Question Raspberry Pi Console Power/Battery help

Discussion in 'Handhelds' started by Tech Flare, May 11, 2018.

  1. Tech Flare .

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    Okay so I am building a portable Raspberry Pi console, and my goal is to make it as close to the Nintendo Switch in form factor and function as possible. I've been thinking about how I want to go about this and I have come to a few conclusions:

    I'm going to use a 7" screen that runs on 12 volts (although I think it can run at as low as 3.7 volts)
    I'm going to use Linux Joystick Mapper to map two 'VR Controllers' into one controller so I can put one on each side
    I'm going to use Retropie to run the games

    My only problem is how to set up the battery circuit. The Raspberry Pi takes micro-usb for power, while my screen takes a DC plug for power. I tried hooking up a LiPo battery to an Adafruit PowerBoost 1000c and then running wires from the LiPo plug on the PowerBoost to the screen, but that fried the PowerBoost.

    So that's where I am at. I'm not very good with battery circuits, so any help will be appreciated.
     
  2. Stitches 2 and a Half Dollarydoos Staff Member . .

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    "from the LiPo plug on the PowerBoost to the screen" I'm going to give you the benefit of the doubt and assume you meant to write: "from the output plug on the PowerBoost", and didn't just run wires straight from the battery input terminal to the screen.

    As for your problem, we need more info. Like:
    • What capacity is the lipo?
    • Where did you buy it from?
    • Was the lipo fully charged?
    • Are you sure the PowerBoost is legit?
    • Photo of your wiring please.
    • Model of your screen and where you got it from.
    • What gauge wire are you using?
    • Have you (carefully) probed the screen's driver board with a multimeter to find its 5v reg?
    • What specific Raspberry pi model are you using?
    • Photo of your wiring please.
     
  3. Tech Flare .

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    here are the answers to your questions:
    • My lipo battery has 3.7 volts.
    • I bought the lipo from Adafruit.com.
    • yes, I charged the lipo
    • yes i bought the powerboost from Adafruit.com
    • The powerboost was fried in the process, so i desoldered the wires. (With all due respect, my question was about a new solution to power my screen and raspberry pi. I don't see how this is relevant.)
    • I bought the screen off of Ebay. Model #QC750BG1
    • I used generic jumper wires with the tips removed. (probably not the best idea but its all i had)
    • The screen's driver board is labeled very well, so I didn't need to. (the screen only has 12 volt pins but when i soldered the 3.7 volt battery to it the screen still worked fine.)
    • I am using a Raspberry Pi 3 model B v1.2
    • again, i desoldered all my wires because the powerboost is fried.
    hopefully this answers your questions! Sorry it took so long.
     
  4. Stitches 2 and a Half Dollarydoos Staff Member . .

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    Capacity mate, not voltage. The capacity of a cell is the number with "mAh" at the end, 2500mAh for example. You also didn't specify how to wired the powerboost to the screen. Did you wire the screen to the output pins of the Powerboost, or the battery input terminal?
    This is the model number of the LCD panel only, what driver board are you using with it? Can you post a photo of the board and panel?

    As for the Powerboost frying itself, it's possible that the driver board was drawing too much power from you undervolting the 12v line. These boards normally step the 12v input down to 5v, and then down again from 5v to 3.3v and 1.8v. Depending on the cheap 5v step down reg they put on that board, it's possible that it didn't like being fed such a low voltage. This could possibly lead to overdraw, which the Powerboost is supposed to be protected from, or perhaps even an internal short. That's the only thing I can think of. If you use a 12v supply to run the screen and board, there should be a number of 8 legged ICs on the board. If you check them with a multimeter you should find that one of them will have a leg that outputs between 4.5v and 5.2v. If you lift that leg off the board and solder a 5v carrying wire to the pad, that should run the screen with significantly less power.

    Unless you want to design and assemble a custom PCB using a 5v step up reg with a higher output current, I'm afraid the Powerboosts are your only safe option. ("safe" being relative to correct operation)
     
  5. Tech Flare .

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    The capacity of my battery is 2500 mAh.

    I can't exactly remember what i did with the wires to the screen's driver board, but i'm pretty sure I sent a 5v output pin from the powerboost to a 'POWER' pin on the driver board (not the DC 12v in connecter) and i sent a wire from the battery input terminal on the power boost to the DC 12v in connector. (again I did not know what I was doing, and I don't how this will help but I hope it does.)

    I did find a few points on the board rated at around 3.3v, so that may work to power the board, but I don't think so.

    Here are some pictures of my driver board:
    548597356_519473.jpg 548597338_219670.jpg
    and I was talking to a friend of mine who is really good with electronics about what I should do, so I sketched out a model of what we were thinking:
    83341.jpg
    'ADA' is the Adafruit Powerboost, the bouard with VOut GND and VIN is a 12volt step-up voltage regulator. (Of course this is just a rough sketch and probably won't reflect the finished product)
     
  6. GingerOfOz send waluigi memes Staff Member . .

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    Wait, so you're telling me that you tried to wire your battery directly to a screen?

    That's bad news if you did.

    And plugging the voltages of your battery straight into a 12V buck converter isn't any better.

    Batteries NEED TO BE PROTECTED AT ALL TIMES FOR EVERYTHING!!! NEVER try to pull battery voltage directly to a load, or else you will damage the cells/damage the load/ cause an explosion.

    This stuff isn't a joke.

    This thread has some really nice information on handling batteries safely, so I'd go through it for sure because what you're doing is quite dangerous. I'd have your friend read through it too because while I'm sure there are areas of electronics he is quite knowledgeable in, batteries aren't the kind of thing you want to guess at.

    Your batteries are protected through the powerboost for your Pi, so you don't have to worry about protection there. But trying to pull voltage direcrly from your batteries to anything wasn't a good idea. That's what probably killed your powerboost.

    I'm sorry if I'm sounding harsh, but if you don't understand what you're doing then your figurative playing with fire is going to turn literal soon enough. You should definitely do more research beyond that thread I gave you, espescially with how other people have safely powered TFTs with Pi setups

    Additionally, how do you plan to step up to 12v? And what you made you think your screen could run natively on such a low voltage? It's not uncommon for TFTs to be able to run off of 5v, but 3.7 is quite a stretch considering that the driver boards generally step down to 5v and 3.3v.
     
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  7. Stitches 2 and a Half Dollarydoos Staff Member . .

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    NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!! You never wire straight from a battery to a load, anything that wants power must be wired to the 5v output of the Powerboost. Also, what do you mean when you say "power pin"? Which pin on the driver board did you power?

    Did you do this as I suggested before? There are two 8 legged ICs on that board, one of them should be it.
     
  8. BocuD .

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    Uhm, please tell me you don't wire 5v to the power pin again. Its supposed to be grounded to turn on the on board 3,3 regulator ;). It goes to a gpio line on the main driver ic which controls the regulator. If you want to power the screen from 5v, you will need a voltage regulator to step it down to 3,3v. The easiest way to do this is probably a PTH08080 and a 1,8kΩ resistor. Use this thread to find out how to wire the PTH08080. Wire the 3,3v output to the following pin on your driver board, after removing the black inductor: 548597356_519473.jpg
    The easiest way to remove the inductor without damaging the pads is by heating one pin up with your iron, pull on the other side of the cap to move it, then heat up the other pin, repeat. Slowly remove the inductor this way.
    About the Powerboost: It might be dead depending on if the power pin on the lcd driver was grounded. I'm not sure about its default state. To be safe I'd just order a new one. And just to repeat it: Don't wire anything to your battery but the powerboost. Then wire everything to the powerboost output.
    Good luck with your project!
     

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