Hybrid RV LA-Lifepo system upgrade

[pdxbill]

First Post! I'm starting this thread to get feedback on an upgrade to an RV hybrid LA+Lifepo system I am thinking about. This is all new to me and am trying to learn as I go. This forum has been really helpful. I'm in the planning phase. I've been researching all kinds of possibilities and recently stumbled across the idea of a hybrid LA-Lifepo system(video link). It seems like an great way to not carve out my current set-up, simply add to it, with the potential to remove the upgrades should I sell the RV down the road.

Current set-up:
RV is 2015 Itasca Navion on '14 sprinter chassis.

• 2 GC2 Interstate 6 V batteries in series for 12V
• 30 amp SRNE mppt solar charge controller and 300 watt huwai(sp) roof mount single solar panel
• solenoid charging from vehicle alternator
• Progressive dynamics battery charger(non-Lithium) powered via shore power or onboard generator.

Needs: I'm looking to add 120 volt capability via an inverter. I'd like to tie it into the house panel, I'd like all my current 120 V outlets to be usable. I'm only planning on a 1000 watt inverter. I understand that this won't run the Air Cond/Microwave and other high current appliances. If I have bigger power needs, I'll run the generator. I like the idea of keeping my current LA batteries in place, that way if I sell the vehicle down the road, I can remove upgraded components and return RV to a near original system.

I ordered 4 of the 280 ah cells from alibaba(generally following this guide), with the 120 amp smart bms. I like the idea of a milk crate battery that I can add/remove easily to the existing system. My total capacity in the hybrid system will then be in the neighborhood of 380 ah. Based on my usage, this is a high reserve. The batteries would only be charged by the solar panel and converter when on shore power/generator.

Some of my initial thoughts and questions on this potential hybrid system:

• Based on my current understandings, I will disconnect the vehicle charging via the solenoid to avoid potential problems with high drain on alternator and mixed battery chemistries. I think based on my needs and large reserve, I won't need to keep this aspect and keep a "simpler" system.
• I don't really have an understanding of what the connections b/n the 2 batteries looks like. A bus bar? Other set up? If anyone has any pics that would be very helpful. I also noticed in the video mentioned above the caution needed when connecting the two batteries, which is a bit anxiety producing.
• Is there a way to set up a battery monitor(shunt) in a hybrid system to keep track of remaining capacity? If no shunt style monitor, is there another way(read cheaper) to tell?
• I'm aware of the feedback back loop that is created when adding the inverter line to the house AC panel. I noticed a separate circuit breaker for the converter and could manually flip that, or I could install a transfer switch.
• Would the hybrid system charge via the current set up? I believe the charger is connected to each end of the 6 V batteries now.

Thanks for any suggestions. It's been a fun process to learn about these systems and design a system that can meet my needs.

 

[HRTKD]

Welcome to the forum!

In my RV, I don't have the inverter tied into the trailer's AC system. The 1000 watt inverter works for my coffee maker. I have a single outlet wired directly into the inverter for the coffee pot. With this setup, there is no need to worry about what power source is active at any time. I do have an on-board generator and shore power. Both of those tie into the trailer's AC system with an Automatic Transfer Switch.

When I upgrade to a bigger inverter, it will be an inverter/charge so I don't have to worry about the AC-DC converter loop.

What you're proposing is complicated. You have to remember to flip switches. I have none of that. I designed it with my wife in mind. No instructions, no sticky notes. She's smart, but she's there to relax, not study schematics.

I have a single lead acid battery and LiFePO4. However, the two battery systems are isolated. Neither one is affected by the other. They each have their own charging sources. I don't have to worry about the LiFePO4 charge profile affecting the lead acid battery and the lead acid battery charge profile affecting the LiFePO4 battery.

 

[pdxbill]

Thanks for the response. As I think about it maybe keeping the systems separate is better way to go. In watching Will's video on a milk crate solar generator, and subsequent update video, I'm curious how the AC charging via the solar charge controller is limited. That is, how does the battery not overcharge? Is it via the charge controller? The battery bms? I'd like to have a simple milk crate solar generator and milk crate lifepo(280 ah as mentioned above). The ability to charge the battery via AC is very attractive.

 

[HRTKD]

The BMS usually has the last word on over/under limits. Solar charge controllers (good ones) are programmable and allow you to set the charge profile to whatever you want. AC-DC converters tend to be rather dumb and don't allow any programming, but they do usually come with a charge profile for a specific battery chemistry.