Modifying a 220V Switching Power Supply (PS30SWIV) for 100V Use

This article contains sections describing modifications and usage methods that are likely not intended by the equipment manufacturer or seller. The content of this article is provided completely without warranty. Reproducibility is not guaranteed, and no support will be provided. Furthermore, the parties involved shall not be held liable for any damages resulting from the use of this article. Everything is at your own risk.

Introduction

When practicing Amateur Radio^[1], one often faces financial challenges. In other words, if you try to enjoy it as much as you want, you may run out of money, and unless you are very wealthy, there is a possibility of falling into a state of financial distress. In recent years, coupled with rising prices and the weak yen, the prices of almost all related items—radio equipment, antennas, cables, and other peripherals—have been increasing. Reducing expenses, even by a little, is an urgent matter. This time, focusing on power supplies (switching power supplies) where the price increase is particularly noticeable, I will introduce how I purchased a 220V specification QJE PS30SWIV via overseas mail order and modified it to be usable at 100V.
https://ja.aliexpress.com/item/1005006066277973.html
I hope to provide information not only to penniless radio enthusiasts (Musenka)^[2] struggling with the high cost of living and lack of funds, but also broadly to people who want to use 200–240V specification equipment at 100V.

About the author...

Years ago, when I was an elementary school student, I obtained a Fourth-Class Amateur Radio Operator license simply because it seemed cool and was a cost-effective way to gain some prestige. After entering junior high school and being freed from the pressure of entrance exams, I became addicted to amateur radio and club activities, partly because I had a friendly senior in the school club. My passion never cooled down, and having successfully celebrated the 20th anniversary of my station's opening a few years ago, I built a tower in the wilderness of a remote area.
As amateur radio became even more fulfilling, I continued to spend money according to my desires, eventually developing "penniless-ness disease" and becoming a Musenka. Around that time, something strange happened to the power supply unit I had been using for over 20 years.

If you are in a hurry, you can jump to the photos of the modification points from here.

With very few exceptions, a license is required to enjoy Amateur Radio. Amateur radio licenses can be obtained through national examinations^[3]. The Fourth-Class license for beginners is easy to obtain^[4] through training courses. Please note that amateur radio cannot be used for work. If obtaining a license is too troublesome or if you need to use radio for work, you should consider Digital Simple Radio (DCR), Low Power Radio (License-free), or IP Radio.

Power Supply Price Increases

While the prices of various items have been rising in recent years, the price increase for power supplies in the amateur radio field seems particularly notable.

Price Trend of the DM-330MV

The list price of the DM-330MV, the most famous power supply among amateur radio operators, is a staggering 55,000 yen (as of July 4, 2025).
DM-330MV | Radio Equipment ALINCO INC. Electronics Division
The increase in street price is also significant. While it could be purchased on Amazon for around 15,000 yen when it was first released, it is now approaching 30,000 yen.
Amazon | ALINCO DC Stabilized Power Supply Switching Type 32A DM-330MV

Considering Alternatives

The following are considered as alternatives to the DM-330MV. Both can be obtained for around 20,000 yen.

"God" Power Supply (Kami-Dengen)

I heard the name comes from the fact that it has low noise, a quiet fan, is durable, and is inexpensive. Many people around me use it and it has a good reputation.
https://linear-amp.jp/?product=product-273

JESVERTY Power Supplies

https://www.jesverty.com/
Recently, CQ OHM started carrying them, so I've begun seeing them around. I haven't heard any bad reviews.
https://www.cqcqde.com/c/199/27/30/sps30ii
https://www.cqcqde.com/c/199/27/30/sps1332

However, if you know the prices from the old days, they all feel expensive.

Finding a Way Out with AliExpress

Many of the items listed as alternatives seemed to be made in China. So, why not try purchasing directly from China? When I searched on AliExpress, I was able to find something that looks exactly like the SPS-1332. Depending on the environment^[5], it appears to be available for around 7,000 to 10,000 yen.
https://ja.aliexpress.com/item/1005006066277973.html
I bought it immediately, only to realize that this power supply has an AC 220V input. Check carefully before you buy (a note to self).

220V specification (green arrow) with no selector switch
Looking back at AliExpress again, I hardly saw any switching power supplies for radio equipment that could be used in Japan with 100V–125V specifications. I guess it's not that easy to buy them cheaply.

Modifying the PS30SWIV for 100V

So, I decided to proceed with the modification.

Disassembly

First, I opened the cover. The cover was removed by taking out four screws on the sides (yellow arrows). The manufacturing precision didn't seem very high; the bends were tight, so I removed it by applying moderate force to avoid deformation. By removing the four screws on the bottom (green arrows), I was able to take the heatsink and circuit board out of the case.

Composite photo of the back and sides

Interior view: The modification points are located behind the bridge diode and smoothing capacitors (yellow arrows)

Next, I separated the board to make the work as easy as possible. Since the board and heatsink were fixed with screws from both sides, I removed these six screws (yellow and green arrows). Removing the screw holding the thermostat (blue arrow) and unplugging the connector linking the board and the front panel also made the work easier.

Photo of the heatsink viewed from the back

Circuit Verification

Although the PS30SWIV is a 220V input model, I reasoned that it should theoretically operate even with a 100V AC input.

The unit operating on 100V AC in a disassembled state. Naturally, the output voltage dropped.

I input 100V AC and conducted an analysis by checking voltages at various points on the board. After passing through a line filter, the AC was rectified by a bridge diode and smoothed by two identical capacitors. The voltage between the green asterisks, which are the modification points, was 45V AC, and shorting them in an unloaded state resulted in a current flow of 17mA.

Board analysis: AC section shown in pink, DC section shown in light blue.

Modification

The modification was achieved by jumping the modification points with a suitable wire. While simply shorting the points seemed sufficient, if you are concerned, cutting the legs of the diodes indicated by the red arrows might be a good idea.

Modification points: Jump the yellow arrows together.

Be extremely careful: if you input 220V after this modification, it will exceed the rating and could cause the smoothing capacitors to explode or lead to a fire!

After the modification, I reassembled the unit following the disassembly steps in reverse and confirmed that it output 13.8V DC without issues when 100V AC was input. Although not shown here, no particular problems occurred when using it with a 100W transmitter.

Principle

In machines that can be used with either 220V or 110V, they often switch between bridge diode rectification and full-wave voltage doubler rectification. In other words, when 220V is input, rectification is performed using four bridge diodes, and when 110V is input, voltage doubler rectification is performed using only two of those diodes.

Bridge Rectification and Full-Wave Voltage Doubler Rectification

A circuit with a selector switch: the red side is used for 220V, and the black side is used for 110V

Since the PS30SWIV lacks a selector switch and only has wiring for bridge diode rectification for 220V, it can be converted to full-wave voltage doubler rectification using only two diodes by jumping one side of the AC input to the midpoint between the two smoothing capacitors.

脚注

1. In short, radio used for self-training, communication, and technical research carried out by individuals for personal interest rather than for financial gain. Simply put, legal radio play. By obtaining the necessary qualifications and applying for a radio station license, you receive a callsign from the government. Legally, it is defined as "radio communication service for self-training, intercommunication, and technical investigation carried out by persons solely out of personal interest in radio technique without pecuniary interest (Radio Act Enforcement Regulations, Article 3, Item 15)."

2. A play on the word "Amateur Radio Operator" (Musenka) used to describe those who have run out of money ("Musen") while enjoying the hobby.

3. Things have changed from the past, and it seems Fourth and Third-Class exams are now taken via CBT. In my time, I passed easily by memorizing all the questions and answers from a pocket-sized book called Complete Memorization and taking the test. For detailed information, please refer to Examination Guide | Japan Radio Association, National Examination for Radio Operators | CBT-Solutions Candidate Portal, etc.

4. Nowadays, things seem to have changed, with e-learning being offered in addition to in-person courses, and even the Second-Class license can be obtained through training courses. It is wonderful that the doors are open to many people and the number of fellow hobbyists may increase. Please refer to Let's Start! Amateur Radio | Amateur Radio Operator Training Course | QCQ Planning, JARD Training Course <4th/3rd Class (Group Training)> | Japan Amateur Radio Development Association, etc.

5. Aliexpress seems to have different selling prices depending on the buyer. I don't know exactly how it works, but it seems to look at things like purchase history and usage frequency (whether it's the first time).