Want to power some farkles... need help converting 5v to 3v. Any electronics gurus?

[CZroe]

OK, I can't believe that there aren't Instructable or Makezine guides for powering your traditional AAA/AA devices off of rechargeable Li-Ion cells or 5v sources (USB, for example), but that's kinda what I need to do. Best I can find are packs that offer multiple voltages including 5v USB, so I figure I'll just start with a couple 5v packs, especially seeing as how I found the perfect, flexible, ones for fitting on the exterior of a helmet (idealy, I want to use the snaps and Velcro under a helmet skin).

Let me start off by saying that I have only limited electronics experience including modding video game consoles and building electronics kits. In other words, I can use a soldering iron to follow instructions but I'd have no idea what I'm doing 90% of the time. I've done some difficult surface mount work with the limited temp-controlled solder station I have and I've done things like replace a 40-pin connector to salvage a rare model 2 Super Nintendo Entertainment System (before the counterfeit clones diluted the value).

Anyway, I've looked for pre-fabbed solutions and found that there is no shortage of universal Li-Ion/Li-Polymer battery packs with selectable voltages, but none I can find offer 1.5 or 3V. From what I understand, it takes a power supply regulator based on LM338 or LM317. I see kits for sale, but if it could do what I want I would expect there to be no shortage of pre-built devices or guides that can regulate 3.7v, 5v, or more to 1.5v or 3v. Will this work for me? Will I have to be concerned about heat generation? If so, is there something like this that can do ~3.0v from 5v? With less heat generated, would it be more efficient? Can the LM3xx VRMs be miniaturized enough to fit under a helmet skin along with the batteries?

I want to power a 2xAAA helmet cam (2.4-3v) and a 4xAA sound-activated EL panel (4.8-6v) off of two flexible Li-Ion packs that output 5v. I am unsure about the amps it can output but I'm pretty sure it's capable of outputting more than the .5A/500mA USB spec because it's not a USB "device," per se.

Much of this is inspired by the helmet cam being useless in cold weather due to requiring expensive use-once Lithium battery cells. By removing the battery door and creating my own housing, I hope to make it somewhat water-resistant while I'm at it. With or without some degree of water resistance, I still want it all to be removable from the helmet so that they can be stored /secured elsewhere. The sound-reactive EL panel EQ will hopefully serve two purposes... one is to act similarly to a safety brake-lamp modulator and the other is to let people know that I am not ignoring them when I can't hear them over my music (I'm surprised at how often people try to talk to me at stop lights). I think the SkullSkins allow light to show from underneath because they sell headlight covers which can and they seem to be the same material.

[CZroe]

Originally Posted by g21-30

It looks like you want battery packs, rather than a permanent power source ON the motorcycle.

For USB, you could use one of these:

*snip*

Along with wiring a cigarette lighter receptacle for it.

I installed a receptacle and I have one of those w/1A QuickCharge port and a regular 1/2 amp port. I use it to power my phone (0.5A-1A), which is also my stereo/GPS, as well as charging my Parrot SK4000 (0.5A) on long-hauls, like when I crossed the US. The phone is connected to the helmet via wireless Bluetooth A2DP/AVRCP and HFP, so it would be a pretty big step backwards to start jacking in for the less useful parts.

EDIT: I forgot to mention that I would STILL need to convert 5v to ~3v. I don't have a problem getting a 5v power source either wired or battery-operated. It's where I go from there that I need help with.

[CZroe]

Thanks, but that's for connecting logic, meaning circuits carrying compatible 1s and 0s (on-off signal pulses), between devices with incompatible voltages. For example, before standard SD cards, there were 5v SmartMedia cards and there were 3.3v SmartMedia memory cards. A card reader used in your project may be compatible in every other way but voltage, so they made this. I don't know what it would do with a sustained voltage across it because that's not what it was meant for. It doesn't supply or convert the curent/voltage, just accepts one type of signal and repeats it on the other side using the voltages supplied by the devices on either side.

[HKr1]

You get a .6 voltage drop thru a diode. Why not use three in series for 1.8 v. 5v - 1.8 would be 3.2v

[HKr1]

One more for ya:

[CZroe]

Originally Posted by HKr1

You get a .6 voltage drop thru a diode. Why not use three in series for 1.8 v. 5v - 1.8 would be 3.2v

Is that really how it works? I mean, aren't there, like, a million different kinds of diodes with different specs? I know that isn't the point of a diode (only allow electricity to pass one-way), but can it be relied on? If you are talking about LEDs, I think I would I would need resistors in series first. If I knew how do do that, I could just use resistors in the first place, if I'm not mistaken. I wouldn't know how to figure Ohms and such plus I'm color blind so I've never been able to figure out how to read the specs of a resistor. The fact that no one has suggested one tells me there's a draw-back... like heat generation or something.

Originally Posted by HKr1

One more for ya:

I'm lost.

Like I said, my electronics experience is pretty limited. Now, if anyone knows EXACTLY what resistors or resistors + LEDs or diodes to buy and use, I could do that.

Thanks.

[HKr1]

Schematic is a voltage regulator.

Diodes have different uses. Just so happens they loose .6v going thru them. Get some normal diodes from radio shack 1n4003, 1n4001. Just stay away from zener diodes, the let curent flow in opposite direction at there set voltage.

[CZroe]

Originally Posted by HKr1

Schematic is a voltage regulator.

Diodes have different uses. Just so happens they loose .6v going thru them. Get some normal diodes from radio shack 1n4003, 1n4001. Just stay away from zener diodes, the let curent flow in opposite direction at there set voltage.

Thanks. Heh, I had the Wikipedia entry for "Zener Diode" open already when I read that (other page said that they were used for voltage regulation). I think 4 in a series and a drop to 2.6v may be more appropriate, considering that most 3v devices are also designed to run on 2.4v (1.2Vx2 NiMH/NiCD). That would put it nicely in-between.

Anyway, do I have to worry about current/amps or anything like that through a diode? Will it get hot? Part of the desire for Li-Ion is capacity/run time... is a VRM more efficient?

I may want to do one of those LM3xx kits anyway due to the adjustability (power a 1.5v device if I need to).

Thanks again.

[HKr1]

There good for an amp, little more on peaks. They make bigger ones...........

[CZroe]

That *may* be enough. The 4xAA EL panel should be fine off of 5v directly because it's right in-between 4x1.2v (4.8v) and 4x1.5v (6v). Actually, I shouldn't assume that the EL panel's battery chamber isn't wired in parallel or a combination of the two... I'd better wait until I get it to make that call.

[alex.s]

Hi,
I'm not an expert, but i've tinkered with electronics and robotics quite a bit.

using an LMxxx regulator (looks like a transistor), you should be able to simply wire it up so that its input is connected to the positive output of the battery (maybe switched so it doesn't drain the battery), the ground is connected to the negative of the battery (this is a shared ground, so this is also the negative output), and then the last lead on the regulator is the ouput line which combined with the shared ground output your regulated power. i wouldn't worry about heat very much unless you're really putting a lot of amps through it (they make different versions rated for different power demands). you could solder the wires on and tape/heatshrink around it so its as small as a large wire coming off of the battery pack.

a simpler solution (although it would provide less power) would be to remove some of the cells in the battery. i'm not sure if that would be a good idea with those flexible batteries, but with a 9v for example you can remove the outer metal layer and use only 3 cells for example to get a lower voltage.

hope this helps!

[CZroe]

Thanks. I took the question to a few electronics forums and they suggested the diodes in series method (.6v drop per diode). I think they said that a VRM needs at least a 3v drop and 5v just isn't a high-enough starting point.

Thanks!