Re: Portable batter packs and Solar Charging?

From Wear-Hard Mailing list Archive (WH) Maintained by R. Paul McCarty

On 7/13/06, Craig M. Armstrong  <> wrote:
> OK I did some math today:
..
I did some more math, but seemed to have misplaced the paper right
now. But the thought was to use AA sized NiMH batteries.

Intuitively, I'm guessing my idea won't work. I'm hoping someone will
point out where this plan will run in to difficulty:

Am I correct in thinking that connecting the 10V output of the solar
panel on the backpack to eight AA's in series (9.6V) should to charge
them up?

And if I connect leads across five of those batteries I'll have six
volts, which looking at my Nokia phone charger and my WristPDA wall
warts, is what they put out. So it could charge them, and I'm guessing
any mini-USB chargeable device?

And if I put twelve of them in series I'll have 14.4V which will be
enough to run an inverter. Then the trick would be to switch which
eight I was charging so that all twelve of them end up being charged
from time to time.

1.2V * 2Ah * 12 batteries = 28.8 Wh (it is energy, 1Wh = 3600 J)

I'm guessing the problems will arise when current is drawn from all 12
batteries, and is simultaneously trying to go in to eight of them. Or
perhaps when current is going in to eight of them and trying to come
out of only five of them. Or perhaps charging the middle four
batteries twice as often as the outer eight.

Questions for Abe:
If this does work, would you be able to eliminate either your voltage
regulator or DC DC converter?

Your battery pack: 6Ah * 7.2V = 43.2Wh.

Would 28.8 Wh be enough for you? If it's not enough energy, you could
put pairs of AA's in parallel to double the power, or use C or D cells
instead of AA's.

I'm sure this idea will break down somehwere as I don't know what the
solar panels will generate in room lighting. But if you were able to
average one quarter effieciency from the backpack (1W per hour), then
after 10 hours of light you'd have 38.8 Wh you could use before
charging up the battery again instead of just 28.8, which is nearing
the capacity you have now.

What is your wearable setup comprised of? I'm interested to see your
average power consumption and how long your wearable lasts.

--
Craig

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