LED current consumption

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4472
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LED current consumption

Postby 4472 » Tue Nov 14, 2017 11:55 am

I have a number of 1amp 12v power supplies suitable for wiring up. I don't want to overload them so would like to know approximately how many LED's I can connect. They will all be set up for 12v operation with the necessary resistors already attached, as I am avoiding 3v. What is the wattage of a single bulb is the short version of the plea

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Gordon H
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Re: LED current consumption

Postby Gordon H » Tue Nov 14, 2017 12:27 pm

4472 wrote:I have a number of 1amp 12v power supplies suitable for wiring up. I don't want to overload them so would like to know approximately how many LED's I can connect. They will all be set up for 12v operation with the necessary resistors already attached, as I am avoiding 3v. What is the wattage of a single bulb is the short version of the plea

What value are your resistors?
Without knowing that, you cannot say what the current drawn will be per LED.
Ideally, you would also want to know the LED forward voltage to get a more accurate figure.

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Flashbang
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Re: LED current consumption

Postby Flashbang » Tue Nov 14, 2017 1:00 pm

I would suggest for 12v DC operation and as a generalisation/guide, use a 1K0 (1000 ohm) series resistor per LED. This will give around 10 milliamps (0.01A) per lit LED on average.
Therefore 100 lit LEDs could be fed from a 1Amp (1000 milliamp) DC power supply. Realistically though reduce the total to around 90 lit LEDs to allow some leeway.
If possible use a Regulated power supply. 'Regulated' means the output voltage remains virtually constant regardless of loading.

This web site is worth bookmarking as it offers an easy LED series resistance ohm value calculator...http://led.linear1.org/led.wiz
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4472
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Re: LED current consumption

Postby 4472 » Tue Nov 14, 2017 2:42 pm

I am buying them over the internet, probably from layouts4u, so don't know resistor value, but I do know they sell 3V lamps with resistors to allow 12V operation if that helps. And no, I am not into soldering no matter how much cajoling !!
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Flashbang
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Re: LED current consumption

Postby Flashbang » Tue Nov 14, 2017 3:41 pm

I feel you need to ascertain whether the 'lights' are in fact LEDs or filament lamps.

LEDs draw very little current. Typically they can have a maximum of around 25milliamp (ma) but this is normally reduced to around 10ma without causing loss of illumination while a filament lamp can consume up to 70ma each.
LEDs have to be connected one way around on a DC supply or they wont light while filament lamps will light either way around.

If filament lamps and they are rated at 3 volts connect them in series in groups of 4 across the 12v DC. Or use individually and each with a resistor.
If LEDs I would wire each with its own dedicated series resistor across the 12v DC.
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4472
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Re: LED current consumption

Postby 4472 » Tue Nov 14, 2017 7:29 pm

They are definitely LEDs, not filament, so if the current draw is 10ma would that mean that up to 100 lamps could run off 1 1amp transformer
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Flashbang
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Re: LED current consumption

Postby Flashbang » Wed Nov 15, 2017 11:19 am

Technically yes, but see my post #3 above re leeway.
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Bramshot
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Re: LED current consumption

Postby Bramshot » Wed Nov 15, 2017 11:42 am

At 12 V supply you can put up to 3 LEDs in series with a single resistor and get 3 times as many lights.
I have even connected 3 lights with integral resistors for 12 V in series, without removing the resistors and they still work on 12 V with realistic illumination levels.


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