# Can I power 12V 2A through Vin on an Uno?

Trying to get started with the Arduino, so I'm trying to do something kinda simple. I'm following this tutorial: Build Your Own Dynamic Ambient Lighting For A Media Center

However, I'm still confused about one, most likely simple and self-explainatory, thing: Take a look at this image - is that DC connector on the bottom left the one that's one my Arduino? Do I simply have to connect the 12V wire from the RGB LED stripe to Vin?

After using google for a bit, I read this: the diode and trace width are other limiting factors. The diode is rated at 1 amp and the board traces can't handle much above 2 amp.
Does that mean I can only use 1A because of the diode? If so, why does it matter how much the board traces can handle?

I'm trying to power a 12V 2A RGB LED stripe.

I'd appreciate your help and I hope this is the correct subreddit to ask that. :S

What are you using for a (separate) power supply?

Just run two wires from it to the LEDs and two wires from it to the Arduino. You shouldn't need to draw power from the Arduino board for the LEDs at all.

What are you using to drive the LEDs?

As you don't take any current from Arduino's 5V pin and only very little from the signal pins, you can feed Vin (or the barrel jack) with 12V. Arduino will take about 50 mA, which is nothing compared to the LED strip fed in parallel.

In one of my system I used a 12v power source to VIN of a Nano. As @michael suggested, if you dont draw much current then it's fine.

Since the UNO powers it's 5V circuitry from the onboard regulator which is limited to 800 mA, and the regulator has to dissipate 12V-5V = 7V (at whatever load current is being drawn) at worst case , if the regulator was supplying 5V @ 800mA to all the circuitry connected to the 5V pin, then the regulator is dissipating:

P= I*V

= 0.800A* (12V-5V)
= 0.8A*7v
= 5.6W of power in the form of heat.

On the other hand, the BEST case is 50 mA (as already indicated) so,

P = 0.05*7V=0.350 W ( 350 mW)

Since the arduino cannot really draw more than 800mA because the 5V regulator goes into thermal shutdown, it makes no difference if the 12V supply you connected to the barreljack was rated for 5000A because 4999.666A would NOT be use because the arduino could only draw 0.333A @12V
(5V*0.8A=4W =>4W/12V=0.333A)

Thus, if you are only drawing 50 mA for the arduino the rest of the current available from your external power supply could be used for your other circuitry (leds or whatever)

1n9i9c7om:
Does that mean I can only use 1A because of the diode?

Yes.

1n9i9c7om:
If so, why does it matter how much the board traces can handle?

Because the diode might survive the abuse for a while. And as a result you might damage the Vin track.

I don't think there's any point in discussing pcb trace rating since the regulator can k ly draw 0.333A @12V from the Vin pin because the current is determined by the load, not the source and if tge load draws more than 800 mA @ 5V the regulator will shutdown long before the Vin trace can be damaged.

raschemmel:
I don’t think there’s any point in discussing pcb trace rating since the regulator can k ly draw 0.333A @12V from the Vin pin because the current is determined by the load, not the source and if tge load draws more than 800 mA @ 5V the regulator will shutdown long before the Vin trace can be damaged.

Right, but it’s not what the OP was asking. If I understand right, I want to supply the leds at 12V using the Vin connection of Arduino, so in this case current throgh the diode and traces matter, and is independent for whatever the 5V load is.

Ciao, Ale.

I am not getting why can the LED power from 12v directly and why the LED needs to draw the power from Arduino VIN.

sarouje:
I am not getting why can the LED power from 12v directly and why the LED needs to draw the power from Arduino VIN.

Yep. That's exactly what I said in reply #1.

Sorry Steve, my bad, I didn't notice that comment.

sarouje:
Sorry Steve, my bad, I didn’t notice that comment.

No need to be sorry. I wasn’t complaining.
I was just agreeing. The discussion on diode rating, PCB trace width, and even the regulator dissipation are really irrelevant. Edit: Although I guess it had to be said that the diode and PCB traces shouldn’t carry 2A or more.
Bottom line is that the supply for the LED strip shouldn’t be taken from the Arduino board at all.

OldSteve:
No need to be sorry. I wasn't complaining.

I understand you were not complaining :), but if I seen that comment, to respect your judgment I need to quote it.
I think we better wait for OPs response.

sarouje:
I think we better wait for OPs response.

We may not get one. He hasn’t been back yet to respond to any of the replies, and actually answered his own main question in the opening post anyway:-

After using google for a bit, I read this: the diode and trace width are other limiting factors. The diode is rated at 1 amp and the board traces can’t handle much above 2 amp.

is that DC connector on the bottom left the one that’s one my Arduino?

Yes

Do I simply have to connect the 12V wire from the RGB LED stripe to Vin?

No

It doesn't matter why the OP is asking the question. The answer is NO . PERIOD.
The OP MUST modify his cable ghat plugs into the barreljack to convert i to a "Y" cable.
If he lacks the soldering skills he can use twist nuts ( Wire-nuts) Otherwise he must use separate supplies. He could use butt splices but that might not work with the small guage stranded wire used in wall-wart cables.
Any way you cut tge cake he CANNOT power the heavy load from the Vin pin . He MUST make a "Y" cable or buy a supply that comes with a "Y" cable. It's up to us to tell him what he can of cannot do and that means telling him he must split the power at the supply instead of at the arduino.

@OP,

The fact that you posted this question:

After using google for a bit, I read this: the diode and trace width are other limiting factors. The diode is rated at 1 amp and the board traces can't handle much above 2 amp.
Does that mean I can only use 1A because of the diode? If so, why does it matter how much the board traces can handle?

I'm trying to power a 12V 2A RGB LED stripe.

I'd appreciate your help and I hope this is the correct subreddit to ask that. :S

almost certainly indicates you lack the soldering skills to make or adapt a splitter cable to power your leds. You did not link your power supply so we don't know what it looks like. If you are asking the question because you can't solder, now is the time to tell us.