On 17/11/10 01:21, john briese wrote:
All this "Math" forgets using 50% of charge on T105s and using 80 to 100% on Nife.
Lets complete the math.
Some where in the pile of doco I have about my T145s Trojan say they rated them for 80% DOD. Yes they recomend 50% for optimum life, but the cycle rating given is for 80% usage.
My T145s will die of old age before they die of excessive cycles even if I took them to 80% every use, which I don't. I think the most I've even taken them to is 60%. My usage is relatively low though. My boat spends more time sitting on a trailer than any thing else.
To: electricboats@yahoogroups.com
From: ewdysar@yahoo.com
Date: Tue, 16 Nov 2010 08:47:47 +0000
Subject: Re: [Electric Boats] Picking batteries - NiFe
Kevin,
I did the math with the data on the link that you provided. One 100Ah 1.2V cell weighs 4.9Kg (dry weight?), so 10 dry cells would weigh 49Kg which is 107.8 pounds. That battery would be rated for 1200Wh which is 11.1 Wh/lb. But the page says that you need to add distilled water to make them work, and of course the link doesn't say how much. If a 100Ah cell takes only 2 cups of water, then one cell is close to 12 pounds and we're back to 10Wh/lb. Looking at the 200Ah cells, they are 26.4 pounds dry or 264 pounds for a dry 200Ah 12V (2400kWh) battery. Add water and you're probably past 280 pounds or 8.5Wh/lb.
Alternatively, a T-105 weighs 62 pounds (according to Trojan) and is rated for 225Ah @ 6V or 1350Wh. That works out to 21.8 Wh/lb. Take two in series and you've got a 225Ah 12V battery that weighs 124 pounds.
Are you really sure that size doesn't matter? Lets compare the 200Ah 12V NiFe to the 225Ah 12V T-105s
2400Wh NiFe = 13.2" x 32" x 13.6" = 5745 cu. inches, 280 pounds
2700Wh T-105 = 10.4" x 14.3" x 10.7" = 1591 cu. inches, 124 pounds
The NiFe battery is more than 3 times the volume of the two T-105s for 10% less rated capacity.
I'm not passing any judgement, just doing the math so that people can decide for themselves.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Kevin Pemberton <pembertonkevin@...> wrote:
>
> Eric,
>
> According to this page batteries supplied by Ironcorebatteries
> http://www.ironcorebatteries.com.au/page8.php 100Ah weigh almost 100lbs
> for 12v pack. T 105 6v about 67lbs. No problem discharging NiFe to 80%,
> big problem discharging the T 105 to 80% over the long haul. Was two
> optima blue tops. 120 lbs for 100Ah when large discharges a re not
> figured in. Where is weight a problem?
>
> mount in wood mount because fumes are non corrosive, can be mounted
> anyplace if vented outside. Size becomes no problem.
>
> And yes I see the weight problem with anything other than batteries
> easily distroyed by over charge or over discharge.
>
> Kevin Pemberton
>
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