Circuit for 12V lights to come on each evening.

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?

Reply to
Terryc
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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.

Reply to
kreed

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.

Reply to
Mr.T

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.

Reply to
Bruce Varley

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.

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Reply to
Jasen Betts

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

Reply to
Harry Pfeifer

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

Reply to
Ban

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