I'll look for other rating numbers on the garden
tractor batteries to see if we can establish an
AH reference. I probably do pull about 50% from
them for most cycles. I've recharged one battery
at least 40-60 times and its still outputs nearly
as much as my newer ones. The fast
chargea-bility (and low cost!) made me go lead
acid for long take set-ups. I need the exercise
anyway. Rob D.
At 7:53 PM +0000 11/2/05, werainey wrote:
>--- In Rob Danielson <> wrote:
>The CCA figure of 240 is for engine starting [see a battery terminology
>FAQ/glossary like http://www.payless-batteries.co.uk/Batterytip/tips.php\]=
.
>With batteries rated for extended discharge
>(e.g., deep cycle) there should be=A0
>another number which will be about a factor of ten less. This rating-- the=
one
>relevant to your task -- will be something like the maximum number of Amp
>hrs obtained discharging over 20 hrs to a final voltage of 10.5.
>
>The deeper you discharge nearly any lead acid battery the fewer total
>discharge-recharge cycles you get out of it before capacity begins to decl=
ine
>rapidly. Deep cycle batteries are built to
>handle this much better than starting
>batteries. Spec sheets at the web sites of Yuasa or other mfgrs have graph=
s of
>number of cycles vs. proportion of capacity discharged. Gel cells are ofte=
n
>rated as better than AGM in this respect, *but*
>they don't tolerate high charge
>rates.
>You want to extract ca 72 Ahr. An impractically conservative value (favori=
ng
>long total battery life) would be to discharge to 50% of capacity, but th=
is
>would entail carrying 70-80 lbs of batteries. With lead acid to get the we=
ight
>down, you have to substantially shorten the life of the batteries. More=
=A0
>expensive batteries with higher mass energy density and different respons=
e
>to deep discharge because of different
>chemistry are appealing if it is all on
>your back.
>
>bill r.
>>
>> I'm cheapie at heart. Maybe to a fault! "240 Cranking Amps" is what
>> they say on top. They're about 9"X 6" X7", come with carrying handle,
>> cost $30 each and you are absolutely right, they can be spilled!
>> Many times I've toted one for miles inside of a backpack wrapped
>> inside of an 1/8" thick rubber sheet. Never spilled a drop so far but
>> I wouldn't hike on loose gravel either. Gell cells would be
>> fantastic and much safer. How many cells/packs would one need to pull
>> down 3 amps at 12vdc for say 24 hours? How about bulk and weight?
>> Cost? Too often I prove that my motto, "You never have enough power
>> and disk space." is correct. I can stop at an AC outlet to put a 50
>> amp quick charge on a garden tractor battery and be 95% sure I'm
>> heading out with enough power to get me through two days if needed
>> (no powering external hard drive though). Rob D.
>>
>> At 8:39 AM +0000 11/2/05, werainey wrote:
>> >Rob,
>> >
>> >Is the 240AHr a typo? That would be a big lead acid battery. After
>> >inconvenient accidents with tipping and
>>draining of wet cell garden tractor
>> >batteries, I'd suggest the more expensive option of ganging equivalent
>> >capacity of smaller gel cell or AGM batteries. No orientation
>> >issues, easier to
>> >carry, more tolerance for deep discharge if the right models are
>> >chosen/available..
>> >Bill R.
>> >> One thot here: Be prepared with more than one "solution" to the pow=
er
>> >> challenges. For your fixed site recordings, I'd consider one or two
>> >> "small" ~240AH 12 volt garden tractor size lead acid batteries.
>> >> They'll run a 722 for days, but best of all, they can be fast-charg=
ed
>> >> with car battery chargers you're likely to find even in remote plac=
es
>> >> or with a small 1-2 amp trickle charger you can carry with you. The
>> >> Sound Devices site has considerable discussion about power options
>> >> too. For portability with long duration ability too, I recently add=
ed
>> >> two more cells to one of my D-Cell NiMH packs and the MAHA charger
> > >> seems happy charging it (while on AC!). The 722/744 runs much long=
er
>> >> on 12 cells (than 10) because of the large voltage drop to 10.8
>> >> volts, the cut-off point.
>
>
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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