Quote:
Originally Posted by KTP
According to the load voltage curve from Lifeline, their AGM batteries have the following voltage drop at the 8hr rate (45 amp draw on 375AH battery bank) assuming you have four batteries in series for a 48V system:
90% 12.6V * 45A = 567W * 4 batteries in series = 2268W to motor
80% 12.51V = 2252W to motor
70% 12.39V = 2230W to motor
60% 12.25V = 2205W to motor
50% 12.11V = 2179W to motor <--LiFePO4 187.5AH bank is dead here
40% 11.98V = 2156W to motor
30% 11.79V = 2122W to motor
20% 11.32V = 2037W to motor
10% 11.15V = 2007W to motor
0% 10.50V = 1890W to motor
So you maintain over 2kW to the motor all the way down to 10% remaining on the Lifeline AGM. Hardly what I would call "massive" drop. But this is only facts and stuff...don't let it deter the thread
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Unfortunately for us mere mortals we need to try to and figure out what this table means to us so I will try to have stab at it using a typical deep
keel 24 foot cruiser
boat as a example steaming in calm waters
I shall assume the craft does 3.5 knots at 2268W
rpm of prop unknown size and type of prop unknown
~45 amp draw on ~375AH makes ~8 = 0.125C or just over 10% of the battery capacity
The importance of this is if you ask ~50% capacity from the battery such as ~50 amp on ~100 AH battery you will be lucky to get ~50% the energy the battery has
Also it would be hard get a more than ~1 hour of the battery running with a AGM battery and many FLA type batteries wont even go there
Extreme C rates waste most the
power in heat losses due to IR^2 making heat loses increase exponentially
So low C rates between ~8 % to ~12% as tops with ~20 % in extreme requirements in
emergency use for AGM and FLA battery types to get battery to return the most useful
power ratio over time .
Needless to say drawing the power from AGM and FLA battery over ~20 hours or ~0.05C will return the best power efficiency ratio over time but not much useful power for motors
So 24 foot
boat doing 3.5 knots using 2268W over 8 hours might look more like this
1 hour ~2250W = 3.5 knots
2 hour ~2200W = 3.2 knots
3 hour ~2150W = 3.1 knots
4 hour ~2100W = 3.0 knots
5 hour ~2090W = 2.9 knots
6 hour ~2050W = 2.8 knots
7 hour ~2030W = 2.7 knots
8 hour ~2010W = 2.6 knots
23.8 miles completed
If the choice was to go at 4.5 knots the amp draws might be 100 amps range will drop probably look like ~11 miles range over ~ 3hours and 0.4C on 375AH
If the choice was to go flat out 5.5 Knots amp draws of ~200 amps range could drop to ~5 nautical miles over ~1 hour
The best energy ideal for many deep
keel boats willl tend to be at ~60% of the ultimate waterline speeds
As we progress towards the max waterline speeds the power demands go up exponentially
The life span of FLA and AGM will benifit from not exceeding draw rates that will flatten the battery before ~8 hours
However that increases cost a lot
Many
electric boat projects will opt to use rates in excess of this ideal such as ~20% draw down on the battery AH per hour but only for short duration and low ranges such as one mile range to exit the harbor
FLA and AGM can return OK life spans from ~20% demands abuse use for short duration of the battery if full and power is restored to battery shortly after the abuse such as battery recharged after ~4 hour sailing session
There might exist
electric calculators that can inform the users of what to expect from any sets of battery used on various crafts so as to reduce risks of choosing the wrong sets of
equipment for the boats
The problem with many of the Lithuim cells ls the cycle life divided into cost by power ratios often make them cost more than lead solutions
Li-ion 18650 type of cells have the highest power density ratio and can if sourced correctly and built by amateurs return benefits that exceed Lead Battery solutions but the cost risk ratio are high in this time .
If we used FLA battery golf car types at ~$100 X 8 = ~$800 for a 6V battery of 220 AH on a 20 foot
sail boat
drawing ~30 amps for ~7 hours about ~1500W to motor
going at ~2,5 knots or range of ~15 Nautical miles
with a 550 cycle life
= about ~8200miles or about ~0.42cents a mile or $6.30 for each ~15 Nautical mile trip
(in realty closer to ~$8 a trip in terms of battery cost ife ratio with
head winds and
current and other factors added in ) .
NB the last ~100 cycles might drop from ~15 Nautical miles to ~10 Nautical Miles range with incremental drops in range with each cycle as batteries sulfate .
With AGM often costing double the
price often you can nearly double those cost per nautical mile numbers so many AGM solutions for this type of boat will tend to be ~100 to ~150 AH to reduce costs but with reduced ranges .
They will often be the types that use ~2 miles ranges to enter and return to harbors where 220 amps weight and costs cannot be justified .
With most of the Lithuim families costs and power density in this time its easy to double or quadruple the costs again per mile over the AGM battery solutions in this time
With Lithuim ions 18650 cells using methods like sourcing batteries bulk cheaper and even
buying slightly used types and building the packs as amateurs sometimes cost per Nautical have been able to match AGM costs .
Some might say well good old
diesel works best is cheaper .
However when all costs are factored into most
Diesel solutions they often come out even on 20 BHP inboards well north of ~$1 dollar a nautical mile
Many boats rarely used with
winter summer
maintenance costs can exceed easy ~$5 a mile
Much Bigger Diesel engines can pluck a number from the ether and then double it for luck and still be very wrong .
The
marine environment is very harsh on diesel engines compared to land based diesel
engine solutions
Back to
safety electric solutions done right rarely have
engine failures especaily at critical points like exiting a harbor .
Diesel engines can let you down at critical points when you need them most anything from
water in the
fuel to plant growth in the
fuel tanks or pipe works and other mishaps
Electric battery fire hazards are low but if ignited tend to be tricky to stop fires without forward planning and suitble fire stoping solutions and
training
the
Lithium ion
family of the LiPo type being the riskiest for fire and exlosions and LIFE types being the lest risky with 18650 type nearly as low risk as the LIFE types .
The FLA types have Hydrogen gas risks but has proved itself to be a rare event fire explosion risk if done correctly .
AGM battery types are probably the least risky for fires of the lead acid battery
family
Diesel engines are also a risk for fires and depending the amounts of uel the risks increase .Cruising boats can and do often carry extra fuel on the decks in jerry cans which might risk to ignite from other fire sources .Diesel fuel fires are very difficult to stop once they start .
One 65 foot boat crossing the Atlantic engine room fire required three fire extinguishers to stop the fire and it was a local fire around the engine not so big but fuel lines were feeding the fire .
The least fore risk is to have no power source other than the
sails not even
solar cells or domestic battery or
cooking solutions like gas or any electric power for domestic solutions .
Not too many sailing dingy s ever catch fire
Hopefully next year I will install a golf cart battery solution to a ~21 foot boat that i intend to buy if things
work out but i probably opt for ~24 volt solutions . I would also if possible try to add a suitable 2kw gasoline (petrol Benzine )
generator to the mix to increase the range somewhat .
The prime reason is the 4 battery 24 volt combo of 220Ah will return a lot of good use for domestic battery demands with short engine runs to enter and leave harbors .
Boats above ~22 feet to about ~35 feet have to do the 8 battery 48 V solutions. Above that size starts to become mega serous costs
In few years time the costs of
Lithium ion 18650 cells might drop enough to kill of lead acid but the jury is still out on that .
Realistically I cant see any type NiCads Or NiMh being useful for boats use,
NiMh types if they catch fire are nearly impossible to put the fires out as the Battery is filled with oxide materials that love to burn with great heat something like LiPo does. Also their power density is low with their 1.2volt per cell .
However the Li Ion 18650 cells makes great projects to replace the 12 lead acid solution for the
tender dingy or 24/36 volt batteries for the electric bikes that device the boats .The
learning curve from those projects can teach the solution for the future Li ion projects
Hope that helps the
boating community