On Sunday 27 April 2003 08:39, Byron A Jeff wrote:
> But the question is the discharge characteristics of each battery as yo=
u
> point out below. And as Olin stated in another post, you have incorrect
> conversion units.

3am brain-glitch.  Corrected that now.


> > ...
> > I have a limit of 3A out.  But hopefully that won't be a problem.
>
> Probably not.
>
> > Now, all I need is to figure out the charge and discharge characteris=
tics
> > of a
> > (or this) gel-cell,
>
> And here is your problem. See batteries are magical devices ;-). The fa=
ster
> you pull power out of them, the less power you get.

Fair enough.  Sort of like an alkaline cell.



> Generally the AH rating gel-cell is over a C/20 (1/20 the battery capac=
ity)
> discharge rate. But the more current you pull, the less time the batter=
y
> will last.
>
> And that's in full effect here. Presuming a 90% DC/DC conversion the in=
put
> battery will need to provide ((16V*3A)/12V)/0.9 -> 4A/0.9 -> 4.44A of
> current. So instead of a discharge curve of 7A/20 -> 350ma you have a c=
urve
> of 7A/4.44A -> C/1.5. I can tell you at that rate the battery won't las=
t a
> 1/2 hour befure being totally discharged. And I'll bet that it'll get a=
s
> hot as hell in the process.

That's a drastic change.  But then considering the typical battery that c=
omes=20
with the laptop, I generally get 2hrs on each of those.  Perhaps the powe=
r=20
draw is much, much less than the 3A mentioned previously?  I should reall=
y=20
measure this first.



> > and build a ckt to monitor the remaining power and one to
> > charge the gel-cell.  I haven't found a suitable gel-cell charger ckt=
 on
> > the net yet, but still looking.  And if I find the discharge specs, I=
'm
> > sure I can whip up a quick PIC-based (of course!) power monitor.  I c=
an't
> > even find a website for Yuasa.
>
> For charging modes I have a post:
>
> http://tinylink.com/?CY8eaWXWht

Very fitting thread.  Just went thru it quickly, and it seems simple enou=
gh. =20
I'll re-read and play with the numbers a bit to see what's the best optio=
n=20
given expected charge time and cost/complexity/PS's I have available. =20
Thinking that my DJ500 printer PS will be perfect for this project (20VDC=
 @=20
2A), and would finally give me an excuse to upgrade to a color printer :-=
)



> > Any assistance/pointers appreciated.  And I'll even accept a "what th=
e
> > hell are you thinking" before I really get started.
>
> WHAT THE HELL ARE YOU THINKING!!! ;-)
>
> The Li-Ion and other advanced battery types are expensive for a reason.

Yep, but more my purposes, I can't seem to justify ~$130 on a laptop that=
's=20
worth ~$450, when I think I might upgrade this soon.  And I really just n=
eed=20
a power source when in Barnes and Noble, which has only one power outlet =
in=20
the coffee area, and I never seem to get it nowadays.  I'm thinking gel-c=
ell=20
in bag, and a 3-ft power cord should be a great answer and an excuse to b=
uild=20
another project.

Much thanks,
-Neil.



>
> > Cheers,
> > -Neil.
> >
> > --
> > http://www.piclist.com hint: PICList Posts must start with ONE topic:
> > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

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