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How much amps do I need?
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Old 22-11-2018, 15:25   #1
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How much amps do I need?

Hi,

I'm planning on playing around with some LED lights (well a variation on neopixels..).. and I'm trying to workout the power supply that they would need.

Wattage: 0.3W/pixel
Working voltage: DC 5V
50pcs pixel per string

so.. from my googling....
amp = watt / volt

which means : .3/5 = 0.06
so each pixel draws 0.06 amps, right?

so 50*0.06 = 3amps..
and if I wanted to run 100 lights, I'd need 6 amps?

So a power supply that can give 5V and 6+amps should be good right?

Just want to make sure that I'm looking for the right thing...

Thanks!
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Old 22-11-2018, 17:23   #2
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Re: How much amps do I need?

Yes. You've got it right. Volts x amps = watts for DC circuits.
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Old 22-11-2018, 17:47   #3
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Re: How much amps do I need?

Quote:
Originally Posted by heero_yuy View Post
Yes. You've got it right. Volts x amps = watts for DC circuits.
awesome - thanks.

I would rep you, but apparently I haven't spread it around enough...
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Old 23-11-2018, 09:55   #4
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Re: How much amps do I need?

There is usually a bit of switch-on surge current in most electronic circuits, so I'd rate the PSU a bit higher, at least 10%. Plus running a PSU at it's maximum rated current can often reduce its life.
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Old 23-11-2018, 10:13   #5
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Re: How much amps do I need?



Always a good idea to have some in reserve. When I fitted LED lighting strips in the kitchen (above and below the cupboards) I used a PSU of double the rating I needed. Very little cost penalty and handy as later I added more LEDs to light the gallery rails and shelves without any worry that the PSU would be overloaded.
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Old 23-11-2018, 12:23   #6
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Re: How much amps do I need?

Thanks for the advice.
I'm looking at an 8A power supply - which should be more than enough, I was finding that anything higher than that I was needing to get from China.

This is really for some christmas tree lights, so I don't imagine I'll be adding lots more other than the original 100...

My plans are stuck at the moment, as I need one of these : https://thepihut.com/products/adafru...o-5v-74ahct125 - but they're out of stock everywhere

---------- Post added at 12:23 ---------- Previous post was at 10:49 ----------

Been having a dig around, so I've found this : https://thepihut.com/products/adafru...-level-shifter but I think that only shifts from 5v to 3.3v - so don't think that would do.

but... I was rummaging through my component box, and I found one of these : https://thepihut.com/products/adafru...verter-txb0108

That should let me shift from 3.3v to 5v right?
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Old 23-11-2018, 14:28   #7
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Re: How much amps do I need?

The Level shifter is for logic circuits only, It cannot drive LED's.

---------- Post added at 14:28 ---------- Previous post was at 14:26 ----------

https://www.tlc-direct.co.uk/Main_In...mer/index.html
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Old 23-11-2018, 14:34   #8
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Re: How much amps do I need?

That level shifts control signals. So if the driving device, such as a raspberry pie is on 3.3v and the neo pixel is on 5v then the signals will interface correctly.

Often you will find that the slave device even on 5V will happilly accept 3.3v control signals directly.

Can you say what the LED neo-pixel part is and what you intend to use to drive the interface line(s). Then I could check the levels for you.

Here's a useful resource: https://learn.adafruit.com/adafruit-...c-of-neopixels
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Last edited by heero_yuy; 23-11-2018 at 14:37. Reason: Resource link
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Old 23-11-2018, 14:51   #9
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Re: How much amps do I need?

Quote:
Originally Posted by heero_yuy View Post
That level shifts control signals. So if the driving device, such as a raspberry pie is on 3.3v and the neo pixel is on 5v then the signals will interface correctly.

Often you will find that the slave device even on 5V will happilly accept 3.3v control signals directly.

Can you say what the LED neo-pixel part is and what you intend to use to drive the interface line(s). Then I could check the levels for you.

Here's a useful resource: https://learn.adafruit.com/adafruit-...c-of-neopixels
Essentially looking to do as in the picture here.
using something like this : https://www.amazon.co.uk/ALITOVE-Dif.../dp/B01M7TN8A2 in terms of lights, and this : https://www.amazon.co.uk/Switching-A.../dp/B0174JDFWE as a power supply
Attached Images
File Type: jpg led_strips_raspi_NeoPixel_Level_Shifted_bb.jpg (184.2 KB, 7 views)
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Old 23-11-2018, 14:53   #10
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Re: How much amps do I need?

Realise my posts are probably confusing - as I'm asking 2 different questions in the same thread - one was about a power supply for the LEDs, and the other was about a logic level converter for controlling the LEDs.
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Old 23-11-2018, 15:07   #11
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Re: How much amps do I need?

I did cotton on as the LEDs are controllable. In addition to the reference I posted above here's another that might be of use:

https://www.edn.com/design/led/44387...trips---Part-1

Sounds like a fun project. I like the idea of being able to control the colour of each LED individually. Good luck.

If you have any technical questions please feel free to ask as I'm an electronics and software (primerrily embedded C) engineer by profession.
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Old 23-11-2018, 15:23   #12
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Re: How much amps do I need?

Quote:
Originally Posted by heero_yuy View Post
I did cotton on as the LEDs are controllable. In addition to the reference I posted above here's another that might be of use:

https://www.edn.com/design/led/44387...trips---Part-1

Sounds like a fun project. I like the idea of being able to control the colour of each LED individually. Good luck.

If you have any technical questions please feel free to ask as I'm an electronics and software (primerrily embedded C) engineer by profession.
I'll let you know how it goes - hopefully with a video

I'm a software engineer too, so hopefully codewise I'll be ok, but I'm sure I'll be back with more electronics questions
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Old 07-12-2018, 12:23   #13
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Re: How much amps do I need?

I've got my lights all working now, and written routines that run for several minutes. I'll post a video of them working in all their glory later
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