Mixed battery type charging

Having researched my Motor Home's Battery Control Center (BCC) unit (F73-1020) I have discovered that there is a dynamic battery-charging priority logic built into this BCC. This logic provides that the system gives charge priority to the chassis (starter) battery when the engine alternator is feeding the system and once it reaches full charge the BCC switches charge current to the house batteries.

In the alternative, the BCC feeds shore power and the generator charge current through the converter to the house batteries first and to the chassis battery when the house batteries are fully charged.

If I convert the house battery bank to LiFePO4 batteries...
With the solar system's Charge Controller feeding directly to the house batteries I am afraid that there will be a conflict because the house/chassis batteries are mismatched and their respective charge cycle parameters are different.

I know that the Pb-acid type battery charge profile (that the converter will have resident) cannot hurt the LiFePO4 house batteries because this charge profile will not produce very high current flow, and will not even provide adequate voltage for the LiFePO4 battery. But I do I wonder if the Solar Charge Controller's LiFePO4 charge profile will damage the Pb-acid chassis battery?

Ideas/opinions?

BrianG said:

because this charge profile will not produce very high current flow, and will not even provide adequate voltage for the LiFePO4 battery

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I am curious about how you know this?
What voltage and current flow are you talking about?

This:
https://www.power-sonic.com/blog/how...po4-batteries/

And Will often speaks to the issue of selecting battery type with various charge controllers and battery chargers.

That is an interesting article. I am in the middle of charge profile testing so having an extensive document like this is great, thanks for sharing.
They lose me when they say LiFePO4 full charge is 13.4v and that batteries sustain damage when charged significantly above this. Yet all their graphs show charging over 16v (4v per cell) for what looks like 5 hours of charging. So i don't get that, seems highly contradictory.

The power-sonic controller looks REALLY sophisticated. Is this the charger you intend to install?
Or is there a SCC that uses this lithium charge profile?

......

MisterSandals said:

That is an interesting article. I am in the middle of charge profile testing so having an extensive document like this is great, thanks for sharing.
They lose me when they say LiFePO4 full charge is 13.4v and that batteries sustain damage when charged significantly above this. Yet all their graphs show charging over 16v (4v per cell) for what looks like 5 hours of charging. So i don't get that, seems highly contradictory.

The power-sonic controller looks REALLY sophisticated. Is this the charger you intend to install?
Or is there a SCC that uses this lithium charge profile?

Click to expand...

I am still very much in the information gathering phase of this project. The RV I am working with is a 1999 model year so the technology isn't very current (pardon the pun). It has a starter (chassis) battery, a house battery bank (currently 2 X 6v golf cart batteries). The coach has a 12v system for it's lighting, furnace fans, and water pump as well as a converter to run the 12v system and to charge the batteries. It also has a 110v a/c system that has a shore-power feed and an onboard 5500w genset.

It has a OEM battery control center ( BCC) that executes a certain charging logic, depending on which sources are energized. The BCC is also responsible for managing the AC inputs.

All of this seems to make installing a solar system a challenge, especially if one includes the installation of an inverter.

To make this all the more entertaining, I would like to make the house battery system 24v.

So, I have quite a bit of information yet to gather. ?

MisterSandals said:

They lose me when they say LiFePO4 full charge is 13.4v and that batteries sustain damage when charged significantly above this. Yet all their graphs show charging over 16v (4v per cell) for what looks like 5 hours of charging. So i don't get that, seems highly contradictory.

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I agree. I think the author doesnt know the differences between the chemistries or pulled a chart from the wrong battery type. I also have never seen current drop like that shows during the constant current phase. It does illustrate the natural settling the battery does after charging stops. Topping charge is another new term. They are a reseller so I am dismissing it as marketing stuff.

BrianG said:

If I convert the house battery bank to LiFePO4 batteries...
With the solar system's Charge Controller feeding directly to the house batteries I am afraid that there will be a conflict because the house/chassis batteries are mismatched and their respective charge cycle parameters are different.

Click to expand...

Off the top of my head you may need a BMS that can cutoff the current from the BCC in order to get any control over the top voltage to a LFP in that scenerio. It is just a hypothesis that you may need to test. There are BMSs that can seperately control load and charging inputs. I would have to think about how you would later integrate that with solar charge controller but I think it is going to matter what voltage the BCC cuts off current to the aux battery and whether that can be advjusted. If not a work around for brainstorming purposes is a voltage controlled relay but I might have to work that out on a paper diagram to figure it out. Before doing that. I would would need to know the voltage cutoff of the BCC.

BrianG said:

The RV I am working with is a 1999 model year so the technology isn't very current (pardon the pun)

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Thats not far from what i am looking to do.
I have a circa 2011 progressive dynamics pd4650 that i replaced the oem charger (non solar) with.
They make a lithium version of this now but i was going to give it a go to see how it works.
I expect most of my charging to be from a separate Victron 100/30.

Progressive dynamics makes bolt hole and wire for wire compatible replacements, i recommend seeing if they make one for yours.
Its a well spent ~$225 if you can make it work in my opinion.

I hope to have my LiFePO4 installed in the next week or 2. I will chime in if i get any interesting an relevant info on how my charge behaves with LiFePO4.

Yes, I think that integrating a modern LiFePO4 charge controller with the old school Battery Control Center (BCC) unit (F73-1020) by
Rv Custom Products is going to be the challenge. Adding an inverter will add to the complexity.
I think I'll write to them and see what they have to say. Perhaps they have a modern replacement, also.

BrianG said:

Perhaps they have a modern replacement, also.

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Or even a firmware update.

Morningstar had a firmware update for my 2011 Tristar 45 which pretty much made it a modern unit (but still has a serial port).

MisterSandals said:

Or even a firmware update.

Morningstar had a firmware update for my 2011 Tristar 45 which pretty much made it a modern unit (but still has a serial port).

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I think my 1999 controller still has vacuum tubes in it! Certainly I don't see any data ports.

I think you should rethink converting to 24v.
In a house setup up it makes some sense, but not in a system that already runs on 12v. \Check out the marine section of this forum. It addresses your issues.

Dauntless said:

I think you should rethink converting to 24v.
In a house setup up it makes some sense, but not in a system that already runs on 12v. \Check out the marine section of this forum. It addresses your issues.

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Ongoing research reveals that your are right about staying with 12v for the house system. I was concerned about having to run expensive heavy gauge wire from the solar panels to the battery bay, but there are a number of charge controllers which can accept a high voltage input and convert it to 12v to feed the battery bank.

The charging challenges for this overlapping LiFePO4 / Pb-acid system is the overlap. Conversation with the BCC provider has resolved that issue, as the interconnect function can easily be defeated by removing one fuse. This resolves the matter of over -amping the alternator when it tries to charge the Lithium battery as well as the issue of the Lithium programmed converter overcharging the Pb-acid chassis battery.

If you check out the marine forum, there is a link to a very simple, yet safe (for your alternator) hybrid system.