Sourcing a 2x USB Type A plugs to 1x Type A socket, without data - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: April 08, 2025, 06:58:54 am
content: Bit of an odd one. Does anyone know where I can source a high-quality, robust USB cable that has no data pins. It's purely going to be used for power and requires x2 Type A plugs on one end, that both connect to Type A socket on the other end.The purpose is to be able to power a device that exceeds the current draw of a single USB 500 mA socket, by feeding x2 power lines into the one output. Having no data lines at all is particularly important as the device will be connecting to untrusted hosts, it merely needs to be powered by said hosts. It does need to be of decent quality though as it will be bent, twisted and tossed into bags with other gear.

author: tom66
author_rank: Super Contributor
timestamp: April 08, 2025, 07:37:12 am
content: Strictly speaking, you would never find a compliant cable to do this, since you have to negotiate the power output from each port to get more than 100mA. Very few master devices do actually enforce that though - laptops are the worst offender if you do find one.To that end, have you tried just using a single port and being a bit naughty? If you're going to break the standard, you might as well go all the way and pull 1A from the port. I've not found many ports that won't let you do that - they usually do have a global current limit, though.You can use a 'USB Condom' to isolate the data lines for untrusted hosts. It has practical uses too: I used it in my old car to charge my phone from the USB port. If I didn't use it, the car would try to play files on the mass storage (mostly empty) instead of via Bluetooth/Spotify.https://www.amazon.co.uk/PortaPow-3rd-Data-Blocker-Pack/dp/B00T0DW3F8?th=1

author: Halcyon
author_rank: Unknown
timestamp: April 08, 2025, 10:06:22 am
content: Quote from: tom66 on April 08, 2025, 07:37:12 amYeah a single port won't do it. I was under the impression that if a USB host can't negotiate the current, it will just supply up to 500 mA. To be honest, it's been a long time since I've looked into anything like this. I do have some other options, it just means packing more cables into a kit. I was hoping to get away with a small "adapter". I do have a USB data blocker, but it's USB-C only.Since I travel a lot and stay in all kinds of hotels, what I'm basically doing is to make up a small, lightweight, travel kit that contains my Chromecast (so I can stream media from my server back to where ever I'm staying). The Chromecast can be quite hungry for power though. I ran into an issue this week where I couldn't get my Chromecast close enough to a power outlet to power it by my mains adapter, and the USB sockets on the back of the TV don't supply enough power (there is also only a single power outlet behind the TV). I've had success with some TV's that can supply enough power from a single USB socket (usually those designed for plugging in external hard drives), but this particular model isn't designed for that.

author: sleemanj
author_rank: Super Contributor
timestamp: April 08, 2025, 10:10:02 am
content: Trivially available on Aliexpress etc.First result from a google Aliexpress listing 1005007565885103Used for exactly your case, high draw devices. Used to be common to have such Y cables with external hard drives, not so much these days with more efficient ones.

author: Halcyon
author_rank: Unknown
timestamp: April 08, 2025, 10:11:19 am
content: Quote from: sleemanj on April 08, 2025, 10:10:02 amI'm aware these cables exist, I have a stack of them at home, however I specifically don't want to be plugging data into my own devices from an untrusted source while travelling.

author: sleemanj
author_rank: Super Contributor
timestamp: April 08, 2025, 10:15:27 am
content: Quote from: Halcyon on April 08, 2025, 10:11:19 am5 minutes with a razor blade and one of the cables from your stack fixes that problem.

author: Halcyon
author_rank: Unknown
timestamp: April 08, 2025, 10:17:16 am
content: Quote from: sleemanj on April 08, 2025, 10:15:27 amYep I could do that, but like most things I do, I tend to go for the "over engineered" option. Why? I have no idea... fun perhaps?

author: thm_w
author_rank: Super Contributor
timestamp: April 08, 2025, 10:47:00 pm
content: Seems like there are two options, if you want off the shelf parts: use the y splitter with adata isolator(heatshrink it on so it doesn't fall out). Total cost $4-5.If you want to make it yourself, you know what to do already. Quality can be a bit higher.

author: Infraviolet
author_rank: Super Contributor
timestamp: April 13, 2025, 08:17:24 pm
content: "I was under the impression that if a USB host can't negotiate the current, it will just supply up to 500 mA"Depends what the "host" is. A USB wall wart or powerbank will often supply as much as the whole 2A maximum, although some wall warts or powerbanks will only give 1A due to their internal design, if the thing attached is trying to draw that much, no questions asked, no negotiation at all. For devices containing USB ports which can put out power, some might be build internally just like a wall wart, including where data lines are operating too, others will need the attached device to negotiate before they'll supply more than a limited current.If you have time to spare and want to know the quality of every part involved would be to buy the relevant USB connectors, solder each to an appropriate custom circuit board which would adapt to strain-relieved power and ground wires (some sort of multi-strand wires, rated for lots of bending, you could make them much thicker than you'd find in purchased options), 3d print covers to protect the circuit boards a bit further, and provide more strain relief. Then add braid style cable sleeving around the wires.

author: tom66
author_rank: Super Contributor
timestamp: April 13, 2025, 08:36:07 pm
content: By default, a USB device gets 1 load unit on connection, one load unit is 100mA. If you want more, you have to negotiate it.The reality is, very few master devices do check this. When current limiting is present, it's usually a fixed limit rather than programmable. The reason for the enforcement is, in theory, a 'hub' can say no if it is not powered, because it is limited to 5 load units max or 500mA, so obviously it cannot allocate 5 devices x 500mA as it can only draw 500mA from the UFP. And a clever hub can realise it is connected to external power, switch to the external power and -then- allocate those 25 load units because it knows its external PSU can do that. In practice, very few hubs do this.As long as you aren't a total moron, you can usually get away with pulling at least 500mA from a master.USB C fixes some of this with the Power Delivery protocol, where you can negotiate up to 100W. In many respects USB C is a far better implementation for power management, of course, 30 years of R&D will get you that. Unfortunately, with all of those fun features - things like display hubs that can sink power -or- charge the laptop, for instance - comes a mind-boggling level of complexity.

author: Smokey
author_rank: Super Contributor
timestamp: April 13, 2025, 09:19:19 pm
content: Quote from: tom66 on April 13, 2025, 08:36:07 pmHaving done a device recently that charged from a USB port, I can say that in testing I didn't find a single example of a thing that limited to 100 mA without negotiation. Obviously it's out of spec and you can't rely on it, but I feel like moden stuff just expects everything will pull 500 mA from USB and acompdates that.

author: Zoli
author_rank: Frequent Contributor
timestamp: April 13, 2025, 09:27:35 pm
content: Did you consider DIY?

author: TheWaterbug
author_rank: Contributor
timestamp: April 17, 2025, 04:17:01 am
content: Use a USB-Y cablewith aUSB data condomon the data wire.