Advice on changing voltage/battery type of system

[georgia088]

I have had an off grid system on my dock for the past couple of years. It has always been a 12v system in which I have used a deep cycle lead acid single battery (100aH). I have a Harbor Freight 100 watt (4 25 watt panels in series) and another 100 watt single panel wired in parallel to the 100 watt harbor freights. I have a 12/24V 20A MPPT charge Controller. Typical use for the system is running a wifi access point (24v that I have to step up from the 12v) a wifi camera, a couple of Low Voltage Wifi switches, and an amazon echo dot for music playing and controlling the wifi switches. All of that needs to be active 24/7. I have a couple of dc lights that I use occasionally at night and I have cheap 120v inverter for the rare occasion I need to plug something in 120v for short periods.

I just recently purchased a 24v trolling motor and two lead acid 12v batteries (series 24v) for the boat. It stays at the dock 24/7 (except when out fishing/boating). The current 12v battery I have running the dock is bad. It needs to be replaced. I was considering replacing it with 4 LIFEPO4 wired in series 105aH cells. However, now that I have the trolling motor/24v system, I am not sure which route to go?

A couple of things I have considered, but I am not sure how well they will work.

If I convert my system to 24V, Could I create a receptacle at my dock that I could "plug" in when the boat is docked to charge the 24V used for my trolling system (also use this to run my dock when the boat is present) and have a smaller Ah set of batteries (24v) connected permanently to the solar system to run everything when the boat was gone? Is there a good way to do this? I so, I would likely need to run the wire from the "permanent" set of batteries approximately 15 feet. What size wire would I need to use to prevent energy loss?

I couldn't have both lithium and lead acid batteries tied together so I guess this eliminates me getting the LIFEPO4 unless someone has a suggestion?

I appreciate any and all advice!

Thanks!

 

[chrisski]

You could use us dc to dc charger like this to charge a lithium battery from lead acid or vice versa.

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-Smart-DC-DC-chargers-isolated-250-400W-EN.pdf

For plugging it in, I do not know a good weather proof plug for a dock. I use Anderson plugs outdoors, but not in a rainy environment. Perhaps in a weatherproof box. I also would not want to use a standard plug, like 120 volt, in case someone would plug something in.

 

[georgia088]

For plugging it in, I do not know a good weather proof plug for a dock.

Ok, The dock is actually covered so that will help. I can use a less common type of plug to prevent accidental plug ins, but what size wire would be needed?

As for the dc-dc charging, I am trying to wrap my head around how my system would work. Could it work so that:

24v batteries connected to trolling motor are being charged while the boat is under the dock from the solar panels/mppt charge controller

The 12v lithium battery that will be permanently mounted at the dock (even when the boat leaves the dock) will be charged from the 24v battery pack of the trolling system?

How would the 24v system "know" when to charge the 12v Lithium system? Would it need to be on some kind of timer?


So wiring it up like this would be possible?


Thanks for the help!!