AC/DC and solar -> MPPT to lead acid / LiFePO4 battery

DIY
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First post, but veteran Gen-X online. New to RV’ing; I have a 2023 Grand Design Imagine with 120VAC/30A (L6-30P) AC input. It currently has what looks like a group 24 (wet) 12VDC lead acid battery. The 120VAC goes to (what the RV shop calls) a converter (power supply) to charge the 12V battery when AC power is provided to the RV. In parallel with those battery leads is a non-Victron MPPT but it’s pretty limited; 9-16VDC solar input, max input (solar) current 37.5A, charging voltage 9-14.9VDC, no SOC status, no BT. The solar panels appear to be approximately 12VDC at 200W. During travel, the RV has the 7-way power connector that uses the truck power (up to 25A) to charge the 12V battery.

I’m an electrical engineer but haven’t dabbled in this region as I’m mostly a high-speed PCB design engineer. However, not wanting to reinvent the wheel, and really liking Victron’s MPPT (I have a 100V/30A for home backup purposes) and app, I really like their engineering.
So my question is in regards to what system works best for an RV, and the best way to keep this system working efficiently and reliably using one device instead of two or more. Many LFP batteries have internal BMS so it can take the overvoltages typical for lead-acid charging systems (so they can be used as drop-in replacements for lead acid). But, I cannot find any offerings that, say, use OR’ing diodes to bypass solar when there’s DC power (from AC) available to more reliably charge the batteries when DC power is available, or some other mechanism (i.e., use less DC power from converter when some solar power is available). This is likely tricky but I guess it could have some benefits of overall using less generator power (fuel) when off-grid. I have yet to see any manufacturer integrate AC and solar charging into their MPPT/BMS solution, but this could also be that I did not pick the correct keywords for search engines. My goal is to get this system to work for now using the lead acid but then switch over to a LFP battery.
Another related question is regarding my 100/30 MPPT charger. It has the options of 12/24 and wet, AGM, and LFP batteries. If the LFP battery has a BMS, that is supposed to emulate lead-acid batteries, does the Victron selection know this, so should I use LFP or wet battery type?
Thanks again for reading, and I welcome your positive suggestions!

Regards,
-Rob

UPDATE1: Seems this topic is relevant, partially, but it’s always best to measure ten times, cut once. :slight_smile:

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MASSIVE disclaimer: I’m not a wizard, and I barely know the basics of electronics.

I’ve DIY-ed 2 batteries so far. First battery is a 10s1p li-ion 36v/60Ah one for an e-bicycle (230 euro total costs/~2.2 kwh worth of storage), and the second battery is a 4s1p LiFePo4 12v/280Ah battery for my boat (300 euro’s total costs/~3.6 kwh worth of storage). Both batteries have a JBD BMS installed, and both have bluetooth features. Using the “overkill solar” app, I can see the charge/performance of the battery and each cell. I can also set up all kinds of limits for the battery. So probably also “emulate” (not sure why you’d want to) a lead-acid battery. If you know what you’re doing (I kinda don’t probably), it would be a few minutes effort.

Can’t really comment on the Victron stuffs. But I did see you mention a generator of some kind. And that might relate to my off-grid boat setup. Because of the amount of kwh in my boat battery, I’ve got a really solid buffer for electrical activities you’d usually encounter on a boat/RV. I’ve also covered the top of the boat in solar panels. With normal electrical usage and during “summer time usage” (expecting you’ll be doing the same with your RV), there is no need for an added “hard wired” alternative power source, like a generator or main-grid charger.

When I do NEED to charge the battery, I just manually disconnect the solar charger/connect a 12v generator. (made out of an car alternator and lawnmower engine) For the very rare cases I’d need to run this generator, it’s not worth adding a complex/expensive automatic setup. I might end up getting a random switch to easily connect/disconnect the solar panels, and an wall-mounted charging connection for my 12v generator.

Hope you found some value in this reply!

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I thought it might be relevant to add some pertinent information regarding Victron MPPT chargers for NewTiPower LFP batteries (available on Amazon). I had asked many questions, not all were answered but perhaps enough to help others here. Please feel free to correct anything I got wrong (inquiry).

I need to know what the two voltage levels are for this battery: Absorption voltage, and float voltage, and if there is an equalization voltage. I have selected the battery type to be LFP, and it defaults to 14.2V for absorption, and 13.50 for float voltage, and equalization voltage is disabled. From your charger voltage chart, you show the charging voltage to be 14.6V, should I use this for absorption voltage, and what would be the float voltage and equalization voltage? The absorption duration can be either adaptive or fixed absorption, Re-bulk offset is set to 0.1V meaning, when battery voltage drops 0.1V below float voltage for one minute, the charge cycle will restart. At present, with defaults, this is set to 13.4V but not sure if this is appropriate for your battery. What should the low temperature cut-off be set to (for charging to stop when temperature goes below a certain value)? It is currently set at 5C but that may be too low? Another parameter is temperature compensation, mV per degree C for the whole battery bank, what should that setting be?

We recommend using a charger specifically designed for lithium iron phosphate. If you must use a controller for charging, please ensure that the parameters are set correctly, otherwise it may cause abnormal charging.
The following are the parameters we recommend for our battery:
High Volt Disconnect: 14.8V
Charge Voltage: 14.6V
Equalize Charge Volt: 14V
Boost Charge Volt: 14.4V
Float Charge Volt: 13.8V
Boost Char Return Volt: 13.2V
Over Disc Return Volt: 14.2V
Low Voltage Alarm: 12V
Over Discharge Volt: 10V
Discharge Limit Volt: 10V
The above parameters refer to a single 12V battery system. If it is 24V or 36V, please multiply the above parameters by 2 or 3.
Our battery BMS has a low-temperature protection function, which usually starts protection and stops charging between -5-0 degrees Celsius outside.

EDIT 20251003: OK I am confusing myself but I have to ask the obvious question… none of those settings may be needed if the NewTiPower battery has an integrated BMS, right? It should take care of limiting charging and discharging current, voltage levels, and even allow over-voltage charging (that would be safe for lead-acid batteries). The camper I have uses, for lead acid charging, an AC-DC converter; input 120VAC 956W, output 13.6VDC 55A (LA), 14.6VDC 50A (L1) (whatever that means). Point is, during AC input, the converter outputs up to 14.6V at 50A, and the BMS should turn off input when the battery is fully charged, right? The Victron should only be needed for solar charging, and do I even need to configure the Victron for LFP or should I just use the lead acid mode, assuming the Victron in LFP mode would be needed IF the battery did not have a BMS. I’m hoping someone could shed some light on something that should be obvious but isn’t.

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I’ve been told that all LFP batteries with more then 1 cell, (should) have a BMS. At least for balancing purposes, with the posibility of added features and/or protections.

The battery I made myself, has a decently smart BMS, with bluetooth. And there are obviously also stock/bought batteries, which do have bluetooth/smart features. I’d highly recommend investing in a battery with Bluetooth features.

Also, think you’ve mentioned you were belgian. Don’t Belgians use 220v?

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Response from NewTiPower battery manufacturer:
Our batteries are equipped with a Battery Management System (BMS) that triggers protection in case of overvoltage charging. However, it’s important to note that lead-acid battery charging modes may not be suitable for our lithium batteries. We recommend configuring your controller according to our recommended charger parameters. Using a lead-acid battery mode for charging may not cause immediate issues, but the battery could begin exhibiting abnormalities within about six months, such as rapid power loss or charging failure. This occurs because the internal battery cells have become damaged. Therefore, we strongly advise configuring the lithium battery charging mode according to the parameters we previously provided. Lead-acid batteries and lithium batteries are fundamentally different types of batteries. Their parameter settings are not interchangeable.

So it sounds like the BMS in the 12V 300AH battery is more of a “backup”, and we can tweak the parameters in Victron MPPT to those recommended by the battery manufacturer.