the question is too wide Re: Is lithium really safe ?
Non rechargeable lithium cells button types in cameras watches are real fire bombs but not interesting for
marine power use
Lithium
family is large but LiPo lithuim polymer types are the most prone to fire even when not
charging or discharging
Probably due to lack of power density and low cycle lifes typicaly sub ~500 cycles not interesting for boats electric
engine use
Other LiFE types are too
low power density but real hard to break in use
Lithuim Ions Li-Ion types are the best power to weight density but have low C rates for charging and discharging in this time( but rapid improvements are already in the pipe line ETA the market looks to be for ~2023 ).
They are fragile cant take much abuse as it wrecks them easy.
The Li Ion cells need to be done properly and not thrown together in hap hazard ways or treated negligently
However costs are not affordable for the average joe in this time for being a
marine electric
engine source for large boats .
Can be interesting as domestic power source or for yaught
tender or shore electric bike uses.
Cheapest way is to buy the cells and make your own pack .THE Li-Ion CELLS CANNOT BE SOLDERED they can explode from the heat and heat can wreck their chemistry .
They have to be spot welded with special spot welding units (can be home made look up youtube how to make spot welders for Li-Ion cells) or they can be fitted to specail boxxes (expensive ) The clesss abilties are limited to 1C discharge rates sometimes 2C depending on quality .Recharge times are long less than 2c rates often 0.5c rates or two hours to recharge .They need proper battery management system solutions and most off the shelf BMS dont
work properly and wreck the Li-Ions.( look up
google on best BMS for Li-Ions
For marine eletric power soultions in this time the best looks to be the flooded acid Golf cart 220amp 6 volt lead acid battery .They do plus ~550 deep cycles eg more than ~80%
depth and plus ~1000 cycles at 50%
depth. (You need to arrange the acid cant come out in heavy seas /real thick lead plates ensure long life cycles
Normal Marine 12 volt deep cycle are often sub ~200 cycles for deep cycle and sub ~1000 cycles for 50% discharging .
AGM Is a tad better than than normal marine deep cycles but real expensive
Gel cells are ultra fragile low discharge rates and low recharge rates .Note many battery suppliers call
AGM a gell cels and that confuses everybody
There exists a lesser well known type of lead battery called Lead crystal battery .When the electrolyte is discharged it turns into powder type of Crystal solution . When recharged the Crystal turns into a more liquid acid form of electrolyte . The adverts claims seem to be exaggerated ~3000 deep cycles .Experts seems to indicate its not a whole lot better than AGM types and costs are orbital for lead type battery solution .The jury is out on the Lead crystal battery
There are many conversions of boats from
diesel to electric or Hybrid using golf cart batteries or lead acid types including AGM.
There are very few
commercial car and boat conversions using Lithium ions as the costs are off the
charts typically $10 a lithuim ion cell of 2 amp makes a typical 12 volt battery with 40 amps eye watering $$$$ with its BMS and casing and marine testing etc
Last figure I saw on the subject was I think a ~9 kilowatt ~320 volt pack li-ion from a German maker was more than ~$12,000
Lithuim ion for domestic battery looks to good idea in this time the increased cycle life looks like it will return the investment in due course and have no big risk for fires compared to other lead acid solutions
Electric boat conversions tend to suggest that ~2 kilowatts of electric power can replace ball park ~8 BHP or ~ 6 kilowatt of
diesel power
This is because the Diesel engines tend to be about ~7 global efficiency
The Diesel engine might be ~20 efficiency at the shaft but losses in
gearbox and shafts and props often reduce this to ~ 3% to ~10% global efficiency at the
water propelled .
~7 global efficiency looks to be averageefficiency with modern boats in cruising speed mode in flat calm waters .
Eletric proulasion might start with 90% efficiency at the motor with modern 3 phase motors (NOT DC BRUSHED MOTORS) but looses can bring that global effiency down to ~7% to 25% making ~15% global efficiency a good ball park number to
work from using Brushless motors and lighter plastic props .
Bad quality batteries and brushed motors and
cheap electronic controllers that make too much heat can reduce the global efficiency further
A typical lead acid AGM 48 volt ~150 amp
electric motor system on ~24 foot sailing boat will give ~4 miles range flat out at ~6 kilowats and 5.5 knots and ~20 miles range at 2.5 knots at about ~1.5 kilowatts ( from my memory these numbers when i looked it last time )
Starting out with a 6 volt Golf cart battery solution for ~48 volt systems which should last a few years. That means that when the newwer Li-Ion with power density reaching 350 Watts per Kilogram arrive in 2023 if the prices drop enough would make it affordable to swop out the 6 volt golf cart batteries and replace them with newwer li ion solutions
Hope that helps you and the rest of the
boating community