Help me calculate the correct amount of current (LED strip + Arduino Uno)

Projects General Guidance
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Hello,
New to the forum, my question might be a basic one but I need guidance.
I have an SMD5050 LED strip and I plan to drive them using N-channel MOSFETs using PWM from the Arduino Uno. The strip is of 20 segments per meter. The strip will consume 60mA per segment so the overall current is 1.2 A per meter. Say I want to hook up 5 meter long strip, 1.2*5 = 6 A.

The above suggests that I NEED at least 12VDC @ 6A to drive the strip ALONE. What if I want to share the SAME power supply to power up the strip AND Arduino Uno via its DC input jack? How much current the overall project will draw?

I have a 12VDC @ 2A power supply but I guess it won't work right?

Thanks.

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Welcome to the forum

It is unlikely that the Uno will take more than 200mA but if you are worried then you can power it separately from the LEDs

You are right. The 2A power supply is not suitable to power that many LEDs but you could use it to power the Uno alone but powering it with 12V is not ideal. 5V to its 5V pin would be more suitable

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And possibly more risky when you connect the USB at the same time, e.g. for a code upload.

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Which strip? Can you post a link?

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Not the very best. PWM switching a rather heavy load will create ripple, noise, on the 12 volt line. That could cause trouble for the controller.
I have practical experience how to make even a good power supply shake on all its outputs pulling high PWM currents on one output.

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Another thing to worry about is the heatdissipation of the ledstrip.. If you plan to pump over 70 Watts of power in that strip you seriously have to considderate a decent cooling and bypass powerlines.

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That shouldn't be a problem. The 5V regulator has an extra 7V to "play with" and the regulator doubles as a filter.

That's usually not a problem either with the heat spread-out over 5 meters. An LED strip of any length has a certain number of watts-per-meter and that's how it's designed to work. (If it's coiled-up you should be careful.)

But I'll warn of something else... You'll probably get a voltage drop through the "thin" conductors on the LED strip. If the LEDs are the far-end are dim you can apply power and ground at both ends. With 5V strips they usually recommend connecting power every meter but that's probably not necessary with 12V. This is just parallel wires.... Same MOSFETs and everything.

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Thanks for your reply, so 0.2A drawn by the Arduino when all its inputs and outputs are hooked with equipment's (max load)? I ask this because I might add up more to the board than just the LED's in the future.

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Its a 20 segments per meter non-waterproof strip.

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Thanks for your insight, will keep it in mind.

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Thanks for your reply, the strip will be mounted on a flat surface in a well ventilated area. Am not planning to use all of the 5 meters, rather just 1.5 or so. Another thing is that the strip will be ON for 6-8 hours a day so it won't consume that much power like if I left it 24/7.

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The Arduino pins are designed to be used to communicate with external devices, not to provide power to them except in the case of sensors. Even then the maximum current from each pin should not exceed 20mA continuously. In addition, the board can supply a maximum of 200mA so you could not supply 20mA form all of its pins at once

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I currently have a 12VDC @ 2A power supply with a DC male jack. Lets say that I only used 1.5 meters of the strip, the current drawn by the strip will be 1.2 + 0.6 = 1.8 A. Based on @UKHeliBob (again thanks for your help), the Arduino require 0.2 A. Adding these currents we get 1.8+0.2 = 2 A.

Now, If I placed a female DC jack to my PCB board and supply it with my 12VDC @ 2A power adapter and then split the power to feed the Arduino Vin pin as well as to the +12VDC required by the strip, will this risk my Arduino or my LED strip to burn or not work properly ??
Keep in mind that based on the calculations above, the power adapter will be working at its maximum capabilities.

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This is usually a bad idea and should be avoided

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Small current from a pin can switch a power transistor ON/OFF to switch external power ON/OFF. The main power goes around the board, not through.

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So both @UKHeliBob and @GoForSmoke suggest to power up the Arduino separate from any load whether its an LED strip or anything else. Sharing both the control and power circuits with a common power supply is bad as far as I understood.

My best option is to feed the Arduino with the 12VDC @ 2A power supply and buy a separate power supply for my LED's.

If anyone want to add up on the discussion feel free, for the time being thanks all for the help.

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CAN BE bad if you don't have more power available than load. But that is a design error, not a problem in itself.

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