what is the largest Li bank you have?

[KTP]

In our electric powered 34 foot PSC sailboat we have about 18kW of AGM right now, weighing in at around 800 pounds (no diesel engine or fuel tank so just a bit heavier than a standard PSC with a couple of house batteries).

It is fine for what we are doing right now, mostly day sailing around the Puget Sound, but with the price of LFP coming down near AGM (and the lighter weight and greater usable capacity), well...

I think we could swap out to about 40kWh of the LI time drop in batteries for a pretty reasonable price. This would triple our range on battery power. In calm waters we do about 6 knots using 4kW (if the hull is clean lol).

I had been toying with a small diesel generator but they are very pricey right now and it has been nice having no noise, fumes or mess (or maintenance). We just step on the boat, turn the key and slip out of the marina without even waking up a cat.

[Pete7]

I think that would be a great project, particularly if your AGMs are a few year old now.

By chance do you have a speed v kW graph. I made this one up from some numbers I was given as rough guide. Electric Yachts put together a spec for me for our Moody 31 and their figures without prompting were very close.

However, the cost to go EV and the fact that we only use 100 litres of diesel a year is difficult to justify £10 - 12k.

Pete

[KTP]

I can't find my exact speed/watt measurement right now but I did see the measurements we made several years back are closer to 4.5 to 5 kts for 4000 watt input (although the hull was not sparkly clean. This matches your chart.

6 kts is probably 8,000 to 10,000 watts.

Right now we putter around at 2500 to 3000 watts because I usually only draw down the AGM to 50% at most. We do sail quite a bit.

10,000 watts is reasonably close to what the original engine was putting out at 1/3 throttle or so, which makes some amount of sense.

I don't think electric makes sense if you have a working diesel...we did not. Then again, I have not had to do any maintenance to the "engine" in the past 5 years, and it starts up every time.

[s/v Jedi]

Originally Posted by KTP

In our electric powered 34 foot PSC sailboat we have about 18kW of AGM right now, weighing in at around 800 pounds (no diesel engine or fuel tank so just a bit heavier than a standard PSC with a couple of house batteries).

It is fine for what we are doing right now, mostly day sailing around the Puget Sound, but with the price of LFP coming down near AGM (and the lighter weight and greater usable capacity), well...

I think we could swap out to about 40kWh of the LI time drop in batteries for a pretty reasonable price. This would triple our range on battery power. In calm waters we do about 6 knots using 4kW (if the hull is clean lol).

I had been toying with a small diesel generator but they are very pricey right now and it has been nice having no noise, fumes or mess (or maintenance). We just step on the boat, turn the key and slip out of the marina without even waking up a cat.

I think you mean you have 18kWh right? (instead of 18kW). At what voltage? With Lithium,you can only connect so many batteries in parallel and in series because of BMS limitations on system voltage and maximum amperage.

For example, for 12V I think with LiTime batteries you can only go up to 20kWh using four of their largest batteries in parallel.

[donradcliffe]

I think the key missing number is the voltage of your existing bank and motor.

[KTP]

Sorry, it is a 48 volt system and 48 volt brushless 10kW motor and controller. We have a 50 amp DC-DC that converts 48V to 12V for our house systems.

So our bank is 3s4p of Lifeline 12V 125AH AGM. 18kWh technically but really you can only use around 9 to 10kWh.

Our charger/inverter is a Magnum 48V input which is capable of charging the 48 volt bank at around 50 amps using 30 amp 120V shore power. It has settings that would be compatible with LFP as well.

[s/v Jedi]

Originally Posted by KTP

Sorry, it is a 48 volt system and 48 volt brushless 10kW motor and controller. We have a 50 amp DC-DC that converts 48V to 12V for our house systems.

So our bank is 3s4p of Lifeline 12V 125AH AGM. 18kWh technically but really you can only use around 9 to 10kWh.

Our charger/inverter is a Magnum 48V input which is capable of charging the 48 volt bank at around 50 amps using 30 amp 120V shore power. It has settings that would be compatible with LFP as well.

Okay so let’s say you take these batteries: https://www.litime.com/products/liti...00a-bms-5888wh

With two in series you get 11,7kWh so add strings up to four maximum for 23.5kWh, 35.2kWh or 47.1kWh which is the maximum they support.

[goat]

Hi KTP. I'm on a Orion 27 with the 10kw Electric Yacht system. I've got 9.5kwh of lithium batteries. I made my own pack using the plastic cased Calb 180ah cells. It works out to about 200lbs. You can buy cheaper, lighter, cells now, but I like these cells better than the thin skinned aluminum ones. It's plenty of battery for the lifestyle I lead. Solar is a big one, especially where you are at this time of year. Summer you'll enjoy the faster charging lithiums.

Good luck on whatever you choose to do.

goat

[TBW]

It would be useful to know if anyone has had a positive approval from their insurance company for the installation of lithium batteries (brand?). Markel is 1 M. total, liability and boat.