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  • Convert A Computer Power supply to a Variable Bench Top Lab Power Supply

    Hi, I made this project. I also added a 2 port usb i hacked from the same old computer. I simply connected green (power on) to GND (black) to make the original switch work. This case I don't have the above mentioned 5V when plugged in but not switched on. I consider working on that to i order to power the usb port.My observations:The PSU itself gives only 23V. After adding the variable circuit with the LM317T it dropped another 1V, so the schematics states correctly (in my case), that output is 22V. Problems to clarify:I observed a .1 to .3 variation on the voltage output. I have a suspicion that it could come from my digital multimeter, so I made the following steps to verify:1. I wired a 1K load on the output. Result: around .5 volt dropped but still varying .1 to .3.2. I measured wi...see more »Hi, I made this project. I also added a 2 port usb i hacked from the same old computer. I simply connected green (power on) to GND (black) to make the original switch work. This case I don't have the above mentioned 5V when plugged in but not switched on. I consider working on that to i order to power the usb port.My observations:The PSU itself gives only 23V. After adding the variable circuit with the LM317T it dropped another 1V, so the schematics states correctly (in my case), that output is 22V. Problems to clarify:I observed a .1 to .3 variation on the voltage output. I have a suspicion that it could come from my digital multimeter, so I made the following steps to verify:1. I wired a 1K load on the output. Result: around .5 volt dropped but still varying .1 to .3.2. I measured with an analogue display multimeter. Result: stable.3. I wired a 24V 50W halogen bulb to it. (This was at hand). Result: visually stable. Ampmeter showed steady 1.5A.4. I took measurement on 5V (red) and GND (black) on the PSU itself. Result: variation.I'm still concerned with this variation. I will test it with other multimeters when I have the chance, to determine whether it is a measurement error or not.

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