WHY DO I WANT LITHIUM-ION BATTERIES?
Gayle Evans explains why they ditched their lead-acid batteries
I live full-time on our 44ft ketch with my husband, Tim, and our dog, Pip. Tim is an engineer, and over the past few years, he has become a bit of a lithium battery geek. I have a more limited understanding of the subject, received by osmosis through Tim’s musings.
This question of ‘why do we want lithium-ion batteries’ came up last year. Our trusty Trojan T105 lead-acid batteries were nearing the end of their life. Despite having had a life of daily float and never being discharged below 80% the heat and old age were slowly killing them. Less caring owners would have probably killed them sooner. Their capacity was slowly declining.
So why lithium-ion rather than more
Trojans? Tim was keen to build a lithium-ion battery and put all that he had learned into practice. The number of cycles (6,000) and therefore their longevity was compelling and we’d be freed of the necessity of floating our battery bank daily, in fact, they like to be in a discharged state.
Now having lived with lithium-ion for nine months, it would be very, very hard to go back!
The first surprise for me was that our 720W of solar panels were giving us a lot more daily power. So with the same solar panels, the energy that we could use was a lot more. Previously we would get up to 2kW daily, now we were getting over 3.5 kW! Wow! Suddenly I was cooking on our small induction hob, normally reserved for marina use and I use the gas oven only when I want to bake anything. Refilling our gas bottles is a thing of the past. The heat in the galley is a lot less, ditto the humidity as we no longer have the level of moisture we used to have in the boat due to gas combustion.
We use this extra power for heating water on the immersion heater, vacuuming up dog hairs, and running our 240V watermaker.
Secondly, lithium-ion batteries are really small and quite light in weight. You may need to redistribute some stuff around the boat as we have done. We monitored the bulk, absorption and float phases of our lead-acid batteries over the years, and we used to be a bit miserly with power in the evenings to make sure the voltage was high enough for the fridge loads overnight. We do not worry about that any more and are happy to watch a movie, turn on the lights and cook dinner. In fact, we now need to consume energy so there’s some space in the lithium-ion batteries ready for them to receive their solar charging in the morning.
How we built our own lithium-ion battery
Building your own lithium-ion battery is not as hard as it sounds.
For our first battery, we chose CATL grade A, 280Ah cells and a JKA 200A BMS with 2A active balancer.
We built a second battery with EVE grade A 105Ah cells. We used an additional identical BMS. The following description relates to our second smaller lithium-ion battery.
From a fancy kitchen shop, we bought
a huge nylon chopping board an inch thick. We could have bought some good plywood but the cutting board was not expensive and it looks more professional. It’s durable, easy to work with, drill and shape to size.
From a chandlery, we bought a 6mm threaded rod, nuts and washers and some small diameter pipe, big enough to sleeve the threaded rod. This stops any possible chafe between the threaded rod and the battery cells and also provides electrical insulation.
We bought some thin A4 glittery blue foam sheet (colour is optional) from a craft shop and a 5mm thick piece of clear polycarbonate to make a cover plate which is bolted to the top of the chopping boards with appropriate spacers. This allows you to access the fuse, BMS and shunt without the risk of dropping a spanner across the live cell terminals and causing a short circuit.
As we are on a 24V system we have eight 105Ah cells in series. This gives us a 24V, 105Ah battery. If you are on a 12V system you’d need four cells in series to give you a 105Ah battery at 12V.
We cut the foam sheet to fit between each cell to prevent any chafe and additionally, it provides electrical insulation. We lined up the cells in series.
The piece of nylon chopping board was cut to form end plates. We made it 2cm wider and 5cm taller than the cells. This allows room for the connecting rods and space at the top for the cover plate. A length of threaded rod was fitted at each corner, sleeved with the pipe, and tightened with the nuts and washers to provide compression and a way of holding the cells in place.
Our cells came with busbars. So now it was just a case of connecting the individual cells in series. The BMS wires connect to each cell terminal. We then wired up the fuse holder to the positive terminal followed by an isolator rated for 200A, and the BMS to the negative terminal followed by the Victron Smart shunt. The battery was then connected to the charger and the BMS settings were configured for our battery via the Bluetooth BMS on a phone. The battery was fully charged.
A BMS with an active balancer can perform a top balance of the cells. With a BMS that doesn’t use an active balancer, it would be better to top balance the cells before assembly into a series pack. Top balancing involves charging the cells in parallel first. Not a difficult job but it can be time consuming.