Advice needed on how to power 2 single LED's from Dusk to Dawn using Solar.

[Bill68]

I have posted here a the 'DIY Electrical Advice' is locked preventing me from posoting.

I would like to power 2 superbrite LED’s, any voltage, 12v, 5v or whatever.

I want the LED’s to come on a dusk and off at dawn and I would prefer them to be powered by a battery, I’m thinking something like a sealed Lead Acid 7AH, the sort of thing found in an alarm panel and for the battery to be charged by a solar panel. I know I need the obvious, a solar panel, a battery, 2 x LED’s and a ‘Dusk to Dawn’ photo sensor but that’s all I know.

Can you get 12v photo sensors?
How do I prevent the solar panel from over charging the battery, does it have a built in regulator?
What units do I require?

If it is cheaper to power the LED’s from the mains what do I need to buy. I’ve heard of an LED Driver which I imagine is a regulator that takes mains 240v AC to 12v DC.

 

[Octopus]

Gosh so many ideas. So many things to go wrong. Me thinks you are trying to over complicate things.

What, in a nutshell are you trying to achieve?

 

[Richard Burns]

Your simplest solution would be to buy a solar powered dusk to dawn LED floodlight, this would remove the need to design something that is already in mass production.
Helios Solar Spotlight | Maplin
Selene Solar Spotlights - Set of 2 - Lyco Direct
Thea Solar Garden Spotlight - Lighting Direct
Helios Solar Spotlight

However 12V photocell switches are available just search amazon or ebay.
A small solar panel will not overload an already charged battery.

 

[tazz]

Energy for nothing is a hard game.....so 12v 7 a/h battery will require at least a solar panel of at least 15 watts charging over 8 hours of sunlight per day at its best.................leds need 2omA per unit at 1.2v per forward voltage.....so you need to work out your idea and limiting resistor so you can then put your project forward.
R=(Vs - Vl) / I.....or Resistance = Supply voltage - led forward voltage / led current

 

[Bill68]

Gosh so many ideas. So many things to go wrong. Me thinks you are trying to over complicate things.

What, in a nutshell are you trying to achieve?

I have two doorway thresholds which I want to illuminate during the hours of darkness. I only just want to illuminate not light the whole area, I have tested one superbrite LED over each door head and the light level is perfect.

Can I do want I want with any less 'things'?

 

[Octopus]

I have two doorway thresholds which I want to illuminate during the hours of darkness. I only just want to illuminate not light the whole area, I have tested one superbrite LED over each door head and the light level is perfect.

Can I do want I want with any less 'things'?

Why do you want to use battery power?

 

[Bill68]

Your simplest solution would be to buy a solar powered dusk to dawn LED floodlight, this would remove the need to design something that is already in mass production.
Helios Solar Spotlight | Maplin
Selene Solar Spotlights - Set of 2 - Lyco Direct
Thea Solar Garden Spotlight - Lighting Direct
Helios Solar Spotlight

However 12V photocell switches are available just search amazon or ebay.
A small solar panel will not overload an already charged battery.

Thanks for the info. The lights you linked to are all too bright and only last upto 10 hours so will not cover a winters night. I thought a 7AH battery would power two LED's for several nights if the light during the day was poor.

You say that a small solar panel will not overload and already charged battery. Are you saying that HAS got a built in regulator? What size is SMALL?

 

[tazz]

What are the specifications of the leds.......forward voltage and current...?

 

[Bill68]

Why do you want to use battery power?

As I said in my original post I'm happy to use mains I just thought it might be the more expensive route but maybe I am wrong, what would I need to buy to achieve this?

 

[Bill68]

What are the specifications of the leds.......forward voltage and current...?

Now you are getting a bit technical for me :O). I tested with a very bright LED that I use as nav lights on my model aircraft and it was too bright so I would want less powerful LED's. This is the info I have on the LED I tested: 5v 1.25W 90 Lumen.

 

[Bill68]

Your simplest solution would be to buy a solar powered dusk to dawn LED floodlight, this would remove the need to design something that is already in mass production.
Helios Solar Spotlight | Maplin
Selene Solar Spotlights - Set of 2 - Lyco Direct
Thea Solar Garden Spotlight - Lighting Direct
Helios Solar Spotlight

However 12V photocell switches are available just search amazon or ebay.
A small solar panel will not overload an already charged battery.

Could I remove some of the LED's from these units to reduce the brightness or is this not possible?

 

[Richard Burns]

At its simplest an LED requires a power source a current limiting resistor and the LED.
The size of the current limiting resistor would be determined by the characteristics of the LED and the power source.
However is you have been testing them then you may have a practical solution.
If testing an LED on a battery, a battery has effectively (not in reality) an internal resistor that will limit the current and avoid blowing an LED, this may not be the case with a power supply.

Using a 10W or less solar panel (roughly) will not require a charge controller to protect the battery, though one could be used.
If you bought one of the floodlights and disconnected the LED array, checked the voltage being supplied by the battery and then connected in your LED and a suitable resistor then you would have a solution.

If you read Tazz's post about charging batteries with solar you will gain an idea of the size of panel you will need based on the current draw of your LED.

For supply from a mains power you would need a dc power supply of suitable voltage for the LED / resistor you have and connect this through the photocell, you could then use a 230V photocell on the input side of the power supply.
This may be better than a ELV photocell on the output side as the power supply may well draw current even if there is no load.

 

[Bill68]

Using a 10W or less solar panel (roughly) will not require a charge controller to protect the battery, though one could be used.
If you bought one of the floodlights and disconnected the LED array, checked the voltage being supplied by the battery and then connected in your LED and a suitable resistor then you would have a solution.

If you read Tazz's post about charging batteries with solar you will gain an idea of the size of panel you will need based on the current draw of your LED.

For supply from a mains power you would need a dc power supply of suitable voltage for the LED / resistor you have and connect this through the photocell, you could then use a 230V photocell on the input side of the power supply.
This may be better than a ELV photocell on the output side as the power supply may well draw current even if there is no load.

Rather than replacing the LED's in a floodlight with my LED could I just disconnect 3 of the four existing LEDs for example?

If I go the mains (240v) way I had decided to use a 240v photocell on the input side. As for the power supply so long as its input is 240v AC and its output is the same voltage (DC) rating as the LED I am going to use (ie. 12v) should it be good or is there something else I have to consider? Are the power supplies able to work with only the load of two single LEDs?

 

[Richard Burns]

It really does depend on how the LEDs are wired in the floodlight, they could be wired in series so any one out would stop a whole section, or they could be in parallel, which would need careful current control to prevent burn out if one (or more) were removed.
You need to ensure that the current through your LEDs is not too high it is not just about voltage..
You might try reading these web pages, though the Ads and pop ups are really abysmally over powering, as it may help you decide who to design your circuit.

 

[Bill68]

It really does depend on how the LEDs are wired in the floodlight, they could be wired in series so any one out would stop a whole section, or they could be in parallel, which would need careful current control to prevent burn out if one (or more) were removed.
You need to ensure that the current through your LEDs is not too high it is not just about voltage..
You might try reading these web pages, though the Ads and pop ups are really abysmally over powering, as it may help you decide who to design your circuit.

Understand, thanks.