Subject:
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Re: Lego Solar Cell Specs
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 12 Jul 1999 16:35:04 GMT
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Viewed:
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935 times
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Alan Carmack wrote in message ...
> In lugnet.robotics, Christopher Alas writes:
> > > Specifications:
> >
> > > 3 V, 200 mA at full sun outdoors
> > > 3 V, 100 mA at full sun indoors through window
> > > 2.5 V, 8 mA with light from 60 w incandescent lamp
> > > with 25 cm >distance to solar cell (2000 lux)
> > > 2.5 V, 40 mA with light from 60 w incandescent lamp
> > > with 8 cm >distance to solar cell (10,000 lux)
>
> So, at three volts, a typical LEGO motor will run maximum at 1/3 power. It
> would take linking three of these LEGO panels to bring one up to 9 volts.
> Other panels, such as sold by Edmund Scientific, are 9 - 12 volt in just • one
> panel.
Do you happen to know the detailed specifications of the Edmunds
Scientific panels? I ask because you need to know both the voltage and the
current that will be supplied by the solar panel under typical lighting
conditions when evaluating other solar panels. You really need to compare
the POWER output, not just the voltage or current. (The power is calculated
by multiplying the voltage by the current.)
Above, they state 3 volts x 200 milliamps for the Lego panel in direct
sunlight. So 3 volts x 0.2 amps = 0.6 watts.
If you take the same solar cells and wire them together a different way
(in series instead of parallel) you will get higher voltage but lower
current. So in theory**, you could buy the 3-volt Lego panel, take it
apart, (did I mention kiss your warranty goodbye?) and re-wire it to give
you 9 volts, but only at a reduced ~ 67 mA. It is possible that the Edmund
Scientific panel provides three or four times the voltage simply by dividing
the current by the same factor.
Long story short, you could end up buying, say 3 of the 3-volt x 200mA
panels from Lego and wiring them up in series to get 9 volts at 200 mA
(probably not _quite_ as much juice as the RCX really wants) or you could
end up buying 3 say, 9-volt x 70 mA panels (again, I don't know the actual
specs on the Edmunds Scientific parts) and wiring them up in parallel to get
9 volts at 210 mA.
Long story even shorter, the first law of Thermodynamics is: "There is no
free lunch." If they're giving you higher voltage from the same panel area,
they're probably dropping the current.
Play nicely, and don't run with a hot soldering iron in your hands!
Chris.
p.s. I mustn't forget the legalese:
** I haven't seen the Lego solar panel, so I don't know what configuration
of solar cells they used, and therefore I cannot tell you the exact
re-configurations that would be possible if you took a soldering iron to
your solar panel. But regardless of the exact makeup of either product, the
same principles apply.
Also, be very careful when wiring up any custom power source to a device
like the RCX. You can very easily cause permanent damage to the electronics
and even cause a fire. Did I mention kiss your warranty goodbye? I believe
that Lego has a specific clause protecting them when a non-Lego power supply
causes damage to your RCX.
You've been warned, so don't come crying if/when you smell that burning
ABS!
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Message is in Reply To:
 | | Re: Lego Solar Cell Specs
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| (...) So, at three volts, a typical LEGO motor will run maximum at 1/3 power. It would take linking three of these LEGO panels to bring one up to 9 volts. Other panels, such as sold by Edmund Scientific, are 9 - 12 volt in just one panel. Alan C (25 years ago, 11-Jul-99, to lugnet.robotics)
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