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Isolation of Chassis and Coach 12 Volt Systems


Seward G
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I am planning the replacement the lead acid coach batteries with lithium iron phosphate on our 2013 Monaco Monarch.   A DC/DC charger will be needed to prevent overloading and overheating the chassis alternator.  The plan is to install a 60 amp Renogy charger.  How do I isolate the chassis and coach 12 volt systems?  

Attached is a photo of the circuit board where the two systems are tied together.  Please help me identify the function of the black terminal block and comment on how to safely split the two systems.  

I have tested the voltage across the two terminals on the block; they are virtually the same.  I tested with the engine running, engine off, and salesman switch on/off and all showed no voltage difference. 

The Renogy charger has a lead to go to the truck ignition circuit; I am unsure how this is used.  Is it that the charger only is active when the truck is running? 

Am I looking in the wrong place to separate the systems?

Thanks!

Unknown Connection Block.jpg

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What is the advantage of changing the chassis batteries away from typical flooded?  Seems like the extra cost for different batteries, a different charger and the labor would negate any benefit. 

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1 hour ago, Chargerman said:

What is the advantage of changing the chassis batteries away from typical flooded?  Seems like the extra cost for different batteries, a different charger and the labor would negate any benefit. 

Good morning, Chargerman

The plan is to replace the four coach batteries with lithium iron phosphate. The existing coach batteries are lead acid and are at the end of their useful life. The chassis battery will not be changed.

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17 hours ago, Seward G said:

The Renogy charger has a lead to go to the truck ignition circuit; I am unsure how this is used.  Is it that the charger only is active when the truck is running? 

I am undertaking the same project on my '97 Dynasty. I can't answer most of your questions as my electrical setup is much different from yours :).

However, I too am planning to use the Renogy 60A DC-DC charger. You are correct, you need to identify a source wire that will output 12vDC when the key ignition is turned to on, this will inform the DC-DC charger to begin charging from the source chassis battery. I thought I read somewhere that the DC-DC charger could also be configured to instead sense the output voltage of the chassis battery, and when it exceeded 14.5v or something like that (that would only happen when it was itself being charged) that would turn on the DC-DC charger. I'd prefer that approach I think if feasible so as to not add a potentially high load to the chassis battery before the engine has actually been started.

 

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Hello!
There should be existing isolation between the two systems already. On my 2000 Windsor, there are a few spots. One is the boost solenoid. The other is through a battery minder that has functions that delay and isolate the two under specific conditions. Do you have a BIRD or similar device? The electronic disconnect is only to connect the chassis battery to the rest of the coach for service.

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The angle u show on the black post does not give a front view. It does not look big enough to be a relay and u can not see if any smaller gage wires attach so your description of it being a terminal block with internal connection between the posts appears accurate. The voltage levels also would lead you to believe they are internally connected. That would lead one to believe that the isolation relay would be somewhere else. I would follow the house/coach cable back towards the house battery and look for a big relay that this cable would connect to and then continue on to maybe the house battery switch. The relay will also have smaller wires for 12v + and - to close the relay.  At some point, I would pull the house cable off at one or both end(s) and then determine when the relay closes.  If one end is left connected, this cable will have 12v and could carry 100s of amps if accidentally connected to a ground. Do u have a dash switch to combine and a sense circuit to combine when engine running or charger on? 

While lithium batteries are not normally used for starting engines, you MAY want to keep some method of connecting the two banks to "dump" charge into the engine battery if it is low and then disconnect b4 starting the engine. That would require leaving some form of relay in place. I installed a Blue Sea ACR between my house and chassis and I am very pleased.  The automatic connect of the ACR would NOT be good between Lithium and wet cell. 

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Thanks for your response and interest, waterskier_1

Attached are three photos.  The panel fuse diagram is turned 90 degrees clockwise from the actual panel.  There are so many wires that it is hard to tell much in the photos, and is still hard to tell staring at it in person.

Panel Fuse Diagram.JPG

Panel View from Below.JPG

Panel View.JPG

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The fuse diagram doesn't help.  I was looking for wiring for the solenoids.  I believe from the last pictures that the isolation relay (solenoid) is the large one at the bottom of both pictures.  If so, all you need to do is identify which of the two heave red cables is the house (coach) battery cable and disconnect it - both ends.  That will keep the isolator relay (IRD or BIRD) from connecting the chassis and coach batteries together.  Note that this will also inhibit the Battery Boost function since it also uses this same relay to tie the two systems together.  I don't find this a problem, because I really don't want my LiFePO4 batteries subject to that high (several hundred amps) current draw.  If there is an emergency, and I don't have another vehicle to any other way to start the main engine, then I would consider using jumper cables from the house to chassis positive terminals.  Note that this will also inhibit your inverter/charger from charging the chassis batteries (if it currently does).  Again, I haven't found that a problem, first because the charger profile (algorithm) is not set for Lithium, and 2) I have one (the original) solar panel dedicated to maintaining the chassis battery.  I also have a battery maintainer that I could (haven't had to) put on the chassis battery, powered through the Block Heater outlet, but it would only work when shore or genny power was on.

 

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18 hours ago, waterskier_1 said:

 

The fuse diagram doesn't help.  I was looking for wiring for the solenoids.  I believe from the last pictures that the isolation relay (solenoid) is the large one at the bottom of both pictures.  If so, all you need to do is identify which of the two heave red cables is the house (coach) battery cable and disconnect it - both ends.  That will keep the isolator relay (IRD or BIRD) from connecting the chassis and coach batteries together.  Note that this will also inhibit the Battery Boost function since it also uses this same relay to tie the two systems together.  I don't find this a problem, because I really don't want my LiFePO4 batteries subject to that high (several hundred amps) current draw.  If there is an emergency, and I don't have another vehicle to any other way to start the main engine, then I would consider using jumper cables from the house to chassis positive terminals.  Note that this will also inhibit your inverter/charger from charging the chassis batteries (if it currently does).  Again, I haven't found that a problem, first because the charger profile (algorithm) is not set for Lithium, and 2) I have one (the original) solar panel dedicated to maintaining the chassis battery.  I also have a battery maintainer that I could (haven't had to) put on the chassis battery, powered through the Block Heater outlet, but it would only work when shore or genny power was on.

 

This is the same configuration that I'm going to go with as well:

1. Remove the factory battery isolator and maintainer.

2. Rewire the solar charger so it only charges the chassis battery.

3. DC-DC converter to charge the LiFePO4 House battery from the Chassis battery when the alternator is running.

I haven't decided on whether to keep the battery boost feature or not. Mine isn't working currently so I might try to rebuild the solenoid it and if that works, fine, otherwise remove it.

I'm hoping the solar panel will keep the chassis battery charged while the rig is in storage (with battery cutoff enabled).

 

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11 minutes ago, RoadTripper2084 said:

This is the same configuration that I'm going to go with as well:

1. Remove the factory battery isolator and maintainer.

2. Rewire the solar charger so it only charges the chassis battery.

3. DC-DC converter to charge the LiFePO4 House battery from the Chassis battery when the alternator is running.

I haven't decided on whether to keep the battery boost feature or not. Mine isn't working currently so I might try to rebuild the solenoid it and if that works, fine, otherwise remove it.

I'm hoping the solar panel will keep the chassis battery charged while the rig is in storage (with battery cutoff enabled).

 

Depending on how much solar, and how you solar controller is wired, it should.  I put 720 Watts on the roof of my 97 Dynasty with my own solar controller to the house batteries only.  I had it in storage for 9 months after I bought my Exec. I just used a jumper cable from the house bank to the chassis bank and never had a problem.  Check that your solar controller charges both banks. 

  - Rick N 

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2 hours ago, waterskier_1 said:

Depending on how much solar, and how you solar controller is wired, it should.  I put 720 Watts on the roof of my 97 Dynasty with my own solar controller to the house batteries only.  I had it in storage for 9 months after I bought my Exec. I just used a jumper cable from the house bank to the chassis bank and never had a problem.  Check that your solar controller charges both banks. 

  - Rick N 

Currently I just have the 24 year old factory panel, 80watts (?) and the stock solar charger. I have a new 130w panel that I am planning on replacing the factory panel with, and hoping to use the stock charger but connected only to the chassis battery. Just want it to keep the chassis lead-acid topped up when parked, and will of course also use the alternator to also charge it while driving. But it will not be charged when plugged in or via the generator. I do have a small 2A battery maintainer that I could use by plugging it in if desired, but not planning on using it much.

The House LiFePo4 battery (280Ah) will be charged via the 100A charger on the Freedom 20 converter, either via shore-power or generator. When driving, it will be charged via the DC-DC charger off the chassis battery.

 

 

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8 minutes ago, RoadTripper2084 said:

Currently I just have the 24 year old factory panel, 80watts (?) and the stock solar charger. I have a new 130w panel that I am planning on replacing the factory panel with, and hoping to use the stock charger but connected only to the chassis battery. Just want it to keep the chassis lead-acid topped up when parked, and will of course also use the alternator to also charge it while driving. But it will not be charged when plugged in or via the generator. I do have a small 2A battery maintainer that I could use by plugging it in if desired, but not planning on using it much.

The House LiFePo4 battery (280Ah) will be charged via the 100A charger on the Freedom 20 converter, either via shore-power or generator. When driving, it will be charged via the DC-DC charger off the chassis battery.

 

 

That is similar to what I did.  I left the original panel but replaced the inefficient PWM controller with a new MPPT controller and connected it to the chassis battery.  I have 1300 Watts additional panels I use to charge my LiFePO4 house batteries.  I recommend you monitor you house batteries when in storage for phantom loads.  Of course if you remove the battery cables you should be okay.  

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5 minutes ago, waterskier_1 said:

That is similar to what I did.  I left the original panel but replaced the inefficient PWM controller with a new MPPT controller and connected it to the chassis battery.  I have 1300 Watts additional panels I use to charge my LiFePO4 house batteries.  I recommend you monitor you house batteries when in storage for phantom loads.  Of course if you remove the battery cables you should be okay.  

Yeah I'm going to need to monitor things to see how effective the stock solar charger is. Can always swap it out if needed down the road.

My LiFePO4 battery has a smart bluetooth BMS so I can disable all discharge (and charging) using an app for storage mode.

 

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