Alt-BEAM Archive
Message #01547
To: Jean auBois aubois@trail.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 16 Mar 1999 19:53:47 +0100 (CET)
Subject: [alt-beam] Re: `Green Thumb'
On Tue, 16 Mar 1999, Jean auBois wrote:
> I believe that the basic difficulty with this design is being missed here.
> Someone mentioned that it is very difficult to obtain very efficient pumps.
> Someone else mentioned that the only liquid valves that seem to be
> available are these hulking things that take 12 or 24 volts or the like.
Actually, I'm both someones :)
---8<---
> Given that the typical photobot transforms what available light energy
> there is into mechanical energy pretty efficiently I hope that you can see
> that it just isn't going to be easy to provide enough "oomph" either to
> pump water or to interrupt its flow.
---8<---
> The real challenge would be to invent/design a valve that could operate at
> photo-BEAM energy levels. I think that it would be extremely cool if
> someone could do that.
You're a tad pessimistic, perhaps. During summer holidays, I run a
simple pump and timer system with outlets in four pots. 2 minutes a
day are sufficient. Power use is about 500mA @ 6.5V, resulting in a
daily energy consumption of about 0,1 watthour. Since it is summer,
a small solar panel (like the one used by my clock-motored
Photovore) might well be able to supply an average of 5mA
@ 3V for 10 hours a day. That would provide about 0.15 watthour,
quite possibly enough to recharge a nicad to power a pump of
similar efficiency.
So imho a solar powered Green Thumb & pump system for a single
potted plant is very likely to be feasible.
> Furthermore, if you are using a pump and there is ANY head of
> water above it, you also have to keep the pump from spinning just
> because of hydrostatic pressure.
The pump in my example above is situated on the floor below the
window sill, together with a jerrycan of water. The plants and the
outlets of the system are above the reservoir's water level.
Operation is quite trouble free.
> It is easier to keep one of those terra-cotta plant waterers filled (and
> cheaper as well) than most of the schemes that have been introduced and
> they supply water even more slowly than a drip-waterer.
I've tried them. The capacity of those which fit my potted plants
is insufficient to cover more than a few days of absence. They also
tend to clog or something - anyway, they do not reliably provide
water for thirsty plants like my lemon geranium. The Green Thumb
plus guy with watering can has proved to have superior performance.
I admit that the Green Thumb seems a bit high tech, kind of
overdone. But my better half - who is rather good with plants - is
becoming rather fond of the prototypes. She was very sceptical at
first.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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