Mark,
Agree very important to have bus bars and connections tight and clean. These Chinese cells have alu tapped terminals with iffy screws. I put SS studs in mine. Be very careful installing them, you can over torque them and break into battery cell easily. Bit once they are in a lot easier to change stuff later.
I hit a committent point on my 12 foot cat dinghy last month. Gas or electric. I was making motor mount. Motor mount done for 8 hp gas yamaha. In my opinion, motors not there yet. Batteries are there or very close.
The submersible motors always leak or corrode. I think everything electric needs to live a very sheltered life. I've got ideas, but waiting for someone else to do it.
I do believe one day this will be way to go, but not now.
Jerry
On September 26, 2024, at 12:47 PM, Mark Stafford <mstafford@natca.net> wrote:
Another possible failure point (there are many different types of failure points): each battery connection. Make sure each connection to each post of each battery has the same high amperage surface contact area, the same cleanliness, the same torque value on the nuts or bolts, the same operating temperature, the same washers, the same lug count, etc. The basic concept is that you are trying to drain and charge each battery identically. If one of the posts has a higher resistance to electricity flow (dirty, loose, wavy washer, different size washer, wavy lug, worse crimping of the battery cable to the lug...) that post will run hot, which changes the internal resistance of the battery, which further exacerbates the imbalance, which further drains that battery, which can quickly and permanently change the internal chemistry of the battery.
Most of the time, these slight imbalances amount to a hill of dry beans (dry beans self-level pretty well). But if you cook the beans, the hill of beans can be significant.
The BMS was telling you to stop, in a language that assumed you were an electrical engineer with deep knowledge of LiFePO4 battery chemistry. Sometimes safety requires us to kill the batteries to save the boat, so the nice thing about your BMS is that it let you kill some batteries to save yourselves.
One really helpful simple tool is a $30 temperature gun. A more expensive but automated option is to install calibrated temperature probes on each battery terminal, and feeding that information to a BMS that would alert you to temperature imbalances.
One gallon of diesel compares to roughly 40 kWh of energy. You have roughly 4 kWh in your fully charged healthy 16 battery pack (4,480 under perfect conditions, which they never are). But your e-propulsion is ideally about 5 times more efficient than diesel. This means your 4 kWh pack, times 5 for efficiency, equals 20 kWh diesel power equivalent. So going out with your (16) 280Ahr batteries fully charged is like leaving the dock with 1/2 gallon of diesel fuel. You could go really slow (~1 knot) for ~10 hours, or really fast for ~10 minutes, but then the batteries need charging. Your 2200EU generator allows you to travel at ~1 knot continuously if the generator is running continuously. These are very approximate water speed estimates, not GPS speeds, and are influenced by literally hundreds of variables about your sailboat, the sea state, the weather, people moving around on your boat, etc.
This is the ballpark you are playing in. It is not an argument for or against e-propulsion, just the current state of electricity storage and creation.
My arguments for e-propulsion are:
low operating cost
low maintenance
low stink
low sound
low space requirements
low emissions
high reliability
high precision of thrust
high thrust available
high tech
high investment in a better tomorrow
The hard part: e-propulsion often comes with a high learning curve. Many of our ancestors died during the learning curve of gasoline, but they gifted us cultural wisdom about the dangers of gasoline. We are gifting our progeny with the cultural wisdom of clean energy use. Don't kill yourself in the process: each battery can be lethal.
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