Circuit for 12V lights to come on each evening.

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discussing projects and some stated that he was having trouble finding
and economical 12V timer and that all the timers he could purchase
required mains supply.

The situation is solar panle charges a SLA battery that runs a few 12V
leds for a porch light each evening.

I redefined it to needing a circuit that responded to ambient light
dropping and then switching on some LED lights for a set period of time,
say 2-4 hours, thus removing any need for a "timer" and Rt syncing/drift.

Has anyone come across such a circuit?

Re: Circuit for 12V lights to come on each evening.
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Google will soon reveal plenty of suitable circuits.
along the lines of "light sensitive switch" "light activated switch".

Make sure that you dont use a circuit with a relay if you can avoid
it, if you are trying to extend battery life.
 A relay will chew up power.  A FET will make bugger all difference to
consumption.



This probably is the best way to do what you want to do, though
putting a switch on the porch is probably
better if you only need it on when you are there.

Re: Circuit for 12V lights to come on each evening.

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In fact a bi-stable relay that only needs to be powered for a few
milliseconds for it to turn on or off, will use far less power than a FET!

MrT.



Re: Circuit for 12V lights to come on each evening.

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That's fine as long as the circuit can ensure that the switching doesn't get
reversed as a result of a short power dip or something else.



Re: Circuit for 12V lights to come on each evening.
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latching relays typically need different inputs to switch each way.
(different polarity or on a different pin)

I'm not convinced that a latching relay would use less power than a
mosfet driven by a nor-nor cmos bistable.





Re: Circuit for 12V lights to come on each evening.


A suggestion for a starting point for a light operated control is the solar
powered lights that can be bought for a few dollars for use in a garden.
They come with a LED light at the top,  a plastic tube about  400 mm long,
and a spike to stick in the ground. If you get one of these, remove the LED
and extend the connections that were on the LED to connect to the base
circuit of a transistor or FET which connects power to turn on the lights at
night


OldZ80





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Re: Circuit for 12V lights to come on each evening.


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But that is completely unnessessary, as he has already a solar panel in his
setup. He could use it as a dawnswitch by measuring the voltage across the
diode feeding the battery, so he would only need a timer for the light to go
off.
ciao Ban



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