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Direct connection of 5V from power supply to front USB Answered


I need to charge some devices via USB, but my computer seems to give less than 500mA, so charge takes 12 hours...

I have one unused front USB on my computer, and I would like to ask if it will be a good idea to solder the pins 1 and 4 of this connector, directly to a connector coming from the power supply to get 5V but without the limitation on current.

Any comments will be appreciated.




Use a different charger, these things aren't designed for heavy current. What are you charging anyway?



Thanks for your answer. Actually, I'm not using any charger. What I'm charging is a GPS receiver. It charges by means of a usb cable.
In the user manual it says to plug to a USB in the computer and should take 3 hours to fully charge (a light turns off when charged). Mine has taken 12 hours, with a usb in a desktop computer.
This is the reason give me the idea to use the 5V of the power supply, but I'm not sure if it is safe.

As I understand, if the power supply can provide "a lot" of current bu the device only need a little it should no be a problem, (while the voltage remains in 5V). But of course, my knowledge is small...

What do you think?

Mmm. 12h at 500mA is 6000mAh, maybe 4AA's, 3 hours is only 1500mAh. If this is designed for USB, it shouldn't be trying to "suck" more than half an amp, I wonder whether the charge indicator is screwy - do you know what sort of battery it has in it? Is it new or used?


Hi, thanks for your help.

The battery is a Li based one, something around 1000mAh:

so lets say:
It is supposed to be charged in 3 hours at 500mA (USB specification), so the actual charging current being: 333mA, so probably due to efficiency of device electronics only 66% of the current is used to be put inside the battery.

With my computer as current provider, it toke 12 h to totally charge:
1000mAh / 12h = 83mA And the real charging current was: 83mA / 0.66 = 125 mA.

125mA is a nice number, as I have 4 usb ports, and can be that my computer is spreading the 500mA through them... I do not know...

So what about using the 5V from the power supply? Could I limit the current to 1000mA for safety?



You said that "It charges by means of a usb cable", if it was designed to do this I'd suggest it is defective, or your ports are limited. If it wasn't designed to do this, you maybe need more than 5V for the fast charge?


.  I would suspect the batteries before I would the USB port.
.  I do NOT suggest using your computer's PSU for your experiment. If you want to try a separate 5V supply, I'd steal a PSU from a junk computer and wire up a short cord with USB connector. Don't forget some kind of current limiting.


8 years ago

Be happy your computer sets a limit on the USB current draw. If memory serves, 500mA is pretty close the spec current.

At one point, many manufacturers built their USB supplies to handle a 500mA draw, but didn't implement any over-current safeguards--so the USB PS would simply fry...