Driving LEDs from external power supply

Other Hardware LEDs and Multiplexing
1

I have a basic understanding of leds and current but I always confuse myself when working out how much power something will use.

I am looking at creating a LED lighting unit for my aquarium.

I am looking at this Arduino Shield - Arduino 6 channel led shield 0,35-0,7-1A

So it can be configured to run at:

  • 350ma
  • 700ma
  • 1000ma

It can be bought on EBAY at this http://www.ebay.com/itm/Arduino-6-channel-led-shield-3-currents-can-be-set-0-35-0-7-1A-/370745850727?pt=LH_DefaultDomain_0&hash=item56522cbb67#ht_401wt_892

It requires external power.

I assume from this I can run all channels at 1amp - which would require 6 amps.

So I have been looking at power supplies as well on Ebay

I could buy an external power supply like 24v @10a @ 240w but I could also buy a power supply like 24v @5a @120w

So 5 amp may be able at a stretch run to 6 amp, but if I was only running 4 amp is there a negative to me buying the 10amp version?

Will it cost me more electricity to run? Or is it just capable of producing more power?

Also when talking about LEDs:

If I want to run 1 channel at 700ma and 1 led can consume 700ma does that means I can only run 1 led on this channel?

If I wanted to run 10 leds on a single 700ma channel does that mean each led although could consume 700ma each led will now will only get 70 ma?

Chris

2

A power supply of 10A is capable to supply more current than one of 6A. That is all.
The energy that is wasted depends on the quality and design. Some power supplies waste 50%, others only 2%.

The led shield seems to be able to supply 6*1A, that is a total of 6A.
But if 12V leds are used with a total of 6A, only 3A is needed from the 24V.
The swithing regulators are efficient because they can turn a high voltage into a lower voltage with more current.

I don't know what will happen if you connect more leds to one output of the shield. I have to know more about the shield to answer that question.

3

They look like PT4115 drivers (working on my own board using them) and I see that the seller also sells the PT4115 chip. They are buck drivers (Vin must be greater than Vf of the LEDs). Datasheet is at http://www.micro-bridge.com/data/CRpowtech/PT4115E.pdf

4

iisfaq:
So 5 amp may be able at a stretch run to 6 amp

No. Don't even think about it.

iisfaq:
but if I was only running 4 amp is there a negative to me buying the 10amp version?

Not really. It will run much cooler/less stressed if you're only running it at 40%.

iisfaq:
Will it cost me more electricity to run? Or is it just capable of producing more power?

Overall efficiency depends on the power supply design but running cooler always means you're converting less of your electricity to heat.

5

Thanks for your comments - it has helped me a lot.

Cheers

Chris