DIY Fix for Mingwei Power Supply Voltage Adjustment

If you have purchased a power supply similar to Mingwei's, but the quality is not good, you may want to try a disassembled Mingwei power supply from Taiwan. The quality of Mingwei power supplies is generally good and they have weight to them.

However, if you have bought a disassembled Mingwei switching power supply, it can be used at first and can adjust the voltage in a small range. But when it reaches 35V, it cannot go up anymore. You can solve this problem by changing the instructions to be 0-50V adjustable and following along with the steps.

Generally speaking, the withstand voltage of the output capacitor is only 36V, so when it reaches 35V, the voltage regulator is triggered to ensure that it always outputs at 35V and cannot go up. It's a simple matter of adjusting the voltage, and you don't need any digital displays or anything like that. So you can analyze the problem and operate directly.

Firstly, remove the three 2200UF/35V filter capacitors of the output, and use two in series as one. Put a 10K voltage-sharing resistor on each capacitor, or a larger 100K resistor is better. In addition, you will need a 2200UF capacitor that withstands 35V. Two of these in series will create two 2200UF/70V capacitors. The capacity is slightly smaller than the original three, but still adequate. Two 2200UF capacitors are enough.

Secondly, remove the positive ZD1 voltage regulator protection, and the voltage can be adjusted upwards without triggering the voltage regulator.

Thirdly, the default voltage adjustment range is too small. The built-in 1K potentiometer (and a resistor in series that may short circuit directly, so it's better to add a smaller 330R resistor in series to avoid bottoming out) can be changed to a 10K multi-turn potentiometer to increase the range.

Then test the power supply after putting it back together to ensure there are no problems.

Another issue with this power supply is that its efficiency seems to be quite low. The wattmeter displays 380W, but the efficiency is only 0.636, which means the actual output power at this time is only 240W. Of course, you can test it with a larger load to see if the efficiency improves.