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Does someone know the power consumption of an USB backlit keyboard like the SteelSeries Apex? I'd like to connect it to a Keyboard/Mouse USB Switch that goes to PC by one USB 2.0 cable. The mouse I'm going to use is the SteelSeries Rival. Do I risk to "break" the USB port? I tried googling, but I haven't found any power consumption specification.

Thank you and sorry for bad english.

Edit 1: Do you think that with the 500 mA of the USB 2.0 I will be able to "feed" the keyboard and the mouse? In case, if I plug the USB 2.0 switch to an USB 3.0 port, is it able to draw 900 mA? (My USB hub is powered by just the PC's USB port)

Edit 2: The keyboard has a USB Y cable, but the producer doesn't say if it's necessary to the keyboard alimentation, or if it's eventually necessary to the keyboard's USB hub(it has a 2 port USB 2.0 hub)

Edit 3: I've finally found something about backlit keyboard power consumptions: "Power requirements for the backlit keyboard are less than 100mA @ 5VDC (typical), and all power required for backlighting is taken from the keyboard port of the Host PC": even if the one referred by the link is smaller than the one(so less LEDs) I specified I think that I should be able to feed keyboard and mouse with less than 500mA

Edit 4: I have received the objects, plugged them to the hub and they work correctly.

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Glad to see that it appears to be working for you. If you feel that any of the answers given helped you, consider upvoting useful answers as well as accepting the answer that you found most useful by clicking on the green checkmark outline next to the voting arrows. That is the customary way of saying thank you on the Stack Exchange network. – Michael Kjörling May 22 '14 at 8:13
up vote 14 down vote accepted

USB devices start out as "low powered" (drawing a maximum of one unit load of power, which is 100 mA in USB 2.0, see 7.2.1 Classes of Devices, page 171), and can negotiate "high power" mode in which the device can draw up to 500 mA in plain USB 2.0. At USB's 5 V DC, 500 mA provides 2.5 W of power, plus or minus tolerances.

The operative word here is negotiate. The host is fully within its rights to refuse a USB device switching to high power mode if such amounts of power are not available for any reason, and the device must deal gracefully with failure to switch to high power mode. Likely, it will appear as though it is shut down if the negotiation to high power fails, or in the case of a backlit keyboard the keyboard might work but the backlight might remain turned off if sufficient power for that feature is not available.

As has been pointed out by arch-abit, the power consumption of the keyboard (or even the keyboard and mouse combined) is likely to be significantly lower than the 2.5 W allowed for by USB. Based on Journeyman Geek's back-of-the-envelope calculations in another answer to this question, depending on the specific LEDs used and their light output, it might quite possibly fit well inside the 0.5 W (100 mA) allowed for by the initial low power mode. LEDs are very power-efficient; a few watts into a LED lightbulb is enough to provide general lighting for a small room, so a keyboard certainly shouldn't need more than a few hundred milliwatts (a few tenths of a watt) for its background illumination, and quite possibly significantly less than that. After all, we are talking about background illumination to help you see the letters printed on the keys in otherwise dark conditions, not general illumination.

If all devices involved are USB 2.0 certified and can be used without weird constructs like USB Y cables for power, you likely don't need to worry at all. If the switch has an external power supply (functions as a powered USB hub) then you almost certainly don't need to worry. The worst that is likely to happen is that something won't function, or will function only erratically (depending on the instantaneous power-up ordering, for example).

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The keyboard has a USB Y cable, but they(producers) don't say if it's necessary to the keyboard alimentation, or if it's eventually necessary to the keyboard's USB hub(it has a 2 port USB 2.0 hub) – onimoan May 20 '14 at 8:22
@onimoan Well, that should be easy enough to try; I would just try to use the keyboard with only one side of that cable plugged into the computer, and see what happens. Even my rather power-hungry Unicomp USB keyboard is fine with only a single USB connection; USB status says it has negotiated a maximum of 100 mA current draw and is bus powered, although that one obviously does not have a built-in USB hub as well. My guess would be that the extra power is only needed for the built-in USB hub. – Michael Kjörling May 20 '14 at 9:26
I still don't have the keyboard(I ordered it, it will arrive in 2/3 days). Is your keyboard backlit? – onimoan May 20 '14 at 9:45
@onimoan No, the Unicomp is not backlit. However, being a direct descendent of the original IBM Model M, it has a reputation for being quite power-hungry for a keyboard. – Michael Kjörling May 20 '14 at 9:52

Why not check yourself? Many computer motherboards are able to tell you the power consumption of a usb port via the control panel.

Go into the control panel, system > device manager and find the USB port or hub in question in the list. You'll then see power consumption figures like this:


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Note: this information is reported by the device and may be incorrect and does not reflect the actual usage. – Lekensteyn May 20 '14 at 11:14
It also doesn't help before you actually have the device hooked up. The OP doesn't have the keyboard yet (source). @Lekensteyn – Michael Kjörling May 21 '14 at 7:45

Measure it yourself! USB ammeters are useful little tools.

"Charger Doctor" is one brand of USB ammeter, targeted at seeing how much power a USB charger is actually supplying, but it works on any USB device. However, be aware that it's not the most precise ammeter, it will read zero for very low power devices, such as keyboards. (With my plain keyboard, it reads zero, even when actively typing.)

enter image description here

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This suffers from the same problem as SLC's suggestion; you cannot do it when you, like the OP, don't actually have the device in your possession. – Michael Kjörling May 21 '14 at 7:46

The power consumption is negligible, less than the 500 mA which is where USB 2 is rated. As a comparison, your keyboard probably uses some blue LEDs, they are not going to draw more than 80 mA each, and more likely to draw somewhere between 20 and 40.

If your USB hub is powered, then the keyboard is not going to draw any power from your PC. USB keyboards and mice are made for USB, and they do not usually break anything.

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I would just adjust down a bit the miliamps. a max for really bright on a proper design would be more like 40mA per , and they would probably run 10-20mA if they were just effect lighting. (plus any efficency loss when power converting) – Psycogeek May 20 '14 at 8:10
Do you think that with the 500 mA of the USB 2.0 I will be able to "feed" the keyboard and the mouse? In case, if I plug the USB 2.0 switch to an USB 3.0 port, is it able to draw 900 mA? P.S: My USB hub is powered by the PC's USB port – onimoan May 20 '14 at 8:11
@onimoan It's better to edit the question to include additional information, than to include it in a comment to an answer. Comments are meant to ask for more information or suggest improvements; they are second-class citizens on Stack Exchange, and can (and often will) be purged for many different reasons. Use the "edit" link below your question text to edit it to include additional information or clarify what you are asking for (though don't change the question itself, or you risk invalidating existing answers), then add a comment to direct an answerer to the edit. – Michael Kjörling May 20 '14 at 8:15
How did you come up with those numbers? 80mA for example. – machineaddict May 21 '14 at 8:17
By datasheets. LEDs may be driven by PWM or by other pulse trains higher than without them, and some blue, and especially white LEDs are able to handle up to 80 mA that way. As Psycogeek noted my figures were a bit on the high side, nonetheless over 100Hz or so and with proper cooling LEDs maybe driven that hard to look very bright without flicker. Even in this extreme this should make no difference in power drain over USB 2 though, unless of course there are enough connected (12 +) and driven that hard to draw 500 mA or more. – arch-abit May 21 '14 at 18:05

I don't have the power consumption figures, but the keyboard is USB certified which means it will only draw what its allowed to draw. So there is no risk of 'breaking' the port.

You 'could' run into issues with portable/travel switches that don't have external power, but not you wont damage things.

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A bit of back of the envelope calculations, and common sense might help here.

From a little research the LEDs on a keyboard are similar to these flangeless 3mm leds. Based off the specifications there - it would be 3.5V at 20ma, o7 or ~7mW per key. Assuming a 101 key keyboard its 700mW for the leds alone. Considering USB 2.0 does up to 2.5 amps, You should have quite a bit of headroom

share|improve this answer Chapter 7.2.1 (Classes of Devices) - Page 171: "A unit load is defined to be 100 mA" – onimoan May 22 '14 at 8:04

I am going to go by memory over here.

From what I can remember, the average USB keyboard should require approximately 120 ma to about 140 ma. This is with the standard 3 LED's (Cap Lock, Scroll Lock, and Num Lock) lit up. These LEDs require very little power since they are only simple indicators.

The lit keyboards have various designs depending on the manufacture for the lighting technique. They use a number of LEDs placed around under the transparent keys. The LED light is spread by using various optical design technics. The total power consumption in these types of keyboards can approach 160 ma to 200 ma depending on the design.

A USB optical mouse can require about 80 ma to 100 ma when there is mouse activity. The small defused laser LED and imaging device on the underside can require about 30 ma alone.

The cordless mouse and keyboard adapter that works on the USB port can require about 30 ma to maybe 50 ma.

A USB2 port can safely provide up to 500 ma at its limit range. A USB3 port can safely provide up to 900 ma by specs.

The old PS2 keyboards from the late 1970 to about 2000 before USB was popular can require in to the range of 150 ma.

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The IBM PS/2, with its mini-DIN keyboard and mouse connector, was introduced in 1987. "Late 1970" puts you long before the Altair 8800, and "late 1970s" puts you a few years before the original IBM 5150 PC. – Michael Kjörling Jun 9 at 7:59

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