My LED Calculator - Is it valid?

Using Arduino LEDs and Multiplexing
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Hi

I am wanting to create an aquarium led light - I have a 240V AC to 24V DC Power supply that can deliver 10amps.

Is the following calculator I have created correct for the voltage and current estimations?

Each led on a particular channel is in series
Each channel is in parallel

The spreadsheet is in google docs

Chris

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iisfaq:
The spreadsheet is in google docs

https://docs.google.com/spreadsheets/d/1hrJoIqcv5dqVREaUWUfSxq3JtZ8GWNeM6sfGWXJ5Ic8/edit#gid=896539983

So...it's completely useless.

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fungus:
So...it's completely useless.

The spreadsheet or the power supply?

4

fungus:
So...it's completely useless.

I just noticed that it requires you to logon - I thought it would just work without login.

Here is a static photo

942×458 48.2 KB

Chris

5

Hi Chris. So what do you want us to check, exactly?

Is this power supply regulated to 24V, or is it switch-mode? If neither, its voltage will be higher if you draw less than 10A and that could damage the leds.

For your white channels, how will you regulate the current? The supply voltage isn't high enough compared to the forward voltage of the leds to use a series resistor.

For all channels, you would need to regulate the current, but if you use series resistors, the power dissipation will be very high, 15W for the red channel, for example.

Paul

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PaulRB:
Hi Chris. So what do you want us to check, exactly?

Hi Paul

Sorry for not providing enough information...

I am just wanting to know that my calculator is using the right formula to calculate current and voltage.

For example 6 white leds seem to use 22.8 volts, so I assume this is OK. But not 7 in series which would use 26.6v which exceeds the Power Supply. I am not sure what would happen if I do use 7 in series, does it mean that the
last led would only be getting 1.2v which would not be enough to drive it?

I am going to be using a small constant current module for each channel to regulate the current through the leds.

http://www.ebay.com/itm/high-efficient-led-driver-0-35-and-0-7-and-1A-good-use-Arduino-/370632520478?pt=LH_DefaultDomain_0&hash=item564b6b731e

My power supply is like below (Universal 24V 10A 240W DC Switching Power Supply Driver 110V-240V for LED Strip)

http://www.ebay.com/itm/Universal-24V-10A-240W-DC-Switching-Power-Supply-Driver-110V-240V-for-LED-Strip-/331178026526?pt=LH_DefaultDomain_0&hash=item4d1bbfa61e
Chris

7

7 white leds in series might not light at all, or might be dim or flicker.
You may find that 6 leds in series is a problem also, because they leave only 1.2V for the current regulator to use. This might be ok, you will have to try it.

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iisfaq:
I am just wanting to know that my calculator is using the right formula to calculate current and voltage.

The thing with LEDs is that you don't "calculate" either. You're supposed to supply the amount of current (amps) specified for that LED*.

That's usually a problem because power supplies come in volts and LEDs need amps. You need an LED driver circuit to 'interface' them to your power supply.

{*} Rated power ... or less. In reality it's usually a problem to run them at the rated power because it's a maximum and those LEDs will get HOT at that value. You can only use them for long periods at full power if you have really good heatsinking.

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