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Not All USB Power Is Created Equal

Soulskill posted about a year ago | from the it-should-consider-a-constitution dept.

Power 240

jfruh writes "We've reached a point in our electronic lives where most of our gadgets draw power from a USB cable, and we have lots of USB ports to choose from — some of which live on other gadgets, some of which live on adapters that plug into your wall or car. But those ports supply wildly varying amounts of power, which can result in hours of difference in how long it takes your phone to charge. The Practical Meter, the product of a successful Kickstarter campaign, can help you figure out which power sources are going to juice up your gadgets the fastest."

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Or use what already exists (5, Insightful)

cosmin_c (3381765) | about a year ago | (#45471179)

Like this little thing and also learn what the numbers and values mean. Got two, they work great and they're consistent with more pricier measurement options.

Re:Or use what already exists (5, Informative)

cosmin_c (3381765) | about a year ago | (#45471183)

Re:Or use what already exists (0)

Anonymous Coward | about a year ago | (#45471205)

Let's be honest. You forgot to paste it.

Re:Or use what already exists (5, Informative)

marcansoft (727665) | about a year ago | (#45471241)

Or one of these (it also passes through USB 3.0, which is nice):
http://www.amazon.com/Centech-USB-Power-Meter/dp/B00DAR4ITE [amazon.com]

This isn't new.

Re: Or use what already exists (4, Insightful)

Anonymous Coward | about a year ago | (#45471321)

But that company isn't paying for a slashvertisement.

Re:Or use what already exists (0, Troll)

Charliemopps (1157495) | about a year ago | (#45471771)

Oh my God people, turn in your fucking geek card:
http://www.amazon.com/Etekcity%C2%AE-Digital-Multimeter-Voltmeter-Ohmmeter/dp/B00B7CS3UY/ [amazon.com]

Put it in series with your device and set it to amps. It also has 1000 other uses besides checking that the numbers on the side of your USB adapter are accurate.
Also this, AND the above mentioned devices will only tell your the voltage your device is currently drawing. You could have a 2amp capable USB port but if your device only draws .5 at max load, that's all you're going to see.

I recommend USB adapters rated at least at 2 to 4amps (or in the 12 to 24+ watt range) My phone doesn't generally draw more than about 2. Less than 2 and you'll likely use more power than you'll charge with so if you've got it in your car listening to music it'll die even while it's plugged in. The common grab bag 1amp plugs you can get at the checkout are garbage.

Re:Or use what already exists (1)

kelemvor4 (1980226) | about a year ago | (#45471987)

That's twice now, Charlie Mopps has saved us.

Re:Or use what already exists (1)

The123king (2395060) | about a year ago | (#45471697)

I'd rather spend £10.00 on a charger and £2.50 on a stopwatch than £12.50 on that... At least that way i actually get a charger out of it...

Re:Or use what already exists (1)

Anonymous Coward | about a year ago | (#45471827)

There are even cheaper ones on DX.
http://dx.com/p/usb-av-usb-power-current-voltage-tester-translucent-blue-silver-235090 at $5.99
http://dx.com/p/usb-terminal-power-adapter-voltage-current-tester-grey-black-245604 at $10.99

Pretty much every hardware project idea I thought of, I found that China made them already at close to what I could in raw parts cost. :(

Re:Or use what already exists (1)

wbr1 (2538558) | about a year ago | (#45471701)

And public education is consistent with more pricier education options.

kickstarter link (2, Informative)

Anonymous Coward | about a year ago | (#45471181)

http://www.kickstarter.com/projects/david-toledo/the-practical-meter-know-your-power

External DVD drives (1)

jones_supa (887896) | about a year ago | (#45471187)

When it comes to USB DVD drives, some laptops cannot give enough energy to keep the disk spinning. There's a category of machines which seem to ditch the USB power regulation spec and just connects the USB Vcc rail to the 5V rail of the laptop. That's good and practical in my opinion. Then there's the another category which try to limit the power and have a polyfuse or something more smarter in place.

Re:External DVD drives (1)

SuricouRaven (1897204) | about a year ago | (#45471261)

I've seen that before - USB to 5V direct. Someone vandalized a mouse, tearing the cable apart. It was smoldering and melting a hole in the keyboard when I found it.

Re:External DVD drives (-1)

Anonymous Coward | about a year ago | (#45471339)

did you put your dong in it?

Re:External DVD drives (4, Insightful)

Joining Yet Again (2992179) | about a year ago | (#45471475)

In what way is it "good and practical" to ignore a standard, possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current? At worst this is a fire hazard, as you'd end up delivering an unreasonably high current. If the device isn't intelligent enough to ask for the right current, it should be delivered a safe trickle - as the USB standard asks.

Re: External DVD drives (1)

AvitarX (172628) | about a year ago | (#45471529)

Any device that reacts badly to too much current is poorly designed or defective.
That's therese electricity works, you're half amp light bulb doesn't explode when there's nothing else in the house because there's too many amps available.
A device that issues is most likely already shorted out.

Re: External DVD drives (4, Insightful)

Joining Yet Again (2992179) | about a year ago | (#45471585)

A USB port should react gracefully to a defective USB device - either limiting current or cutting power if draw is too high. It should not give the malfunctioning device the opportunity to catch fire by delivering it as much current as possible.

Liberal in what you accept; conservative in what you send.

Re: External DVD drives (2)

evilviper (135110) | about a year ago | (#45471867)

It's not the job of the power supply to protect malfunctioning devices from themselves. It's the job of the devices to have fuses, regulators, etc. This has been true, forever.

Your wall outlets will provided whatever is requested. Your car's alternator and battery will do the same. 12V devices plugged into a cig plug will get whatever they want, if they were designed so poorly as to not have a dammed fuse.

Re: External DVD drives (2, Insightful)

Anonymous Coward | about a year ago | (#45471935)

Yeah, but the power supply should protect itself. If the damn thing is connected directly to the laptops 5V rail it's possible to make the laptops 5V drop by plugging in a defective decvice. That in turn means all kinds of weird shit might happen, including data corruption and hardware deaths.

Re: External DVD drives (2)

silas_moeckel (234313) | about a year ago | (#45472087)

No your wall outlets provide up to what the wire running to them will support past that and the breaker trips or the fuse pops (granted it's often much after but still generally safe for the wire). Newer homes have arc faults in a lot of places that protect from even more.

Same thing for your car every branch circuit has a fuse of a given rating try getting more than 15 amps through your 12v accessory outlet.

Pretty much the rule is you can not step down the permanent wire size without an over current protection device.

Re: External DVD drives (2)

niftydude (1745144) | about a year ago | (#45471869)

This. A couple of years ago I plugged a defective DVD drive into an alienware notebook. It smoked the DVD drive, then blew up the entire USB subsystem of the notebook.

Needless to say, I don't recommend alienware to anyone anymore.

Re: External DVD drives (0)

Anonymous Coward | about a year ago | (#45472057)

This. A couple of years ago I plugged a defective DVD drive into an alienware notebook. It smoked the DVD drive, then blew up the entire USB subsystem of the notebook. Needless to say, I don't recommend alienware to anyone anymore.

Why would you plug a defective drive into your laptop?

Re: External DVD drives (1)

rickb928 (945187) | about a year ago | (#45471857)

Straight copper wire often reacts badly (in ours and the fire department's humble opinions) to too much current. In what way is it poorly designed or defective?

Or is it the design issue? Using copper wire where a resistive element would have been a better choice? Or perhaps connecting that copper wire to some more appropriate load? Maybe forgetting to include a much smaller wire (fuse) in the circuit?

Sorry, still getting enough caffeine in me to build immunity to the obvious. Devices don't react badly to too much current. They draw too much current and react badly to their own defect. Limiting current is a safety feature. Though 5W isn't a trickle in the real world.

Re: External DVD drives (2)

plover (150551) | about a year ago | (#45472067)

Any device that reacts badly to too much current is poorly designed or defective.

Yes, and if I own such a defective device, I certainly don't want it starting a fire. The thing about electronics is that most people could own a defective component and not know until it's caused some other problem.

Electronic devices can have latent defects: poor insulation that's barely adequate to protect the device through testing, shipping, and installation, but as you use the device and move a wire repeatedly, the gap in the insulation causes a short. Should the purchaser be satisfied simply by knowing that he can sue the manufacturer for damages caused by fires? Does it mean the purchaser should never take other precautions, such as installing fuses, or buying equipment with current limiters?

Thanks, but I want to take all the measures available to me to ensure safety.

Re:External DVD drives (1)

jones_supa (887896) | about a year ago | (#45471535)

In what way is it "good and practical" to ignore a standard

For starters, it allows me to burn and read optical discs. Most external DVD drives want to suck all the power through USB and, while they might have a separate DC power connector too, finding just the right power supply is a pain in the ass. If everything was done properly, every external DVD drive would ship a discrete AC/DC power supply, because the USB spec does not actually allow delivering these crazy, over 1A currents which is needed. But what can you do...

possibly damaging electronics which assume the standard by providing a variable non-guaranteed maximum current?

You are of course correct. As a comment above [slashdot.org] by SuricouRaven pointed out, letting big amounts of current through can cause hazardous situations.

Re:External DVD drives (1)

The123king (2395060) | about a year ago | (#45471773)

As some other users mentioned, having USB attached to the 5V rail is not only a fire hazard, but a dangerous flouting of international regulations. On top of that, I have never met a USB-power-only DVD drive with anywhere near decent read-write speeds. I'll stick to my trusty Freecom 5 1/4" drive-in-a-caddy with it's 20x Read/Write and DVD RAM compatibility. Oh, and I can (and have) gutted it for an emergency PATA hard drive caddy. Best £50 i ever spent.

Re:External DVD drives (1)

jones_supa (887896) | about a year ago | (#45472007)

I agree. Ultimately it's best to just have robust power delivery into DVD drives and not even try to run them through delicate USB power.

Don't really see the market (3, Insightful)

mlk (18543) | about a year ago | (#45471201)

At work I could plug my phone into the computer or... Buy a second plug, that seams a bit pointless even it if it does knock and hour of the phones charging time.

At home I do have choice, but why would I really worry as each night it gets charged and has all night. So again an hour does not really matter.

What am I missing from this?

Re:Don't really see the market (4, Informative)

mean pun (717227) | about a year ago | (#45471279)

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Re:Don't really see the market (2)

heypete (60671) | about a year ago | (#45471323)

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

Re:Don't really see the market (4, Informative)

RabidReindeer (2625839) | about a year ago | (#45471593)

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

Interesting. My wife has a Nexus 7 (2012 edition). It charges just fine (albeit relatively slowly) from 500mA USB chargers. It charges faster with the 2A charger that comes with it, but I've never had issues with it losing charge while plugged in to a standard charger.

How weak is your "weakly charging" USB port? Is it one on a keyboard or some other low-power accessory, or is it a port on the computer itself?

The Color and Tablet Nook devices have two different charge rates. If you use the official "USB" cable with the LED indicator in it, it charges at a 1A (2A?) rate. If you use a stock micro USB cable, it charges at the official 500ma rate. The decision is made by the Nook itself, based on info from extra pins that are in the custom cable.

Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

Moral of story: always check new toys for screwball cables before buying.

Custom cables are almost always unnecessary (3, Informative)

sjbe (173966) | about a year ago | (#45472089)

Which (blankety-blank-censored-blank) is no longer available. And since the cables are no longer made or sold and since they were notoriously prone to fail means that I've been trickle-charging my unit for about a year now.

Exactly why I avoid devices with weird custom cables whenever possible in consumer electronics. It's been my experience that unless a custom cable is so popular as to become a standard itself (like Apple's Lightning) that eventually you are going to run into a problem. Furthermore it adds to the cost of the device (custom cables = $) and it usually means that the company making the device had lazy and/or incompetent engineers. Now admittedly the USB spec is pretty flawed, particularly when it comes to power, but even so I've still seen lots of devices that could have used standard USB (or Firewire etc) had they taken the time to do so.

Now sometimes the standard needs to be updated. I think USB should be beefed up to handle up to 100 watts [computerworld.com] with all due haste.

Bear in mind that my day job is to run a company that makes custom cables. Think about that. I make a living off of custom cables, have the ability and equipment to make a copy of pretty much any cable, and I still think they are a bad idea for most consumer electronics.

Re:Don't really see the market (4, Informative)

necro81 (917438) | about a year ago | (#45471679)

How weak is your "weakly charging" USB port

The USB spec - ya know, that thing that every device carrying the USB logo is supposed to follow - permits a connected device to draw a maximum of 100 mA until it is properly recognized (enumerated) by the host. This is probably what the GP is referring to: 0.5 W of available power (less after conversion efficiency) isn't a whole lot for a device like a Nexus 7.

After being enumerated, the connected device can request higher current levels, up to 500 mA max. It isn't supposed to draw more unless the host permits it. For many modern portable electronics (e.g., smartphones) that have a 3-10 Whr battery, a 2.5-W maximum charge rate isn't much.

There are amendments to the spec that allow for greater power: in 2009, the spec created a Charging Downstream Port, which allows for up to 1.5 A from the host after enumeration; and the Dedicated Charging Port (DCP), which shorts the two data lines together and allows for 1.5 A charge power without enumeration.

Individual companies, such as Apple and Samsung, supply their own USB chargers that allow for even greater charge current, but do so in a way that technically violates the USB spec.

Re:Don't really see the market (0)

Anonymous Coward | about a year ago | (#45471365)

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping...

OK, we can stop right here and determine what the hell the problem is...and it's occurring before you even find a power source.

Go fix or replace your tablet. One should not be trying to power a black hole.

Re:Don't really see the market (1)

unitron (5733) | about a year ago | (#45471399)

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping...

OK, we can stop right here and determine what the hell the problem is...and it's occurring before you even find a power source.

Go fix or replace your tablet. One should not be trying to power a black hole.

I may have accidentally modded the above "redundant" by starting to mod it "informative" and then deciding to read the rest of the thread to see if I was going to want to comment instead of modding.

If so, my apologies to the PP

Re:Don't really see the market (1)

subreality (157447) | about a year ago | (#45471389)

This doesn't add up. The Nexus 7 has a 16Wh battery. The worst USB port possible (100mA) provides half a watt. Either a) your N7, rated for 10h active / 300h standby, is guzzling so fast that it would deplete a full battery in 32h of all-standby, or b) the USB port is defective.

Re:Don't really see the market (4, Informative)

bemymonkey (1244086) | about a year ago | (#45471503)

Your Nexus 7 has runaway background processes. Otherwise there's no way it draws more than 500mA in standby - it would be empty after just a few hours. Check your battery stats to find the culprit...

My girlfriend's Nexus 7 charges just fine off of good old 500mA USB2.0 ports when it's in standby...

Re:Don't really see the market (1)

nightsky30 (3348843) | about a year ago | (#45471579)

This very well could be the issue. With a recent wipe I will check to see if there is any improvement.
And still no KitKat :(

Re:Don't really see the market (1)

nightsky30 (3348843) | about a year ago | (#45471519)

I've noticed this as well when charging from a docking station usb port. It claims it is charging, and it doesn't lose charge as fast as when it's on pure battery power, but still loses charge over an extended period of time. Normal charging from the wall or other usb sources works fine. I think that particular usb port is just too weak. I don't have any issues with my battery life. I'm very happy with my Nexus 7 (2012).

Re:Don't really see the market (2)

Ash Vince (602485) | about a year ago | (#45471577)

What am I missing from this?

One example: my Nexus 7 draws so much power, even when sleeping, that it is possible to connect it to a weakly charging USB port, come back a few hours later, and it has a lower charge level. I'm sure the same is true for other tablets, and possibly even some phones.

I used to have the same problem with an old PC too. If I plugged most devices into my main computer they charged just fine, I had a really shit old small form factor packard bell thing I used to leave always switched on as a router though and if I plugged anything into that to charge via USB it ended up actually drawing power out of the device instead. This was not due to the device though, anything I plugged in to charge did the same thing.

Weirdly though I could plug anything that needed power to run like a usb stick, or usb modem and it worked fine without any issues.

Re:Don't really see the market (1)

jones_supa (887896) | about a year ago | (#45471649)

Mod parent interesting. Can anyone explain what happened in that scenario? Is it a load impedance issue? And, wouldn't there have been a diode to prevent current flow into wrong direction?

Re:Don't really see the market (0)

Anonymous Coward | about a year ago | (#45471819)

My guess would be that the device simply consumed more power than it could draw from USB.

Re:Don't really see the market (1)

wbr1 (2538558) | about a year ago | (#45471737)

I have had two LG phones that either keep a static charge or lose charge when plugged into a cheap car charger with the GPS on. Without GPS it is okay, but I guess GPS and the nav app are such a drain that the poor charger can't deliver enough current. It would be nice to be able to test a charger to see what it's actual output is.

Re:Don't really see the market (1)

Speare (84249) | about a year ago | (#45471755)

A lot of the replies here are incredulous about Nexus 7 power.

My Nexus 7 2012 edition would charge up, even if the screen and wifi was on, if left on a 500mA laptop USB port (usb debugging / storage enabled).

My Nexus 7 2013 edition would not charge up, even if the screen and wifi was off, if left on a 500mA laptop USB port (even with usb debugging / storage disabled). It would drain slowly. It required a 1A from a wall-wart to tread water with the screen on. It took a 2A wall-wart to actually charge up while using it. I still have to find a powered hub that will give more than USB standard 500mA, so I can pass debug/storage data while charging.

Re:Don't really see the market (1)

Skater (41976) | about a year ago | (#45471919)

I had something similar happen with my Samsung S3. It turned out the cable I was using (an Amazon Basics 6' cable) is bad - if you page through the reviews for it, you'll find a few reviews mentioning the same issue. The charger was delivering a full 1 amp or whatever, but the cable had too much resistance. If I was in an area with a weak cell signal and no wifi, my phone would take practically all night to charge, even with Wifi and Bluetooth turned off. Sometimes I'd even wake up in the morning and find it was only charged to 85%. Similarly, when using my phone as a GPS in my car, the charge on my phone would decrease even while plugged in with one of those cables. Unfortunately, I'd bought about 5 of those cables before I discovered the problem. I've replaced the three cables that were causing me the most headache. I replaced the one that was the biggest problem with an official Samsung cable just to be sure.

Re:Don't really see the market (1)

mean pun (717227) | about a year ago | (#45472069)

Exactly! For me the cable was the problem as well. The Nexus 7 2012 I mentioned comes with a wallsocket-to-usb charger, and a special USB cable. I managed to mislay that cable, and with most ordinary cables I had very long or even negative charging rates, even with the original charger. As far as I can tell the trick is to find a cable with low wire resistance, either because it is short, or because it has thick wires.

In any case, I think the whole discussion illustrates that some kind of measurement instrument to determine charging time or current is indeed helpful.

Re:Don't really see the market (1)

Teun (17872) | about a year ago | (#45471371)

Like when I've used the phone as hotspot and have Bluetooth on as well, power goes down rapidly and the day isn't over yet.

Having a quick top-up before getting on the train home is rather useful...

Re:Don't really see the market (1)

evilviper (135110) | about a year ago | (#45471781)

What am I missing from this?

Your car charger would be a big one... Fire up Google Navigation for your weekend drive out-of-town, and connect it to your $2 cigarette lighter charger, and before you get to your destination, your phone shuts off because it has run out of juice. Other apps like the free MapQuest use less power and offer better routing, but even those commonly use more than the 500mAH basic old USB chargers can supply, so your battery will be drained rather than charge.

The second would be a living room USB charger... If you use your phone for lots of things, like reading eBooks or RSS feeds, listening to podcasts, playing games, looking-up information, etc., your phone won't make it through half a day on a charge. An extra charger in your living room allows you to keep things charged, and the FASTER that one charges your phone, the sooner you can un-tether yourself and return to pretending cell phones don't have horrific battery life.

Re:Don't really see the market (1)

evilviper (135110) | about a year ago | (#45471821)

In all those cases, though, I read the specs on the charger, and/or observe how fast my phone is charging, and don't NEED a stupid meter to tell me what I'll find out in a few minutes.

In fact it doesn't MATTER how much power your charger can supply, if it isn't wired in a way your cell phone recognizes it, it won't TRY to draw that much power, anyhow. And Apple and Android were oh-so-nice to choose mutually-incompatible methods of signaling this, so one charger cannot work for both. Though expensive "charging-only" cables offer a workaround.

IMHO, we should switch (back) to 12V DC barrel plugs ASAP, as those will supply enough power for any device, and are infinitely more durable connectors than flimsy and directional microUSB.

It's not sex... (4, Insightful)

Anonymous Coward | about a year ago | (#45471209)

Being the fastest might not be the best for your battery life.

Re:It's not sex... (1)

aliquis (678370) | about a year ago | (#45471235)

How do the boosting using the circuitry work? Why is it faster than Apples own cable for charging an Apple device? Or the cable work worse with PCs by design somehow?

Faster isn't always better (4, Interesting)

Lennie (16154) | about a year ago | (#45471211)

I believe most types of battery when charged faster actually degrade faster.

Life fast die fast ;-)

Re:Faster isn't always better (-1)

Anonymous Coward | about a year ago | (#45471237)

at a guesstimated teravolt per second, my ipod nano still wont charge when either the Persian playlist or the AC/DC songs are on it!
Must have been those little-smart-ass-kids that called their band "STUXNET" and "ACTA"......

wiki "Leked", for an interresting read.....

Re:Faster isn't always better (0)

Anonymous Coward | about a year ago | (#45471245)

Life fast die fast ;-)

Type fast, fail fast.

Re:Faster isn't always better (1)

Joining Yet Again (2992179) | about a year ago | (#45471493)

Smartass fast - run-on fast.

Re:Faster isn't always better (1)

hcs_$reboot (1536101) | about a year ago | (#45471255)

The Fukushima rods would indirectly charge anything very fast. But they won't die any time soon, unfortunately.

Re:Faster isn't always better (1)

Anonymous Coward | about a year ago | (#45471441)

If they could convert gamma rays to electricity directly, instead of messing around with steam, we wouldn't have Fukushimas.

Re:Faster isn't always better (0)

Anonymous Coward | about a year ago | (#45471385)

I believe most types of battery when charged faster actually degrade faster.

Life fast die fast ;-)

My battery my die faster, but I won't, due to the lack of stress I have throughout the day by charging every night and walking around with a functional smartphone.

It's rather nice not knowing how a dead battery would impact me, as I see "techies" struggle with that every day.

Re:Faster isn't always better (1)

Joining Yet Again (2992179) | about a year ago | (#45471497)

Your threshold for what counts as stress + your tense overuse of italics suggest you may wish to consult your physician before you have a coronary.

Re:Faster isn't always better (0)

Anonymous Coward | about a year ago | (#45471415)

And probably screwing up the device's battery stats which doesn't help.

Re:Faster isn't always better (1)

Sockatume (732728) | about a year ago | (#45471673)

The device should only draw as much power as it wants, which is controlled by the charging circuit in the phone, regardless of how much is available. Which raises the obvious question of how they're getting iPhones which want a 120-minute charge cycle, to charge in 90 minutes by using a special cable.

Basically an Ammeter (4, Informative)

hcs_$reboot (1536101) | about a year ago | (#45471213)

Instead of that ugly one, you may get something that gives an exact value, like this one [amazon.com] . A new iPhone/iPad expects 2A, the MacBook (10W) expects also 10/5 = 2A.

Re:Basically an Ammeter (1)

thsths (31372) | about a year ago | (#45471295)

And a bad one, too, with a terrible resolution. Just get an amp meter and a cable, that should be under $10 together.

Typical slashvertising. I miss the good old days.

Re:Basically an Ammeter (3, Funny)

hcs_$reboot (1536101) | about a year ago | (#45471611)

Typical slashvertising

Impossible, I disabled ads thanks to

As our way of thanking you for your positive contributions to Slashdot, you are eligible to disable advertising.

Re:Basically an Ammeter (2)

CODiNE (27417) | about a year ago | (#45471925)

That won't work as USB amperage is based on resister sensing.

me IPOD don`t seem to like this.... (-1)

Anonymous Coward | about a year ago | (#45471225)

uhhh, could be because of that Persian song i recorded down at the communisty centre..... I might have named the file with English words which have been copywritten.
naaaa..... doesnt make sense; my ripped AC/DC tunes play fine, except when i type the words "STUXNET", "AKAMAI", or "METADATA"

betcha there wuz a virus in the Borat Khazarkstanian national anthem......

This is News? (0)

Anonymous Coward | about a year ago | (#45471271)

News for whom? Who didn't know fifteen years ago that USB ports provide varying amounts of power? Come on.

Re:This is News? (1)

Teun (17872) | about a year ago | (#45471387)

Yo doofus, it is because we know they can be different that we sometimes need to measure to know what's up.

Re:This is News? (0)

Anonymous Coward | about a year ago | (#45471663)

News for whom? Who didn't know fifteen years ago that USB ports provide varying amounts of power? Come on.

It's still interesting to talk about it.

Or.... (1)

Anonymous Coward | about a year ago | (#45471311)

Or just use a voltmeter.

Re:Or.... (0)

Anonymous Coward | about a year ago | (#45471373)

And fail at physics.

Re:Or.... (1)

Joining Yet Again (2992179) | about a year ago | (#45471507)

Perhaps AC has a spare voltmeter and was planning to add a shunt resistance in parallel?

Re:Or.... (0)

Anonymous Coward | about a year ago | (#45471967)

I'm sure that was the case.

Re:Or.... (0)

Anonymous Coward | about a year ago | (#45471383)

You mean "ammeter."

Re:Or.... (1)

Neil Boekend (1854906) | about a year ago | (#45471561)

I can tell you the voltage: 5 V +-0.25V (assuming the USB port is within spec). What you need is the current, so an ampere meter is required. A multimeter is custom. However, that is clumsy. You need to get to the power leads, without shorting the power or data leads (as shorting the data leads defaults the current to 100 ma).
The idea is good but there are better solutions, as indicated by other posters.

won't help for Samsung note 2 (3, Interesting)

leehwtsohg (618675) | about a year ago | (#45471313)

Samsung seems to measure the "reliability" of the supply or the cable, and limits power based on those values. Then the same supply will charge at different rates depending on the cable used.

Re:won't help for Samsung note 2 (4, Informative)

AmiMoJo (196126) | about a year ago | (#45471505)

Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.

Re:won't help for Samsung note 2 (4, Funny)

ThatsNotPudding (1045640) | about a year ago | (#45471637)

Indeed they do. If the charger says "I can supply 1.5A" but due to thin wires in the long, cheap cable that results in a significant voltage drop the device backs down to a lower level.

This is why I build my own USB leads using #00 welding cable.

Re:won't help for Samsung note 2 (1)

leehwtsohg (618675) | about a year ago | (#45471647)

I don't think it has to do with voltage drop. A cable usually will not show a voltage drop ~0 resistance for 2m of cable. And, same cable will charge other devices without any problem. A cable might burn out with too much current. Maybe that's the worry? I haven't really heard of that happening....
Even the originally supplied cable is rejected sometimes. And, if you get a bad charging rate, just unplug and replug the cable for another roll of the dice.
No, I think it is a simple bug in the charging control in the phone.

Re:won't help for Samsung note 2 (2, Informative)

Anonymous Coward | about a year ago | (#45471939)

Voltage loss over such a cable is very real. At 0.14 mm^2 (AWG 26) you get 0.14 mOhm/m. For a 2m cable, 2 wires you end up with 0.56 Ohm. At 1.5 A that's a voltage drop of 0.84V.

Also note that such a cable is only rated for 0.36 A

Re:won't help for Samsung note 2 (0)

Anonymous Coward | about a year ago | (#45471695)

U=RI (ohm's law), and you can model an USB cable supplying DC to an USB device as a simple resistance (i.e. R is a real number), which makes it easier to understand for the math-challenged.

When the cable is "too thin", its resistance will be too high and cause U to "drop". The phone reacts to that by limiting the input current, so that U can go closer to 5V.

Isn't there a spec on how much power ... (1)

Ihlosi (895663) | about a year ago | (#45471391)

... USB ports have to supply (and USB devices may draw)? Drawing more power is outside the spec.

Also, don't USB devices usually have to request the high power mode explicitly? Some USB power supplies are "dumb" and only supply power, but don't speak USB. Some devices are curteous enough not to draw 500mA if they haven't received permission from the USB host to do so. In this case, they'll slowly load with 100mA ...

Re:Isn't there a spec on how much power ... (0)

Anonymous Coward | about a year ago | (#45471469)

Yep, when connected to an actual USB port the limit is 100mA or 500mA if negotiated.

The issue here would be the "dumb" charging ports of various chargers and other power devices.

Tricks have been developed to get around this. Most of the time a charger (proper one anyway) will set a certain voltage on the DATA+ and DATA- pins of the USB cable and the charging device senses this to know when it is appropriate to draw more power.

Re:Isn't there a spec on how much power ... (0)

Anonymous Coward | about a year ago | (#45471541)

then there is USB3 where I think you can negotiate for 900mA, and if it through a hub you might not get that because another port is already using the available power, some USB ports may also have the ability to act as a "dumb" charger and supply 2A

Re:Isn't there a spec on how much power ... (1)

necro81 (917438) | about a year ago | (#45471713)

Most of the time a charger (proper one anyway) will set a certain voltage on the DATA+ and DATA- pins of the USB cable and the charging device senses this to know when it is appropriate to draw more power

Unfortunately, that method is not reliable, because every manufacturer implements it differently - it is not a part of the USB spec.

Following the spec, the only way to know the current rating is to either negotiate with the host (not usually possible for a standalone, "dumb" charger) or to have the data pins shorted together (a DCP according to the USB spec), in which case the available charge current should be 1.5 A min.

Re:Isn't there a spec on how much power ... (1)

RabidReindeer (2625839) | about a year ago | (#45471605)

... USB ports have to supply (and USB devices may draw)? Drawing more power is outside the spec.

Also, don't USB devices usually have to request the high power mode explicitly? Some USB power supplies are "dumb" and only supply power, but don't speak USB. Some devices are curteous enough not to draw 500mA if they haven't received permission from the USB host to do so. In this case, they'll slowly load with 100mA ...

There are several generations of specs. The original was hard-wired for 500ma max. Later versions can negotiate.

Re:Isn't there a spec on how much power ... (0)

Anonymous Coward | about a year ago | (#45471909)

No, the original spec is 100mA max, device has to negotiate for 500mA.
USB3 upped the max that can be negotiated for to 900mA.
USB charging spec to 1.5A.
Charging spec also defines a dumb port that has D+ and D- shorted together and provides a minimum of 1.5A without negotiation.
In all cases devices should monitor bus voltage at currents > 500mA and gracefully scale draw back to 500mA if voltage droops below 4.75V (weak host/thin cable/bad contact/...)

...or.... (0)

Anonymous Coward | about a year ago | (#45471397)

you can read the fucking documentation that came with the thing or the sticker on it??? This Kickstarter thing has jumped the shark about as bad as 3D printing seems to me.

Add quality of the power (0)

Anonymous Coward | about a year ago | (#45471455)

that too varies wildly. Some looks pretty bad in terms of ripple currents etc.

Re:Add quality of the power (0)

Anonymous Coward | about a year ago | (#45471603)

Ripple current is what is circulating in the filter capacitors... This affects you how?

Problem? (0)

Anonymous Coward | about a year ago | (#45471569)

What's the problem in just connecting your phone and checking on it how much current it takes and what voltage it is given? I can check that on my Neo Freerunner within few seconds...

Simple (-1, Offtopic)

16Chapel (998683) | about a year ago | (#45471613)

Just don't plug it into a Mac keyboard.

Charging spec compatibility? (1)

Sockatume (732728) | about a year ago | (#45471653)

Different devices have subtly different ways of asking how much currently they can draw. Your iDevices and Androids and whatever are fairly interoperable with each other's chargers now, but there's still the occasional stupid outlier like the PS Vita that insists on having a specific shorting of the USB pins before it'll draw more than 500mA. I'd like to see a gizmo that could not only measure the current available, but act as a universal adaptor for those sorts of devices.

Change the spec (1)

sjbe (173966) | about a year ago | (#45472139)

I'd like to see a gizmo that could not only measure the current available, but act as a universal adaptor for those sorts of devices.

The answer is not a different gizmo to work around existing limitations in the spec but updating the USB spec to reflect real world conditions and handle more power and handle power more gracefully than it does now. There is some evidence [computerworld.com] that this might occur in the near future.

You should care more about safety... (0)

Anonymous Coward | about a year ago | (#45471729)

What does the charger use for ground? I found out before Apple started its trade in program, that other electrical characteristics are more important. If the charger uses one of the pins as power pins as ground, other than the third ground pin (which most chargers do not have), then you are at risk of an electrical shock if you touch any electrically connected metal. In my case, it was the headphone out adapted to rca plugs to connect to an amp.

so much for (0)

Anonymous Coward | about a year ago | (#45471891)

industry standards and industry certification... bah! yet another gadget to languish in a drawer

Let's talk (-1, Troll)

Blahblagger (3438807) | about a year ago | (#45471957)

Let's talk about a real problem here. Not how fast devices charge and a little dingbat meter, but about how ubiquitous USB is, many devices fail to live up to part of that when it comes to charging, that is being -UNIVERSAL-. I have the following devices iPhone 4 Motorola Admiral(work) Asus Transformer Prime Infinity(fuck you Asus, this was supposed to be premium, why is it[Tegra 3] and Android so shit? Also, your tech support sucks) iHome speaker(charges via USB) Kindle You know what? Of them, the Motorola Admiral and the Transformer fail to charge from some chargers. I don't care if it takes 24 hours to charge for the tablet, it should be FUCKING CHARGING if I plug it into a USB port. And because of the ubiquity of things that charge via USB, I recently got a 4 port charger... and I can't even charge half my devices on it.

Apple vs. Other Devices (4, Insightful)

coolmoose25 (1057210) | about a year ago | (#45471959)

I'm an Apple Abhorrent... I don't use any of their products, not even an Ipod. I'm an Android/Windows guy. But my daughter decided she had to have an iPhone and bought it with her own money. I have one of those little plugs you put in a cigarette lighter in the car. My car has two up front, one that is ignition keyed, the other is always on. The dongle is in the one that is always on. And I have a standard USB cable to charge phones and other devices from it. It charges all of my Android phones fine. It charges the GPS fine. It charges pads like the Galaxy Tab and the Nexus fine. It won't charge my daughter's iPhone, even with her white Apple USB cord. To this situation, my daughter tells me that the little dongle I have is a POS. I smiled and was reminded, yet again, why I won't buy Apple products.

Let's Talk (0)

Blahblagger (3438807) | about a year ago | (#45471973)

Let's talk about a real problem here. Not how fast devices charge and a little dingbat meter, but about how ubiquitous USB is, many devices fail to live up to part of that when it comes to charging, that is being -UNIVERSAL-.

I have the following devices
iPhone 4
Motorola Admiral(work)
Asus Transformer Prime Infinity(fuck you Asus, this was supposed to be premium, why is it[Tegra 3] and Android so shit? Also, your tech support sucks)
iHome speaker(charges via USB)
Kindle

You know what? Of them, the Motorola Admiral and the Transformer fail to charge from some chargers. I don't care if it takes 24 hours to charge for the tablet, it should be FUCKING CHARGING if I plug it into a USB port. And because of the ubiquity of things that charge via USB, I recently got a 4 port charger... and I can't even charge half my devices on it.

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