We've fairy lights in the garden with their own little panels, in winter there isn't enough energy collected and the lights don't glow for very long.
So I thought i'd replace them with a DIY setup, I have a spare 12v battery and a solar panel but i'm struggling to find 12v lights. Is that because of the nature of LEDs? Is it going to be easier to use a transformer? Or....?
You can get 12V LED strips, white or RGB, in rolls of 5m [1] (which can be cut up into short lengths). You will have to put them in something waterproof. With the RGB you can have any colour you like, or with dimmers.
[1] Maplin used to sell them in cut lengths. I don't know whether anyone still does that.
That will always be true unless you have an insanely oversized panel.
There are smart radar powered signs round here that say "Please go round the dangerous bend" (not everybody does). They work brilliantly in midsummer but are stone dead an hour after sunset in mid winter.
On a cold frosty morning with the bend covered in sheet ice there is no chance at all of it flashing up a speed warning. That said some people don't make it around the bend in midsummer and a dry road in sunshine.
Strategically shaped gaps in hedges at the exit points of most sharp bends (and straight on at some T junctions).
Constant current supply is what you want. LEDs are current based devices. Each colour has its own particular working voltage ranging from about 2v for red to 4v for blue. They need some form of current limiting or constant current supply or your will burn them out.
Something like this ought to meet your needs (but buy it from Rapid or CPC if you can since RS are never cheap - just the first hit I got).
I think it's because 5V is the new standard , well since TTL started in the ~1980s Most LEDs seem to be 1.2 to 4.4V . Most of the LED strips I've seen are 5V and can be controlled by modern things link Arduinos. These strips can need about 5W per metre with 30-144 LEDs per metre so quite power hungry when all the LEDs are on.
But I don;t really like to see these lights in gardens at night. One off parties OK but not every night. I've heard it upsets the insect life and therefore effects everything else that really has seperate night and day lighting for the past few billion years.
I can find loads of lights (in fact I have some) that are circa 4 volts, but I have a 12v battery charged from a solar panel/regulator.
I presume the item at the above link isn't going to help me with the voltage issue?
Such never occurred, i'll make amends by smashing the streetlights out front and driving without headlights :)
The voltage to an LED - or chain of LEDs - doesn't much matter provided above the minimum. You just set the current to be correct. There are online calculators that give suitable resistors for various combinations.
Cool. I'll get a constant current driver from CPC then, they're not too far away.
Provided the wattage and price is acceptable it should convert 12v into a suitable current drive for your LEDs (check the datasheet that it is good for at least 17v on a fully charged nominally 12v lead acid cell). It claims to be DC-DC converter but 12vAC in the table (obviously translated from Chinglish). Expensive for what it is. Simple series resistor is probably your best bet for this to limit the current.
It is basically a current driver module for LEDs that converts 12v into whatever the LEDs working voltage happens to be at 350mA drive current. Your problem might well be that the fairly lights only want 50mA/string.
The other way to do it would be to string three sets of your fairy lights in series with a modest resistor to limit maximum current that can flow from the battery. This is a much cheaper solution.
Back of the envelope 2 sets in series with 470R 1/4W or 3 sets in series with 220R 1/4W ought to be OK in the worst case. Depending on how bright you want them you can perhaps drop them by about another factor of 2 without destroying the sorts likely to be in fairly lights. Power LEDs in torches will stand an amp or so with suitable heat sinking.
They really won't like being connected directly to a voltage source and can easily be fried if the voltage goes too high.
1960s.
If you extrapolate the light output back to zero current, the slope of the Vfzero versus wavelength gives Plancks constant.
This is a lab you do in some physics class in school :-) So you'll have something for the trivial pursuit file. Measure a bunch of LEDs, plot on graph paper and such.
That's why a red LED is 1.5V and a blue LED is 2.5 to 3.0V or so. The more energetic part of the light spectrum, the higher the LED Vf voltage. A white LED is just a blue LED with a phosphor coating on top (yellow goo). The LEDs go out to the ultraviolet (LEDs on that end of the spectrum can be expensive).
And this is important when making DC circuits, working out voltage drops and current flows.
*******Circuit voltages have been constantly dropping. When I started, it was normal to have -12V, 12V, 5V and so on. Some DRAMs had three voltages. The first computer I designed and built, used
12V swing on clocks (four phase non-overlapping NMOS drive). And there were CMOS back then, which could operate off unregulated voltages from 5V to 15V or so.Then, there was a "golden time" for a couple years, where everything ran off +5V. No more power-sequencing nightmares, for those two years. But power-sequencing nightmares came back, in the form of five voltages on Southbridge chips.
Logic now, operated below 1.0V . It's possible you may be able to do logic now, at around 0.65V or so, but perhaps not at full speed. But these things are worthless, without some means to do IO at the edge of the chip. And then other voltages may be involved.
You can also do operational amplifiers at low voltage. They may have operated from 1.0V and ground. Sometimes designs like that, have internal bias generators, so that they can amplify signals all the way down to ground. Whereas opamps when I started, might have run at +/- 18V. And the analog computer in school ran off 100V (shock hazard! :-/ ) We've lived in crazy times.
Paul
Martin Brown formulated the question :
That is not a particularly tight bend, I have been round it a few times.
It is at the end of a long fast straight though. Car straight into living room is not an acceptable scenario.
That crash happened in mid summer when the sign would have been working!
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