Hi Power USB Charging.

[nativepaul]

Hi all, I bought a smartphone and it is an amazing device I have loaded all my music onto it and it connects to my car via bluetooth and plays through my stereo, I also use Google maps as a GPS to stop me getting lost if I don't know where I am going which works better than my old TomTom, however when I use both apps together it draws more power than the Samsung car charger can supply and on long road trips the battery drains down and eventually dies.

I have noticed that even with no apps open the car charger does not charge it as fast as plugging into my desktop PC, nor does plugging it into the wall charger or my laptop, so I believe the phone is capable of charging faster than I can feed it.

I am thinking about wiring a Castle UBEC into the 12v side of my car set to 5v, and run the 5v leads up through a hole in the dash near where my phone goes, and wire into a micro USB plug.

Is the Castle BEC stable enough to do this? Both in voltage (as RXs seem to be fine on between 3v-7v) and in ripple (both infeed and outlet as it will be fed slightly dirty current from an alternator not pure clean DC like in a model, and I don't want to risk my expensive phone. If not, is there anything I can do to clean it up so it is suitable (maybe some capacitors in the leads to and from it)?

I have looked at the pinouts of the USB and I know what I have to do for the most part, pin1 is +5v, pin5 is ground, pin 2+3 are datacables and have to be shorted so the phone knows it is attached to a charging socket not a data socket and it can draw more than 500mA, Pin 4 is the mystery to me, some diagrams don't show it connected at all, but on those that do, it is a second ground but with a 130Kohm resistor in line and marked "sense" or "detect", the other USB-A end of the cable only has 4 pins and this is the missing one, it is simply tapped off the pin5 ground inside the plug. As I only want to charge through the lead not use it for data I don't know whether I should use pin 4 or not, either way I would like to know what it does.

[BrianG]

I've used a BEC and it works fine (even cheap ones will do over 2A easily). To clean up any possible dirty voltage, add a capacitor to the output - 1000uF or higher rated for 10v or more will be fine. Low esr is better but not required. A similar input cap, but rated for ~20v, wouldn't hurt either. You can even add a ferrite donut to the output wires.

However, the small contacts of a micro usb connector tend to drop a little voltage as charge current increases, so the phone is likely only getting 4.8-4.9v when trying to charge at higher rates. The included charger probably boosts the 5v up a little to compensate. So I would bump up the BEC output so the phone sees a solid 5v. Usually 5.1v-5.15v is good and is still well within the USB spec (spec allows up to 5.25v). The method to boost voltage varies by BEC maker. For a CC BEC, it's programmable - just be sure to measure the output (I've seen actual measured output vary considerably from the programmed setting). For other BEC types, I've modded some in the past to provide a specific voltage; it's not too hard as long as your soldering skills are adequate.

Shorting the two data lines is typically what you'd do to enable high speed charging, but some phones/tablets use other methods. Some older Samsung phones/tablets (galaxy s3 era) need a 200 ohm resistor between the D+ and D- lines instead of shorting. Apple uses a completely different scheme involving voltage dividers between the power and ground being fed to the data lines. And, yes, some even use that sense line - although it seems to be fairly uncommon. So, before you assume shorting the lines will work, check forums for your specific phone.

Just be aware that ANY bec can fail where it will send full input voltage to output (in your case: ~14.4v). Any decent USB charger will contain a little extra protection circuitry, but this is missing in any BEC I've seen. The chances of a BEC going bad when being used at moderate levels though is small, but just thought I'd state that warning seeing as how it will be hooked to a device costing a few hundred dollars.

[nativepaul]

Brian, you are a god amongst men. I thought you may know what is what but I didn't dream that you would have done it before and be able to give me that much detail. Thank you.

I hadn't thought to double check the programmed voltage, I will make sure to do so.

My phone is a Galaxy S3, so your info on the 200ohm resistor is invaluable, I never would have guessed it needed that.

I have a spare 16v 470uh and 25v 1000uh ultra low ESR capacitor left over from ESC mods I can use, should they be fitted in the same way as they are on an ESC, bridging the positive and negative wires? That makes sense to me as they are doing the same job, but for some reason I feel that they should be bridging a gap in the positive.

As you can tell I know nothing, so thanks again for your help, I would be lost without you.

[Arct1k]

Just buy a 2amp car charger.