At 12:46 AM 10/07/2010, Harry Wilkins wrote:
>The overarching goal is to be as efficient as possible by cutting losses.
><snip>
>The best practice would be to store your power in your battery bank
>at whatever voltage your biggest load will be. In the case of
>electric propulsion that would be your motor voltage.
G'day All
I'm coming in a little late on this one, however, it may not be
necessary to store the power at the voltage needed, depending on the
circumstances of charging vs discharging.
Talking of 144V systems in small boats pretty much eliminates hybrid
operation (where you are charging to range-extend whilst you are
discharging). If this is the case, it is possible to use three, 48V
battery packs, normally charged and for 'house' use discharged as a
single 48V block, with the 48V stuff attached to a 'base' block, and
two extension blocks paralleled up.
When high-power propulsion is needed, the two extension blocks can be
switched in series with the 'base' block using contactors, allowing
discharge as a 144V system, also allowing the use of cheaper 48-volt
contactors to do the switching (although a diode really needs to be
associated with each of the contactors, in case of opening under load
so that the contactor does not see more than 48V).
It would be possible to build a system that uses a cheaper 48V
controller to drive the motor when cruising and operating in 48-volt
hybrid mode, plus a more expensive controller for 144V high-power
mode, alternately switched to the same motor. This would also provide
some redundancy in the event of controller failure.
It also means that the system as it 'sits' is safer to work on/live
with (48V is less likely to kill you).
As for the comment that there are "no good quality 120VDC input
inverters" (or words to that effect) Selectronic in Australia make
very good ones: http://www.selectronic.com.au but may be higher power
than what was being looked for.
Regards
[Technik] James
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