Further to requests from members viewing the Alpha 42 thread I thought I would share some of my ideas WRT onboard gensets and blue water
I am currently 12 months into the build of a new series of Catamarans, with another 3-4 before we splash. The Architect is Roger Hill from NZ and the design is based on the 42 ft Montebello from AU built in 2010. Phil of Multihulls and Roger worked to create a second generation of the boat. It was great because we were able to closely critique the first generation, which was a very nice boat in itself, and build on that success to create a new series called the Balance 451.
I was fortunate enough to be able to design my own electrical
and mechanical systems. My challenge was that I wanted a fast, light cat while still wanting some of the creature comforts that would allow my wife and I to enjoy the boat for years to come and that means having ample electrical
supply and some air-con for tempering and de-humidification.
Together with the builder
we decided on a 24V system as this significantly reduces the copper requirements and 24V products are readily available now.
Then I decided to go with a Lithium LiFePo4
system. The Boeing event caused some reflection but with a good enclosure, a complete BMS (battery management system) and redundant banks, each fully independent, I feel we are in good order(I hope I don't have to eat these words) This gave me over 800 amp hours (1600 at 12V) of power, while weighing the same as just 4 8D AGM
The real beauty of lithium batteries is their ability to accept a high rate of charge, right up to 95%. These batteries can be charged at up to 3C. That means that if a battery
has a 200AH rating it can be charged at up to 600 Amps, or fully charged in just 20 minutes.(to be safe I have kept it to 1C)
Many of you know there is nothing worse than having your genset screaming away for hours and watching your charge rate drop to almost nothing, because the system has gone out of bulk mode.
And even better, they can be discharged to 20% vs AGM
which is 40-50%, thus significantly increasing our effective capacity.
They do seem to be more intolerant of complete discharge, but with a good monitoring system and full redundancy we should be ok. After a few months on the water
I will try to give everyone an update.
For shorepower charging
and A/C I am using a 24/3000 Victron multiplus.
while at sea I decided not to use a small genset.
I looked closely at the Panda 4200, and several other 4-5K gensets, but it just didnt make sense to add yet another engine
to the boat. Why add another 400-500 lbs when I already had two great 39HP Yanmars available?
After doing a series of daily load calculations, allowing for refrig, instruments and 3-4 hours of aircon, I determined I could add a high output (4kw) 24V alternator
to each of my propulsion
engines and running one of them for only 1-2 hours per day would yield me all of the power I needed. This is only made possible because the batteries can easily take such a high rate of charge. And now instead of a tempermental genset that needs maintenance
, spares, oil
changes, etc... I have a fully redundant charging system for the house batteries as well and it was still significantly cheaper than a genset.
And with almost a kilowatt of solar
, and 300 watts of wind
, in favourable conditions I may not have to run an engine
for several days. The challenge with the solar
was in boosting voltage up to 28.4V and getting a Lithium hi output charge profile. Bruce Schwabb was a great help here and recommended the Genasun Solarboost. I am also using his External alternator
regulators with the 28.4V LiFePo4
charge profile on 2 x 28V 160A APS alternators so I can minimize engine charging run times.
For aircon I chose two 9KBTU mermaid units. I have them Y ducted to either the salon
or the cabin
, with one in each hull
. I chose these as they were capacitor start units with a slow startup current
(lock rotor) and both should be able to run happily off the one Inverter
. (If not, I will add a second inverter) They will not keep it cool in the heat of the summer but they will temper and keep the humidity levels down. Beer
will do the rest!
If anyone is interesting in more detail just let me know.