Professional BoatBuilder - December-January 2018

DECEMBER/JANUARY 2018 41

SYSTEMS: Battery Technology

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President, Jarrett Bay Boatworks

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converted to heat. If the heat is not

removed, the windings will fry, and

the diodes will fail.

In a “traditional” charging situation,

the batteries accept the alternator’s full

rated output for only a short period of

time, a er which the battery charge

acceptance rate declines, the alternator’s

output reduces, and the fan within

electronics and a potential  re risk for

windings, cables, and connections.

Alternators are the worst case, because

the average alternator is, at best, only

60% e cient at converting mechanical

energy onto electrical energy (note

that specialized alternators are consid-

erably more e cient than this).  e

remaining 40%+ of the input energy is

battery pack, rated at around 10-kWh

capacity, will be able to absorb the full

output of the machine up to almost a

100% state of charge.  e 95%+ battery

e ciency will ensure that little charg-

ing energy is wasted as heat.  e abil-

ity to withstand near 100% discharges

for thousands of cycles will enable us

to utilize at least 8 kWh of the 10-kWh

battery capacity at each cycle.  e

immunity to damage from sulfation

will permit operation in a partial state

of charge whenever, and for however

long, we want.

With lithium-ion applications in

mind, we have designed our alterna-

tor-type device such that even if it is

open-circuited at full output, it will

not generate a damaging spike: if the

BMS disconnects the batteries, the

boat’s electronics will not blow out.

 ere is no need to have a lead-acid

bu er battery in the system.

On our cruising sailboat, with our

current energy needs of less than 3

kWh a day, one battery charge will

keep us going for three days. Or,

alternatively, 20 minutes spent setting

or retrieving the anchor or getting in

and out of a slip will give us all the

energy we need for 24 hours. I am

thinking of converting to electric

cooking and getting the propane sys-

tem o the boat.

Hot Alternators

 e newly developed capacity of

battery systems to absorb very high

levels of charging current allows opti-

mization of electrical systems in ways

not previously possible. However, this

high charge acceptance rate has the

effect of forcing charging devices

(alternators and battery chargers) to

maximum rated output for extended

periods of time, and subjects the cables

in the system to high continuous cur-

rents. Both of these conditions present

some new challenges to systems

designers and installers.

No charging device is 100% e -

cient, nor is any cable 100% e cient at

conducting charging currents. Ine -

ciencies translate into heat, and heat

translates into damage to sensitive See us at • Booth 1

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