A
andy
Guest
On Fri, 27 Aug 2004 14:29:23 +0000, CFoley1064 wrote:
have been working on the last month (on and off). I'm building it for some
friends who live out in the country, and have a big polytunnel greenhouse
which needs watering once or twice a day from a tank that fills off the
roof of one of the buildings. They don't have mains power - just a
windmill / battery / inverter system which isn't always reliable, so I'm
trying to build it as a standalone solar powered system. It's meant to be
as automatic as possible, so they can mostly just leave it running and
forget about it. E.g. if they want to go away for a few weeks. I'm also
trying to build it so the design can be used by anyone else in a similar
situation, and as cheaply as possible - i.e. use cheap, standard parts and
simple construction rather than exotic components.
The main circuit triggers a 0.5s 12A pulse through an electromagnet when
the light goes from day to night or vice versa. This is all working and
tested on breadboard. The circuit uses about 0.7-0.8 mA when it's waiting
to trigger, and 12A during the pulses, which makes:
24*0.7mA=17 mAh/day for the controller
12*.5*2/3600=3.3 mAh/day for the electromagnet
= 20 mAh/day total.
I've kept the current as low as possible, because the solar panel will be
the most expensive single component - I've found someone who does a 1 W
(rated) panel for about 10 UKP, and these panels only reliably provide 70
mAh/day in uk winters, 250 mAh/day in the summer. The battery will be a
1.2 or 2.1 Ah yuasa NP battery.
The battery protection circuit is probably icing on the cake. There ought
to be enough charge in it to cover a long run of dull days, but I wanted
something like that in there to stop battery damage if something goes
wrong. Also, there are other similar projects I'm thinking about which
would need this more.
The important thing is that when the circuit is switched off, the current
drain should be well under the drain in normal use, so the solar panel can
recharge the battery. Say no more than 2 mAh/day, which would make 80 uA
average current. And during normal use, it shouldn't add to much to the
total current consumption - say 200 uA max. A reset button would be an
annoyance - there's no way to tell if it's working properly without
waiting for the circuit to trigger, or maybe pressing a button to activate
a power test led, but this would mean there would be something else to do
every day to make sure the system was working, which would spoil the point
of making it automatic.
Like I said, I'll have a proper look at all the designs people have
posted, and then build something based on them. Thanks to everyone who
has replied - I reckon I know enough now to get the thing built, so I'll
probably leave off posting about it until it's finished and written up on
the web, and then post a link.
--
http://www.niftybits.ukfsn.org/
remove 'n-u-l-l' to email me. html mail or attachments will go in the spam
bin unless notified with
OK, I'll be specific. The main circuit is the watering timer controller I
have been working on the last month (on and off). I'm building it for some
friends who live out in the country, and have a big polytunnel greenhouse
which needs watering once or twice a day from a tank that fills off the
roof of one of the buildings. They don't have mains power - just a
windmill / battery / inverter system which isn't always reliable, so I'm
trying to build it as a standalone solar powered system. It's meant to be
as automatic as possible, so they can mostly just leave it running and
forget about it. E.g. if they want to go away for a few weeks. I'm also
trying to build it so the design can be used by anyone else in a similar
situation, and as cheaply as possible - i.e. use cheap, standard parts and
simple construction rather than exotic components.
The main circuit triggers a 0.5s 12A pulse through an electromagnet when
the light goes from day to night or vice versa. This is all working and
tested on breadboard. The circuit uses about 0.7-0.8 mA when it's waiting
to trigger, and 12A during the pulses, which makes:
24*0.7mA=17 mAh/day for the controller
12*.5*2/3600=3.3 mAh/day for the electromagnet
= 20 mAh/day total.
I've kept the current as low as possible, because the solar panel will be
the most expensive single component - I've found someone who does a 1 W
(rated) panel for about 10 UKP, and these panels only reliably provide 70
mAh/day in uk winters, 250 mAh/day in the summer. The battery will be a
1.2 or 2.1 Ah yuasa NP battery.
The battery protection circuit is probably icing on the cake. There ought
to be enough charge in it to cover a long run of dull days, but I wanted
something like that in there to stop battery damage if something goes
wrong. Also, there are other similar projects I'm thinking about which
would need this more.
The important thing is that when the circuit is switched off, the current
drain should be well under the drain in normal use, so the solar panel can
recharge the battery. Say no more than 2 mAh/day, which would make 80 uA
average current. And during normal use, it shouldn't add to much to the
total current consumption - say 200 uA max. A reset button would be an
annoyance - there's no way to tell if it's working properly without
waiting for the circuit to trigger, or maybe pressing a button to activate
a power test led, but this would mean there would be something else to do
every day to make sure the system was working, which would spoil the point
of making it automatic.
Like I said, I'll have a proper look at all the designs people have
posted, and then build something based on them. Thanks to everyone who
has replied - I reckon I know enough now to get the thing built, so I'll
probably leave off posting about it until it's finished and written up on
the web, and then post a link.
--
http://www.niftybits.ukfsn.org/
remove 'n-u-l-l' to email me. html mail or attachments will go in the spam
bin unless notified with
HTML:
or [attachment] in the subject line.