Lithium battery

At the time we bought the boat, we did not have working batteries. Since we knew we would be working on the boat for a while, we did not want to buy the best batteries right away. So we put in 2 12v AGM batteries of 185AH. This allowed us to sail stand-alone for several days. Should our plans for a big trip really take shape, we would look into Lithium again.

We are now 3 years down the road. Next spring we want to leave. So it was time to start working on the batteries. We wanted Lithium batteries because we can discharge them deeper and they last longer. They also take up less space than an AGM battery. We decided to make a 280AH battery on 24v.

A friend of ours told us that he wants to start selling Lithium self-build kits. He had built 1 himself a year ago and also had it in use for a year. This was to his satisfaction. The advantage of self-building at this time is that the costs are then considerably lower. On average 50% lower. On the other hand, it takes more time. It is also important to study a BMS, thickness of cables and a fuse. So that safety can not be compromised. With the advice of our friend and his promised help, we started this project. We ordered cells, a BMS and cables and got to work.

Making a plan

We had a rough plan. Through the Dutch website NKON.nl we ordered the cells. 8x a cell of 3.2v LiFePO4.
On advice, we ordered a BMS (Batery monitor system) from Seplos. A BMS keeps an eye on the voltage of the cells, the temperature and the upper and lower voltage of the battery.

We also bought the other parts we needed for this project:

A waterproof case for the BMS
Stainless steel plates and wire ends to hold the cells together
Cables of various thicknesses, heat shrink tubing, cable lugs, bus bars ect.

From the supplier Seplos we received an extensive manual on the BMS and how to build such a kit. In addition, we spent some hours watching all the Youtube videos made by others before us.

Building the battery box

First we connected the cells by means of 4 threaded rods and 2 stainless steel 316 plates 3mm thick. Between the cells we placed rubber sheets. The cells can expand when used, so it was important to place them in a box.

Then we started to finish the box with wood. The BMS is connected with wires to all the cells, so it must be possible to place it close to the cells. To make this possible, we built from wood a lid that can open above the cells.

On the cover we were able to mount the waterproof box for the BMS and 2 poles for the output. Since the battery will be on our boat we gave the wood a good protective coating with a strong varnish.

The BMS

We installed the BMS in a waterproof container because we wanted to protect it properly. The position is not perfect because this way we cannot reach all the ports and see all the lights. For firmware updates, we unfortunately have to unscrew the tray. However, we can easily keep an eye on the display in the boat. This we thought was the most important thing. We labeled all the cables from the BMS, so that a mistake during assembly is reduced. We also screwed the BMS and the fuse securely into the waterproof box.

We checked 2 more times that everything was connected correctly and ventured out. Fortunately, the LCD screen fired right up and everything worked perfectly!