Lithium Battery System

[deLight]

Has anyone tried updating the house system to Lithium batteries? I have nearly finished my solar cockpit cover and since my batteries are not up to snuff, am thinking about a Lithium system. I have ordered parts from China to construct a 750 Whr battery for testing. Charging via solar, engine and shore power. Discharging via 12v system and 110v inverter. Max

[Matthew Balch]

I have not done this yet for the main battery bank.  However, there is a lot of discussion about this on the Cruisers and Sailing forum.  That forum site would be worth a look for more information. From what I have seen there are some special considerations regarding the voltage regulator and solar charge controller settings, as well as other tips for an optimum system.
Matthew

[deLight]

I plan to build the battery out of Panasonic 18650 cells. It looks like the charge/discharge characteristics of the battery are fairly simple. The cell voltage versus charge is fairly linear from 20%-95% charge. The charge rules seem simple also: 1. Limit the charge current to prevent overheating and cell damage. 2. Do not overcharge i.e. limit the maximum voltage.

There are multiple options from China on power converters which are both voltage controlled and current limited. I plan on using 3 of these DC-DC converters one each for my solar banks. The big issue is using my current engine alternator. I have a circuit in mind to use the alternator battery voltage sense input and a couple of op amps to give the alternator a low voltage feedback until the lithium battery voltage reaches the 95% charge level then rapidly raise the sensed voltage to cut off the alternator charge before the reaching the 100% level.

I will experiment and see what happens.

Max

[Soggy Geek]

We are in the process of converting the 14 year old Gel batteries on our new Soggy Paws (a catamaran) to LifePO4 Lithiums.  We chose a DIY approach, and ordered 3.2v cells from RJ Lithium in China, a total of 8 cells which results in a 540 Ah battery bank, that takes up about half the size and weight of our previous Gel batteries.

RJ Lithium LifePO4 Cells

We have just put them in and are still finishing the install.  But before installing, we did some capacity testing, using a precision load, one cell at a time.  Here is the result for one cell, we took a full cell that was resting at 3.3v (13.2v in a 4 cell battery) and put a constant 35 amp load on it, and it took 7 hours for the voltage to drop below 3.15v (12.6v), and we got a measured 250Ah (from a 270Ah cell).  It's pretty amazing!



You do need to make some adjustments to your battery charging and monitoring methods as using standard lead acid chargers/charge profiles will kill your lithium batteries (and/or your alternator).

We'll let you know how we like it after we've cruised with them for a year.

A good place to start learning about converting to LifePO4 batteries is here:

https://marinehowto.com/lifepo4-batteries-on-boats/

and this one:

http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/

Sherry