Alt-BEAM Archive

Message #10790



To: beam@sgiblab.sgi.com
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Thu, 24 Feb 2000 21:52:04 +1100
Subject: [alt-beam] Re: Combining Solar Cells



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This is exactly the conundrum I faced with my Seaplane robot:

http://wollongong.apana.org.au/~ben/seaplane/

I used a 2911 solar cell, and I used two SCPD's to boost the voltage. So
what's going on with your circuit?

Well, the mini solar cells boost voltage, sure, but they HAVE A MAXIMUM
CURRENT THROUGHPUT. This means that as soon as you start pushing too much
current through them, they actually develop reverse voltage across them!

So here's what to do:

Put all ten SCPD's in parallel. Now attach the common negative terminal of
this SCPD bank to the positive terminal of your SC2433. Now you should have
an extra 0.45 volts to charge your solar engine with! That is, the voltage
of the SC2433 + 0.45 volts.

I did this with two SCPD's on my Seaplane because I wasn't too concerned
with how long it would take to charge, but I did want good low light
performance. I would suspect that your ten SCPD's in parallel will boost
your performance a lot. I did notice that the maximum rate of firing slowed
from 3 times a second to once a second when I added the two SCPD's (This is
just like you described). But the low light performance is a lot better.

Have a look at the schematic (attached) to see how I did it, and in your
case I would just keep adding solar cells in parallel with the two that I
have shown in my diagram.

You could also make two lots of five SCPD's, and put each bank of five in
series with each other and the Solar panel to give you an extra 0.9 volts.
This will boost your low light performance more, but you will pay for it in
terms of longer charging time in bright light.

It's always a tradeoff, isn't it?

Ben

----------
>From: "FCO Enr."
>To: beam@sgiblab.sgi.com
>Subject: Combining Solar Cells
>Date: Thu, 24 Feb 2000 20:23
>

> greetings,
>
> Well I've been experimenting with my 1381 SE and
> trying to figure out how to boost it's energy gathering capability.
> My idea was to use 10 SCPDs and a SC2433 together to make
> a solarengine that could work quite actively under my normal
> room lighting.
>
> I did a few tests, wiring the 10 SCPDs in series WITH
> the SC2433 under my regular lighting produced a pin to pin
> voltage of 5+v, but when I wired it to the SE circuit and monitored
> the circuit voltage, I was seeing a super slow increase in voltage.
> When I removed the 10 SCPDs I noticed it was charging FASTER!
>
> So then I tried using the SC2433 in parallel with the 10 SCPDs
> wired in parallel I noticed everytime I connected the 10 SCPDs into the
> loop whatever circuit voltage I had dropped to aprox 0.45 volts and
> it stayed there!
>
> I looked through my electronics theory book but I didn't
> see any mention of such wiring and so I don't know what could
> possibly be wrong.
>
> I would appreciate any help, especially theoretical info
> that could help me put it into perspective.
>
> thank you for your time!
>
> Andy
> fco@total.net
>
> hrdware's digital sanctuary - mindless oddities
> http://www.angelfire.com/pq/hrdware
>
> The Factory - TF Map Making Tutorial
> http://www.planetfortress.com/factory


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Attachment: schematic.gif

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10791 Thu, 24 Feb 2000 02:57:58 PST [alt-beam] Re: Seals on motors for aquabots beam@sgiblab.sgi.com "Timothy Flytch" On boats they use a "stuffing box"... Basically it is just a tube about 1
1/2 the shaft diameter with seals at each end that the shaft passes
through... then it is stuffed with packing grease... I have used them both
on full size and models...
For beam I think a small length of drinking straw and some teflon washers or
O rings with vasiline(petroleum jelly) should work... only question is
drag???
Timothy...

>I haven't had any leaks yet but I only tested it once. One thing that I
>have tried is to make my own rubber seal. I haven't tested it yet but
>it looks really good. What I did was put a thin film of vaseline on the
>shaft of the walkman motor and then place silicone rubber around it.
>You have to cover up mounting holes with tape or wax paper so the
>silicone doesn't get into the motor. Then I cut out a same diameter
>hole in some wax paper, put it over the motor shaft and carefully
>flattened out the silicone rubber so it has a nice flat surface. Mine
>was about 1/16" thick. It may take a few days for it to cure since the
>only exposed area is at the edge of the paper. This way you get a seal
>all the way up to the shaft of the motor. It hasn't been tested and it
>may make mounting the motor more difficult but it's a new twist.
>
>
>Tod
>

______________________________________________________



10792 Thursday, 24 February 2000 1:01 Re: Walker problems beam@sgiblab.sgi.com Jim Taylor
>
>
>
>> probably a 4 foot tall killer walker :-)
>BING BING BING....show him what wonderful prizes he has won :) I think I
>will only need to move maby 2, 3 amps at max, but I still would like a
>cushion to fall back on. I had been thinking of using some homemade
>airplane Speed controllers. They work on PWM though, more complexity, plus
>I don't have any that will do proportional reverse. Remeber I need to be
>able to drive these puppys in CC, and CCW.
>
>
>
>> I'd go for a commercial motor driver, i've got these free ones that
handle
>> 55v at 3 amps from national semiconductor - but they are expensive.
>
>any idea of the part number? Don't need that many watts, prolly only 70
>watts at max.
>
>
>> David
>
> |___|
> -------O()O-------
>James Taylor
>URL: http://fly.to/springmeadows
>

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