Powering LED Strip

[ex_directory]

Am just wanting to make sure I understand this right as I am a hobbyist but not an electrician!

I have 5m 12v 4.8w p/m led strip light.

I want to be able to dimm this so my set-up will be:

wall -> led driver -> led controller -> led strip light.

1, I need an led driver that can handle 5 x 4.8m, so let's say 30w min?

2, Some led drivers say they are non-dimmable, is this just meaning you need to add a controller to dim or does it mean the driver should not be used even with a controller for dimming?

3, Reading up it is recommended to get a constant voltage led driver. Is this the same as PWM? Is this what stops the flicker?

4, All the ebay led strip light uses power bricks as led drivers, do these produce constant voltage, or should I be investing in to more expensive led drivers like the ventilated/non-ventilated ones that need wiring to??

5, I have an old power brick lying around (ITE PSU), it is Input 100/240v 1.0A, Output 12v 1.25a
I assume at 240v, load will be 0.4amps (100v = 1.0A).
At 12v, the PSU can provide approx 20 times as many amps, i.e. up to 8 amps MAX
At led full brightness, my leds use say 25w, A = W/V, Amps ~= 2

So this brick would be fine? (or i don't understand the Math)

Any help to any questions is appreciated!

Thanks,
Ex

 

[stillp]

4, I have an old power brick lying around (ITE PSU), it is Input 100/240v 1.0A, Output 12v 1.25a
I assume at 240v, load will be 0.4amps (100v = 1.0A).
At 12v, the PSU can provide approx 20 times as many amps, i.e. up to 8 amps MAX
At led full brightness, my leds use say 25w, A = W/V, Amps ~= 2

So this brick would be fine? (or i don't understand the Math)

Any help to any questions is appreciated!

Thanks,
Ex

No, the output is limited to 1.25A whatever the input voltage. 2>1.25, so you will not be able to drive 25W of LEDs with a 12 x 1.25 = 15W output PSU.

 

[ex_directory]

stillp, ok, thanks, so need about 2.5A psu then, but should I get a psu brick or one or the dedicated led driver blocks?

 

[stillp]

Depends what the specification of your LED strip calls for. Oh, and the non-dimmable ones are not suitable for dimming. If you add a dimming controller you'll possibly damage it, or the LED strip, or both.

 

[ban-all-sheds]

Surely the LEDs have no idea whether they are dimmable or not?

Surely if you pulse them on where on:off is a small value they will appear dimmer than when it is a higher value?

 

[stillp]

Depends what other components (if any) are on the LED strip.

 

[ex_directory]

Depends what the specification of your LED strip calls for. Oh, and the non-dimmable ones are not suitable for dimming. If you add a dimming controller you'll possibly damage it, or the LED strip, or both.

The led strip has single colour Epistar SMD3528 chips and is dimmable.

Are you saying the way the leds are dimmed is by varying the voltage? Is it not the case the controller takes the constant voltage as input but then outputs a variable voltage?

 

[stillp]

Ah, sorry, I thought you'd said the LED strips were non-dimmable.
Depending what other components are on the strip, dimming them can be achieved by pulse width modulation, which as you might guess varies the width of pulses of current to the LEDs. Varying the voltage won't work very well, as the LEDs will change from off to on within a very narrow range of voltage.

 

[ex_directory]

Ah, sorry, I thought you'd said the LED strips were non-dimmable.
Depending what other components are on the strip, dimming them can be achieved by pulse width modulation, which as you might guess varies the width of pulses of current to the LEDs. Varying the voltage won't work very well, as the LEDs will change from off to on within a very narrow range of voltage.

Few, was confused for a minute.

So to be clear, a non-dimmable (constant voltage) led driver is ok as it is the controller varying the PWM and keeping the same 12v DC voltage supplied to the LED strip?

 

[stillp]

I'm not sure what you're saying there. What do the instructions say?

 

[ex_directory]

I'm not sure what you're saying there. What do the instructions say?

Say I use a 2.5A 12V DC PSU (laptop style brick). I assume this is offering constant voltage.
My LED controller (as I just checked) has these specs:
Type PWM, Constant Voltage DC Power 12-24VDC, Output 3A x 3 Channel, 36W x 3, Watts 12VDC - 108 Watts
My LED strip is dimmable.

I was just trying to confirm it is safe to use the PSU as the voltage required will always be 12V DC (when on at any dim level), only the amps will vary.

Ultimately I am trying to decide if a laptop style brick PSU is suitable or if I need to spend quite a bit more on a proper LED driver.

 

[stillp]

Surely your "LED controller" incorporates the drivers?

 

[ex_directory]

? The LED driver is doing the AC to DC. I thought that was the point to get constant voltage as required by the LED strip.

It means I can have

wall -> led driver -> led strip light.
or
wall -> led driver -> led controller -> led strip light.

The led controller requires 12-24 VDC.

 

[stillp]

An LED driver is intended to drive LEDs, not LED controllers. The thing that converts AC to DC is called a rectifier. Can you post a link to your LED controller?

 

[ex_directory]