Suppose I wanted to hook up 1000 super bright leds into a large array. Each led has a voltage drop of 3.6V at 20mA. What would the safest way to power these be?
The leds are arranged in a large grid, but can be grouped in any way to make supplying power easier.
Thanks!
If efficiency wasn't that critical, I'd probably go for a standard 48v dc supply and parallel 100 chains of 10 (plus current limiting device)across it.
If efficiency was also an issue, I'd probably still stick with a 48v supply but use a low drop regulator as a constant current source for each chain and use a dozen in all but one of the chains.
I like Sue's answer. If you can't get a 48 v supply at >2 amps, you could do what another poster did: use a $9.95 12 volt 10 amp supply from MPJA (15625 PS) and make 333 strings of 3 LEDs with a 51 ohm resistor in series with each string. He even posted the artwork for his PC board on ABSE.
Ed
Which of the two is safer? A 48v supply at 2A or a 12v supply at 10A? This display will be in a public area so I want to minimize the chances of Bad Things (tm) happening.
Matt
ehsjr wrote:
I would be happy with either. Each has advantages and disadvantages.
The 12v solution uses more components and so is more likely to have a failure - but the failure will effect fewer LEDs.
The 48v needs thinner cable and/or can be sited further away from the mains unit. This may allow the mains unit to be located somewhere safer.
The 12v solution may be easier to find the components for, but will take longer to build.
It would be easier to provide battery backup for a 12v solution - it could be run from a car, if need be.
So, it is going to be factors other than safety which will probably produce the decider.
I would also suggest fusing your branch circuits and your main power supply should also be protected from overcurrent. The power supply for 1000 LED's is going to be enough to concentrate a large amount of power in a very small area during a short and will cause a hot arc to form should there be a fault. Typically the spacing on a circuit board for low voltage, individually low current devices is very tight, which is fine if polarity is observed and there are no shorts from loose solder/debris.
Beachcomber
Maybe a 24V supply. That way, this could be fed by a Class 1 Limited Power circuit as defined in the NEC Article 725.
totally dependent on whatever suitable power supply is available.
you need about 72 watts for lights plus power lost in current limiting resistances.
if you can find a couple 10 A (or larger) 5 volt power supplies, drive each LED individually with its own resistor.
if one LED fails... you will not lose a whole string.
likewise low wattage resisters are easier to deal with and cheaper to come by, and less likely to burn up about .028 watts ea).
savaki schrieb:
Hello,
you should analyse the different risks: fire, electric shock, overheating, failure of single leds or leds groups....
Bye
savaki schrieb:
Hello,
you may use also four 24 V supplies with 0.8 A each. Each supply for 200 leds in 40 groups of 5 leds in series. You should think about total power too, with 48 V you need 96 W, with 12 V 120 W, and with 24 V 76.8 W. There is an error, you only need 6,66 A with 12 V or 79.92 W.
Bye
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