt 9).  Pages 210 and 211 show a “maintainer”.  This IRD is installed to provide power or “steals” voltage (current) from the HOUSE to the CHASSIS when you are plugged into SHORE.  IT MAINTAINS the CHASSIS then.  It was not designed nor will it work to charge your HOUSE while driving.  Therefore, your voltage measurements are a bit confusing.  The 11.9 is low…really LOW.  ALMOST like the alternator is NOT charging and the 11.9 Is the “load” voltage that the batteries are actually putting out….as in, instead of being charged, they are the only source of power to keep the engine running.  Yes…a wise decision.

Now…What about the 15.8 on the house.  One possibility is that your solar panel controller is “out to lunch”.

15.8 VDC has to be understood.  If that is the solar, then the current is low….very low.  Odds are, unless there are multiple panels, the original one was 60 watts…divided by the voltage….around 4 amps.  Now…that is OK as a maintaining current…a little high and could eventually “dry out” the cells.  

Bottom line, unless there was a major high current connection failure as in the 4/0 chassis cables were loose or there is corrosion on the negative ground studs, sounds like your alternator or the voltage regulator is flaky.  Your solution was logical and correct.  Jumpering the banks is what most would do.  The genny does put out 120 VAC and your inverter then was charging….and since the combined voltage was probably, with genny on, in the 14 range.

OK…what I would do.  Continue to drive with the jumpers and Genny….that will protect your chassis from being damaged.  But do some testing before you leave.

If you are on say 50 A, and jumpers still hooked up.  Measure both banks…engine Off.  Should be equal.  NO shore on.  Disconnect the jumpers.  Turn on the headlights for a few minutes.  That knocks off the surface charge of the chassis.  Wait a few minutes and measure the chassis.  You also need to shut off all interior lights and fans.  If you have a residential upgraded refrigerator, unplug it.  No Tv or home entertainment on.  Do this while you wait… measure each bank then.  We need these numbers.  If you properly recharged the chassis, you should see 12.6/7 max.  Anything over 12.4 is fine.  At 12.0, your house is “50%” charged… now, if they can be charged up, the surface charge knocked off…then measure 12.6/7…that means they are fine.   But…if all they read after being fully charged is say 12.0, then that means they are “half dead” or they can only be RECHARGED to 50% of their original life.  I am providing a link to our “battery primer”.  Read it…you need to understand this…snd that is no disrespect to your knowledge, except we find many members do not have the fundamentals or in depth knowledge to keep their batteries maintained.

NEXT STEP.  IF you are in an open, non shaded site, then we have got to eliminate the solar.  Either, if you are able, climb on the roof and cover it and repeat your no shore & no engine running measurements.  The other option, read the manual and locate the controller.  There should be two terminals…battery 1 & battery 2.  The solar was hooked up to charge both.  Disconnect the positive on both bat 1 & bat 2 terminals….now measure…

This is the real status of your batteries.  There is a chart in the paper…

NOW…what I would do.  And it is up to your physical limitations and also the CG surface.  Turn off both banks.  Remove shore. Should disconnect solar but not critical.  Loosed ever nut, slightly, on ever battery.  If there are obvious signs of corrosion, use a baking soda poultice or molasses’s consistency mix and clean. Wear glasses…and not your Sunday best shirt.  Then scrape clean and use a cloth and water and rinse. If no major corrosion, you can, with the nuts slightly tight so you can barely rotate or move the cables side to side…then do that.  That polishes or abrades the mating surfaces so you have a clean connection.

Then…reassemble.  Now, if you were to slide or skinny under the area of the battery boxes, you will see the cables up and behind.  Look at the NEGATIVES.  They go to Ground studs.  These are notoriously prone to NO MAINTENANCE.  Loosen the nuts…still fairly tight, then aggressively rotate side to side…all of them, to polish.  OR, PULL OFF. Clean and reassemble.

Thats all I would do.  I would leave the solar disconnected….and then when i left the CG, LOOK at my BlueFire.  I would stop…with engine running…measure each bank.  If you still have a high reading on the house…there may be a failure in the maintainer…but that is a guess and someone will have to tell you specifically how they totally disconnected it to test..  if the chassis voltage is not, running and charging, above say 13.4 up to 14, alternator issues.

under no circumstances do anything except out the jumpers on and head home.

We have had too many members stop at a local shop and the unkowning shop “fixed” it and popped in a new or rebuilt alternator…. Monaco used really nice Leece Neville unit.  It is totally described in your manual.  It is a DUVAC style and there are few shops that understand that.  The first advice is to call Leece Neville and find an authorized repair shop and have it rebuilt.  Totally, especially the diodes. Soecify thatbthonly use Leece Neville parts.  Odds are…it will last a long time.  Many folks get a few hundred miles out after the new “guaranteed to work” fails. They did not get or keep the original.  They spend a lot…

Thats it…others may chime in…and they may simplify what I said… I try to teach as well as recommend…

 

[timaz996]

3 hours ago, Mike Wahl said:

Last evening we were head for our weekend destination and ran into an issue with the alternator/charging system.  I noticed we were slowly losing volts on the chassis battery's.  I found a spot were we could safety stop and check the problem out before we ran the chassis battery to low.  When I stopped, I checked the voltage at the battery's and I was getting 11.9 volts on the chassis battery's and 15.8 volts on the house battery's.   For some reason the system is overcharging the house battery's and not charging the chassis battery's when running off the alternator. 

When I would press the battery boost switch, I could watch the volts increase on the chassis battery's.

To get to a place we could overnight, I took a pair of heavy jumper cables and connected them from my house battery's to my chassis battery's.  This worked fine and both sets of battery's then charged.    When I run the generator both battery banks look to be charging properly.  My understanding of the system is that when supplying 110 volts the battery's charge off of the invertor. 

My question is what can be causing the charging problem?  I haven't researched or worked on this part of the electrical system so I don't know it that well.  From my initial investigation it looks like the alternator is working, however I'm not sure what is not functioning properly to cause this.

On a side note:  When we purchased the coach 3 years ago, one of the recommends from this group was to get a engine monitoring system.   We purchased a Bluefire and I have been working on updates to the custom dash.  I quickly saw that we had an issue with the voltage on the Bluefire dash.  I would have not noticed this issue nearly as quickly with the dash gauges.

My guess also is your dual battery isolator has died. What you are describing Happened to me and that what it was.

[Tom Cherry]

37 minutes ago, timaz996 said:

My guess also is your dual battery isolator has died. What you are describing Happened to me and that what it was.

Comments from the peanut gallery.  If that part has failed, then it looks to be a simple member should be able to fix.  If that would not work, then instead of paying for a new one and labor, I’d find a good tech…this is a chassis or truck issue, not a MH and get s quote on converting the boost and maintainer to the simple, base model Blue Seas ML-ACR.  Eventually the boost solenoid will or could fail.  The $350 ML-ACR will then give you automatic BIRD charging and is highly reliable and not that much more trouble to install. Labor will be a littler more….but you get NEW Technology and NEW parts and a much better system and your batteries will last longer.  The boost solenoid, which will be replaced and the IRD failed device probably will be 75% of the parts cost for the ML-ACR.

Just my unsolicited advice from a lot of reading and hearing and helping with problems..

[waterskier_1]

My 2001 Dynasty wiring diagrams (should be the same for 2001 Signature)  show that it had a Solid State (Diode) Isolator along with a Lambert LE-415 Battery Maintainer.  The IRD (Isolator Relay Delay), not a BIRD (Bidirectional Isolator Relay Delay) came later.  

I suspect, as posted above, that the Isolator diode for the Chassis Battery has Opened (versus Shorted or Closed).  This has left the Chassis battery without any charging.  The House batteries are "overcharged" because the DUVAC alternator voltage regulator is connected to the Chassis batteries, which are continuing to drop in voltage, signaling the alternator to put out more, which is only going to the house batteries, which have not feedback to the alternator.  

A temporary "fix" is to move both the outboard cables to the center terminal which is the alternator output.  This will restore charging to the chassis battery, and alternator voltage regulation.  BUT, it will allow the house to discharge the chassis battery, hence the "temporary fix" designation.  Once you stop driving, you will have to remove the chassis battery cable to manually "isolate" that battery bank until proper repairs can be accomplished.  The Blue Sea ML-ACR is a good choice to replace the Solid State Isolator.

  -Rick N.

[Rocketman3]

Another option…

I eliminated the blue battery isolator. (Connected the alternator wire to the chassis battery wire - no connection to house battery wire).
I have installed a bunch of solar (1400w) and lithium batteries for the house batteries.  Thus I needed to “break” the electrical connection so the alternator could not charge the house battery.  

I did add a Victron Dc-Dc charger so when the engine is on it will slowly (30amps) charge the house battery if needed (and to the correct charging specs).

[timaz996]

I have done the same thing with my setup. 

[jimc99999]

Just a small correction, the BlueSea ML-ACR is only $190 on Amazon, not $350. It replaces the battery isolator, battery boost solenoid, and chassis battery trickle charger (if you have one). You will have to run an extra wire if you want to use the remote switch.

Since I only ever needed battery boost to start the generator when the house batteries were low, I just switched the generator start circuit to the chassis battery at the same time so I've not needed battery boost function since, I've just left the ML-ACR in automatic mode and it's been perfect. Both banks of batteries get charged whether I'm on genny or shore power, or using the alternator while driving. Once the diode-based battery isolator is removed you no longer need a duvac alternator either, a regular Delco Remy 28si alternator will work just fine.

[Tom Cherry]

5 hours ago, jimc99999 said:

Just a small correction, the BlueSea ML-ACR is only $190 on Amazon, not $350. It replaces the battery isolator, battery boost solenoid, and chassis battery trickle charger (if you have one). You will have to run an extra wire if you want to use the remote switch.

Since I only ever needed battery boost to start the generator when the house batteries were low, I just switched the generator start circuit to the chassis battery at the same time so I've not needed battery boost function since, I've just left the ML-ACR in automatic mode and it's been perfect. Both banks of batteries get charged whether I'm on genny or shore power, or using the alternator while driving. Once the diode-based battery isolator is removed you no longer need a duvac alternator either, a regular Delco Remy 28si alternator will work just fine.

There is one catch….possibly.  Call Blue Seas and ask them if you have an Amazon purchased one, and need a warranty claim, will they honor it?  Magnum now hesitates…so does ESCO (ATS manufacturer).  So does Remco (RV55 Pumps).  We are seeing more issues where a seller on Amazon is NOT an authorized distributor or dealer…and then, the warranty says…sold by an authorized dealer.

I did not realize that Amazon was undercutting the RV online folks that much.  I will take a chance and not even bother Blue Seas if my Amazon $30 replacement switch were to fail..I’d call and not argue.  But, on an item that is selling for much more? 

OK, if I understand correctly, the 7620 is what most buy…rated at 500 amp and has the “on/off/auto” switch, mounted near by….not the upfront remote…more install labor.  The 7622 has the same, but an additional “manual” yellow switch.  I am truly sorry that I took what others had posted and thought the price was $350. Googling, Hodges Marine is a known and trusted vendor for many brands.  Of course verify that they ARE an authorized dealer.  They are within a few dollars of the same PN as Amazon.  Hands down, I would used Hodges…assuming they are and they sell so many inverters and have a complete lineup of all the major vendor’s accessories.

Bottom line.  I would not sink any money into an old technology like the “thieves”… or the OEM Lamberts or “Amp-L-start….they are NOT BIRD and we have many “OMG, it didn’t work” topics. I would install the Blue Seas and get rid of the boost solenoid and walk to the bay to switch it to ON and then use my boost…then switch back to Auto.  Major improvement and cost of installation would probably the same as the ML-ACR replaces the Boost.  A real WIN WIN.  Thanks for correcting my misinformation and also understanding why one needs to be cautious on Amazon.  I LOVE them.  But, for example, if I order a DeWalt power tool, I use the OFFICIAL DeWalt Store so I have a valid warranty…

[jimc99999]

3 hours ago, Tom Cherry said:

There is one catch….possibly.  Call Blue Seas and ask them if you have an Amazon purchased one, and need a warranty claim, will they honor it?  Magnum now hesitates…so does ESCO (ATS manufacturer).  So does Remco (RV55 Pumps).  We are seeing more issues where a seller on Amazon is NOT an authorized distributor or dealer…and then, the warranty says…sold by an authorized dealer.

That's a good point, Amazon is a cesspool of knockoffs these days, and I'd also seek out another vendor like Hodges. 

I did get the 7622 with the remote switch, but I haven't installed the remote switch. At first I wanted to install it just for the status LEDs to see what it was doing, but before too long I realized it didn't matter, it was doing what it said it would do. If there is charging voltage on one side, battery banks are connected so both are charged. If not, batteries are separated. Simple and perfect.

One of the good things about the ML-ACR is it can handle 500A, so for example if the alternator stops working, you can run the generator and the inverter/charger will easily keep up with the power required by engine, lights, etc, while an Amp-L-Charger will not. 

[Yoaks5]

It's my understanding that you should not start the motor while the ML-ACR is on or both sets of batteries connected since that can damage the house batteries. Is this correct? 

I guess to defeat this you could just shut the charger off on the magnum remote. 

I do like having the switch but mine was easy to install since monaco ran extra wires from the RRB to the dash that I was able to use. 

 

[waterskier_1]

I can't read the drawing you posted.  I'm not sure if it is applicable to your question, but my answer does not consider the drawing.

Unless you have manually turned the ML-ARC "ON" with a switch, which is not the normal mode of operation, the relay will be "OFF" meaning the battery banks are disconnected.  From the ML-ARC data sheet, when the device is in Auto Mode (normal operations mode) it will only combine the banks when either one of the banks has a voltage above 13.5 volts for 30 seconds or above 13.0 volts for 90 seconds.  Additionally, there is "Start Isolation" which provides temporary isolation of the house loads for 3 - minutes while cranking the engine.  There is also Undervoltage and Overvoltage Lockouts.  I suggest you check out the data sheets online for more info.  If you have questions, please ask and I'll try and help.

  -Rick N.

[Tom Cherry]

6 hours ago, Yoaks5 said:

It's my understanding that you should not start the motor while the ML-ACR is on or both sets of batteries connected since that can damage the house batteries. Is this correct? 

I guess to defeat this you could just shut the charger off on the magnum remote. 

I do like having the switch but mine was easy to install since monaco ran extra wires from the RRB to the dash that I was able to use. 

 

https://www.bluesea.com/products/7622/ML-ACR_Automatic_Charging_Relay_with_Manual_Control_-_12V_DC_500A
 

Have you gone to Blue Seas site and researched.  I did…just for curiosity.  There is a “grid” page that has all the models.  You read the “feature” on the LEFT..then scroll LEFT and see if your model Choice has it…. I posted the specs.  

I don’t see any concerns…as a matter of fact, the Blue Seas has a better “emergency or boost” start ratings or loads than does the traditional 200A Intellitec Big Boy.

BUT…many do not read nor understand how to use boost.  Boost, per Monaco and Intellitec, depends on “HAVING VOLTAGE ON THE CHASSIS BATTERY”. Thus if the Chassis is flat DEAD…NEVER use boost.  Follow the instructions.  Holding it ON for the 15 or 30 seconds….and repeat many times…see the manual, puts ON a flash Or surface charge.  If they batteries are totally dead and will NOT accept a charge…then you are NOT suppose to use the Boost.

Personally, and I have only had to do this once….I did not use the Boost.  i killed both banks.  Hooked up a positive Jumper.  Then turned on the banks.  Started the Genny…let it CHARGE the Chassis…maybe 30 minutes.  Shut off genny.  I may have turned off banks or removed jumpers….but then started engine….it ran fine.  Let it run a while.  Shut off…removing the jumper since there was a charge negated any issues.  Safe way…kill disconnects.  Remove jumper…turn on disconnects. Engine should start….maybe if still a little weak, a smidge of boost….but mine did not need it,

The Reason, and very critical on a CCM chassis.  You don’t want the arcing and such on the electrical system of the engine.  So, you isolate or disconnect the chassis….like you were changing out…then jumper.  When you turn both banks ON…it like positive battery switch or KNIFE switch.  Banks are in parallel and NO arcing while you fool around with the clamps for the best connection….that fiddling around sends surges to God knows where…easy to fry an ECM or the CCM.

Common sense and following the manual.  If had an ML-ACR….shut down battery disconnects.  Attach cables.  Then turn on each bank.  Then push the ON button…like a heavy duty light switch.  No stray arcing or spikes.

PS EDIT….doesn’t the 7622 have the manual switch on the top.  Doesn’t that actually overide and you do a manual “make the high current circuit”?  You ML-ACR guys chime in….I read too many specs…and maybe misinterpret…

OR…call BLUE SEAS….their techs are great.  I know a lot of info is posted here and other places based on what folks might have read elsewhere…and presumed to be right…but we often have to do some research or a member with practical and experience and full understanding of the device often chimes in.  In some cases, if the error or supposition was drastically wrong….we edit to prevent damage or injury….we like to stay factually correct.

My take and understanding….

[Mike Wahl]

1st off thanks for all of  the input.  We made it back home yesterday without issue.

I was able to do some checking when we got to our destination and found that the “Dual Battery Isolator” has failed.  The chassis side checks open when checking in both directions, and the domestic side check with resistance when checking positive to negative and open in the reverse. 

I have read and reread the posts and it looks like the Blue Seas ACR 7622 looks like the way to go.  I have the wiring diagram for the "Dual Continuous Solenoid High current plate" and after reviewing it, I also see someone has done some other changes and has the continuous solenoids jumped out.  From my understanding this would be the override or deletion of the "salesman switch".  

Just for my clarification I should be able to remove the following items and replace it with the ACR7622?

• 200 Amp battery isolator
• Battery Boost Solenoid
• Mattery Maintainer/protector

While I’m doing this is there any reason I couldn’t eliminate the continuous solenoids while doing the rewire of this panel?

 

Edited September 11, 2023 by Mike Wahl

[jimc99999]

On 9/10/2023 at 9:35 AM, Yoaks5 said:

It's my understanding that you should not start the motor while the ML-ACR is on or both sets of batteries connected since that can damage the house batteries. Is this correct? 

I don't see why starting with batteries connected would damage the house batteries. After all, that's kind of the purpose of the battery boost solenoid they all come with. If your batteries are connected due to the inverter/charger supplying charging voltage, the charger may provide a spike in charging current due to current draw from starting, and that may not be good for the charger. My old Xantrex doesn't seem to have a problem with it, and if it's powered (by genny or shore power) it starts pushing 50A or so when I turn on the key while the intake pre-heater is heated (while the "wait to start" light is lit).

The ML-ACR can be wired for automatic battery isolation on start, all you'd need is to run a wire from the appropriate lug on the starting solenoid to the correct wire on the ML-ACR harness. The ML-ACR latches and unlatches in a couple milliseconds so it should be unlatched by the time the starting solenoid latches closed to provide power to the starter, long before the starter actually starts to draw power.

Edited September 11, 2023 by jimc99999

[Rocketman3]

I replaced the two “salesman switch “ solenoids with two Victron smart BP-65 (battery protects).

My reasons:

1. I never use the salesman switch to cut off power.

2. I wanted an automatic cutoff that would cut off power in case lights were left on with a low battery.

3. I wanted to keep the ability to easily turn the the furnace(etc) on and off to power cycle it.

4. Any most importantly the old solenoids used a lot of power - the new BP65 use almost no power - since we boondock a lot - this was important to us.

Also I can read the voltage at that point on my phone.

or you can just bypass them.

[waterskier_1]

50 minutes ago, Mike Wahl said:

1st off thanks for all of  the input.  We made it back home yesterday without issue.

I was able to do some checking when we got to our destination and found that the “Dual Battery Isolator” has failed.  The chassis side checks open when checking in both directions, and the domestic side check with resistance when checking positive to negative and open in the reverse. 

I have read and reread the posts and it looks like the Blue Seas ACR 7622 looks like the way to go.  I have the wiring diagram for the "Dual Continuous Solenoid High current plate" and after reviewing it, I also see someone has done some other changes and has the continuous solenoids jumped out.  From my understanding this would be the override or deletion of the "salesman switch".  

Just for my clarification I should be able to remove the following items and replace it with the ACR7622?

• 200 Amp battery isolator
• Battery Boost Solenoid
• Mattery Maintainer/protector

While I’m doing this is there any reason I couldn’t eliminate the continuous solenoids while doing the rewire of this panel?

 

 

 

Mike, 

Regarding the continuous high current solenoids, you are correct - someone has jumpered across both of these, basically removing their functionality from the circuit.  You are correct that these were controlled by the "Salesman switch".  You can remove both but you will have to find a way to connect the output heavy cables to the fuses or the the input cables.  The easiest way would be to simply leave the solenoids in place, but disconnect the small gauge wires going to the coils, so they will never be able to be energized, and thereby won't consume any current.  The Salesman switch function will be inhibited, as it already is.  I've indicated (please take no offense if you already know this) in red how the cables would need to be routed, if they are long enough to reach the respective fuses.

You are correct on removing the three items, whose function will be replaced by the ML-ACR device.  The biggest issue will be physically connecting the cables (hopefully the cables will be long enough).  

  -Rick N.

53 minutes ago, jimc99999 said:

I don't see why starting with batteries connected would damage the house batteries. After all, that's kind of the purpose of the battery boost solenoid they all come with. If your batteries are connected due to the inverter/charger supplying charging voltage, the charger may provide a spike in charging current due to current draw from starting, and that may not be good for the charger. My old Xantrex doesn't seem to have a problem with it, and if it's powered (by genny or shore power) it starts pushing 50A or so when I turn on the key while the intake pre-heater is heated (while the "wait to start" light is lit).

The ML-ACR can be wired for automatic battery isolation on start, all you'd need is to run a wire from the appropriate lug on the starting solenoid to the correct wire on the ML-ACR harness. The ML-ACR latches and unlatches in a couple milliseconds so it should be unlatched by the time the starting solenoid latches closed to provide power to the starter, long before the starter actually starts to draw power.

The only time you would have problem with attempting to start with the house batteries, especially when the chassis batteries is if the house batteries are Lithium Batteries.  Lithium batteries can not support the current draw that could be necessary to start a big diesel engine.  The typical Lithium battery was rated at 100 AHs and could supply a maximum of 50 to 100 Amps of current before the internal BMS should disconnect the battery from the system before the cells were destroyed.  Most have a couple of these batteries, so it's more like 100 - 200 Amps, and few may have 500 + AMPHrs meaning they are border line on supplying enough current for the starter, but we don't know how much additional current will be drawn by the depleted Chassis battery in addition.  That is why, as a general rule (I make it a firm rule on all the systems I design, but eliminating any Boost Switches) not to use the Lithium House batteries to jump or start the main engine.  If you need a jump, use your toad.  

All this only applies to Lithium House batteries.  No matter what some will say, they are not direct "drop-in replacements".  They may not be damaged immediately but it will decrease their life.   Just like discharging a lead acid battery well below 50% may not show immediate damage, but it will have lost life.

  -Rick N.