Powering 3 devices with varying voltage/amps - cheap and effective?

Discussion in 'The Projects Forum' started by draynoe, Jun 29, 2015.

  1. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    Hi everyone,

    I just wanted to start by saying I appreciate any help anyone can give on this topic as I am completely new to electronics/circuits etc.!

    The project I am attempting to implement is wiring up a 10.1" LCD monitor that utilizes a control board with a Raspberry Pi 2 to my car's current power and head unit. I would like to convert the HDMI audio out to RCA R/L audio (which plugs into the rear aux port on the head unit via a R/L to 3.5mm cable that I already have). I'll like the main items below that I would like to use.

    The problem is that I have no real understanding of electrical wiring or electricity in general so I wanted to get your opinions on the best (and hopefully cheapest) way to power the following items in my car. I have looked around a lot and tried to read about powering multiple devices with different voltage/amp requirements, but I can't seem to grasp or find a real answer to my specific situation.

    Basically, I would really like to power all 3 of these devices from 1 power source (I am assuming 12v in the car somewhere that would only turn on when the car is running) and supply the appropriate voltage/amperes to each device as to not damage them. Also, I want to install some type of power switch or toggle on the Pi's power cable so it doesn't just shut off when the car does; I've done this on my home Pi and it works just fine.

    Each of these seem to come with a standard ac adapter (US plug) but again it would be nice to power all 3 from 1 source.

    From what I can tell, the different power requirements are: Monitor - 12V/2A; Raspberry Pi - 5V/2A; and HDMI Splitter/Converter - 5V/1A. I figure (guess) that this would really only require between 40-50 watts, 12V/6A or so? I'm just not sure and definitely not sure how to make sure I don't fry everything. :) Oh and if it helps, this is in a 2002 Nissan Xterra that has an aftermarket JVC cd player/head unit that is spliced into the car speakers etc. (I've thought about adding one of those cheap back-up cameras too, but I don't want to complicate the power situation further right now hah)

    Here are the items on Amazon (*Note: I would like to have 2A to the Pi because of the USB port power pulls):

    Monitor: http://www.amazon.com/Resolution-Raspberry-including-Triggered-Automatic/dp/B00VE72DLC

    Pi: http://www.amazon.com/Adapter--20-G...Supply--Kingston-Adapter--HDMI/dp/B00MV6TAJI/

    HDMI Audio Converter: http://www.amazon.com/dp/B00KBHX072/

    In case anyone is wondering, I want to split the audio from HDMI because the 3.5mm output on the Pi contains a lot of static etc. and I've read that this converter works great.

    Any help is greatly appreciated!

    Thanks!
     
  2. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    Sorry I didn't see a way to edit my post but wanted to add:

    I did mean to mention that I have to keep the stereo in the car for sound (aux input) to the speakers coming from the adapter (and Pi). So I'm really just relocating it and then running the L/R to 3.5mm cable to the head unit itself. I hope that makes sense!

    Thanks! :)
     
  3. #12

    Expert

    Nov 30, 2010
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    500 words and it still isn't clear whether you want a 120 Volt AC converter or a couple of DC converters. :confused:
    I think I'm suffering from, "not enough coffee" right now. :(
    Is this, I don't know?, I don't care?, Choose one for me?
    If everything already comes with its own DC adapter, how about just one AC converter?
    Magic Eight Ball says, "Please try again".:)
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Simply run the monitor to a "switched" (switched = has power only when car is on) 12V source capable of 2A.

    Then you will need a 12V to 5VDC converter capable of 3A or more (15W+ rating)

    The converter input will be supplied directly from the battery and the 5V output will be split to the HDMI and PI.
     
  5. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    Thanks #12 and mcgyvr - sorry if I wasn't clear about 120 Volt AC or DC converters.

    All 3 items come with their own ac adapters that plug into a standard US home outlet. Sorry if I don't quite understand the terminology - I am very new!

    mcgyvr - so you are saying I can splice the monitor directly into a 12V power source (like a cigarette lighter) and then for the HDMI and Pi I will need a converter that will output 5V to each of them? If I run it directly from the battery wouldn't that cause it to always be powered and not just when the car is running? Sorry if I misunderstood. If you have any examples of this type of converter please link them for me - I suppose it just needs to have two outputs at 5V each and I just splice the existing adapters into?

    Thanks again and sorry for not being clear! Hopefully this helps clear it up! :)

    Edit - if it helps, this is the type of power adapter all 3 come with #12 - just that the HDMI is 1A not 2A and only the Pi is USB - the monitor and HDMI are both a barrel type input: http://www.amazon.com/NorthPada-Supply-Charger-2000mA-Raspberry/dp/B00OY7HR1U/
     
    Last edited: Jun 29, 2015
  6. #12

    Expert

    Nov 30, 2010
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    One word out of place confused the TS. The converter input will be supplied directly from the battery through a switched power point.

    Right?
     
  7. #12

    Expert

    Nov 30, 2010
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    I happen to have an AC converter laying around, so I would just connect that to a switched power point, plug in a 3 way recepticle adapter, and plug in the 3 DC converters you already have.

    If you have some 12V to 5V converters laying around, that would be convenient, but you don't.
     
  8. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    Alright I think I understand now - if you guys have any links to a recommended ac converter/switched power point etc. I would appreciate it too. :)

    Thanks again!
     
  9. #12

    Expert

    Nov 30, 2010
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    The switched power point is someplace inside the car, and you haven't even said what kind of car it is! Some cars use the accessory position on the ignition switch. Some cars send a signal from the accessory position to a relay and the relay powers everything that needs to be switched on or off. In some cars, the cigar lighter is switched, in some it isn't switched.

    The AC inverter I have is a cheap POS, so I can't recommend it. I will leave that to somebody else.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I thought the OP wanted the PI on all the time (I also assumed it was fine to leave the HDMI converter on too) .. Hence why I didn't put "switched" in that section..
    If they JUST want the PI on all the time then wire one of the converters to a "switched" 12V source and one directly to the battery (with a fuse...in fact all devices should be fused)

    For the 12V to 5V converters there are tons of these on Ebay
    Either get 2 of the 5V @3A or find one with 4A+ to only need 1 (if you don't want the hdmi to be on)
    http://www.ebay.com/itm/like/130721834041?lpid=82&chn=ps
     
  11. #12

    Expert

    Nov 30, 2010
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    OK. Just reciting the list here: Some of the components will be connected to a place where the power is on all the time and some will need to be connected to a place where the power is controlled by the switch you put the car key into. It is up to the Thread Starter to clarify his wishes.
     
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
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    If it was me I would use the aux power output from the JVC head unit, normally used to switch on power amplifiers and power antennas, to activate a small relay that sends power to the monitor and to a pair of common 2 amp 12 volt USB power adapters or one higher capacity one that can give you the ~3 amps you need.

    As for source power for the 12 volt supply you could either go off the lighter power lead being most of them are fused at 10 - 12 amps or off of a power tap point in the fuse panel or from a dedicated and fused line directly off the battery.

    Either way you do it a bit of vehicle schematics reading and you should be able to set this up in a fair day yourself without burning the neighborhood down.
     
    #12 likes this.
  13. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    Hi all -

    I mentioned the type of car in the original post :) (It is a 2002 Nissan Xterra).

    Just to clarify - I only want all 3 devices to receive power while the car is running as I do not want to drain the battery. I don't want any of the 3 devices to receive power when the car is off. So I just need to wire up the monitor to a 12V source that is only on when the car is running and the Pi and HDMI converter to a 5V source that is only on when the car is running. (The Pi will have an on/off toggle on the power cord but that is unrelated).

    I hadn't thought about the power out from the head unit tcmtech, but I will look at that too.

    Thanks!

    Edit - mcgyvr, could I potentially just wire all 3 devices to the same 12V source in the car if I wired the monitor directly and the Pi & HDMI converter using two of the regulators you linked on eBay? Thanks again and sorry for the confusion everyone.
     
  14. #12

    Expert

    Nov 30, 2010
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    Oops. :oops:
    What can I say? I was short on coffee today. :D
     
  15. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    Hah - that's completely understandable #12!

    :)
     
  16. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    This helped me understand what you guys were talking about a lot too: http://www.techguys.ca/howto/power.html

    My car does have the ACC/ON/START positions so I think the best option for me is to find the ON 12V source (or an equivalant such as the lighter) and directly wire the monitor and two of the 12V to 5V converters mcgyvr mentioned in his last post to it.

    I think this would work fine and only supply power when the car is "ON." Do you guys see any issues directly wiring all 3 of these to that 1 power source?

    Thanks again! :)
     
  17. #12

    Expert

    Nov 30, 2010
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    The mystery to me is why you think you have more than one power source in a car.
    One is switched and one isn't?
    But, to answer the question, a cigar lighter is more than capable of driving the whole pile you have.

    40 or 50 watts on a 12 volt system is about 4 amps. I don't think anything in that car has a fuse that small!
     
  18. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Another option for power would be to tap into the power leads for the head unit. Most head units use under 10 amps peak but areon 15 amp lines so the extra few amps the new gear will add will likely not affect anything.

    Depending on how your head unit works it will either draw it primary load from the live line or the switched line. I know pioneer head units tend to use the live line for their primary power but other brands use the switched line for primary power.

    Either way you will have one line going to the head unit that has very little power draw on it and it would only be a matter of using a relay to tap into it to make it a switched line if it's not already.

    Also the majority of the 12 volt USB power converters are buck converters so their 12 volt input side current is only a fraction of the output current meaning a 5 volt 2 amp USB converter might only draw .9 - 1 amps on the 12 volt side at worst fully loaded.
     
  19. draynoe

    Thread Starter New Member

    Jun 29, 2015
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    #12, I just mean the one power source as in the lighter itself - not the overall single power source for the car. :) I just wanted to be sure that splicing in all 3 devices wouldn't cause any issues when they are all connecting to the same source (the lighter etc.).

    tcmtech - thanks for the ideas, I will look into them a little more and see what I can come up with. I like the idea of utilizing the head unit in some way too.

    I think I have enough to work with and understand how to draw power now for all 3 devices and where to get it from. Thank you all for your help, it is hard to understand how some of this works having never worked with it myself.

    Thanks!
     
  20. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Using the head unit aux power output would allow everything to turn on and off when the head unit is turned on or off. Sort of a one button does everything convenience if nothing else.
     
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