Ok, I goofed on the price per mile for the two different batteries.
T-125 = 4.25nm/cycle * 650 cycles = 2762.5nm. $1000/2762.5 miles = $0.362/nm
LiFePO4 = 14.5nm/cycle * 2000 cycles = 29,000nm. $8000/29000nm = $0.276/nm
LiFePO4 is 23.75% cheaper per mile at full battery lifespans in your boat at 3.8kts.
Will you ever motor 29,000nm at 3.8kts in your lifetime? Probably not.
Maybe a smaller (lighter and cheaper) Lithium battery pack would be more appropriate. :)
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Eric" wrote:
>
> Hi Carter,
>
> I know that your plan is largely solar and you've got generator and a full diesel driveline as backups, but here's some battery only performance data.
>
> So your eight T-125 (530 lbs) have a 20hr rating of 12kWh, but at a 25A load, the total capacity drops to 10kWh (that's the Peukert Effect kicking in). Put the load up to 50A and the total capacity is 8.4kWh. And at 80A (you said earlier that 80A = 3.8kts or 4.4mph), the total rated capacity falls to 7.5kWh, a loss of 37% to Peukert's effect. Limit your discharge to 60% of total capacity and you batteries will last 1.12 hours at 80A draw. At 3.8kts that works out to 4.25nm range on a full charge of your batteries.
>
> The Balqon pack with a 20hr rated capacity that is 67% higher than your FLA pack seems like a luxury, but let's check the same loads. Balqon doesn't list the weight, but it should be right around 500 lbs like your current pack. Starting with a total rated capacity of 20kWh, at 25A the rated capacity drops to 19.86kWh, very close to the 20 hour rated capacity. At 50A, the rated capacity is still 19.45kWh. Finally at 80A, the Balqon pack rates to 19.2kWh, losing only 4% to Peukert's Effect. Since LiFePO4 batteries can be consistently discharged to 80%, you could run the motor at 80A for 3.83 hours for a range of 14.5nm. That's 3.4 times the FLA range at 3.8kts under batteries alone.
>
> So at the cash register, the Balqon battery looks 8 times more expensive than the T-125s. But if you consider the increased range without any weight, the Balqon pack is only 2.3 times the cost of the T-125s. Trojan says that the T-125 is good for 650 cycles. At 2000 cycles for the Balqon, you would have to buy 3 sets of Trojans for the same number of cycles. If you factor in the full life span in cycles, the Balqon works out to 12% cheaper per mile than 3 sets of T-125s.
>
> I know that this doesn't change the fact that the original investment takes a bigger wallet, but that could ultimately save you money in the long run.
>
> I know that you didn't ask for this, but I like running the numbers, and it's been a while since anyone has done the math in front of the group. I figure that this exercise might be helpful for new mebers here.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
> --- In electricboats@yahoogroups.com, Carter Quillen wrote:
> >
> > Followed the link to check it out. Nice battery and made in America, (mostly), to boot.
> > Â
> > Wish I had an extra $8 grande, I'd buy one tomorrow. Puts my 8 pack of Trojan T-125s to shame but since I only paid about a thousands bucks for an 8 kW pack I don't feel that bad. Looking forward to the day when you'll be able to buy Lithium for the cost of lead and it's coming. In mean time, I'll have to be content with my horse and buggy and wait for the model 'T's of batteries to hit the market.
> > Â
> > Carter
> > www.archemedesproject.blogspot.com
> >
> > From: James Sizemore
> > To: "electricboats@yahoogroups.com" electricboats@yahoogroups.com>
> > Cc: "electricboats@yahoogroups.com" electricboats@yahoogroups.com>
> > Sent: Wednesday, February 20, 2013 7:24 PM
> > Subject: Re: [Electric Boats] Re: Converting a small trimaran to electric drive
> >
> >
> >
> > Here is a 20kw lithium pack with bms and case for the below 8000, total package.Â
> > http://www.balqon.com/store.php#!/~/product/category=2897128&id=12658249
> >
>
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