I note that Amazon is now offering a AC wall USB charger that is putting out up to 3.5 amps per the listing. Highest current I have seen up to now is 2 amps.
Has anyone tried this? Also anyone aware of any currently made devices that could be damaged by this due to not having their own current limiting circuitry? Looks like for use with safe devices it should minimize charging time but could cause meltdown on poorly designed devices which depend on the power supply to limit current in. After all this has 7 times the power available from a USB 2.0 port and almost double the power a USB 3.0 port can put out per their ratings.
Click on the 3.5A box on the Amazon page. I missed the fact that the page link did not change when the listing did. Below should be a better link, sorry.
The current limiting happens elsewhere. There is no chance of a normal device (phone, tablet, Xtar or Miller charger, etc) being damaged by the extra current on tap. Proper USB devices do not depend on the port’s current limiting, it’s a safety feature (in the same vein of thought as a fuse). Even in the dumbest non-compliant devices, current usage is typically dictated by voltage… and since the voltage isn’t changing, their current consumption will stay the same from one USB supply to the next.
Think of this as plugging a household device into a 20A circuit instead of a 15A circuit.
It seems to have solid reviews. I've had good experience with a few PWR+ power adapters. I have one of the 2.1A mini-USB power adaptors (not a PWR+) which I use to recharge my Tri-18650 power bank. I've only used it a couple of times, but I bought it looking for a high-current mini-USB power adapter.
I knew that is how it SHOULD work but sometimes wonder about some of the Chinese designed and made stuff considering that HKJ has reported wall wart USB power supplies which can fail a Hypot test and risk killing people. Per news reports some have done so. If items like that are being manufactured and sold then items which can be over driven by a high current capable external power supply or charger, even at standard voltage, would not surprise me much.
Failing a hipot test is a PSU problem (a problem with the USB wall wart in other words). USB client equipment which does not function properly when attached to a high current USB power supply is not a PSU problem. That’s not just how it should work, that’s how it does work. That’s why I mentioned that phones, tablets, and decent chargers were all fine.
I’m not sure what sort of current-limited scenario you are imagining here, but maybe this info will help quell your fears: Common USB hubs frequently have no current limiting at all on the ports they provide. They just assume that the USB client will behave properly. Anything that was working on those…
FWIW I suspect that a device which behaved badly enough to be a danger on a high current supply would risk frying the fuses on some nicer PC USB 2.0 ports (many USB ports are not fused of course). The only stuff I’ve heard of that would be a problem on a 3.5A port was already dangerous on a 500mA port.
The ability of the supply current almost has no bearing on the current draw capability of the charging device, unless it’s below the charging devices rated capability, then it can get too hot and burn out or worse, let the magic smoke out.
Tie in the 5vdc rail of a ATX powersupply into a USB port, it is capable of pushing 35A, but the device will only draw what it can to charge it’s batter based upon the Charge Port logic on the data pins of the USB cable
This is why I was fiddle futzing with that 2 port self ranging DCP board …have it tell the device to pull the most it can safely but also be able to have PLENTY of power available for multiple devices, and also have it scalable/expandable in case I wanted to add more ports at a later time.
Plus wall warts are a source for parasitic drain and can drive your power bill up
Either way…just not “hot” on wall warts, never was (plus it’s a pain in the butt to find space for another wall wart on a power strip that is almost full, unless you get one of those fandangly ones with extra space between the plugs )
As alluded to above above a higher than required current isn’t going to speed up charging. If the supply you currently have supplies less than the device requires charging will be faster, otherwise there is no advantage in charging time.
FWIW, look at the 4A version with two connectors. Looks like it has just two conductors coming out of the wall wart. I wonder where/if it does currently limiting, or if you can pull 4A out of one port with a capable device?
For the “actual usability” standpoint with a USB PSU it’s actually 100% critical to have a chip in the PSU which provides a special (simple) notification over the data pins that the PSU is capable of supplying a specific amount of current. Many devices look for that message there in order to know how much current they can pull. If the message is not present they simply pull the minimum current, or maybe do not charge at all (do iPads work like that?). A charger with a 2-wire cable is not providing that message. See here: USB - Wikipedia
While you’re chewing on that, don’t forget that there are actually a handful of different ways to signal this stuff, so there are compatibility issues.
iPads seem to draw low current (prob 500mA, but I haven’t measured it) if they don’t get the right signal. If you turn the screen on, they’ll report “Not Charging”, which is probably true at the time because the screens account for a major portion of the power budget, but if you turn the screen off, they will charge, SLOWLY.
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