Measuring current through USB

usb_current

[gmgfarrand] wanted to be able to measure the current being pulled through his USB.  He realized that even though he could just cut open the wire and measure at any point, a permanent tool for this would be quite useful.  This is a simple modification that shouldn’t take long. All you need is a spare USB cable and an enclosure. He ultimately filled his enclosure with glue to keep everything in there and solid. lets hope his soldering holds well.

Comments

  1. Vincent (gmgfarrand) says:

    When you solder as sloppily as me and use solder in excess, you sometimes need the epoxy! :)

    Thnx!!!

  2. Sprite_tm says:

    Hmm, this hack could be a bit better… first of all, it would be more useful to connect the datalines too, for a device like a scanner which only is testable when driven by a PC. Secondly: why not integrate a shunt into the device? That’d mean you could disconnect the amp-meter without the device going haywire, and wouldn’t require the ugly clip-solution.

    On another note: I’d love to be proven wrong, but it seems all electronic projects on Instructables seem to… errm… lack the quality that most electronics sites have.

  3. Sprite_tm says:

    And on a second note: this article could use a title, Caleb :)

  4. Peter says:

    Hmm, I realize it probably wouldn’t be a big issue, but the exposed wires aren’t shielded. Could easily just use a metal case connected to the ground right?

  5. jproach says:

    sprite: I agree, something like a toggle switch with open/shunt would be a lot easier than the clip (and you could still use an ammeter if necessary).

    Also, I don’t care for the instructables format, I find a simple “handmade” page easier to read. But that’s just me.

  6. pokey says:

    @sprite_tm: straight-up wire taps for USB would screw up the impedance of the bus even if nothing were connected and probably cause a lot of failed transactions. Better would be to roll your own differential hi-z probe to build into the cable.

  7. TD-er says:

    Hmm if I remember correctly, one of the features of an USB-hub is you can see the current drawn for each port in software.
    You can see it in Windows in the device-manager, as one of the tabs in the properties-screen of the USB-hub.

  8. Link says:

    I was able to do this with persistance, patience, a multimeter, and just the female USB slot itself.

  9. Trevor says:

    What? I guess I need to read the instructions before I throw them away next time. What type of hub claims features like this?

    Quote

    Hmm if I remember correctly, one of the features of an USB-hub is you can see the current drawn for each port in software.
    You can see it in Windows in the device-manager, as one of the tabs in the properties-screen of the USB-hub.

    Posted at 1:28 pm on Dec 17th, 2008 by TD-er

  10. pip says:

    “can see the current drawn for each port in software.”
    The Power tab under USB Root hub properties shows the power required for each device. I’m no expert but i believe this is specified by the device not an actual value. unrecognised devices default to 500mA

  11. SuperJdynamite says:

    I’m confused here. Voltage is sourced, not sunk, so every USB device should be 5v. As for the current the USB spec says that devices must not draw more than 500ma so if you’re trying to plan capacity you can just assume that each device is 500ma.

  12. Haku says:

    I made a similar ‘breakout box’ USB cable earlier this year to monitor the power usage of USB drives/CD Roms etc., but I put 3 contacts sticking out the box.

    The +5v line (just tapped into), and the ground lines of each end of the cable. That way I can not only measure the current but the voltage at the same time, which is handy since my Metrix MTX3282 multimeter can read+display both simultaneously and also display the watts.

    I feel it’s important to read both at the same time because when you increase the power drain on the USB port the voltage drops accordingly.

  13. ngth says:

    Let me ask you this: why would you want to know how much current is being drawn out of your USB device?

    The devices that you buy from the store will give a current rating @ 5V. You can safely assume it will never go above the max current rating. For all estimation purposes, you can assume “typical” power consumption at about 70% of the total power.

  14. Vincent (gmgfarrand) says:

    I realize that its not pretty or very functional in the grand scheme of things, but it’s just something I slapped together for basically monitoring current draw for a previous project.

    I’m working on a prettier/smaller solution.

  15. Vincent (gmgfarrand) says:

    Also….
    All devices are not created equal when it comes to current draw.

    Sure the USB standard is 5V for VOLTAGE..
    For example, my Lenovo USB Slimline DVD burner pulls about 120mah, my GPS when it charges about 340mah, my ZEN MP3 player, 450mah.

    When modding USB devices or ports, I need to know what kind of numbers I am working with to avoid a “bad day” ;)

  16. Peter says:

    Not to nitpick, but mAh != mA

    mA = milliampere, a measurement of current (coulombs/second)

    mAh = milliampere hour, a measurement of charge (coulombs/second * hour = coulombs)

    I’m actually surprised that your dvd burner only pulls 120 mA, a cheap optical mouse I just got pulls 100 mA (manufacturer) and it doesn’t use a laser diode.

  17. Steve says:

    @ngth If everything you intend to plug into your USB ports came from the store then you’re on the wrong site.

  18. hex4def6 says:

    Yeah — I think you must mean 1.2a, not 120ma :)… it would take 120ma just to power up the laser on the DVD drive. I’ve seen DVD drives sometimes use a split USB cable that allows you to use two USB connectors to get within the power spec of the port.

  19. JohnZero says:

    “On another note: I’d love to be proven wrong, but it seems all electronic projects on Instructables seem to… errm… lack the quality that most electronics sites have.”

    I have to totally agree.

    It’s okay and nice if someone hacks this together at home. But it’s not sophisticated, anyone who has ever done current or voltage measurement can do it by himself, without instructables.

  20. Vincent (gmgfarrand) says:

    hex,
    No, I mean 120ma.. I thought it was weird as well, which lead me to test it in the first place.

    The burner actually has 2 USB ports on the back and a DC jack.

    One port is just for USB power, and the other is for DATA.

    Really annoying….

  21. Vincent (gmgfarrand) says:

    “It’s okay and nice if someone hacks this together at home. But it’s not sophisticated, anyone who has ever done current or voltage measurement can do it by himself, without instructables.”

    I agree as well, but sometimes, in order to come up with something more sophisticated, you need to start simple.

    With the Instructables I have seen/done, when the complication level goes up, the people on the lower end of the skill spectrum bombard me with sometimes “moronic” questions, or just don’t “get it”

    For the sake of those, and some of the “slower” techs I work with, I keep me better/more complicated projects to myself or to the places/people that have more skill.

  22. nubie says:

    If you want to make this prettier you can build it into a Digital Multi-Meter yourself.

    Cost: $3 DMM from Harbor Freight, $1 USB extension from Dollar Tree.

    Matter of fact you can use two DMM and get the voltage of the connection while you are building a meter.

  23. Vincent (gmgfarrand) says:

    nubie,
    Nice thinking….. might have to try that..

  24. nubie says:

    Thanks, it still amazes me that Harbor freight can move these Digital Multi Meters for $3, every time I visit.

    I totally get that Instructables is on the simple end of the spectrum sometimes and I think it is great.

  25. carlton says:

    120 ma is the average current draw for the burner. laser applications (I believe) are typically pulsed current, which could be on the order of amps, but, with a low duty cycle, the average current measured on the input to the laser power supply (i.e. from the usb) is much less. for example, 1.2 a with 10% duty cycle would be only 120 ma on the input side. a cap provides this pulsed current which the input supply (usb) doesn’t see.

  26. TheBakachan says:

    I’ve never bothered to check the accuracy, but if you go into the windows device manager and check your USB root hubs, it tells you what devices are connected, and what the draw…or maybe just what they’re SUPPOSED to draw… Since it says ‘Power Required’

  27. dcsledhead says:

    I think a DVD burner requires a wall wart power supply for power. The 120ma may just power logic in the interface.

  28. Gunther Hess says:

    I used to hack up USB cables and use a multimeter to test USB current but the meter often interferes with the device operation. I now use an off the shelf device that measures both current and voltage.

    http://www.smartronixstore.com/index.cfm?fuseaction=product.display&product_ID=53

    Lot less trouble.

  29. Tom Henry says:

    In now days some low cost LED based USB Power Meter is already very popular and powerful with less than 10$, for example you can buy the AboveTEK’s USB voltage and current monitor from this amazon website:

    Hope it helps!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 91,872 other followers