“TL DR – I have some questions related to charging 12V LiFePo4 lithium batteries:
*How to best use my solar to charge batteries?
*Assuming I usually keep the lithium batteries at a partial SOC, what if I want occasional 100% SOC?
*What about charging from my tow vehicle?
*What about charging with OEM converter?”
For one 100 amp hour Li battery, don’t sweat the small stuff. Everything you have will do just fine. For two 100 amp hour LI. The same advice.
For more than two, consider limiting charge from tow vehicle. Over loaded alternators get hot and cook themselves to death. This happens less with travel trailers than with motor homes. The TT wiring harness tends to limit tow vehicle charging.
It depends on alternator specs and how much your tow vehicle needs as well as house battery charging.
For more than two, consider higher capacity house charger. It is not necessary, but most Li can accept high charge current. This is more important for generator charging when you want to minimize charge time.
Of course all of this depends on the Li battery BMS. I have read up on Battle Born and my advice applies to them.
*2 x 140 12V solar panels mounted fixed and flat
*Morningstar Tristar PWM controller
*1500 watt PSW inverter
*OEM WFCO converter (55 amp)
… I want to relocate the batteries from on the tongue to the pass through storage alongside the other electrical components. So I am considering a switch to a single lithium (LiFePo4) 12V battery 100Ah. Current top candidates are Renogy, Battleborn, and Dakota. I am contemplating my charging options if I do this swap.”
100 amp hours may be a little limiting compared to what you now have. Do you dry camp or boondock? If so, consider 200 amp hours. That will provide more than what you have now.
“How to best use my solar to charge batteries? The Morningstar controller is fully programmable and I downloaded a suggested lithium battery charging profile from their website. It relies on the concept of never bringing the lithium battery to 100% SOC as this can be stressful to the lithium battery.”
Plan looks good. Again, don’t over think it. Li batteries work well and for a long time compared to lead acid. Fully charging to 100% and discharging to 20% works for thousands of cycles. Storing at 50% SoC will increase life. How long do you expect to be still using the system? Do you want to live forever?
But what if I want occasional 100% SOC? My thought is if we’re heading out camping for the long weekend, then I do want to recharge to 100% just prior to and if possible during each camp day. It seems like a few of the lithium battery manuals say that FLA charging profiles that can reach 14.4V and an absorption phase will work fine to fully charge. I think I can put together a “while camping” charging profile based around 14.4V absorption setpoint to accomplish this. 13.3V float?
You are thinking too much like lead acid battery management. Of course if you are going to dry camp, you want 100% charge to start. You only want partial charge for storage or long periods on shore power. Even so, you may never see the Li battery fail.
Battle Born batteries have built in battery management systems. A WFCO will work fine. The new WFCO models have a Lithium setting. The main difference is the Li cycle eliminates the 13.2 volt storage phase that the old WFCO have. Sometimes the max charge voltage is a couple of tenths higher. (Not important).
The Battle Born BMS will disconnect when the battery reaches 100% SoC. At this point while on shore power or generator power, the WFCO powers all 12 volt appliances.
When shore power is disconnected, the BMS automatically reconnects and provides 12 volt power. It is fast enough you will never notice. If the solar provides enough power, the BMS will not reconnect until voltage drops below a preset. I presume the reconnect point is at or near 13.2 volts, so that is why the new WFCO eliminate the storage voltage for Li.
“What about charging from my tow vehicle? My tow vehicle delivers 12V via the trailer plug. No upgrades in wiring or anything there, just whatever the OEM setup is for the 7-pin trailer connector. But I confirm that it brings the trailer battery voltage up to the alternator voltage of 14.2-14.4V. Since this is on the upper end of lithium charging voltage, and considering that I probably don’t want the alternator trying to push 14.4V indefinitely while driving, should I be disconnecting this charging source? Or maybe consider it sort of a topping off charge for the typical 1-2 hr drive to the camp spot?"
Again, don’t over think it. Battle Born batteries have a built in BMS and will take care of themselves. If you are building your own BMS system, there are a lot of technical issues to consider. The BB BMS will disconnect when appropriate.
“What about charging with OEM converter? My OEM converter is a WFCO 55 amp model. I have one time ever seen it charge at 14.4V, every other time I have ever used it I see 13.6V. I usually have it switched off via the breaker panel and let solar do the work. I expect I would continue this practice. But it seems like I could use it if I wanted and assuming it continues to only charge at 13.6V, it should be fine for partial charging?”
All covered above. Don’t worry about it.
WFCO only reaches 14.4 volts in the first 4 hours of charging, and then, only if battery absorption is less than 55 amps. After 4 hours, voltage drops to 13.6. After 4 days in storage the WFCO drops to 13.2 volts. The BB BMS will disconnect when it is full and not reconnect before voltage drops below internal preset.
55 amps for 4 hours is 220 amp hours. It is more than enough to charge two 100 amp hour Battle Born batteries. BMS will disconnect. WFCO will drop to 13.6 volts and supply all 12 volt appliances.
LiPO4 are great RV house batteries. The best have built in BMS. The advantages mean you have much less to worry about. Read the instructions for the battery you buy. Enjoy your camping experience.