Ep 155 LifePo4 Lithium Marine Battery Install | One Year Debrief

• March 28, 2024 by Sailing Talisman |
• Language: EN
• Play Time: 00:25:02
• SAILING YOUTUBERS

EXPENSIVE MISCALCULATION
As longtime viewers will know, the point of this channel has never been to shine a favorable light on ourselves. Instead, we're brutally honest when it comes to admitting our fails. And despite all efforts to be the “no drama” channel, things rarely go perfectly for very long.

So with that in mind, I miscalculated one major aspect of our new battery install last year, and that was in choosing the amperage limit for our Daly BMS units. For sailors (or even RV users), I would say that the issue comes down to how you determine both your battery capacity (in Amp Hours) and how you calculate your BMS size (max Amp draw).

In many if not most cases, these choices will be bounded, literally, by space constraints. My wizened take on the process is to start by making sure your battery capacity is adequate to the need, and once this is determined, simply choose a BMS size that maximizes use of that available capacity. The above might sound obvious, and perhaps it was, but I did it wrong, basing BMS size on expected max draw instead of capacity. It is important to note that Discharge Capacity, or the ability to deliver what most people would imagine as Cold Cranking Amps, is lower for LifePo4 type battery chemistries. For example, a 100Ah hour battery with a 1C discharge limit of 100A will be woefully short if your bow thruster draws north of 600A, as ours turns out to consume. And for sailors, you must add windlass amps to the bow thruster number. This is because you might be needing both pieces of equipment at the same time for Med mooring with anchor. Figure 1500W nominal at 24V=62.5A for our Lofrans Leopard windlass.

When calculating draw vs amp hours, note that amps and amp hours are not the same. Therefore, to provide a simple conversion the battery engineers will tell you that max draw should be 1C or some such, with 1C being 1x capacity for whatever cells you have. Other brands or models of cell could spec different numbers, and even EVE (brand) states that you can draw up to 2C if done rarely. These max discharge limits will be controlled by the BMS, which is programmed internally to intervene as discharge limits are reached. And of course, with each increase in amp draw that is chosen, the BMS units will be physically larger and more expensive.

For me, the error was rooted (as stated in the video) with an incorrect spec shown in our purchasing documents concerning the bow thruster, which is a Vetus monster of a thruster. These thrusters have been manufactured for decades and are still substantially the same today as they were when the boat was manufactured. Yet there are a maddening number of variables involved, including tunnel size, prop size and number of blades, voltage, amp draw, etc. And due to our thruster motor location, squeezed between black and greywater tanks, visual inspection of the manufacturer’s production plate is impossible. No problem. Oyster knew which model they installed, so we went with that.

Except, not. I discovered this when we first started using the bow thruster. With more than a second or two of activation, the entire house bank electrical system would crash. Alarms would sound, the chartplotter and bow thruster controls would reset, rendering them useless. Luckily, engine operation was unaffected. Recovery was quick for the bow thruster, but over a minute for the plotter.

These crashes were the result of the BMS units, all three of them, shutting down at once when they hit their max amp limit. This did the job they were intended for, protecting the batteries, but a shutdown of this sort under intense load is not good for other devices sharing the system due to the large voltage spikes that accompany the event.

Voltage spikes can be devastating, although I suspect them to be more dangerous to 12V systems as the amperage there is doubled in comparison to a 24V system. In any event, it turned out that our older voltage “droppers”, the devices that convert voltage from 24V to 12V, were the most vulnerable. Newer Victron models seemed unaffected. We may have also lost an older GPS antenna, and of course the 24V alternator rectifier and diode pack shown in the episode. And know that fuses and breakers protect against amps, not voltage increases (within reason).

All told, we’re looking at about $1,100 for the upgraded BMS units, upgraded wiring, lugs, etc at $270+/-, $75 for alternator rectifier and diode packs, Raymarine RS150 GPS at $250, 2x Victron Orion 24/12-15 droppers at $45 each, and five full days of labor to complete the install.

We sincerely hope that these lessons might be useful to others.









sailing yacht talisman, sailing, sailing youtube, boating, top sailing, oyster yachts, oyster sailboats, oyster 485, offshore, bluewater, blue water, sailing vlog, sailing vblog, sailing channels, sailing videos, cruising, monohull, EVE batteries, LifePo4, LFP, installing marine lithium batteries, Daly BMS, alternator failure, voltage spike

Sailing Talisman

RYA Yachtmasters Kevin and Wendy Kelley have transitioned from their Oyster 485 to a new Nordic 40, 'Lulu'. Explore their 2026 vessel transition and technical journey.

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Ep 155 LifePo4 Lithium Marine Battery Install | One Year Debrief Location

• Antigua and Barbuda (17.060816,-61.796428)