Develop Bugs

[Q] Please check your car charger's true voltage

Even though it's listed at 12 volts, that may not be the case. Some "12" volt chargers just pass the car's voltage through, unregulated, so it's closer to 14 volts. The Xoom home charger is a well-regulated 12 volts. Mine is actually 12.07. As a rock climber, I'm looking for alternative power sources for the wilderness. It'd be good to know the Xoom voltage tolerances. Thanks!

It appears you are correct about the car charger. I ran some voltage tests and my results were about the same as yours.
With the engine off, it was between 12.70 and 12.74 V.
With the engine on, it was around 14.35 - 14.45 . Revving the enging caused it to get as high as 14.90 V!
I'm no electrical engineer, but a 25% overvolt seems a bit much, doesn't it? I doubt the voltage regulation is in the Xoom itself...
Funny, I had to cut and strip a piece of 18 gauge speaker wire and pull out half the strands to stick into the Xoom's power adapter just to be able to get a reading on the tip - that's the smallest barrel connector I've ever seen!

schick79 said:
It appears you are correct about the car charger. I ran some voltage tests and my results were about the same as yours.
With the engine off, it was between 12.70 and 12.74 V.
With the engine on, it was around 14.35 - 14.45 . Revving the enging caused it to get as high as 14.90 V!
I'm no electrical engineer, but a 25% overvolt seems a bit much, doesn't it? I doubt the voltage regulation is in the Xoom itself...
Funny, I had to cut and strip a piece of 18 gauge speaker wire and pull out half the strands to stick into the Xoom's power adapter just to be able to get a reading on the tip - that's the smallest barrel connector I've ever seen!
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Thanks for taking the time to do this!
Your results were what I expected. It's the tiniest barrel I've ever seen--sizewise, the smallest Nokia is the only good match, so far. Doesn't seem very strong....

schick79 said:
It appears you are correct about the car charger. I ran some voltage tests and my results were about the same as yours.
With the engine off, it was between 12.70 and 12.74 V.
With the engine on, it was around 14.35 - 14.45 . Revving the enging caused it to get as high as 14.90 V!
I'm no electrical engineer, but a 25% overvolt seems a bit much, doesn't it? I doubt the voltage regulation is in the Xoom itself...
Funny, I had to cut and strip a piece of 18 gauge speaker wire and pull out half the strands to stick into the Xoom's power adapter just to be able to get a reading on the tip - that's the smallest barrel connector I've ever seen!
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Yea car power adapters should probably be regulated better because the higher RPM's will cause higher voltages provided by your cars alternator, I'm not sure if that is an issue to the xoom though

I have the xooms car cord and have used it many times in my auto. The xoom works GREAT with the car cord and I have had no over voltage problems

Sounds like your cars voltage regulator is bad. It should only let 12V out for accessories.
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hammer4203 said:
Sounds like your cars voltage regulator is bad. It should only let 12V out for accessories.
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Not necessarily, and in fact the nominal voltage is agreed on at 13.8V .

Since the cigar lighter socket was designed to heat a cigar lighter, using these sockets as power connectors can lead to many problems. In addition to the issues with incompatible sizes, plugs can vibrate out of the socket under normal driving conditions, owing to poor retention. There have been reports of melted plug tips. [6]
A second problem is that nominally "Twelve-Volt" power in cars fluctuates widely. The actual voltage will be approximately 12.5 volts when dormant, (less when cold) approximately 14.5 volts when the engine and the alternator/generator are operating, (more when cold) and may briefly drop as low as 5-6 volts during engine start. [7] DC/DC converters will usually compensate for these small fluctuations. [citation needed]
Rarely, more extreme cases of voltage fluctuation can occur when the car battery is disconnected while the engine is running, or when the car receives a jump start. When the battery is disconnected, a load dump transient can produce very high voltages. A car receiving a jump start from a truck will be subject to its 24 V electrical system. [8] A "double battery jump-start" is performed by some tow truck drivers in cold climates. [9]
Design wise one has to take into account intermittent contact, and voltages outside the nominal 12 V DC like top voltage 9-16 V continuously, top voltage at 20 V during 1 hour, 24 V during 1 minute, 40 V during 400 ms. [10] Protection component tolerance example ratings are +50 to -60 V DC [11] Additionally, issues can occur with temperatures varying between -40 till +85 °C such as humidity and condensation. [10] Equipment connected this way must tolerate large variations in electrical- and climate environment.
http://en.wikipedia.org/wiki/Cigarette_lighter_receptacle

Did anyone come to a conclusion about this issues.
Is the car charger safe for use when the battery is at 15V.
Its my understanding that the car charger should work in 24v vehicles, but this would mean 24v going into the xoom !!!

If you have an unregulated car charger that outputs 12V nominal, an easy fix would be to purchase a 12V linear regulator, preferably TO-220 package, and install that inside the charger itself, given sufficient room. Make sure to choose a part with a larger input voltage range above 12V though, to be on the safe side.
Only downside with this solution is that it'll be pretty inefficient, and won't do anything if the voltage drops below 12V (it should just passthrough). You could invest in a buck/boost switching regulator to fix that, but you might as well get a new car charger with an integrated switching regulator at that point.

After many forum posts and research I was unable to get to the bottom of this.
So I decided to test for myself.
I ramped up the voltage to the car charger and it continued to pass through the same voltage, only at 30v did the car charger stop supplying power to the xoom and killed the car charger.
I spoke to someone at Motorola who said it was supposed to accept 24v, the car charger that is.
So I plugged it into the xoom and charged from dead fine. So it seems the xoom has a far greater voltage tolerance than expected.
The best bit about this is that many people will be able to use their laptop power supply with an adaptor to the get the correct tip, rather than using a second charger.
This certainly solves my anger as no USB charging.

decworld said:
This certainly solves my anger as no USB charging.
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You shouldn't because Transformer owners have to carry around a 15V USB trickle charger and an Asus's proprietary cable.

[Q] Using high amp charger

just wondering if it's safe to use my hp touchpad charger on the gio
Wall AC to USB power adapter, which has input specifications of 100-240 Volt 50–60 Hz 0.4 Amp AC, and output specifications of 5.3 Volt 2.0 Amp DC. It is cylindrical roughly the size of a "D" battery with a foldable 2-prong AC connector and Standard-A USB socket on its two ends.
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pretty high amperage, is it safe to charge with it? done it twice already

Standard charger have 5V output and 0,7A out. I do not recommend the use of higher voltages and currents, can lead to overcharging and thus the explosion.

The internal "censor" of the cell can and wil be fried wen you continue.
0.7 vs 2.0 is about 3 times faster, truth but also a bigger ammount in a shorter time.
If the cell not capable for that, it wil overheat and at worst case it wil blow up in your face...................
And take a second gues, those are not the most expensive celles.............

Charger

I have a car charger that outputs 5.3V and 2A. Will I damage my phone if I use this?

No because the phone will limit it plus it depends on the charges and cable whether it will take an AC charge or USB

Hi
milomak said:
I have a car charger that outputs 5.3V and 2A. Will I damage my phone if I use this?
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The amps aren't a problem as a device will only draw what it needs. The voltage requirements however for USB is 5 Volt +- 5%, which gives a valid range of a maximum 5.25V and minimum 4.75V. If that voltage of 5.3V is the measured voltage and is accurate, it is probably going to be fine, however if that voltage is what it states on the label, then that figure has some leeway also, so if the charger is leaning towards being over rather than under, it is going to be going quite a bit over the USB spec.
Regards
Phil

6 Volt Charger

Recently bought a camping lantern that runs on a built in 6v 4.5 AH lead acid battery. It also has a USB connector which is for charging cell phones. I initially thought that the USB would be giving off a safe 5v but on testing it turns out that it is 6 volts straight from the battery.
Is this safe to use occasionally while camping? Will that extra 1 volt kill the battery or is there some mechanism inside the phone to regulate that voltage to a safe level?

Good question....hope someone has the answer for you.
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executionist said:
Recently bought a camping lantern that runs on a built in 6v 4.5 AH lead acid battery. It also has a USB connector which is for charging cell phones. I initially thought that the USB would be giving off a safe 5v but on testing it turns out that it is 6 volts straight from the battery.
Is this safe to use occasionally while camping? Will that extra 1 volt kill the battery or is there some mechanism inside the phone to regulate that voltage to a safe level?
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Of course there should be.You get more than 6v in a power socket around the house.

Gkikas said:
Of course there should be.You get more than 6v in a power socket around the house.
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No one plugs their phone directly to the wall socket :/ Thats what the charger is for, it only gives 5v to the phone. Just need to know if it can regulate that 6v to a safe level.
*edit. I think no one here would know about the hardware aspects of a phone. Can someone point me to a forum or anywhere where they may know the answer to a question like this?

May I asked how you measured this?
I'd love to check what output my 12v chargers are outputting

TieNN89 said:
May I asked how you measured this?
I'd love to check what output my 12v chargers are outputting
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A multimeter and a stripped usb cable

executionist said:
A multimeter and a stripped usb cable
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ah yeah
My brain has already flicked off for the day LOL

if you use IRC, try the freenode server in the ##electronics channel. they should help you out there. pretty nice ppl in general there.
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?
I'm interested as well. Will 6 volts @ 500mAh fry the phone?

Ok, I am an electronic engineer so a few comments.
I have no idea what kind of charging circuit is in our phones, could probably look it up but ..... in my opinion only 10% above 5V is to be considered safe.
Now you are talking about a 6V battery. That battery is not always 6V. A nice example is the 12V battery in your car which is 12.8V when fully charged. Another example are the cells inside our phones which have a nominal Voltage of 3.7V but are charged to 4.2V.
The Voltage they put on those things is the nominal Voltage.
I would check if there is no electronic circuit in that lamp since I would not connect anything directly to a battery at all.
If you go camping I would check this thing coolook pb-2000. Insert 4 x 18650 batts and you can do a couple of recharges. Very good box for the price and you can salvage 18650 from broken laptop batt packs ... but google and youtube a bit before you do that to make sure you do it the right way.

I'm also interested, any news?

You can see the specs of this type of batteries here. The 6V is nominal, as already mentioned above. The maximum noted is 6.9V and TBH, i would be rather reluctant to test is my SGS3 charging circuit likes the idea of being fed with 40% higher voltage than usual.
Are you sure there is nothing in the lantern that would limit the voltage under load? Could be something as simple as 2 diodes in series, in this case measuring the voltage on the open circuit, totally unloaded, with a DMM that barely draws microamps from it, would show the battery voltage. Try drawing some current from it (use a resistor, a USB LED lamp, etc) while measuring. I seriously doubt a self-respecting vendor would setup a USB port on that thing that would potentially output 40% more than specs, really.
PS: if the port is, indeed, fed straight from that battery, i would rather avoid hooking my SGS3 to it. Even though, it would probably survive.
---------- Post added at 07:08 PM ---------- Previous post was at 06:59 PM ----------
lukesan said:
I have no idea what kind of charging circuit is in our phones...
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MAX77686. Good luck finding the datasheet. And good luck trying to guess if there is anything else potentially fed straight from the USB connector. The bottom line is - i wouldn't dare

Solder this to red wire https://en.wikipedia.org/wiki/Zener_diode
OFC you need 5V model

GR0S said:
Solder this to red wire https://en.wikipedia.org/wiki/Zener_diode
OFC you need 5V model
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Not if it doesn't have a resistor in series. And wait. if the battery is at 6.8 Volt and you have a 5.1 Volt zener and it is charging at 1 Amp so you will need a power resistor. You will have a lot of loss of energy because it will go away in heat.
You could use a dc-dc convertor but believe me forget about it and get one of those charging banks where you can put in your own cells.

lukesan said:
Not if it doesn't have a resistor in series. And wait. if the battery is at 6.8 Volt and you have a 5.1 Volt zener and it is charging at 1 Amp so you will need a power resistor. You will have a lot of loss of energy because it will go away in heat.
You could use a dc-dc convertor but believe me forget about it and get one of those charging banks where you can put in your own cells.
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I'm not sure about how practical it would be to be cutting usb cables and wiring zener diodes just to use this lamp....
I think I had a charger that supplied too much voltage (I'm not positive I didn't measure the voltage output or anything), but I can say that the phone did not like it. It would eventually charge somewhat, but the touch screen wouldn't work and would go bezerk if touched lol.
Again I'm not sure how much V it supplied, but I would assume it was more than 6V. It didn't really damage the phones either, I would try it.

Here's your answer, definitively:
6v at the source (the lantern in this case) will probably be 5v or less at the phone because of the resistance in the USB cable itself. The longer the cable is the higher the resistance will be and thus the more voltage you lose to it. Also, the cheaper the cable (the thinner the wires) the more voltage you will lose per foot.
Here's some specs you can plug into THIS VOLTAGE CALCULATOR:
The USB definition specifies up to 5.3v.
Most USB cables will use 30awg wire or maybe 28awg for the better ones.
Depending on which of the sources I've read, some USB cables/chargers use one pair of wires for charging, and some will use two pairs. You can see that using two pairs of conductors drastically improves the voltage transmission but even still, at 28awg over a 6foot cable you're still losing .75v which puts you at 5.25v and well within the USB spec.
So the lantern is fine to use with your phone with your average 6-foot USB cord.
If you're like me and prefer 10-15 foot USB cords in some places you would actually benefit from a 6v or even 7v power supply at the wall. I've found that even on the OEM Samsung wall charger, when I use a 10-foot cable I don't get enough juice to actually charge my S4. With the screen on the battery charge level still drops. The Galaxy Charge Rate app shows something like 500ma charge rate and that's because there's not enough voltage / too much voltage-drop across the long cable. (Radio Shack sells a modular, adjustable voltage wall-wart power supply as well as USB and micro-USB adapters for it. I'm starting to experiment with it and the long cables.)

USB voltage vs charging current
This is an old thread, but I can confirm that my moto G charges at 6v. Apparently the original Motorola charger outputs 5.75v. I hooked up a variable power supply to my phone. The data lines are shorted together to indicate a high current power source is present. The moto G will test load the power supply before settling on a stable charging current. One that does not cause the voltage to sag excessively. When I applied 5v the charging current was approximately 600 mA. At 6v the charging current was approx 1200 mA. The charging current was measured directly on the phone using an app called ampere.
So I conclude that Motorola use this tactic to ensure their phones charge fastest with their chargers. On the up side, its fun watching my phone go from 40% to 100% in 45 minutes

Power Question.... AC and Onboard.

Long story, but had all my wiring done for the eMMC mod, plugged it all in - and my dog ran over the cables and I thought it was all good, but after that I couldn't get the eMMC to read - decided to make sure it was still good and shorted the resistor pads - but it wont power up now. I know the pad it good, but heres my question -
I'm worried something shorted with my dog incident - The wall Adapter is 16Watts, but when I meter mine its 6v - Is that common??
Next question, is there a good spot on the board to see if I am getting good power?
Thanks....

16 Watt means the maximum power the switching power supply can deliver to a device at full load. You´re not measuring the power you do measure the voltage which has as unit "Volt" and not "Watt".
So this is correct.
I´m not at home so i can´t look onto the power supply of the aTV but i think it must be a 5V type so you´re measured 6V should be right since you measured without the aTV attached and without load a switching power supply can go slightly higher in its voltage then in regular usage.