I’m a beginner in many respects, but quick to learn. That being said, I may have jumped the gun and bought the wrong devices. I have access to a 3d printer and wanted to make a handheld Raspberry Pi, primarily for fun and secondarily for old-school gaming. Here is the power wiring drawing I did really quickly in MSPaint along with a link to all the parts I plan on using. I know the voltages work, but I forgot to think about current flow, and whether or not that will be too much or too little, and result in overheating, underpowered, or other bad conditions. If someone can help me out that would be great. I don’t want to put everything together only for it to fry.
(I hope you’ll forgive the beginner look of this, it was quick and dirty and conveys the information I need to)
I have not included the non power providing lines. Obviously there will be tons more wiring to do. The big question here is, can I make what I want work? Was ensuring the proper voltage enough, or do I have to do more and double check all the current flows through all the devices? I haven’t done anything like this that wasn’t presented as a complete kit, and so I’ve never had to double check on all of it before. Did I screw up and buy the wrong hardware? What is it going to take? I’m not overly concerned about making the case work as that’s a bit down the road, but I do have Alibre Design and am confident I can make a suitable case with the 3d printer.
Oh, I realize I should have double checked the diagram for how the Battery indicator works and it should be in series, not parallel. Forgive that foible please.
Forgot that the audio amp has to be after the BEC. Fixed it. I also apparently need to find a different on/off switch as that one can’t handle the current, most likely.
Agreed, that power switch wouldn’t be my first choice. I am curious as to why you are using a BEC to power this project. But I don’t see anything wrong with it.
I would advise you to get one thing on your list to work and work up from there. Get the RaPi working with the OS (and your game) hooked up to the screen. How are going to play the game? Keyboard, mouse, gamepad hooked to the Pi? Those need power as well.
Then move on to make it portable, adding your battery and charger circuit.
There is an EDIT button on the top right of your posts.
Thanks. I already had the RPi and peripherals for it, and wanted to do something else with it. I’ve got a mini wireless keyboard for it. It does have it’s own battery that needs to be charged separately, but the extra utility was worth it I thought. I plan on just having space for it in the case, and to be able to pop it out whenever, as well as making sure the HDMI port is exposed.
The battery I bought has a PCB module, and I thought that would take care of the proper charging. Perhaps that was just dumb to assume that, but I wanted to try to make the proper charging equipment into the system and use a standard 12-volt barrel charger instead of buying a specialized charger. I will look more carefully at the article you linked me. Thanks! That’s exactly the kind of stuff I need to know.
The BEC is just what I’m familiar with. I dabbled in R/C a while ago, and it seemed to suit my needs. Rather than look more deeply into something that does the same job, I looked more into other things. Is it insufficient?
The BEC is going to be close as far as Amperage goes. I couldn’t find any reference to current consumption for the LCD. I don’t see it using more than an Amp though. All LI-Ion/LiPo batteries have internal circuitry. I expect this will be your biggest hurdle. If I were you, I would get everything working using regular Wall adapters or the like, and then measure the current consumption for the setup. This will tell you what battery you should use, then the charger for that battery. If you want to stick with the latest technology for batteries, then you will need to construct a charging circuit. [Some schematics Googling “Li-ION battery charger.”
I think your audio power-amp need 5V, so may be destroyed if you feed it with anything higher.
A multicell LiPo requires a balance-charger. Be careful with LiPo packs, they can generate massive heat if shorted out. Not sure if you are buying a battery with built in protection.
Suggest that you get the Pi running off of a 12V power pack, then worry about the battery management - then you only have to deal with half the system at a time.
I thought you only need to use a balance charger the first time. The pack I got doesn’t have multiple connections, just two (+/-), and includes prevention from overcharging each cell. Are you SURE I can’t simply charge it with a simple 12v 1a? If not, I’ll just abandon the battery pack and use two 9volts in parralel. My LCD can run on 9volts.
Over many charge/discharge cycles even matched cells that were balanced will become unbalanced, leading to a less than full charge or a reduced lifetime. There are lots of “power management” ICs that choose btw charging, use, booth or aux power even. I even recall a longish thread here where the OP wanted to use a 2S LiPo, charge it as 2 single cells while a redundant 2S LiPo supply took over.
Also be aware that Pololu has quite a few “low” current DC/DC converters that seem to be well regarded. A 2S LiPo might do for your Pi and one of those for other voltages. You might even find a large single cell LiPo (or 2P) that can be boosted and regulated to run the 5v Pi and so eliminate the BEC and simplify the whole charging scheme. Something like, but stronger, than this.
That’s an excellent solution, and the boards are small enough to fit my handheld criteria, and it makes it modern day universal via charging with USb as opposed to charging with an old barrel port. Ive almost got everything I need set up, so now I’ll just check how much amperage runs through my full system and get the right parts. Thanks Mee_n_Mac, that’s a great solution to what I was looking for.
edit: oh, just to be clear, mah goes down inversely as voltage goes up in a perfect no-loss system right? So a 3.7v 2000mah battery boosted to 9volts would only be about 822mah, correct?
Lotus:
oh, just to be clear, mah goes down inversely as voltage goes up in a perfect no-loss system right? So a 3.7v 2000mah battery boosted to 9volts would only be about 822mah, correct?
Correct, Power_out = k*Power_in, power being volts*amps. k = 1 (100% efficiency) for your example.
You can generally assume k = 0.85 if you have no other info.
Also, what would be wrong with using the exact item you linked me to and a single 2000mah battery, so long as I don’t charge/operate simultaneously? I do have a 5v 2a usb port (i don’t know of usb cables can handle that current), but I wouldn’t know where to begin to find a similar product like the one in your link that can take the current. Also considering the LCD screen doesn’t require much current, would [this be okay to use?](Pololu 9V Step-Up Voltage Regulator U3V12F9)
Darn. Do you know where I could find a different suitable one? Or perhaps I could just use a simple charger on a different circuit and two separate step-up voltage boards, one for 5v and one for 9v.
Adafruit does have a nice charger ([this one) that can go up to 1000mah, as well as a larger single cell lipo battery, but I would be unsure of making the changes to it to make it 1000mah as opposed to the stock 500mah configuration. I’m comfortable with a simple changing of a resistor, but I don’t see any instructions on which one, what ohm resistor to replace it with, or anything.
edit: ugh, also noticed that while the battery is rated for 2A continuous, the connectors are not, and since it’s a 3.7v and the stuff I’m powering is at a higher voltage, just the raspberry pi alone at 700mA@5v with an 85% efficient step-up voltage will cause a 1.1A pull on the battery, not to mention the LCD display and speakers I want to also drive. BLECH! The wires I also bought planning to use are probably insufficient ( https://www.sparkfun.com/products/10646 ).
Oh well, that’s what I get for buying first and then learning second. Any suggestions or ideas? I didn’t think the current draw from all this would be such a problem!
edit2: wait, is that the wires or JST connectors that are rated for only 1A? How can I tell what a wire is rated for?
