Re: Another Novice Q. - recharging - Volts and Amps

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Kris Krieger wrote:
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Kris Krieger wrote:

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[edited]


Only *after* I know all that, can I select the specific cells, and
configuration therof...

- Kris

As you said, you are working backwards. You don't yet understand
that doing it that way can result in a specification for cells
that are "unobtanium".

Ed



"Unobtanium"??, it's a modest LED night-lamp, not an airport beacon
:p

I *already* know the batteries and their output, and the input needed
by the LED driver and what it will output to run the LEDs (which will
run off the batteries at night) - those are not the problem.

To charge my 4 little 1.2V AA NiMH batteries, I have seen the
following solar cells (and more, this isn't an all-inclusive list):
0.5V, 200mA
0.5V, 450mA
0.5V, 800mA
0.5V, 2000mA
1V, 200mA
2V, 200mA
3V, 400mA
4V, 25mA
etc.

I also know that, depending upon how I connect cells, I can up the
Volts or up the Amps, or both if it's a series-parellel combination.
The biggest Q. is the volts. I read that, using a 5V solar cell,
charging time would be the battery mA divided by the cell mA, but
what if it was a 2V cell, or a .5V cell?

Well, I'll write to Maxim, since it's their components I'm interested
in. They can prob. best tell me the input I need for the
battery-management IC.

- Kris


Sorry, Kris, but in terms of the necessary specifications,
you have posted nothing useful to make an informed design
decision. That is not an attack on you, it is just that
you are working in an area that is new to you.

I found teh answer to my question here:
http://www.solar-world.com/SolarMini-Panels&Motors.htm

Specifically:
"...the solar operating voltage must be higher than the battery voltage..."

That was all I was asking.

Netting your problem out, you want to drive an unknown
(in terms of voltage and current) load

The Q was not about the "load", it was *simply* and *specifically*, I'll
repeat, this:
Given NiMH batteries, size AA, rated at 1.2V and 1500mA, what would I need
in terms of soalr cell output to charge tem using a battery
charge/control/protection IC (the Maxim DS2715).

I don't understand what in that is "unknown" or otherwise unspecific.


for an unknown amount
of time with an unknown number (but less than 5)

I'd repeatedly specified "between 3 and 4"...

NiMh AA
cells of unknown capacity, said NiMh's to be charged with an
unknown number of solar cells of unknown capacity in an
unknown environment.

*Of course* the number of solar cells was unknown - anyway, the "number" is
not relevant, what is relevant is the *output*, and my Q. was specifically
about *needed output*, so that I could go back to the catalogues, look at
the sizes/ratings, and determine what I'd need in terms of numbers, and
arrangements.

As for environment, not relevant to teh question - the question dealt with
ratings. I'm not so stupid that I think SOLAR cells will "work" at night
or in deep shade, or that they generate the same power on cloudy days as on
bright, sunny days. But I did not ask about differnces in output on cloudy
versus sunny days, I asked, based purely upon ratings, about charging a
specifically-described battery.



The key design question is: how much input power will be
available?

No, the key design question was, as Tom Biasi had notd when I first began
asking my Solar Light questions, was:
"One place to start would be to determine how much illumination you need.
Find LEDs that can give you that. What voltage and current do you need to
power the LEDs for the period of time that you would like? What battery
will provide that?"

The question I asked in this thread was the final question of Tom's initial
input:
"What solar arrangement can charge the battery in the time that you want?"

I didn't know how to do the math. Now I think I might know it.

The surface area of your device that will
be exposed to direct sunlight and that you are willing to
dedicate to solar cells will determine that, in terms of
the maximum that can be achieved.

THat wasn't what I was asking. I was asking what output (from the cells)
I'd need to charge the specified batteries. I didn't ask about sruface
area - I alreasy knew that, which is why I listed several of the available
solar cell outputs, which I'd selected becasue their footprint fell within
the size limits I wanted. So the surface area was not the concern and was
not at all related to the simple question I was asking.

Obviously, the power
will be less if the device is in the shade or the cells
receive less than full sunlight for some other reason.

Not to be rude, but, duuuuuuuuh... Again, tho', not what I was asking.


You are here asking for help - but _ONLY_ you can answer
that question.

Well, between all the different solar-cell-related websites, electronics-
related websites, the Tech Support folk at Maxim, and so on, yeah, you're
right, I finally *am* answering the question I'd asked in this thread about
what Solar Cell output is required to charge the specified batteries.


If we don't know how much power is available, it is not
possible to say definitively if your idea is even feasible,
let alone specify how to do it.


You can't figure out whether it's feasible to run 4 regular (i.e. discrete
5mm dome) LEDs off of a solar-charged battery pack of 3 NiMH AA 1500mA
batteries?, or up to 6 (same type) LEDs off a solar-charged battery pack of
3 or 4 NiMH AA 1500mA batteries?, or what output V and mA you'd need from
solar cells (obviously placed in the sun :p ) to charge even one
1.2V/1500mA NiMH battery? You can't even determine whether that is
*possible*?

OK, whatever...


Thankfully, there were a couple of folks who were very helpful and got me
going in the right direction, whom I'm thanking in a separate post.

- Kris



.

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