An option for 12V DC LED's

Projects General Guidance
1

I have some LED’s I would like to turn on with my Arduino.
They have a wall plug that converts 220v AC to 12V 10A DC output. Decided to keep this always plugged in after my previous question about switch 220v :slight_smile:

Upon motion, I would like to have my Arduino to allow this power to flow through to the LED’s
Looking at this.

Here are the two options I think

  1. A Mosfet such as IRLB8721
    IRLB8721PBF Infineon Technologies | Discrete Semiconductor Products | DigiKey

  2. A 5V Relay Module
    http://www.aliexpress.com/item/Free-shipping-1-Channel-5V-12V-Relay-Module-Relay-control-panel-with-light-coupling-isolated-relay/716353306.html

So my questions are, which of the above 2 options is the best?
Do I need to add shotky diodes or capaciters anywhere?
Such as a 1N4001 Diode rectified on the connection back to the Arduino?
Or does it go on the link where the 12V, 10A are coming in from? Or both?

I was advised to properly use isolation so with the above options, how to properly protect this ?

2

Go with the second one, i.e relay nodule.

3

MalharD:
Go with the second one, i.e relay nodule.

Thank you for your suggestion. May I ask why the relay module is better than the mosfet for switching 12V 10A?

Also, Do I need to add anything else to either
Arduino > Relay/Mosfet
Input 12V/10A into Relay/Mosfet
Output 12V/10A from Relay/Mosfet

4

Well I would say use the FET.
The relay while simpler it will click as it is triggered and a click is so last century.

You don't need to add a diode with a FET just a 10k pull down resistor on the gate.

5

Hi Grumps...

So if I go with the FET approach...

Can you explain what you mean by 10k pull down resistor on the gate.

Did you mean 10k resistor (unless pull-down is a special kind) between the 5V arduino to FET?
Or did you mean between the arduino and the AC Adapter that's providing the 10A/12V ?
Or did you mean from the FET to the LED strips?

If I think it's between the FET and the Wall AC Adapter, what value does it provide since the AC adapter puts out 12V/10A which is what the LED's want.

This is my first project, first time seeing a Arduino (Uno and Nano) and my first time wiring.

6

Pull up or pull down is the usage of the resistor, not a type.

Did you mean 10k resistor (unless pull-down is a special kind) between the 5V arduino to FET?

No that would be a pull up resistor.

Can you explain what you mean by 10k pull down resistor on the gate.

A resistor from the gate of the FET to ground.

7

Thanks Grumps. Makes sense

Is there any need for isolation or other safety items when dealing with 12V/10A Power?

I'm curious how you chose 10k ?

Did you mean like this frm the Gate.

1887×1146 172 KB

But seen others with a resistor on the Drain (toward the consumer)

Thank you for your time and clarification

8

I'm curious how you chose 10k ?

Compromise between noise immunity and low loading. Anyway it is always 10K don't worry.

Did you mean like this frm the Gate.

No, that is not a pull down connecting the gate to the ground is it? It is a series resistor.

But seen others with a resistor on the Drain (toward the consumer)

That is right. Only it is only on the drain because the drain is connected to ground as well

9

I really thought the first link was going to be correct.

What is the purpose of the 10k pull-down to ground?
Is it for safety reasons only?

10

I really thought the first link was going to be correct.

You need to learn the basic vocabulary of this game. As I said that is a series resistor. I did not say use a series resistor.

What is the purpose of the 10k pull-down to ground?

To prevent the FET from turning on if the Arduino is not powered. If you don't have it the FET gate will be floating.

For more on floating see:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

It applies to FET gates as well as Arduino inputs.

11

Grumpy_Mike:
To prevent the FET from turning on if the Arduino is not powered. If you don't have it the FET gate will be floating.

For more on floating see:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

It applies to FET gates as well as Arduino inputs.

Hi Grumps.

Gave this a read and the mention of
"said to be floating. In practice this usually results in reading a succession of highs and lows, seemingly at random. In fact what is happening is that the input is acting as an antenna and picking up lots of signals out of the air."

That makes sense to me. However, the amount of noise would never be enough to trigger a pin high/low or to trigger the coil to closed the FET circuit right?

Am I correct in stating that this is for best practice to ensure a properly functioning design but not for safety reasons correct?

12

No, the amount of noise would trigger the FET.
We are dealing with very high impedance so here so a small electric field can result in a very high voltage, enough to trigger a FET.
Have you ever touched the signal wire on a scope where there is no ground connected? You can easily see a reading of 50V.

13

Cool. Thanks Grumps!

Looking forward to some necessary supplies arriving. The code part I think i've got handled.

Thank you.

14

Which FET did you select?

15

Crossroads,

The only one I've seen mentioned in a similar project and that is

IRLB8721

IF you have another suggestion or if i'm downright wrong, please do advise.

16

IRLB8721 is not bad, 13 to 16mOhm Rds at 4.5V and 25A current flow.
It will dissipate P = I^2 * R = 10A x 10A x .016ohm = 1.6W when on, you may want to add a heatsink.

17

If I'm using it in intervals of about 1 minutes on, maybe 10 minutes off as it'll be for a staircase.

I'm expecting to mount the cables/arduino and such inside a electric box (small white one from the local DIY shop) - So your commend about the heatsink does indeed concern me.

The Source will likely always have power coming in (12V, 10A) as I don't want to mess with 220v AC so i'm wondering if they will create heat even if the FET is closed?

Recommendations on heatsinks for this application?