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ztubbz
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What Power supply to power Raspberry + 10inch screen + LED Light

Wed Mar 27, 2019 11:08 pm

I am building a custom "TV Set" which is essentially a 3D printed enclosure containing a raspberry, a 10 inch screen and a LED light that lights up a logo on the back.

Now I am a newbie when it comes to power supply stuff.

I have a 12V 2.1A power supply but I suspect this could not be enough?

The screen is this one https://bit.ly/2uw9GYH which says 12V 2A
Then the raspberry need 5V 2A
and then there's a LED cob light thats 5V 1A

I do have a stepdown converter module to get from 12v to 5v for the raspberry

Now for the power supply, do just need to add up the Amperes?
So 2A + 2A +1A = 5A? Do I need a 12v5A powersupply?

Or how does this work?

Thanks for your help

klricks
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Re: What Power supply to power Raspberry + 10inch screen + LED Light

Thu Mar 28, 2019 1:59 am

Since you have more than one voltage present, you will need to use Ohms law to calculate the Watts of each and then add up the total Watts.
Find a 12 Volt power supply that can supply the calculated Wattage or more.
Or using the total Wattage, again use Ohms law to calculate the Current needed at 12V.

Also the voltage converter will not 100% efficient. Depending on the converter type it could be 80-90% for a 'buck' (switching type) or much worse for a linear regulator. You will need to account for that loss.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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NGC6543
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Re: What Power supply to power Raspberry + 10inch screen + LED Light

Thu Mar 28, 2019 9:32 am

The specs for that panel and driver are a bit vague; I bet it doesn't actually need 12V*2A=24W. Likewise, your LED light... 5V*1A=5W is a very bright LED. It's enough to fully light a small room. Still, we'll work with those values:

For the 5V parts, you need 2A for the Raspberry plus 1A for the LED = 3A total. Make sure your 12V to 5V converter can do 3A output.

When converting voltage, it's easiest to work in power (watts). The formula you need is Watts = Volts * Amps. So, given the output we've just calculated, we need 5V * 3A = 15W output power.

We could do with knowing what your converter is, it makes a big difference. If it's a switching regulator (buck regulator) then assume 80% (0.8) for efficiency. It might say it's better than that but it varies and better to use the worst case.

So, to get 15W output, the input to the converter will be 15W / 0.8 = 18.75W.

At 12V input, we work the formula backwards to give an amps requirement of 18.75W / 12V = 1.5625A for the converter input.

We know the screen/controller needs 2A, so the total requirement is 2+1.5625 = 3.5625A.

Rounding up a bit to what you can buy, you need a 12V 4A supply minimum. My bet is you could get away with less than that but without better specifications or measurements, that's what your details get us to.

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davidcoton
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Re: What Power supply to power Raspberry + 10inch screen + LED Light

Thu Mar 28, 2019 12:01 pm

klricks wrote:
Thu Mar 28, 2019 1:59 am
Since you have more than one voltage present, you will need to use OhmsWatt's law to calculate the Watts of each and then add up the total Watts.
Find a 12 Volt power supply that can supply the calculated Wattage or more.
Or using the total Wattage, again use OhmsWatt's law to calculate the Current needed at 12V.

Also the voltage converter will not 100% efficient. Depending on the converter type it could be 80-90% for a 'buck' (switching type) or much worse for a linear regulator. You will need to account for that loss.
FTFY. See above for details of the calculation. I really hope the panel does not actually need 24W, and as said a 5W LED will light a small room.
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