Alt-BEAM Archive
Message #01014
To: jfeser@ea.com, TurtleTek@aol.com
From: Steven Bolt sbolt@xs4all.nl
Date: Fri, 26 Feb 1999 09:43:36 +0100 (CET)
Subject: [alt-beam] Re: ARG, stupid 'vore! + V vs A
On Thu, 25 Feb 1999, Feser, Jason wrote:
> I've had the same problem. Using the 24x33 panel and a 1381J, I
> could only get the motors to trigger if the panel was VERY close
> to the lightsource. I would have to get the panel within about
> half a foot of the light before anything happened. I swapped up
> to a 37x33 and it goes like mad! From what I understand, the
> 24x33 will provide about 2.7v @ 16mA
Actually, the nominal voltage is a lot lower at that current. And
you don't get the nominal values anyway, except in very good light.
That's why a Solar Engine should be able to charge its cap with
less than 0.1mA flowing - preferrably *much* less.
> and our trigger (the 1381J) will fire at about 2.7-2.9v. Keeping
> in mind that your panel should always provide a bit more voltage
> than your trigger value we should have noticed right away that we
> probably wouldn't have enough voltage to kick the circuit into
> triggering. Thats why in this case voltage wins over current. I
> think that the 1381G would be the trigger to use with the 24x33
> panel.
The switch-on/off levels should be determined by the task; what
your motor(s) need to shift the load as you want it. Then you
factor in the kind of light in which you still want it to work.
From those two parameters the number of cells that make up the
ideal panel can be determined. Panasonic offers small Sunceram
panels consisting of 4, 5, 6, 8, 16 and more cells, but the cells
differ in size, making selection a bit more difficult.
For example: If you want to work in daylight (not only direct
sunlight), with a switch-on level of 2V to 2.3V, you can use the
24x33 (5-cell BP-243318) if your application is satisfied with less
than 0.1mA. If your app is able to live with less than 0.02mA at 2V,
that panel is sufficient on a rainy day, indoor, not too close to
the windows.
> From: TurtleTek@aol.com [mailto:TurtleTek@aol.com]
> I used a 22x33 sunceram solar cell from SB.
Afaik there is a 6-cell 24x22 panel (BP-242221) and a 5-cell 24x33
which has much larger cells. I'm not aware of a 22x33. What's the
number of cells?
> First of all, it doesn't trigger at 2.7 like it's supposed to.
The J triggers somewhere between 2.6V and 2.9V. Don't count on
every J to have exactly the same trigger point. For those trying to
help you, it would be more interesting to know at what voltage it
does trigger, if at all.
> Another thing I noticed is that the solar cell isn't so great.
> The cap charges to about 2.5 or so when 2 ft away from a 55 watt
> light. Maybe I've just been spoiled by the 37x33.
That one consists of 8 cells (each the same size as those on the
5-cell 24x33). In the same light, it gives you the same current at
a 60% higher voltage.
> The thing is I was told that current is "soo much better" than
> voltage.
Only if the voltage is sufficient in the light conditions you
design for. Once you have the voltage, increasing the number of
cells does not make your SE charge faster, but increasing cell size
does.
> Now I believe more voltage is favorable (as long as you have
> enough current to drive the curcuit) and I will continue with
> this belief until it is _proved_ (or at least explained)
> otherwise.
That's not the right way to look at it.
> BTW, to those of you who don't know, the 22x33 produces more
> current than the 33x37.
I haven't seen a 22x33. Maybe you are comparing the 24x33 with the
37x33? The cell size of those panels is the same; in the same
light, they provide the same current, but the 37 with its 8 cells
does so at a higher voltage than the 24 with 5 cells. Of course, if
you add more load, the voltage drops and current rises. A panel
with 60% more total surface area tends to win.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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