USB power - how much is too much?

[Smeghead]

Whats the limit of USB power? And once exceeded, would adding a PCI USB card give you more?

I am going to have these powered off USB:

Coin slot lights
mouse
Ipac
trackball inputs
trackball power (including light)
Joystick
Sometimes a Memory stick for transferring files

Seems like alot to me. One option is I could use a 9pin serial mouse for the real mouse and power the coinslot lights some other way
But at what point is it going to tell me no more? My other pc I have tells me no more after about 4 devices (ipod/kb/mouse/camera)

[MonMotha]

The limit per port (assuming full power to that port is available which it typically will be for ports hosted on the PC itself) is 2.5W or 500mA @ 5V.  It's best to add up all your ratings and figure out what you're working with.

If you coin slot lamps are incandescent, that will probably hit the limit or put you over right there.

Also, power is managed by having devices "request" power.  Most devices will not request less than 100mA since you get that pre-enumeration, anyway.  This means that your mouse, joystick, ipac, flash drive, etc. all will "ask" for at least 100mA.  Given this, you're at or over the 500mA max.

Note that this is PER PORT for things on either root hubs (physically part of the PC) or powered hubs with full power available (good hubs).  If each one of those gets plugged into a separate port, you're probably fine except maybe your coin door lamps.  If you are using an external hub, make sure it is powered and has a brick rated for 500mA (0.5A) times the number of ports you'll be using.

[DashRendar]

I have about 6 things running on a powered 7 port USB hub.  They are:

* IPAC4
* Trackball
* 2 U360s
* External Hard Drive
* Spinner

I never have any issues with them.  The key here is that it's a powered USB hub, so it can provide ample juice to everything.

[Smeghead]

ok thanks for the replies.
The PC im using has 6 USb ports, a row of 4 and a row of 2 and im using 4 of them right now with no problems.
I do have a nice PCI USB card, from what I just read ^^ sounds like that will help alot

[orchidius]

Is there any way to get more out of one port? For example if I would want to power a bunch of LED's from one port using a PCB to wire them on, could I get more then 500ma out of a port so I could wire more LED's to the PCB?

Or could I just use a molex plug out of my computer and tap the red 5v wire and its ground wire to make a circuit for the PCB? How much power does that 5v wire carries?

[BobA]

Just tap off the power connector.  Drawing more than 500 ma from USB will damage it.

[orchidius]

So there's no harm in just tapping the red wire from a molex plug, wire it to the PCB and complete the circuit with the ground? The LED's won't protest?

[gryhnd]

My preference for powering anything not directly involved with the PC (LEDs, extra cooling fans, other bling) is to run them off a second power supply...removes the strain from the PSU as well as the  when something fubars. That can be as simple as extra wall warts you have laying around, to a full blown spare AT/ATX power supply.

[BobA]

It is fine to wire your LEDs off of a drive power connector.  Make sure you have the proper limiting resistors or LED with built in resistors.

See link on power connectors PC Power Connectors

[MonMotha]

Not that it's commonly done, but if you go tapping the 5V line on a big PC power supply, I'd recommend installing a suitable fuse.  PC power supplies can often source 50 AMPS or more on their 5V lines (hey, that's only 250W) which is more than enough to heat up and melt insulation on AWG22 commonly used for wiring arcade cabinets.  I've accidentally shorted the 5V rail on a modest (230W) supply with a ~1' piece of AWG26 before: the supply did not go into shutdown but rather started making my wire's insulation melt.  That was fun...  I suspect the short circuit protection on those supplies has gotten better, but why chance it?

[Smeghead]

Dont ATX PSUs require some kind of remote turn on switch similar to a car amplifier kind of thing?

I mean simply supplying power to an ATX PSU wouldnt be enough would it?

[Franco B]

Quick answer, bridge pin 14 to GND.

Long answer [here]

[Smeghead]

Quick answer, bridge pin 14 to GND.

Long answer [here]

[gryhnd]

Dont ATX PSUs require some kind of remote turn on switch similar to a car amplifier kind of thing?

I mean simply supplying power to an ATX PSU wouldnt be enough would it?

No, you just jumper two of the pins (search around here, there's lots of talk about it) which keeps it on.  (edit: I see that's been done for you!)

However I prefer the K.I.S.S. method, and usually use good old fashioned AT PSUs. Flip a switch, and it's on. Done. Cheap too if you have to by new. Less than $20 on Newegg

[gryhnd]

But don't discount wall warts you have laying around. LEDs and fans don't require much in the way of amperage.  In my cocktail, I run all the LEDs off a 5V wall wart, and two cooling fans and some other goodies of a 12V. Hey, they were free. For my upright I used an AT PSU, partially b/c my coin door lights are 12V lamps and not LEDs and so needed some extra oomph.

[Smeghead]

*Googles wall wart*


um ok, a 5v AC adapter?

[gryhnd]

*Googles wall wart*


um ok, a 5v AC adapter?

A wall wart isn't limited to 5v, but yes.

I bet you have tons from dead electronics laying around. Most common ones I end up with are 5v, 9v and 12v.

[orchidius]

I just checked a 9v AC adapter that I had nearby, but it only has an output of 200ma... That's even less then the 500 a USB carries... A fully lit RGB LED takes up 60ma, so you'd only be able to power 3 of those from that adapter...

It'd take a hell lot of adapters like that to power my whole CP 

And wouldn't installing a 50amp fuse in the circuit eliminate all possible problems (all LEDs are already wired with the right resistors)? Seems like a piss-easy solution to me 

[Blanka]

I would say any USB led driver has a input for extra power to feed the LED's.

[drventure]

If you are using an external hub, make sure it is powered and has a brick rated for 500mA (0.5A) times the number of ports you'll be using.

That's key right there with hubs. Many hubs (and I've gone through a number of them) are supplied with inputs that won't support all the ports being maxed out, esp some of the 7 port hubs floating around.

Be sure to check the supply.

If you don't, all sorts of things will go wonky, from spinners only moving the cursor in one dir, to buttons mysteriously pressing or locking.

[Smeghead]

ok last Q

If I want to power my coin slot lights,  the trackball power (which is separate from the inputs) and maybe another light which AC adapter should I use?

A 5v one or something more than that?