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I want to increase the amps to my laptop's external USB ports. How crazy is this plan? Answered

My laptop only has two external USB ports. I keep a mouse plugged into one constantly, but I now need to use an external USB drive that needs more amps than one port can supply.  I use a Y cable that pulls power from two ports, but I can't use my mouse at the same time. (Which is really a non-starter with the work I'm doing.)

There are about 5 internal USB buses available, all of which have one port available, all drawing minimal power (fingerprint sensor, web cam, sd card reader, etc.)  

My wacky idea is to tie the voltage pins from one of these 'spare' ports to one of the external ports to provide the amps needed, similar to what the Y-cable is doing but keeping it internal and keeping one more USB port available.  I've had this laptop apart and know that I can do the wiring, but I'm curious about how high the potential is to cause massive damage.

Any pointers?



Best Answer 8 years ago

I think that the amount of current that a USB port can supply is negotiated by software when the device connects, so there must be some way of selecting the current limit in software. The only sensible way that I can think of doing it is as follows: Disconnect the current limited 5v supply from the USB socket in question. Take a 5v from somewhere else in your PC (not another USB port as this will be current limited too) Connect that 5v supply to the 5v pins of the USB socket in question. This way you: 1) get 5v at maximum current from the USB port in question, which may be a bad thing if you ever plug anything in that has a fault on it! 2) Don't damage the switching circuit that currently limits how much current can be provided, as it is now disconnected. You could of course just you an external USB hub that has its own external PSU.

Thanks for the response. That all makes good sense. Of course I could use a powered USB hub, but it ruins the portability which is one of the main objectives.

After giving it some sober thought I think I'll just make a regulated battery box for the drive. I had forgotten about power negotiation, and I'm not really sure what's going on with the Y-Cable, etc. (For example I can plug the HD to 1 USB port and it will have -almost- enough power to work, but Windows won't report that it's asking for too much power... just that the drive is occasionally unreachable) It's my main mobile work laptop, and it would stink if I made a mistake and damaged it by monkeying around.

USB 2.0 has 500mA limit. USB 3.0 can be set to high power which is 900mA. Then use a y adapter, but plug them into different USB hubs. If you plug into 2 side by side ports, they are pulling current from the same source. Which is limited.

Depending on your laptop there are a couple options. USB 2.0 is set to 500 mA. USB 3.0 can be set to 900mA. Then to double your amperage use something like this. ..http://m.sears.com/productdetails.do?partNumber=SPM7022426802P&sid=IDx20130125xMPCOMx009

I can't see a reason it wouldn't work, just run a jumper wire from one of the USB ports (such as the touch pad) over to the port that needs a boost. Of course you will be voiding any warranties.... I'd try it

Rather than tie in internally -- Make a 2 output 1 input passthrough for the mouse. The mouse connects to the passthrough port, and only the power lines are vampired from the mouse to parallel in with the other usb data port used by the hdd. Last option -- pcmcia slot usb card. They are cheap.

It sounds right, but you'd do better using an other power supply that is right for the job. You obviously want to drain the laptop battery, so why not run off another battery?


I want to keep everything as portable and self contained as possible. I get around 8 hours of regular use out of my laptop battery, so draining it a bit more for an eternal HD isn't a big problem for me. If it comes to that the HD has a 5v connector and I'll rig up an external battery and power it through that, so my home kludged solution can only blow out the HD controller, but I'd prefer to keep the number of things I have to carry/charge/etc to a minimum.