First things first. Portable power supply:
The typical method is just to grab a motorcycle batter (12v) and use a Cigg->USB 2.1a converter. Although this gives you hours of use, it could be seen as a great pain to carry around such an atrocity.
The next ploy is to power it using 4 in-line AA's, giving you ~6v at 5~8a. One would simply down-volt this to 5v 0.5~2a and be in business.
The final ploy is to run any number of spare rechargable li-ion batteries (3.3-3.7v @ 0.5-2a per) and down-volt to 5v. These are typically rather small and can be recharged.

The question is, how to down-volt these. Regulators are the key, and digital specifics can be an absolute make-it-or-break-it kinda thing. for example, resistor XRP6272ITC5TR-F will take your 6v input (no more) and output 5v at 2a. 4 in-line AA's would, in a perfect world, last you 4 hours, but power is lost in various occurrences, and you may not be drawing a full 2a all the time. This wouldn't work for your Li-Ion, since you would be overloading it. Also, this has a max voltage loss (it fluctuates you know) of 1.8v. anything below 4.5 and your pi could reboot randomly (oh noes).

So maybe you go with a LD29150DT50R, which takes a max of 14v and outputs 5v at 1.5a and only loses 0.7v at max load (meaning if you really tapped out the pi out, you have rather slim chance of rebooting. Not quite our 2a desired result, but that's 1 whole amp of current the pi itself wont use, so our USB devices should be a little happier.

Even bigger question is, what are the results of pushing 6v through that 14v resistor? What happens if I tried to simultaneously rig 4 500ma resistors for a power source.

Questions indeed. We certainly wouldn't want to fry our pi, now would we.

Finally inquiry, suppose I can rig 3-4 li-ion batteries for 6-14 volts to the 2nd listed resitor and get the desired values. How can I line these up to charge them? Do I just wire the charger directly to it? Do I need to charge them individually? Are there cheap circuits I can use to charge them 1 by 1 and then just feed the battery directly?

Thanks for the info ahead of time :3 My pi appreciates your concern for it's well being.
your question is a little unclear. The Raspberry pi page seems to claim 700 mA for peak power consumption, so the XRP6299 would work. The Data sheet claims 500 mV dropout at room temperature at 5 Vout, so the AA's could last for a while, especially if you set the output voltage to 4.7 or so, which I think is still in spec for USB power supplies.

I'd stay away from rolling your own Li-ion solution, as they can be somewhat explosive.

The easiest thing to do might be to pick up a USB backup pack, like this http://www.energizer.com/portable-power/portable-chargers/universal-multi-port-charger/Pages/energizer-universal-multi-port-charger.aspx which would be useful for other things as well
700mA is peak for basic operations. This includes OS running, HDMI output, and LAN output. USB devices require additional current (up to 2.1a for power hungry devices). Currently, running a usb BT (Microsoft) and a low-power USB wifi (D-LINK DWA-121) I eat 700-800mA.

I would also prefer to run this off of a rechargeable source such as li-ion batteries. NDS batteries dish out ~3.4v a piece. 3 of these meet a low limit for most 12v->5v converters like cigg->usb adapters. I have extras. Problem is, they have slightly embedded flat connectors. If I decide to solder, they will be unable to be charged individually via their original sources (the NDS).

In the (near) future, I'll be obtaining an LCD touch screen circuit and parts that will require a 12v supply, so 4 AA's will not suffice, but 3 li-ion batteries might. The typical method is to obtain Laptop battery cells for this function. I just want to know what will happen if I run a lower voltage through, say, the 14v->5v resitor. Let's assume 6v for the sake of short-term progress.
Err, so to clarify...

Q1: What would happen if I were to input 6v 8a on a regulator that caps at 14v 1.5a?

Q2: What is the best way to connect leads to a flat-pin li-ion rechargable battery?

Q3: If I need to permanently connect them, A: can I link the regulated recharge voltage to them in a linear fassion? B: do I need to charge them individually?

Q4: Supposing I go with the 14v and dish out close to 12v from the rechargables, what is the expected draw from using a 12v power adapter to support the screen in a more raw fassion?
Regulators aren't resistors, though you keep referring to them as such.

A switching regulator will be a better bet than a linear regulator as the linear regulators waste the difference between input and output voltage as heat, and wasting power is not a great idea on a battery-powered device. The bigger the difference between the input and output voltage the lower the efficiency (and the hotter the regulator gets). Suppose your circuit draws 700mA and you used a 12V input you'd be wasting (12-5)*0.7=4.9W as heat.

Batteries are a voltage source, not a current source, so you would need to define "input" for your 6V/8A query. If you mean you were drawing 8A through the regulator and it was only rated to 1.5A then it would likely burn out.

Do not solder leads to batteries. Buy or construct a battery holder with sprung contacts. Similarly, don't try charging Li-Ion batteries by directly connecting them to a voltage supply - use a charger chip.
Not sure I have the option to go with a charger chip. I have 1 'scraps' NDS circuit that i would 'maybe' be able to peel, but my experience is that it doesn't always work out as expected. Especially with printed circuits. Same goes if I grab a few Android batteries. Guess grabbing a few connectors would indeed be best. Then I could swap out and recharge them individually as needed. Thanks!

As you suggested, I'm supposing that if I push 2x 3.4v (~6.8v) li-ion batteries I would lose considerably less that if I powered it via 3x 3.4v (10~12v) li-ion batteries, the the 3rd could help power the LCD screen.
Q: If I rig 10.2v to the 5v regulator, and have a power draw directly from the batteries to power a device rated at 5~12v (12v for backlight) what would be the effect on the power source reaching the other end of said regulator? Would this be based on the current the 12v device draws?
As rfdave pointed out batteries can explode or start fires if mistreated (overheating during soldering, incorrect charging etc) so it's best to play it safe.

With regard to your query about current, you'd have two circuits in parallel - one containing the 5~12V device with a backlight, the other containing the regulator+regulated circuit. The total current draw would be the sum of the two currents flowing through the two different circuits.
Komak57 wrote:
Err, so to clarify...

Q1: What would happen if I were to input 6v 8a on a regulator that caps at 14v 1.5a?

Q2: What is the best way to connect leads to a flat-pin li-ion rechargable battery?

Q3: If I need to permanently connect them, A: can I link the regulated recharge voltage to them in a linear fassion? B: do I need to charge them individually?

Q4: Supposing I go with the 14v and dish out close to 12v from the rechargables, what is the expected draw from using a 12v power adapter to support the screen in a more raw fassion?


Q1 - So a circuit will only draw the current that it needs, you can's really pump current into something like a Raspberry Pi. Because of that, the current will be limited on the output to what the RPi draws, so you won't have a problem there. Now looking at the other specifications of the LD29150 regulator, there are two versions, a fixed output and an adjustable output. The fixed ones are configured to output a fixed output voltage, while the adjustable ones can have their output voltage changed by adjusting the values of two resistors. The Maximum input voltage that you can put into this part is 14 Volts, but you can, and should put in less that that for a 5V output application.
The way a linear regulator works is by acting as an adjustable resistor, so the voltage drop between the input voltage and output voltage shows up as heat, so if you're drawing 700 mA, and dropping (14-5 = 9 Volts), you've got 6.3 watts of heat to dissapate, which is a lot in a small circuit. You might want to start with this http://en.wikipedia.org/wiki/Linear_regulator and do some studying

Q2 - Li-Ion batteries can be a little explody, so I think soldering to one would be a bad idea. Grab the connector if you can.

Q3 - There are Power Managment IC's that take care of charging/discharging Li-Ion cells, as well as managing recharging and operating while you're charging. It get's somewhat complicated, as you can imaging.

Q4 - Not sure. Currents will sum, so there will be a total of whatever the touch screen takes plus the RPi.
A couple of decent articles on power regulators

http://www.edn.com/design/power-management/4420313/Basic-concepts-of-linear-regulator-and-switching-mode-power-supplies--Part-one

http://www.edn.com/design/power-management/4420855/Basic-concepts-of-linear-regulator-and-switching-mode-power-supplies--Part-two
Reading through, i'm getting that the more powerful the source I'm dealing with, the greater the difference, and the more it will take to power the device. The casing I'm using has a 4 AA source soldered to a small circuit-board for a power switch, LED, and 1 button. This circuit actually dims down the 6v i was getting to a ~5.3v that is far safer to tap into the pi, and has been doing wonders at it. I was contemplating on dropping it a tad more by using rechargeables. My largest concern at this stage, is how to power the pi from a wall charger without blowing up the pi. Trying to quickly plug it in and turning off the power has 1 of 3 outcomes. 1) i turn it off too fast, and it reboots. 2) i turn it off pefectly (rare) and nothing bad happens, or 3) i turn it off late, and the pi takes a 10v load for however long it takes.


A) What's the name of the circuit I'm looking to build to power from the batteries as a last-resort (wire as primary). - possibly a XOR gate mixed in?

B) What are the chances I can fit the charger circuit into the casing (6x4x2 cm free space, 4cm tall if it works around the SD card).
B_) I should probably just plan to have it external if A works as desired and run a seperate power supply for the screen whenever needed.

supposing the screen takes the 12v, and the pi takes the 5v, there's a 17v draw I would need to keep both devices perfectly happy. I would either need a better regulator, or possibly pull something like [3.7][3.7]{7.4->5v reg}[3.7][3.7]{14.8->12v reg} with all 4 batteries linear. This would cause the least release on the regulators, but would theoretically drain the first 2 cells faster.

Really wish I was better educated hardware wise. But, I guess that's what the pi helps with.
  
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