At 12:26 PM 26/01/2010, masnami1999 wrote:
>My name is Mazlan Isa. I am planning to build a 35 foot boat using
>outboard electric motor. I am planning to use ultracapacitor as
>energy storage plus Lithium ion battery as power but to gain more
>amp. The boat that i am planning is to be use at fresh
>water/river/
>recharge the energy storage. the amount of power is eq : 600 amp per
>set. we have two set to rotate the charging and loading. Could
>someone have better assemble opinion or suggestion.
G'day Mazlan
Forget the ultracapacitors - they are useful in fast
discharge-recharge application, but the capacity for $ spent is
ungodly expensive. Spend the money on larger Lithium cells, make sure
you are putting a "bulletproof" battery management system on the
Lithium cells. You cannot simply parallel batteries and
ultracapacitors, ultracaps discharge characteristic is that they
loose voltage all the way, and quite steeply, where batteries hold
pretty flat voltage across most of the useful discharge range.
How many volts are you planning? Your description of the batteries
implies that you are intending to use two batteries, each of 600
amp-hour cells, but at voltage that is not stated - available stored
power is amp-hours multiplied by the voltage, so to know how much
power you are storing you need to tell us at what voltage.
The voltage decision is as much one of what motor (and controller)
you plan on using - but unless you are very comfortable working with
electricity one of 24, 36 or 48 volts is the preferred voltage choices.
If you are intending to recharge from a generator, then there is not
much point in using electric - just put a diesel in. If the generator
is only to be used for power security - i.e. used only when you've
been unable to charge, then that is good. There is potential for
efficiency gains if the engine would be spending most of its' time
essentially idling - running at low efficiency. Run the engine hard
for one hour to recharge the battery for 10 hours' cruising should be
more efficient than idling an engine at slow cruise speed for 10
hours. The more time spent charging, the less efficient the exercise
becomes, to a worst case where you are charging the entire time you
are running. There is potential to get some efficiency gains -
running the generator engine at its' most efficient RPMs and using
electric drive to run the prop at its' most efficient is common on
big ships, but little help on a 35' boat.
Your description reads as though you think that there is some benefit
to run from one bank of batteries whilst recharging another from a
generator, then switch banks and run from the bank just charged,
recharging the one you were running from. All that does is waste
energy, so I hope you are not meaning that. If that was what you had
in mind, remember that each time you convert energy you loose some,
so if you were to do that, your energy losses would be something like:
(100% available energy from) Diesel=> (30% available from generator
as) electricity => (now loose 15% of that going through the charger
into the battery) => battery in => (convert the stored chemical
energy back into electricity and loose 5% again coming back out)
battery out => (controller efficiency is pretty good, loose another
10%) controller => (and another 15 to 20% in the motor) motor =>
gearbox => prop.
If you expect to spend a lot of time running from the batteries and
not much time charging there is no need for two battery banks, just
charge the one you are running from. This saves the energy loss of
not doing the 'extra' conversions of the energy being used straight
away. Nothing will get upset that you are running from power from the
genny instead of from the batteries, whilst the 'extra' power from
the genny will go into the batteries. Start and stop the genny to
keep the batteries at a reasonable state of charge, lithium chemistry
is fine working between 20% and 80% 'full', without harm in being
left partly 'flat', so they are a good choice (second only to NiMh,
but they are unobtainable in large sizes).
Your choice of Lithium and desire to use ultracaps implies you have
plenty of money to put into this project, so a hybrid power source
that includes a generator (preferaly running from biodiesel if being
'green' is important to you) plus solar, wind and shore power when
available can be a good solution and is quite achievable.
Sounds like a nice project.
Hope this helps
Regards
[Technik] James
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