Author Topic: Measuring max output current of a USB port.  (Read 6513 times)

0 Members and 1 Guest are viewing this topic.

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Measuring max output current of a USB port.
« on: October 21, 2022, 12:28:41 pm »
I need to know how much current the usb ports on my computer can output.

How can I put a high load upon them and then measure the current?  :bullshit:
 

Offline tunk

  • Super Contributor
  • ***
  • Posts: 1099
  • Country: no
Re: Measuring max output current of a USB port.
« Reply #1 on: October 21, 2022, 12:37:04 pm »
Maybe something like these:
https://www.ebay.com/itm/294572711871
https://www.ebay.com/itm/394010597121
Wouldn't know, but you may risk damaging the port.
 
The following users thanked this post: thm_w

Offline pcprogrammer

  • Super Contributor
  • ***
  • Posts: 4670
  • Country: nl
Re: Measuring max output current of a USB port.
« Reply #2 on: October 21, 2022, 12:41:40 pm »
Do you know the motherboard used in your computer. It might be able to find the specifications for it.

Offline alm

  • Super Contributor
  • ***
  • Posts: 2903
  • Country: 00
Re: Measuring max output current of a USB port.
« Reply #3 on: October 21, 2022, 12:44:22 pm »
What is the host? The max power modern USB-C ports on a computer or charger will deliver depends on what the device negotiates with the host. Look up USB power delivery. There were also older standards for up to 5V/3A or so. Just connecting a DMM across the USB port, or something similar, won't get you the maximum current or power.

I imagine there are devices to test USB power delivery, but I doubt they sell for $10.

Online wraper

  • Supporter
  • ****
  • Posts: 17952
  • Country: lv
Re: Measuring max output current of a USB port.
« Reply #4 on: October 21, 2022, 12:50:20 pm »
How can I put a high load upon them and then measure the current?  :bullshit:
No, if there is a proper overcurrent protection, it will turn VBUS off. If there isn't, something likely will fail.
 
The following users thanked this post: balnazzar

Online Gyro

  • Super Contributor
  • ***
  • Posts: 10174
  • Country: gb
Re: Measuring max output current of a USB port.
« Reply #5 on: October 21, 2022, 12:55:11 pm »
I imagine there are devices to test USB power delivery, but I doubt they sell for $10.

Actually I think they do sell for around $10 from China, depending on type.
Best Regards, Chris
 

Online Eraldo

  • Regular Contributor
  • *
  • Posts: 70
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #6 on: October 21, 2022, 12:57:32 pm »
Just plug it into a phone and see how long it takes to charge it. In my phone 6+ hours means a 5w output and with 2 hour it means 15w.

Or just take a usb cable with wires sticking out of one end and just short it with a multimeter in the Amp range. It won't break anything if you do it quickly (or put a power resistor in series with the multimeter with low enough resistance for 4 or 5 amps to pass just to be safe)
 

Online ledtester

  • Super Contributor
  • ***
  • Posts: 3282
  • Country: us
Re: Measuring max output current of a USB port.
« Reply #7 on: October 21, 2022, 01:02:07 pm »
See this table:

https://en.wikipedia.org/wiki/USB#Power

and this comment:

Quote
Low-power devices may draw at most 1 unit load, and all devices must act as low-power devices when starting out as unconfigured. 1 unit load is 100 mA for USB devices up to USB 2.0, while USB 3.0 defines a unit load as 150 mA.

So you must perform some USB negotiation in order to draw more than 1 unit load.
 
The following users thanked this post: balnazzar

Offline pcprogrammer

  • Super Contributor
  • ***
  • Posts: 4670
  • Country: nl
Re: Measuring max output current of a USB port.
« Reply #8 on: October 21, 2022, 01:08:11 pm »
Or just take a usb cable with wires sticking out of one end and just short it with a multimeter in the Amp range. It won't break anything if you do it quickly (or put a power resistor in series with the multimeter with low enough resistance for 4 or 5 amps to pass just to be safe)

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.

Offline Ranayna

  • Frequent Contributor
  • **
  • Posts: 986
  • Country: de
Re: Measuring max output current of a USB port.
« Reply #9 on: October 21, 2022, 01:23:02 pm »
BigClive sometimes uses an USB Powermeter, in combination with a USB load, to test the output capability of powerbanks and USB Powersupplies.

Similar to these:
https://www.amazon.com/RD-Voltage-Voltmeter-Multimeter-Resistance/dp/B09B211239
https://www.amazon.com/DollaTek-Electronic-Adjustable-Intelligent-Temperature/dp/B07PLDMK5K

I got a set like that, and they work great.
As other have said though: Be careful with your supply. Not all ports are properly protected, and you do not want to fry a port by grossly overloading it.
 
The following users thanked this post: balnazzar

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #10 on: October 21, 2022, 01:29:01 pm »
Do you know the motherboard used in your computer. It might be able to find the specifications for it.

Asus z690-P.

But I didn't find anything in the general (cosumer oriented) specs.. How can they omit those informations??
 

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #11 on: October 21, 2022, 01:34:27 pm »
Maybe something like these:
https://www.ebay.com/itm/294572711871
https://www.ebay.com/itm/394010597121
Wouldn't know, but you may risk damaging the port.

You mean by putting too much load upon them? From usb 3.0 onwards they *should* be protected against that..
 

Offline Ranayna

  • Frequent Contributor
  • **
  • Posts: 986
  • Country: de
Re: Measuring max output current of a USB port.
« Reply #12 on: October 21, 2022, 01:35:09 pm »
How can they omit those informations??
Likely because they follow the USB Specification. 100 mA without negotioation, 500 mA with negotiation on USB 2, 900 mA with negotiation on USB 3.
Beyond that and for higher voltages than 5 Volts, you need USB-PD. If USB-PD is not specified, don't expect to have it.

These values are the minimum. More is quite likely, especially the 100 mA limit without negotiation is often not followed, but drawing more *may* overload the ports and cause them to shut down. Or, if ASUS cheaped out, gross overloads may even damage the ports, or the controller chip, permanently.
 
The following users thanked this post: balnazzar

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #13 on: October 21, 2022, 01:36:31 pm »
What is the host? The max power modern USB-C ports on a computer or charger will deliver depends on what the device negotiates with the host. Look up USB power delivery. There were also older standards for up to 5V/3A or so. Just connecting a DMM across the USB port, or something similar, won't get you the maximum current or power.

I imagine there are devices to test USB power delivery, but I doubt they sell for $10.

The host is a Asus Z690-P board, the device is my shiny new Owon VDS1022i usb scope. It needs 5V@2A, and I wouldn't risk damaging it by providing insufficient current...
 

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #14 on: October 21, 2022, 01:37:50 pm »
I imagine there are devices to test USB power delivery, but I doubt they sell for $10.

Actually I think they do sell for around $10 from China, depending on type.

Doh, I discovered they actually sell from amazon at 10$ too.. 24hrs delivery..
I should still establish if these contraptions can damage the usb port, though...
 

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #15 on: October 21, 2022, 01:39:49 pm »
Just plug it into a phone and see how long it takes to charge it. In my phone 6+ hours means a 5w output and with 2 hour it means 15w.

Or just take a usb cable with wires sticking out of one end and just short it with a multimeter in the Amp range. It won't break anything if you do it quickly (or put a power resistor in series with the multimeter with low enough resistance for 4 or 5 amps to pass just to be safe)

That could be a good idea. Let me see if I can find a usb cable useless enough that I can sacrifice it upon the altar of science...

Ok, maybe that's not the best course of action.
« Last Edit: October 21, 2022, 01:43:10 pm by balnazzar »
 
The following users thanked this post: pcprogrammer

Offline alm

  • Super Contributor
  • ***
  • Posts: 2903
  • Country: 00
Re: Measuring max output current of a USB port.
« Reply #16 on: October 21, 2022, 01:40:25 pm »
I imagine there are devices to test USB power delivery, but I doubt they sell for $10.

Actually I think they do sell for around $10 from China, depending on type.

Doh, I discovered they actually sell from amazon at 10$ too.. 24hrs delivery..
I should still establish if these contraptions can damage the usb port, though...
Do they really support USB-PD? I think a USB-PD IC from companies like FTDI would already take up a substantial part of that money, although no doubt there's cheaper solutions for sale in China.

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #17 on: October 21, 2022, 01:41:24 pm »
Or just take a usb cable with wires sticking out of one end and just short it with a multimeter in the Amp range. It won't break anything if you do it quickly (or put a power resistor in series with the multimeter with low enough resistance for 4 or 5 amps to pass just to be safe)

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.

Ah, mh.

I thought that proper modern mobos from a reputable (so-to-say) brand would have had overcurrent protection o__O
 

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #18 on: October 21, 2022, 01:42:28 pm »
Or, if ASUS cheaped out, gross overloads may even damage the ports, or the controller chip, permanently.

Great!  ;D
 

Offline pcprogrammer

  • Super Contributor
  • ***
  • Posts: 4670
  • Country: nl
Re: Measuring max output current of a USB port.
« Reply #19 on: October 21, 2022, 01:52:38 pm »
I thought that proper modern mobos from a reputable (so-to-say) brand would have had overcurrent protection o__O

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?

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #20 on: October 21, 2022, 01:53:47 pm »
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...
 

Online Eraldo

  • Regular Contributor
  • *
  • Posts: 70
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #21 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.
[/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).


 
The following users thanked this post: balnazzar

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #22 on: October 21, 2022, 02:00:03 pm »
I thought that proper modern mobos from a reputable (so-to-say) brand would have had overcurrent protection o__O

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?

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...)
 

Offline balnazzarTopic starter

  • Frequent Contributor
  • **
  • Posts: 417
  • Country: it
Re: Measuring max output current of a USB port.
« Reply #23 on: October 21, 2022, 02:02:05 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.

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
 

Offline pcprogrammer

  • Super Contributor
  • ***
  • Posts: 4670
  • Country: nl
Re: Measuring max output current of a USB port.
« Reply #24 on: October 21, 2022, 02:06:08 pm »
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/


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf