I recently installed an LTO (Lithium Titanate Oxide)
battery for
engine start and
windlass use. LTO cells are nominally 2.3 V and don't have the flat section on the charge/discharge curve that
LiFePO4 cells have. The full voltage range is 1.5 V to 2.8 V. The advantages of LTO cells are that they can deliver a very high
current for their size and that they allegedly have a long life of 25,000 cycles. A small
battery with the ability to deliver a high
current can be a good choice for
engine start,
windlass and thruster.
The nominal voltage and voltage range for LTO cells means that you can either use five cells in series and maybe have a voltage that is a bit low for 12 V applications or use six cells in series and have a voltage that is a bit high. I went with six cells in series and only
charging them to 2.5 V each. Not being charged to 2.8 V is probably not a problem even long term. I charge the battery using a Victron Orion-Tr 12/12-9 DC/DC converter which delivers around 9 Amps. I programmed a BMS to stop
charging the cells at 2.5 V for a 15 V total battery voltage. The charging restarts at a cell voltage of 2.35 V.
I used 40 Ah cells that are very similar to these:
https://shop.gwl.eu/LTO-technology/Y...l-B-Grade.html
The
electrical system is very simple with only the following components attached to the LTO battery: BMS, DC/DC converter to charge, engine and windlass. The BMS does not do any low or high voltage cutoff, it just controls the DC/DC converter. The engine is a Nanni N4.60 and the Windlass is a
Lofrans Tigres with 12 mm chain and a 30 kg Spade S140
anchor. The engine
alternator is not attached to the LTO battery. Attached are the graphs of what happened during six minutes around the retrieval of 40 meters of chain at 12 meters
depth.
At 0.5 minutes, the engine was started. At 1 minute, enough chain was brought in to take off the snubber. At 4 minutes, the chain was pulled in with about 15 meters left out. Then the engine was used to pull the
anchor out of the muddy bottom. Finally, at around 5 minutes, the rest of the chain was brought in with the spikes at the end bringing the last bit in to have the anchor at the right place on the bow. The bottom (blue) curve shows the current and at around 4 minutes, the BMS decided to activate the DC/DC converter to charge the battery. The top curve (green) is the battery voltage.
You can see that the LTO battery has no problem handling the high loads. The total energy used during this anchor retrieval was around 2.5 Ah, so not very much considering the 40 Ah total capacity of the battery. The charging took around half an hour and the battery was not 100 % charged before this test.
All in all it seems that the LTO battery is a good choice for this application. It is quite small and the cells weigh 7.5 kg in total.
As an interesting aside, it turns out that the engine uses 250 mA when running for the instrument panel and sensors.
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