General > General Technical Chat

Measuring max output current of a USB port.

<< < (5/9) > >>

balnazzar:
Now I was thinking.. Even with one of those 'usb-testers', I don't think it will attempt any negotiation. It will simply measure the maximum unnegotiated current output...

Eraldo:
Here is some bad advice :palm:

Do not do this unless you know what you can expect. It can either blow something up in your computer or in your multi meter.

When trying something like this always start out with a low current and work your way up, but then still you can blow up something in your computer when it does not have a proper USB power implementation.
[/quote]

Almost all motherboards have current limiting in their usb ports. But what you said is correct. Going for a short circuit the first thing is stupid. I was giving a  cheap and dirty way of doing it quickly without any specific tool.
Yeah, having a digital load would make it more simple.

My first advice is still valid though. First check if you have a fast charging phone. Then use your charger as a reference and check the charging speed (eg 15w charger takes 1.5hours). Then plug it on the pc and compare. The bad thing is that if your pc can deliver more current than your phone needs you won't know. At that point try the power resistor thing with multimeter with a resistance of 1 ohm (for a max of 5 amp. But check the voltage first too. Also the power rating should be ideally 25w ). You can also put a fuse in there just in case (5 amp or less depending on your needs).


balnazzar:

--- Quote from: pcprogrammer on October 21, 2022, 01:52:38 pm ---
--- Quote from: balnazzar on October 21, 2022, 01:41:24 pm ---I thought that proper modern mobos from a reputable (so-to-say) brand would have had overcurrent protection o__O

--- End quote ---

Yes, but it could just be a fuse that blows when overloaded. Some will have reset-able fuses, that restore after disconnect. Some will have electronic current regulation.

What kind of cable came with the scope you bought? Back in the days spliced cables were used with an extra USB connector to allow drawing current from two ports. Or does your scope have a separate power input for a power supply?

--- End quote ---

No separate power input, *and* the scope indeed comes with a cable with two usb plugs. It works with these two plugs inserted. Not tested with just one, lest I could damage it.

I was trying to establish if I can actually power it up properly with only ONE plug inserted (and a quality cable). I don't like being dependent upon this cable, and wasting one more port.. That's one thing.
The other is that my laptop only has one usb-a ports and few usb-c ports, and I'd rather not meddle with adaptors (these usb-c ports seem to be pretty beefy though, since one of them powers up an external 4K 17.3" monitor without needing a separate power supply...)

balnazzar:

--- Quote from: Eraldo on October 21, 2022, 01:57:25 pm ---Here is some bad advice :palm:

Do not do this unless you know what you can expect. It can either blow something up in your computer or in your multi meter.

When trying something like this always start out with a low current and work your way up, but then still you can blow up something in your computer when it does not have a proper USB power implementation.

--- End quote ---

Almost all motherboards have current limiting in their usb ports. But what you said is correct. Going for a short circuit the first thing is stupid. I was giving a  cheap and dirty way of doing it quickly without any specific tool.
Yeah, having a digital load would make it more simple.

My first advice is still valid though. First check if you have a fast charging phone. Then use your charger as a reference and check the charging speed (eg 15w charger takes 1.5hours). Then plug it on the pc and compare. The bad thing is that if your pc can deliver more current than your phone needs you won't know. At that point try the power resistor thing with multimeter with a resistance of 1 ohm (for a max of 5 amp. But check the voltage first too. Also the power rating should be ideally 25w ). You can also put a fuse in there just in case (5 amp or less depending on your needs).
[/quote]

The pc fully charges a M1 ipad pro (11") in less than one hour. Seems to be pretty strong, now that I think about it...  :o

pcprogrammer:
Ah a modern laptop. Yes USB-C can handle a bit more. There are cables that on one end have USB-C and on the other end the USB connector needed to plug into the scope. Just a google search away 8)

Have you searched this site for threads about your scope?

Here is one: https://www.eevblog.com/forum/testgear/owon-vds-1022i-review/

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod