Your biggest problems would be weight, possible corrosion, lack of
enough power for much use for a fast computer, efficient conversion to
the desired voltage for use inside the wearable, and internal battery
constraints (this is off the top of my head, there are better experts
here but I'm trying to learn by saying what I know & learning what I
didn't know as well as what I don't say that I do know <G>)
Lead-Acid is heavy for the power you get from it (aka "Low Power
Density".) If it works for you, it's good (Lead-Acid IS cheap.) Carry
it around for a day, see if your arm falls off <VBG>
Corrosion: Drop it, crack the case, watch the wearable get etched by
the fumes <Ack!> - or the same to your clothes & skin. Unless it's a
gel cell, those don't have that problem. (This can be handled by a good
case around the battery, for a wet battery.)
Insufficient power: 12 Amp-Hours is enough for many tasks but I
wouldn't try running a P2-333 system off of it necessarily <G> Or at
least not for too long (if you can run it mostly off AC or a car
adapter, and only need some lifespan, might work well.) Of course, 12
Amp-Hours IS quite a bit of power if your converter's efficient (It
would run a PC110 [486SX33, PCMCIA HD, etc.] for about ?12 hours or so?
with no power savings turned on, you'd want a power efficient wearable
machine for long lifetime...
You'd want an efficient converter and some power safety circuitry (if
you're charging the system off a car cigarette adapter, you need to rig
it so you don't accidentally discharge the battery through a short
across the plug (i.e. either a series diode, or keep the plug in a safe
place when not charging & be careful when charging. The series diode
would slow recharging the system, potentially...) You'd want to make
sure the converter could handle higher input voltages than 12V (a "Load
Dump" where the charging system is charging the main car battery & a
load is turned off {turning the headlights off, or the air conditioner
shuts off, etc.} - the battery voltage shoots up for just a fraction of
a second, until the charging system compensates) into the converter if
it's connected (i.e. you're running the computer) while charging, can
put a rather large voltage spike into the adapter plug, the battery will
of course reduce the spike a lot which is good, make sure you wire the
battery 'tween the input power plug & the output to the power converter
- (you don't want to blow your converter.) And 12,000 mAh times 30%
conversion efficiency = only 3,600 mAh (the rest dissapated as heat in
the converter; some GOOD inexpensive converters have been discussed
here, 92% or so efficiency, which is great.) Some regulators (for
example, the good old 7805) are NOT designed for efficiency, don't use
one of those <G> - converters are usually rated & designed with
efficiency in mind.
Internal battery constraints: You'd want a "Deep Cycle" battery not a
car or motorcycle battery, as those are designed for shallow cycling
(start the car, drive away & charge it back up, lots of room under the
normal discharge amount for starting in cold weather or starting,
driving 2 blocks, then re-starting later) unlike deep cycle batteries
(like trolling motor batteries, RV batteries, etc. where they're
designed to be deeply discharged & then recharged. But your battery
pack may well be a deep cycle battery, which is what you'd want here.)
Mark, have you looked at the battery FAQ at
http://www.ingenuityinc.com/ttsnicad.htm, which is about Ni-Cads (their
second installment at http://www.ingenuityinc.com/ttssla.htm is
specifically about sealed Lead-Acid batteries which might be good for
your project!?)
Mark Willis "the verbose"
Mark Lenigan wrote:
>
> I have a 12 volt, 12 Amp-hour lead acid battery with a fuse and "car
> cigarette lighter adapter." With the proper voltage regulation cicuit,
> would this be a suitable power supply for a budget wearable?
>
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> http://www-personal.umd.umich.edu/~mlenigan/
>
> "End the discrimination! Support dyslexic vending machines...after all,
> they don't care which way you insert your dollar."
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