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Powering a PI (and accessories) from a 12v 15A rail.

halkun

I'm getting together parts for a project that will put a Pi 3 with touch screen in my car. It's replacing the radio, but the 12v line that went to the radio has a 1A fuse, which is too low for the 2.4A power needed for the PI 3. However, under the radio is the cigarette lighter, which has a 15A fuse. Sadly, most of the 12v lighter to 5v USB adapters have a 1A limit. I'm going to need some kind of breakout that's going to power PI and it's various attachments.

 

Breaking down further -Things I need to power.

 

Raspberry Pi 3  - (5v 2.4A)

Touch Screen - ? (the pi powers it)

Pi Cam (Powered from Pi)

 

7 port USB hub (5v - 2A)

GPS module (Powers from USB hub)

External Webcam (Powers from USB hub)

 

What parts do you think will make something like this? I'll most likely be dong this in some perfboard. My guess is that I'll break out to:

-One USB (+5 and ground only @ 2.4 amps) to the  Pi/touchscreen complex and

-One wall wart "tube" power jack (5v  2A) to the USB hub.

 

Any ideas on a part list?

Parents
  • 0

    There are some adaptors that have dual 2.1A or a 2.1 and 1A output.

    Most portable USB drives come with a double USB lead for powering the drive from two USB outlets.

    This could be an option.

     

    The alternative is to find a proper 12v to 5v step down regulator.

     

    Personally I would use the cigarette outlet and change the fuse to something like 5A.

     

     

    It's probably time to rip apart the 2.5 A supply to see if it's a switch mode version.

    If the design is what I'm thinking then it could run with 12v input.

     

    Mark

  • 0 in reply to mcb1

    Hi Mark,

    Are there reasons other than personal preferences for your choice of the cigarette outlet?

    John

  • 0 in reply to jw0752

    John, I think that's because he thinks that the 1A fuse in the radio power lead will limit him.

     

    Joshua, all power-requirements are usually "maximum required". It should be safe to calculate with those. But on the other hand, it pays to quickly look at what you are REALLY going to use. So for example the pi3 power requirements include drawing 500mA on each of the four USB ports. Similarly your USB hub specifies a similar powerbudget that includes lots of maximally loaded ports. My guess is that if you look a bit more carefully at what you are going to use, then you can quickly decimate your power requirements. First you're not going to use ALL of the USB ports. And secondly you're not going to use them all at 500mA.

     

    Officially USB devices should report their power requirements in 2mA increments. That USB camera can be examined easily. Just connect it and use lsusb -v to list its requirements.

     

    Cheap LM2596 based DCDC converters are fine to power a pi or a hub. If you really want to go for the "full 5A" you can split the work between two of them. One for the pi, one for the hub. And, as has been said: just put in a 2A or 3A fuse, that should be plenty.

Reply
  • 0 in reply to jw0752

    John, I think that's because he thinks that the 1A fuse in the radio power lead will limit him.

     

    Joshua, all power-requirements are usually "maximum required". It should be safe to calculate with those. But on the other hand, it pays to quickly look at what you are REALLY going to use. So for example the pi3 power requirements include drawing 500mA on each of the four USB ports. Similarly your USB hub specifies a similar powerbudget that includes lots of maximally loaded ports. My guess is that if you look a bit more carefully at what you are going to use, then you can quickly decimate your power requirements. First you're not going to use ALL of the USB ports. And secondly you're not going to use them all at 500mA.

     

    Officially USB devices should report their power requirements in 2mA increments. That USB camera can be examined easily. Just connect it and use lsusb -v to list its requirements.

     

    Cheap LM2596 based DCDC converters are fine to power a pi or a hub. If you really want to go for the "full 5A" you can split the work between two of them. One for the pi, one for the hub. And, as has been said: just put in a 2A or 3A fuse, that should be plenty.

Children
  • 0 in reply to rew

    When you say "decimate your power requirements" do you mean?

    verb (used with object)

    , decimated,

    decimating.      

    1.
    to destroy a great number or proportion of:
    The population was decimated by a plague.

    2.

    to select by lot and kill every tenth person of.

    3.

    Obsolete. to take a tenth of or from.

    I assume you are not out to destroy people even every tenth one (#1 & #2), so do you want 1/10 of the power requirements as in #3?image

    Clem