| Electronics > Beginners |
| ATX (bench) Power Supply Outputting Voltage but not Current |
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| soldar:
Pretty much the definition of 5 volts is "that voltage which will push 1 Amp through a 5 ohm resistor". If you have a 5 volt source and connect a 5 ohm resistor and get no current and you still have 5 volts.... I'd like to know how it's done. |
| FrankvHoof:
@Soldar I can get current through a resistor or LED. I just can't get anything to charge over USB, even after adding voltage dividers on the data-pins |
| Brumby:
My suggestion is to perform a range of tests with "dumb" loads - ie resistors - before trying anything with active electronics. Using simple resistors avoids any questions about what the load might do. They will respond according to Ohm's Law - pure and simple. Don't forget - if you put you meter in series for current measurement, you will get a voltage drop across it (burden voltage), so make sure you take that into account. (Random thought - If your meter has one, the current range fuse is intact ...yes?). Alternatively, measure each resistance you use before you place it in circuit, then simply measure the voltage across it when in circuit. Ohm's Law will tell you the current. Do this and maybe draw up a graph to see how things are behaving. |
| ledtester:
I found this article, and it suggest something slightly different from the above SO answer: https://www.quora.com/How-can-I-use-a-laboratory-power-supply-as-a-USB-charger "... If your bench supply can output at least 1.5A, tie the white (D+) and green (D-) wires to either end of a small resistor, something in the 33–200 ohm range will be fine. This is the bus condition a USB device uses to detect Battery Charging mode. That specification delivers a minimum of 1.5A at 5Vdc, though a few devices can pull more. ..." Another person replied with: "... To signal to the device that it can draw up to 1.5A (maximum specified by the standard), short the other two wires together. Obviously make sure you set the current limit to 1.5A or above before you plug the device in. ... I presume the D+ and D- leads should be shorted. |
| soldar:
--- Quote from: FrankvHoof on July 31, 2019, 12:01:12 am --- @Soldar I can get current through a resistor or LED. I just can't get anything to charge over USB, even after adding voltage dividers on the data-pins --- End quote --- It seems the problem has nothing to do with the power supply and all to do with the load in which case the thread title is misleading. The PSU is fine and giving 5V. The load is not taking in any current. Does it do this only with this PSU? I suspect it would do the same with any 5V PSU. |
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