Complex solar integration concerns for a motorhome

I plan to add a solar energy source to my older motorhome but the OEM energy management system is creating a concern about this addition.

These older motorhome have a so called BCC (battery control center) which is a solid state manager for the charging inputs from shore power, engine alternator, and onboard 5000W genset for charging the house battery bank and the chassis (starter) battery. It has its own logic for directing charge current to these batteries.

My concerns are many but let's start with the concern for conflict with the OEM BCC and the addition of the new charging supply of the solar system.

1. If I provide the solar power directly to the house battery bank, will the OEM BCC see anything other than the net state of charge of the house battery/solar input?

2. The chassis battery is a sealed Pb-acid battery. I'd like the house battery bank to be LiFePo4. Can these two disparate types coexist in this system?

3. Will the alternator require protection if I use lithium house batteries in the system?

What brand is the BCC system? Intellitec? Precision Circuits? They may have a solution available. Most of these systems are somewhat modular depending on age. They almost always have provisions to disconnect devices when sufficient power is not available to drive appliances (Load shed). Air Con disconnect is very common on 5/6 kw generator equipped MOHO with multiple air Con units.

1) yes, BCC should just see SOC
2) no, different charging profiles required
3) yes, if the BCC doesn't limit current (i don't think it does)

mapguy525 said:

What brand is the BCC system? Intellitec? Precision Circuits? They may have a solution available. Most of these systems are somewhat modular depending on age. They almost always have provisions to disconnect devices when sufficient power is not available to drive appliances (Load shed). Air Con disconnect is very common on 5/6 kw generator equipped MOHO with multiple air Con units.

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The BCC is a RV Custom Products unit which is common to most Fleetwood motorhomes. The consultant from RV Custom Products suggests connecting the solar charge controller directly to the house batteries, but that the critical issue is the charge voltage setting which should not exceed 13.6 volts as that is where their system trips from the house batteries to supply the chassis battery.

I am still uncertain that this will provide sufficient charge to a LiFePO4 battery bank, but I think it will be ok, if only a little suboptimal.

Certainly, the alternator will also require an over-current protection device.

Does this make sense?

Yes it makes sense. The beauty of LFP is that you don't have to worry about sulfation like you would with Pb if you don't charge them all the way. I don't know the dynamics of how you are going to use that rig but so far this discussion has been about charging from the alternator. You have talked about solar and of course there is also the possibility of shore power charging.

That's another thing... the alternator is a rather poor source of charging because of its low current capacity and the need to protect it's output limit when supplying lithium batteries.

I'll have to also review the capacity and programability of the OEM converter charge points for compatibility with lithium batteries. This might require replacing it with a modern inverter/charger that is programmable. At least, that would not be a huge extra investment considering that I was going to want to install an inverter, which isn't in the current system, anyway.

Oh what fun!!