LITHIUM BATTERIES – GAMECHANGER!

About me…

• Degreed & licensed electrical engineer
• 30+ years in data center facility systems
• Critical power system reliability, testing, and commissioning, expertise
• Started sailing & fishing at 10

Consider a water tank…

Connect a fire hose to it…or…

Connect some of this to it…

Either way, does the amount of water the tank can hold change?

Fire hose: lots of water flows for a shorter time

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Fish tank tube: less water flows for a longer time

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Volume of water the tank can hold does not change

Batteries are the same way, aren’t they?

NO!!!!

• Electrons can’t enter and leave a battery as easily as water molecules can enter and leave a tank
• Result…to know if a battery is a good fit for your application, you need to know more about it than its capacity

Please remember this one letter of the alphabet…

C

…As in “C Rating”

Consider a “100 Amp-hour” battery

• Assumption: “20 hour rating”
• Aka “C 20”
• Divide A-h by C #
• 100 ÷ 20 = 5
• 5 amps

In other words:

• You can expect a typical 100 amp-hour battery to actually deliver 100 amp-hours
• As long as you don’t draw more than 5 amps

Consider a basic cruising sailboat:

• Conventional diesel engine
• 12-volt house loads: lights, fans, instruments, small fridge, no inverter
• 10 amps max? Sounds about right
• 200 Amp-hour battery @ C20? OK

What about electric propulsion?

• Mostly offered between 3 & 25 kW
• Voltages: 48, 72, 96 and higher
• Currents: 50, 60, 80 amps not unusual, peak may exceed 120

Concerns…

• More voltage? Solved; add in series
• More energy? Solved; add in parallel
• More current? Solved; low C rating
• C2 instead of C20 = a 200 amp-hour battery can handle 100 amps

What happens when you power an electric propulsion system with C20 batteries?

• Vicious cycle – resistance lowers voltage; current rises, more heat, more resistance, voltage drops more, etc.
• Batteries quickly deplete…or die

How Do You Make a Low-C Battery?

• Make it easier for electrons to come & go
• Just like a cable – make the connection to the plates bigger
• More, thinner plates for lead-acid

Where to find low C-ratings?

• Golf cart batteries: C3-5
• Thin Plate Pure Lead batteries: C2-3
• Lithium Ion batteries: C1 or less

Golf Cart Batteries

Advantages

• Cost: Cheap
• Easy to find
• Large selection of chargers and monitors available

Disadvantages

• Flooded: must top off liquid electrolyte
• Sealed: don’t last as long
• Typically, 6 volts; more connections
• Heavy, can’t use full capacity

TPPL Batteries

Advantages

• Cost: Moderate
• Sealed, long life
• Easy to monitor
• Fast charge acceptance
• Flexible installation
• Can use most of capacity

Disadvantages

• Fewer manufacturers
• Limited selection of chargers
• May sulfate quickly if left in discharged state
• Heavy

Lithium Batteries – Recent Years

Advantages

• More compact
• Very long life
• Very low weight
• Fast charge
• Tolerant of very deep discharge

Disadvantages

• Harder to monitor
• Need good-quality BMS
• Harder to find compatible chargers
• Cost still an issue

Lithium Batteries – Now

Advantages

• Same as before, +
• More providers offering fully integrated systems
• More competition
• More compatible accessories offered

Disadvantages

• Mostly going away
• Scale – can supply chains keep up with demand?
• Cost still higher, but now favorable over long haul

Conclusion – Electric Boat Owners Should Use LiFEPO4

• Lighter & smaller = boat weighs less and has more space for other uses
• LiFePO4 lifespan = 4 lead acid lifespans
• Low C rating means much lower voltage drop at typical electric propulsion system currents
• Cost is now lower for equivalent capacity at typical electric propulsion system currents

QUESTIONS?

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David M. DiQuinzio, PE

ddiquinzio@annapolishybridmarine.com

443 924 4484