Wh is a much more useful comparison as we can easily break capacity per dollar into $/Wh.
Soo... that does bring up another important point I was going to save for another segment.
Higher voltages mean lower amperage, and therefore less heating effect and lower cable thickness and weight.
Higher voltages have more chance of arcing and electric shock (albeit at lower amperage and therefore technically safer possibly).
As some of the electric cars run at 100s of volts in potentially very wet conditions, what would you folks recommend for a harsh marine environment for a boat of this size?
I am thinking at least 144V. If it were your project, would that be fine. Would you go higher? 240? 480?
* Please discuss the pros and cons as you see them.
* How would you wire up the batteries to achieve this
* Also staying with the battery pack part of the project, what are your "must have" safety concerns.
* What specific vendors would you/have you used, and what $/Wh did you pay?
Thanks to all!
Bill
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Hi James,
>
> By saying 800Ah, you aren't giving any real indication of the overall capacity of a battery pack. If you insist on using Ah as a measurement, you need to include the pack voltage so that we can figure out what you're suggesting. Using Wh as a measurement, you get past the voltage thing.
>
> For example, I could buy 4 200Ah LiFePO4 cells and hok them up in series for an 800Ah 3.2V (2650Wh) bank at the low cost of $1200, including shipping and a simple BMS. Buying 64 of the same cells, could be configured to create an 800Ah 48V (38.4kWh) bank for $19,200, including shiping and simple BMS. Using the same type of cells to build an 800Ah 72V system will be even more expensive. There are people in this group that are running 144V systems, so we can't assume that we know what you're describing.
>
> Fair winds
> Eric
>
> --- In electricboats@yahoogroups.com, James Sizemore <james@> wrote:
> >
> > I have priced Corvus packs and they are four times the cost of your typical chinese prismatic cells. they are in the same price range a Mastervolts lithium cells. Basically they are unaffordable.
> >
> > Best to buy the cells and BMS yourself, and build your pack. If you want to stay anywhere near your 100K target. With current pricing you can buy a 800 AH LiFePo4 pack for around $18,000 with BMS. I recommend the cells below. I have no recommendation on BMS (still undecided myself.)
> >
> > http://www.evsource.com/tls_lithium_calb.phphttp://lithiumstorage.com/index.php?main_page=product_info&cPath=&products_id=40&zenid=i92g73ucddgr7o1l1a4gb1u561
> >
> > On Aug 22, 2011, at 11:16 PM, Galstaf wrote:
> >
> > > Batteries:
> > > Goals –
> > >
> > > Use a Li based system for energy density, lower mass, and ease of use. Really interested in something that is as easy to manage as possible. As Eric estimated I would need 110,000 Whr approximately to go for 24 hours at 5 knots without any replenishment at an estimated cost of $46K, I have revised that to half that figure for weight and expense reasons.
> > >
> > > 12 hours of drive time should be sufficient 90%+ of the time. If I need the extra umph at that point, it is time to kick on the genset.
> > > So that would put me at 55000Wh of capacity at an estimated cost of $23K, right?
> > >
> > > I have been interested in the Dow Kokem marine duty batteries for a while now just because they claim they are pretty much indestructible regardless of DoD and charging rates. They also say each battery has it's own web server engine to provide centralized health stats on each battery.
> > >
> > > http://www.corvus-energy.com/marine.html
> > >
> > > Questions:
> > > * Are these claims pie in the sky?
> > > * Does anyone know of anyone that has used these batteries and BMS in production?
> > > * Does anyone know approximately what these Dow batteries cost per Wh?
> > > * Does anyone know anyone else that can boast of these properties at a lower cost?
> > > * What are your recommendations on where to shop for Li batteries?
> > >
> > > The manufacturer claims that you cannot hurt these batteries by fast charging them. They also claim no damage even with a full 100% discharge. Would it make sense then to buy an oversized genset and charging system so that a replenishing charge could be dumped into the batteries in short order and the genset (with it's incessant vibration noise) could then be shut down?
> > > The oversized Genset could also help push the motors along in case of emergency when speed IS key to avoiding a storm or getting to safe harbor. Comments?
> > >
> > > Any other comments about the BATTERY portion of this project, please feel free to be as verbose as possible. Links to manufacturers, and any and all pricing and performance data is sincerely appreciated.
> > > My best,
> > > Bill
> > >
> > >
> >
>
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