Unusual?? USB ports for other than 5V? - Page 1
Forum section: electronics / general

author: Lee697
author_rank: Regular Contributor
timestamp: October 13, 2014, 10:43:56 am
content: I bought a pair of pretty nice European LED light fittings for my aquarium today, get home and take a look at the power supply.... it does mention on the label it isn't a USB charger, but in fairly small writing.... I wonder how many USB gadgets have died from this sort of manufacture? I can't recall ever seeing USB ports used for any voltage you like before...

author: ludzinc
author_rank: Unknown
timestamp: October 13, 2014, 10:51:43 am
content: OMG. Thanks for the warning!

author: Whales
author_rank: Super Contributor
timestamp: October 13, 2014, 11:40:15 am
content: That's rather disturbing. Tangentially: let's find out which models of phones use a step-down DC-DC converter that's happy to take this.Lee697: I approve of your avatar

author: Lee697
author_rank: Regular Contributor
timestamp: October 13, 2014, 11:56:56 am
content: Whales - cheers.... can't say I'd love a cup of ethylene in the morning though!

author: richard.cs
author_rank: Super Contributor
timestamp: October 13, 2014, 12:11:59 pm
content: I can't remember where but I came across a 12V USB port in a consumer product once, but it was much better labelled than that.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: October 13, 2014, 12:19:00 pm
content: Not the same thing, but I once saw someone use USB cables creatively. He needed to do four terminal resistive measurements from x number of sensors of some kind. USB fit the bill exactly. Two wires capable of a high current, two wires suitable as sense wires, in a shielded cable. And of course readily and cheaply available connectors and cables.Speaking of USB killers, there are cables with type A connectors, the type you normally plug into the computer, on both ends. These are used for plugging into to some network gear for configuration, if I recall correctly. But they have the unfortunate side effect of often creating large stray currents if connected between two computers, because of the slight voltage difference between the +5V rails on the two computers "fighting" against each other.

author: David Hess
author_rank: Super Contributor
timestamp: October 13, 2014, 04:26:51 pm
content: I cannot say I am surprised at all. They wanted an inexpensive connector and found one.

author: SeanB
author_rank: Super Contributor
timestamp: October 13, 2014, 06:55:57 pm
content: At least they are not placing direct 120VAC mains on those sockets. There are some that might survive having that applied for a while.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 13, 2014, 11:17:48 pm
content: The Asus TF101 uses 15V over USB for charging, but the PSU only supplies the full power if it detects a pullup on the USB 3 ground. There's also a USB standard in the works that can switch to supplying 20V or so.

author: Galenbo
author_rank: Super Contributor
timestamp: October 14, 2014, 08:27:29 am
content: The TF300T does the same. If you connect it to a normal USB port, it charges very slow.

author: SirNick
author_rank: Frequent Contributor
timestamp: October 14, 2014, 07:13:18 pm
content: Maybe it's just me, but I hate to see a standard get bastardized like this. It's reasonable to expect that you'll get 5v @ 500mA, and anything else needs external power. There's enough to keep track of with pull-ups just for enumeration and speed capabilities, much less having a wall-sized flowchart of special cases with power supplies. Yuck.

author: Unknown
author_rank: Unknown
timestamp: October 14, 2014, 07:33:55 pm
content: Quote from: SirNick on October 14, 2014, 07:13:18 pmI agree. At theveryleast, throw a big bright label on it saying "This is not a USB Port!"

author: SirNick
author_rank: Frequent Contributor
timestamp: October 14, 2014, 08:48:24 pm
content: Oh man, I just meant official and compatible uses of the USB interface -- like HV charging with prior negotiation. Makes me shudder. Leave USB alone and add a suitable companion connector if necessary.But, using the physical plug on a commercial project to carry nothing even remotely related to USB is even worse. It's bad enough you never know what to expect with barrel and RJ jacks. At least USB has been pretty much safe to mate with a physically compatible plug until now.

author: richard.cs
author_rank: Super Contributor
timestamp: October 14, 2014, 10:54:00 pm
content: Quote from: SirNick on October 14, 2014, 08:48:24 pmI'll admit to having used a usb3 connector for combined jtag and rs232 on a commercial product. It is only intended for factory use though and a fair amount of thought went into the pinout to ensure nothing breaks at either end if it is connected to a real port.

author: Lee697
author_rank: Regular Contributor
timestamp: October 14, 2014, 11:51:17 pm
content: Quote from: David Hess on October 13, 2014, 04:26:51 pmAre USB connectors less expensive than a plain barrel plug??

author: David Hess
author_rank: Super Contributor
timestamp: October 15, 2014, 04:09:18 am
content: Quote from: Lee697 on October 14, 2014, 11:51:17 pmI checked prices and they are about the same.

author: victor
author_rank: Regular Contributor
timestamp: October 15, 2014, 06:17:47 am
content: Why not dc plugs or a custom connector

author: SL4P
author_rank: Super Contributor
timestamp: October 15, 2014, 06:23:51 am
content: Or some method of keying them to avoid the inevitable accident...

author: Psi
author_rank: Super Contributor
timestamp: October 15, 2014, 07:00:40 am
content: Quote from: NiHaoMike on October 13, 2014, 11:17:48 pmyeah, i saw that USB 3 power standard. The 20V version is 100W from memory.Could be interesting if laptops have a USB3 power output and input.You could plug 3 laptops together in a ring arrangement and get them to all recharge each other

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: October 15, 2014, 12:02:55 pm
content: I nearly killed myself a couple of weeks ago while repairing a product that was using a 9 way D connector for 240V mains. Not happy!

author: leppie
author_rank: Frequent Contributor
timestamp: October 15, 2014, 12:50:50 pm
content: Quote from: richard.cs on October 14, 2014, 10:54:00 pmI thought about using a micro B for SWD + GND/+3V. It would not be exposed to user though.

author: amyk
author_rank: Super Contributor
timestamp: October 15, 2014, 12:57:05 pm
content: Quote from: SirNick on October 14, 2014, 08:48:24 pmAgreed, especially when one of the failure modes of accidental misnegotiation is a device getting several times its rated voltage.19.5V is in the laptop standard voltage range, using a barrel plug would be the right thing to do.